fix(client): validate suppressed tree objects

fix(client): preserve operation observation ownership
fix(client): preserve normalized request ownership
2026-09-30 09:45:53 +09:00 · 2026-09-30 09:38:28 +09:00 · 2026-09-30 09:21:44 +09:00 · 2026-09-30 09:09:20 +09:00 · 2026-09-30 08:59:53 +09:00 · 2026-09-30 08:46:12 +09:00
34 changed files with 10826 additions and 581 deletions
@@ -2,12 +2,44 @@
 # It is not intended for manual editing.
 version = 4

+[[package]]
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+checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+
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+
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+]
+
 [[package]]
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+[[package]]
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+dependencies = [
+ "percent-encoding",
+]
+
 [[package]]
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@@ -20,6 +52,120 @@ version = "0.17.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ed5909b6e89a2db4456e54cd5f673791d7eca6732202bbf2a9cc504fe2f9b84a"

+[[package]]
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+dependencies = [
+ "bytes",
+ "itoa",
+]
+
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+dependencies = [
+ "displaydoc",
+ "potential_utf",
+ "utf8_iter",
+ "yoke",
+ "zerofrom",
+ "zerovec",
+]
+
+[[package]]
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+ "displaydoc",
+ "litemap",
+ "tinystr",
+ "writeable",
+ "zerovec",
+]
+
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+dependencies = [
+ "icu_collections",
+ "icu_normalizer_data",
+ "icu_properties",
+ "icu_provider",
+ "smallvec",
+ "zerovec",
+]
+
+[[package]]
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+
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+dependencies = [
+ "displaydoc",
+ "icu_collections",
+ "icu_locale_core",
+ "icu_properties_data",
+ "icu_provider",
+ "zerotrie",
+ "zerovec",
+]
+
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+
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+checksum = "d27bbb9d3abbefac45d55f647c9de1d44aafcd1186eb91879afef17c396c3e73"
+dependencies = [
+ "displaydoc",
+ "icu_locale_core",
+ "writeable",
+ "yoke",
+ "zerofrom",
+ "zerotrie",
+ "zerovec",
+]
+
+[[package]]
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+checksum = "3b0875f23caa03898994f6ddc501886a45c7d3d62d04d2d90788d47be1b1e4de"
+dependencies = [
+ "idna_adapter",
+ "smallvec",
+ "utf8_iter",
+]
+
+[[package]]
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+version = "1.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+dependencies = [
+ "icu_normalizer",
+ "icu_properties",
+]
+
 [[package]]
 name = "indexmap"
 version = "2.14.2"
@@ -36,12 +182,33 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"

+[[package]]
+name = "litemap"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47d9d19d1d6efa0109d2f65ff4c85cddd50bd572e5a00127ab10987290bcefae"
+
 [[package]]
 name = "memchr"
 version = "2.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"

+[[package]]
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+checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
+
+[[package]]
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+checksum = "d83eb9bc6d8e5cf568e7a1101d60ee05e81ed50ea106026f3d18deeb046d7661"
+dependencies = [
+ "zerovec",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.107"
@@ -111,6 +278,18 @@ dependencies = [
 "serde_core",
 ]

+[[package]]
+name = "smallvec"
+version = "1.16.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f9395f0f0eee849a9b707b2f06bb92a6a422090e2123bb2ef8e87a0e61892a8e"
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ce2be8dc25455e1f91df71bfa12ad37d7af1092ae736f3a6cd0e37bc7810596"
+
 [[package]]
 name = "syn"
 version = "2.0.119"
@@ -133,6 +312,17 @@ dependencies = [
 "unicode-ident",
 ]

+[[package]]
+name = "synstructure"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "901704edd0dfe137f1987838ee4f259e4e063c31371bdb423f7ae38ec6f77f02"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+]
+
 [[package]]
 name = "target-tuple"
 version = "1.0.2"
@@ -148,6 +338,16 @@ dependencies = [
 "winapi-util",
 ]

+[[package]]
+name = "tinystr"
+version = "0.8.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b1e27c91459209c2986af3dcf603a5a74a4368754ce37414f59acc971167f643"
+dependencies = [
+ "displaydoc",
+ "zerovec",
+]
+
 [[package]]
 name = "toml"
 version = "1.1.6+spec-1.1.0"
@@ -208,6 +408,24 @@ version = "1.0.26"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d245f478577f809a851594d02313b640fb437e0bb33866753cff937863096954"

+[[package]]
+name = "url"
+version = "2.5.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ff67a8a4397373c3ef660812acab3268222035010ab8680ec4215f38ba3d0eed"
+dependencies = [
+ "form_urlencoded",
+ "idna",
+ "percent-encoding",
+ "serde",
+]
+
+[[package]]
+name = "utf8_iter"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b6c140620e7ffbb22c2dee59cafe6084a59b5ffc27a8859a5f0d494b5d52b6be"
+
 [[package]]
 name = "winapi-util"
 version = "0.1.11"
@@ -238,6 +456,14 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b97319f7b8343df12cc98938e5c3eb436064524c8d2b4e30a1d3a36eecdf81"

+[[package]]
+name = "wip-client"
+version = "0.1.0"
+dependencies = [
+ "wip-https",
+ "wip-protocol",
+]
+
 [[package]]
 name = "wip-host"
 version = "0.1.0"
@@ -247,6 +473,18 @@ dependencies = [
 "wip-protocol",
 ]

+[[package]]
+name = "wip-https"
+version = "0.1.0"
+dependencies = [
+ "base64",
+ "http",
+ "serde",
+ "serde_json",
+ "url",
+ "wip-protocol",
+]
+
 [[package]]
 name = "wip-interface"
 version = "0.1.0"
@@ -278,6 +516,89 @@ dependencies = [
 "wip-protocol",
 ]

+[[package]]
+name = "writeable"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ad82d2a33cdc9674dc7465672f271e096168fcdbe0f799d9e6db8c5892679dc"
+
+[[package]]
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+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "709fe23a0424b6a435d82152b1bd3fdfb0833487d5fa90d05d42762a9891fef5"
+dependencies = [
+ "stable_deref_trait",
+ "yoke-derive",
+ "zerofrom",
+]
+
+[[package]]
+name = "yoke-derive"
+version = "0.8.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "33811428bee40dbceb6d545e95754741d17a6aef9a4849f0fd62e2ba4f412a78"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+ "synstructure",
+]
+
+[[package]]
+name = "zerofrom"
+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ec05a11813ea801ff6d75110ad09cd0824ddba17dfe17128ea0d5f68e6c5272"
+dependencies = [
+ "zerofrom-derive",
+]
+
+[[package]]
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+version = "0.1.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f75b4683f6c7f45248d4d64056a24298c6281e0993356d7d1b4a1a962ef10d4a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+ "synstructure",
+]
+
+[[package]]
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+version = "0.2.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ea269c3bd32f0a32c321907a2ae912ba6f4649bb0fc764a15627e99a7095a3f"
+dependencies = [
+ "displaydoc",
+ "yoke",
+ "zerofrom",
+]
+
+[[package]]
+name = "zerovec"
+version = "0.11.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bb0464e17806c1d976d5cba29399c7f08e516e279e2ba493f63123b5fca67dd8"
+dependencies = [
+ "yoke",
+ "zerofrom",
+ "zerovec-derive",
+]
+
+[[package]]
+name = "zerovec-derive"
+version = "0.11.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34df6fc39dbd26ddc9c10e6a2984476e13acce22e64e4487636ef494369225da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+]
+
 [[package]]
 name = "zmij"
 version = "1.0.23"
@@ -1,22 +1,3 @@
 [workspace]
-members = [
-    ".",
-    "crates/wip-host",
-    "crates/wip-interface",
-    "crates/wip-interface-macros",
-    "crates/wip-protocol",
-]
+members = ["crates/*"]
 resolver = "3"
-
-[package]
-name = "wip-public-api-example"
-version = "0.1.0"
-edition = "2024"
-description = "End-to-end example of the public WIP Rust APIs"
-license = "MIT OR Apache-2.0"
-publish = false
-
-[dependencies]
-wip-host = { path = "crates/wip-host" }
-wip-interface = { path = "crates/wip-interface" }
-wip-protocol = { path = "crates/wip-protocol" }
@@ -2,15 +2,22 @@

 Rust building blocks for the Web Interface Protocol (WIP).

-The repository currently provides a transport-independent protocol model, a
-Rust interface-authoring facade, and a request-scoped host runtime. HTTP and
-other transport bindings are intentionally outside the supported slice.
-
+The repository is a resolver-3 virtual Cargo workspace whose packages all live
+under `crates/*`. It provides a transport-independent protocol model, the
+standard framework-independent WIP over HTTPS v1 binding, a stateful
+presentation-independent client runtime, a Rust interface-authoring facade, a
+request-scoped host runtime, and a private public-API conformance consumer. The
+repository root is not itself a package.
 ## Crate graph and responsibilities

 ```text
 wip-public-api-example (workspace-only executable, integration tests, doctest)
 ├── wip-protocol              logical declarations, values, calls, and validation
+├── wip-https                 standard HTTPS v1 routes, JSON codecs, envelopes, and batching
+│   └── wip-protocol
+├── wip-client                stateful Known Space, lazy tree, observation, and call runtime
+│   ├── wip-https
+│   └── wip-protocol
 ├── wip-interface             application DTO codecs and interface authoring facade
 │   ├── wip-protocol
 │   └── wip-interface-macros  proc-macro implementation detail
@@ -22,33 +29,42 @@ wip-public-api-example (workspace-only executable, integration tests, doctest)
 | Crate | Responsibility | Does not own |
 | --- | --- | --- |
 | `wip-protocol` | Transport-independent descriptors, object/call/result types, logical `Value`s, validation, and stable protocol error categories. | Application DTOs, implementations, persistence, or wire encoding. |
+| `wip-https` | Standard HTTPS v1 endpoint/route derivation, UTF-8 JSON codecs, direct success bodies, error/status classification, and retrieval batches. | HTTP I/O, TLS termination, authentication schemes, server frameworks, filesystem projection, or client presentation/cache policy. |
+| `wip-client` | Endpoint/security-context-isolated Known Space, normalized object and interface observations, lazy entry trees, immutable operation call contexts, stale transitions, and bounded histories. | HTTP I/O, credentials, persistent cache, automatic operation retries, or presentation widgets/events. |
 | `wip-interface` | The public `WipType`/`interface` authoring API, Rust-to-protocol codecs, generated descriptors, and typed implementation dispatch. | Object publication, backend lifetime, or transport policy. |
 | `wip-interface-macros` | Procedural-macro expansion used by `wip-interface`. It is not an application dependency. | A supported direct user API. |
 | `wip-host` | Opaque interface registration, explicit object membership, validator checks, and interface-qualified dispatch against one host-owned instance. | Backend atomicity, global object lookup, or network serving. |
-| `wip-public-api-example` | An independently compiled consumer of only the three public crates. Its DTOs and traits are application-owned; its implementation and backend handle remain host-private. | Reusable library API or a production server. |
+| `wip-public-api-example` | An independently compiled consumer of the protocol, authoring, and host public crates. Its DTOs and traits are application-owned; its implementation and backend handle remain host-private. | Reusable library API or a production server. |

 The boundary is intentional: protocol types describe what can cross a
 transport; application DTOs opt into that model with `WipType`; a host-private
-implementation owns credentials, handles, and backend state; and a future
-transport maps its own routes/envelopes to `CallOperationRequest` and
+implementation owns credentials, handles, and backend state; and `wip-https`
+maps standard routes/envelopes to `CallOperationRequest` and
 `CallOperationResponse` without placing transport-specific types in descriptors
 or application traits.

 ## End-to-end example

-[`src/lib.rs`](src/lib.rs) is the complete public-API example and
-[`src/main.rs`](src/main.rs) runs it. It demonstrates all of the following:
+[`crates/wip-public-api-example/src/lib.rs`](crates/wip-public-api-example/src/lib.rs)
+is the complete public-API example and
+[`crates/wip-public-api-example/src/main.rs`](crates/wip-public-api-example/src/main.rs)
+runs it. It demonstrates all of the following:

-1. public application DTOs derived as `WipType` records and unions;
+1. public application DTOs derived as `WipType` records, enums, and unions,
+   including canonical entry paths and schema-opaque JSON;
 2. two public traits declared with `#[wip::interface]`;
 3. a private host struct implementing both traits;
-4. explicit publication of both interfaces on one object;
-5. registry observation and validation of generated descriptors;
-6. calls made with interface references, operation names, and `Value` arguments;
+4. explicit publication of both interfaces as an ordered set on one object;
+5. separate observation of opaque interface references, descriptors, and
+   descriptor validators;
+6. calls qualified by `target.path`, object validator, interface reference and
+   validator, operation, and schema-neutral `Value` arguments;
 7. validated result values decoded back to the typed application result;
 8. independent dispatch of the same `status` operation name on both interfaces;
-9. a domain rejection returned as data and a backend failure returned as a host
-   error.
+9. distinct domain rejection, rollback-confirmed and outcome-unknown
+   host/backend failures, `PermissionDenied`, stale validator recovery, interface
+   membership, and lookup failure codes; and
+10. canonical failure precedence when several request fields are invalid.

 Run it inside the development shell:

@@ -57,10 +73,17 @@ nix develop
 cargo run --package wip-public-api-example
 ```

-The normal integration test is in [`tests/end_to_end.rs`](tests/end_to_end.rs).
-Unit tests beside the example additionally cover every host dispatch failure,
-invalid arguments and results, interface membership, validators, and
-same-named operations.
+The public-only conformance suite is in
+[`crates/wip-public-api-example/tests/end_to_end.rs`](crates/wip-public-api-example/tests/end_to_end.rs).
+It covers canonical object/descriptor shape, ordered interfaces,
+schema-neutral record/enum/union/entry/JSON values, fully qualified calls, and
+the distinct domain, host, authorization, validator-recovery, and interface
+failure classes. Exhaustive public type construction and matching make legacy
+ObjectId, descriptor `name`, and semantic `Value` variants compile-time
+regressions. Unit tests in the public crates additionally cover every host
+dispatch failure, `InvalidRequest` versus descriptor-bound `InvalidArguments`,
+invalid local responses, validators, same-named operations, and exhaustive
+per-interaction protocol error-code sets.

 ## Interface authoring

@@ -185,19 +208,39 @@ are never projected by `WipObject`; host-private fields and backend handles are
 also excluded.

 Application domain failures belong in a derived result union and are returned
-through `Ok`. `wip::HostError` is reserved for runtime/backend failures. Invalid
-arguments are rejected before invocation; malformed encoded results are
-reported as `InvalidResult` and never returned as application data. Validator,
-membership, authorization, and result failures retain their distinct canonical
-protocol error codes.
+through `Ok`. `wip::HostError` is reserved for runtime/backend failures. A
+structurally malformed call is `InvalidRequest`; only argument values checked
+after the current Interface Descriptor is fixed are `InvalidArguments`. A Host
+must never return a wire `InvalidResult`: Clients keep invalid Object,
+Descriptor, operation-result, and error responses as local `InvalidResponse`
+failures, while unsupported descriptor formats remain local
+`UnsupportedDescriptorFormat` failures.

-Providers remain responsible for backend atomicity. Enter a transaction, lock,
-stable-handle scope, or conditional-update primitive before invoking the
-`with_object` callback, and retain it until the callback returns. Mutable
-operations must make validator comparison and backend commit atomic and return a
-validator for the committed state. The runtime never validates one object and
-then resolves a second snapshot, but it cannot make an arbitrary external
-backend atomic by itself.
+For operation calls, `Internal` and `ResourceLimitExceeded` guarantee that the
+operation did not run or that its effects were rolled back.
+`OperationOutcomeUnknown` is the only protocol code that makes no such
+guarantee, so Clients must not automatically retry it. `wip::HostError`
+therefore requires both a `HostErrorKind` and an `EffectGuarantee`; implementation
+panic, result encoding, and result validation default to an unknown outcome.
+Host-private diagnostics are bounded locally but never copied into protocol
+messages.
+
+`ExecutionContext` carries a runtime-neutral cancellation token, monotonic
+deadline, and optional Host-defined resource budget through resolution and
+execution. Cancellation and deadlines are cooperative: the runtime checks them
+immediately before typed invocation, while providers enforce them during backend
+work. A pre-invocation limit failure is `ResourceLimitExceeded`; after invocation
+it is safe to use that code only when non-commit or rollback is confirmed.
+
+Providers remain responsible for backend atomicity. `with_object` returns a typed
+`ProviderResult`, and `execute_operation` receives an `OperationAttempt` that
+separates `NotStarted` from `Started`. A transactional provider holds its
+transaction across the callback, commits successful attempts, and may call
+`OperationAttempt::confirm_rollback` only after every operation effect has been
+rolled back. Without that proof, post-invocation failures remain
+`OperationOutcomeUnknown`. Mutable operations must still make validator
+comparison and backend commit atomic and return a validator describing the state
+that becomes committed.

 ## Validation

@@ -208,10 +251,14 @@ nix develop
 cargo fmt --all -- --check
 cargo check --workspace --all-targets
 cargo test --workspace --all-targets
+cargo test --workspace --doc
 cargo clippy --workspace --all-targets -- -D warnings
+RUSTDOCFLAGS='-D warnings' cargo doc --workspace --no-deps
+cargo run --package wip-public-api-example
+git diff --check
 ```

-`cargo test --workspace --all-targets` includes the public example integration
-test, runtime failure tests, and `trybuild` compile-fail suites. Run
-`cargo test --workspace --doc` when validating the checked rustdoc examples
-separately.
+`cargo test --workspace --all-targets` includes the public-only conformance
+consumer, runtime failure tests, and `trybuild` compile-fail suites. The separate
+doctest, rustdoc, executable, and whitespace checks are all required acceptance
+steps.
@@ -0,0 +1,10 @@
+[package]
+name = "wip-client"
+version = "0.1.0"
+edition = "2024"
+description = "Presentation-independent stateful WIP client runtime"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+wip-https = { path = "../wip-https" }
+wip-protocol = { path = "../wip-protocol" }
@@ -0,0 +1,247 @@
+use std::collections::BTreeMap;
+
+use wip_client::{
+    CallOutcome, Client, ClientErrorKind, ClientLimits, Completion, DiagnosticKind,
+    ObservationState, OutcomeUnknownReason, SecurityContext,
+};
+use wip_https::http::{Response, StatusCode};
+use wip_https::{
+    Limits, encode_fetch_interface_response, encode_fetch_response, encode_protocol_error_response,
+};
+use wip_protocol::{
+    FetchInterfaceRequest, FetchInterfaceResponse, FetchRequest, INTERFACE_FORMAT_V1,
+    InterfaceDescriptor, Object, OperationDeclaration, ParameterDeclaration, ProtocolError,
+    ProtocolErrorCode, ProtocolInteraction, ReturnDeclaration, TypeExpr, Value,
+};
+
+fn limits() -> Limits {
+    Limits::new(64 * 1024, 64 * 1024, 64, 64).unwrap()
+}
+
+fn setup() -> (Client, wip_client::SessionId) {
+    let mut client = Client::new(ClientLimits::new(2, 16, 16, 16, 16).unwrap(), limits());
+    let session = client
+        .open_session("https://example.test/wip", SecurityContext::new("subject"))
+        .unwrap();
+    (client, session)
+}
+
+fn response(status: StatusCode, body: &[u8]) -> Response<Vec<u8>> {
+    Response::builder()
+        .status(status)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(body.to_vec())
+        .unwrap()
+}
+
+fn object() -> Object {
+    Object {
+        name: "item".into(),
+        description: None,
+        interfaces: vec!["math".into()],
+        r#ref: None,
+        validator: Some(b"object-v1".to_vec()),
+    }
+}
+
+fn descriptor(format: &str) -> InterfaceDescriptor {
+    InterfaceDescriptor {
+        format: format.into(),
+        documentation: None,
+        types: vec![],
+        operations: vec![OperationDeclaration {
+            name: "calculate".into(),
+            documentation: None,
+            parameters: vec![ParameterDeclaration {
+                name: "value".into(),
+                required: true,
+                documentation: None,
+                r#type: TypeExpr::Integer,
+            }],
+            returns: ReturnDeclaration {
+                documentation: None,
+                r#type: TypeExpr::Integer,
+            },
+        }],
+    }
+}
+
+#[test]
+fn malformed_json_unknown_fields_duplicates_and_invalid_success_are_invalid_response() {
+    let cases: &[&[u8]] = &[
+        b"{not json",
+        br#"{"name":"item","interfaces":[],"unknown":true}"#,
+        br#"{"name":"item","interfaces":["math","math"]}"#,
+        br#"{"name":"wrong","interfaces":[]}"#,
+    ];
+    for body in cases {
+        let (mut client, session) = setup();
+        let request = client.prepare_fetch(&session, "/item").unwrap();
+        let error = client
+            .complete(request.id, response(StatusCode::OK, body))
+            .unwrap_err();
+        assert_eq!(error.kind, ClientErrorKind::InvalidResponse);
+        assert!(matches!(
+            client.object(&session, "/item").unwrap().state,
+            ObservationState::Error(_)
+        ));
+    }
+}
+
+#[test]
+fn disallowed_code_and_status_success_contradictions_are_invalid_response() {
+    let cases = [
+        (
+            StatusCode::NOT_FOUND,
+            br#"{"error":{"code":"interface_not_found","message":"wrong"}}"#.as_slice(),
+        ),
+        (
+            StatusCode::OK,
+            br#"{"error":{"code":"not_found","message":"wrong status"}}"#.as_slice(),
+        ),
+        (
+            StatusCode::CREATED,
+            br#"{"name":"item","interfaces":[]}"#.as_slice(),
+        ),
+    ];
+    for (status, body) in cases {
+        let (mut client, session) = setup();
+        let request = client.prepare_fetch(&session, "/item").unwrap();
+        assert_eq!(
+            client
+                .complete(request.id, response(status, body))
+                .unwrap_err()
+                .kind,
+            ClientErrorKind::InvalidResponse
+        );
+    }
+}
+
+#[test]
+fn valid_error_envelope_is_authoritative_and_status_mismatch_is_diagnostic() {
+    let (mut client, session) = setup();
+    let request = client.prepare_fetch(&session, "/item").unwrap();
+    let error = ProtocolError {
+        code: ProtocolErrorCode::NotFound,
+        message: "missing".into(),
+    };
+    let mut encoded =
+        encode_protocol_error_response(ProtocolInteraction::Fetch, &error, limits()).unwrap();
+    *encoded.status_mut() = StatusCode::IM_A_TEAPOT;
+
+    assert_eq!(
+        client.complete(request.id, encoded).unwrap(),
+        Completion::ProtocolFailure(error)
+    );
+    assert_eq!(
+        client.object(&session, "/item").unwrap().state,
+        ObservationState::Stale
+    );
+    assert_eq!(
+        client.diagnostics(&session).unwrap().back().unwrap().kind,
+        DiagnosticKind::HttpStatusMismatch
+    );
+}
+
+#[test]
+fn non_success_without_valid_envelope_remains_transport_failure() {
+    let (mut client, session) = setup();
+    let request = client.prepare_fetch(&session, "/item").unwrap();
+    let error = client
+        .complete(
+            request.id,
+            response(StatusCode::BAD_GATEWAY, b"gateway html"),
+        )
+        .unwrap_err();
+    assert_eq!(error.kind, ClientErrorKind::Transport);
+}
+
+#[test]
+fn unsupported_descriptor_format_is_distinct_from_invalid_response() {
+    let (mut client, session) = setup();
+    let request = client.prepare_interface(&session, "math").unwrap();
+    let logical = FetchInterfaceRequest {
+        interface: "math".into(),
+    };
+    let value = FetchInterfaceResponse {
+        interface: "math".into(),
+        descriptor: descriptor("future-format/2"),
+        validator: Some(b"v2".to_vec()),
+    };
+    let encoded = encode_fetch_interface_response(&logical, &value, limits()).unwrap();
+    let error = client.complete(request.id, encoded).unwrap_err();
+    assert_eq!(error.kind, ClientErrorKind::UnsupportedDescriptorFormat);
+}
+
+#[test]
+fn malformed_call_success_after_dispatch_is_outcome_unknown_and_stales_object() {
+    let (mut client, session) = setup();
+    let fetch = client.prepare_fetch(&session, "/item").unwrap();
+    client
+        .complete(
+            fetch.id,
+            encode_fetch_response(
+                &FetchRequest {
+                    path: "/item".into(),
+                },
+                &object(),
+                limits(),
+            )
+            .unwrap(),
+        )
+        .unwrap();
+    let interface = client.prepare_interface(&session, "math").unwrap();
+    client
+        .complete(
+            interface.id,
+            encode_fetch_interface_response(
+                &FetchInterfaceRequest {
+                    interface: "math".into(),
+                },
+                &FetchInterfaceResponse {
+                    interface: "math".into(),
+                    descriptor: descriptor(INTERFACE_FORMAT_V1),
+                    validator: None,
+                },
+                limits(),
+            )
+            .unwrap(),
+        )
+        .unwrap();
+    let call = client
+        .prepare_call(
+            &session,
+            "/item",
+            "math",
+            "calculate",
+            BTreeMap::from([("value".into(), Value::Integer(2))]),
+        )
+        .unwrap();
+    client.mark_dispatched(call.id).unwrap();
+
+    let completion = client
+        .complete(
+            call.id,
+            response(
+                StatusCode::OK,
+                br#"{"result":"not an integer","unknown":true}"#,
+            ),
+        )
+        .unwrap();
+    assert!(matches!(
+        completion,
+        Completion::Call(record)
+            if matches!(
+                &record.outcome,
+                CallOutcome::Unknown {
+                    reason: OutcomeUnknownReason::ResponseDecode,
+                    failure: Some(failure),
+                } if failure.kind == ClientErrorKind::InvalidResponse
+            )
+    ));
+    assert_eq!(
+        client.object(&session, "/item").unwrap().state,
+        ObservationState::Stale
+    );
+    assert_eq!(client.in_flight_len(), 0);
+}
@@ -18,11 +18,14 @@
 //!
 //! A provider is responsible for entering a backend transaction, lock,
 //! stable-handle scope, or conditional-update primitive before invoking the
-//! callback and retaining it until the callback returns. The runtime does not
-//! reopen the path or select another implementation after checking validators,
-//! but cannot make an arbitrary external backend atomic on its own. Mutable
-//! operations must make object-validator comparison and backend commit atomic;
-//! the validator returned after dispatch must describe the committed state.
+//! operation callback and retaining it through commit or rollback. The typed
+//! [`OperationAttempt`] boundary distinguishes pre-dispatch rejection from started
+//! execution. Only an implementation-supplied non-commit guarantee or a
+//! provider-confirmed rollback allows a post-invocation failure to become
+//! `Internal` or `ResourceLimitExceeded`; every other outcome is
+//! `OperationOutcomeUnknown`. Mutable operations must make object-validator
+//! comparison and backend commit atomic, and the validator returned after dispatch
+//! must describe the state that becomes committed.

 #![deny(missing_docs)]

@@ -31,19 +34,23 @@ use std::collections::{BTreeMap, HashMap, HashSet};
 use std::error::Error;
 use std::fmt::{self, Display, Formatter};
 use std::marker::PhantomData;
+use std::panic::{AssertUnwindSafe, catch_unwind};
 use std::sync::Arc;
-use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::atomic::{AtomicBool, AtomicU64, Ordering};
+use std::time::Instant;

 use wip_interface::DispatchError;
-pub use wip_interface::{InterfaceDefinition, InterfaceImplementation};
+pub use wip_interface::{
+    EffectGuarantee, HostError, HostErrorKind, InterfaceDefinition, InterfaceImplementation,
+};
 pub use wip_protocol;
 pub use wip_protocol::{
    CallOperationRequest as CallRequest, CallOperationResponse as CallResult, InterfaceTarget,
    Target,
 };
 use wip_protocol::{
-    FetchInterfaceResponse, InterfaceDescriptor, Object, ProtocolError, ProtocolErrorCode,
-    ValidationError, Value,
+    FetchInterfaceRequest, FetchInterfaceResponse, InterfaceDescriptor, Object, ProtocolError,
+    ProtocolErrorCode, ValidationError, Value,
 };

 /// Opaque bytes used as a conditional execution precondition.
@@ -64,6 +71,122 @@ impl Validator {
    }
 }

+/// Runtime-neutral cooperative cancellation signal.
+///
+/// Clones observe the same atomic state, so transports, providers, and worker
+/// runtimes can share the token without depending on a particular async runtime.
+#[derive(Debug, Clone, Default)]
+pub struct CancellationToken(Arc<AtomicBool>);
+
+impl CancellationToken {
+    /// Creates a cancellation token in the active state.
+    #[must_use]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Requests cooperative cancellation.
+    pub fn cancel(&self) {
+        self.0.store(true, Ordering::Release);
+    }
+
+    /// Returns whether cancellation has been requested.
+    #[must_use]
+    pub fn is_cancelled(&self) -> bool {
+        self.0.load(Ordering::Acquire)
+    }
+}
+
+/// Execution controls propagated through object resolution and operation dispatch.
+///
+/// Cancellation and deadlines are checked immediately before typed implementation
+/// invocation. Providers also receive the complete context and remain responsible
+/// for enforcing controls while backend work is in progress. `resource_budget` is
+/// an opaque Host-defined work-unit ceiling; this crate deliberately does not
+/// prescribe an async runtime or accounting mechanism.
+#[derive(Debug, Clone)]
+pub struct ExecutionContext {
+    cancellation: CancellationToken,
+    deadline: Option<Instant>,
+    resource_budget: Option<u64>,
+}
+
+impl Default for ExecutionContext {
+    fn default() -> Self {
+        Self {
+            cancellation: CancellationToken::new(),
+            deadline: None,
+            resource_budget: None,
+        }
+    }
+}
+
+impl ExecutionContext {
+    /// Creates an execution context without a deadline or resource budget.
+    #[must_use]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Uses `cancellation` as this call's cooperative cancellation signal.
+    #[must_use]
+    pub fn with_cancellation(mut self, cancellation: CancellationToken) -> Self {
+        self.cancellation = cancellation;
+        self
+    }
+
+    /// Sets the monotonic deadline for this call.
+    #[must_use]
+    pub fn with_deadline(mut self, deadline: Instant) -> Self {
+        self.deadline = Some(deadline);
+        self
+    }
+
+    /// Sets an opaque Host-defined work-unit ceiling for this call.
+    #[must_use]
+    pub fn with_resource_budget(mut self, resource_budget: u64) -> Self {
+        self.resource_budget = Some(resource_budget);
+        self
+    }
+
+    /// Returns the shared cooperative cancellation token.
+    #[must_use]
+    pub fn cancellation(&self) -> &CancellationToken {
+        &self.cancellation
+    }
+
+    /// Returns the monotonic deadline, if one was supplied.
+    #[must_use]
+    pub fn deadline(&self) -> Option<Instant> {
+        self.deadline
+    }
+
+    /// Returns the opaque Host-defined work-unit ceiling, if one was supplied.
+    #[must_use]
+    pub fn resource_budget(&self) -> Option<u64> {
+        self.resource_budget
+    }
+
+    fn preflight(&self) -> Result<(), CallError> {
+        if self.cancellation.is_cancelled() {
+            return Err(CallError::new(
+                CallErrorKind::ResourceLimitExceeded,
+                "operation was cancelled before execution",
+            ));
+        }
+        if self
+            .deadline
+            .is_some_and(|deadline| Instant::now() >= deadline)
+        {
+            return Err(CallError::new(
+                CallErrorKind::ResourceLimitExceeded,
+                "operation deadline elapsed before execution",
+            ));
+        }
+        Ok(())
+    }
+}
+
 /// Opaque host-assigned reference to one registered interface artifact.
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
 pub struct InterfaceRef(String);
@@ -88,14 +211,26 @@ pub struct InterfaceObservation {
 }

 impl InterfaceObservation {
-    /// Converts this host observation to the canonical protocol response.
-    #[must_use]
-    pub fn protocol_response(&self) -> FetchInterfaceResponse {
-        FetchInterfaceResponse {
+    /// Converts this host observation to a validated canonical protocol response.
+    ///
+    /// A Host-side response construction failure is returned as `Internal`; it is
+    /// never emitted as a successful response for a Client to reinterpret as a
+    /// local validation error.
+    pub fn protocol_response(&self) -> Result<FetchInterfaceResponse, ProtocolError> {
+        let response = FetchInterfaceResponse {
            interface: self.reference.0.clone(),
            descriptor: self.descriptor.clone(),
            validator: self.validator.as_ref().map(|validator| validator.0.clone()),
-        }
+        };
+        response
+            .validate_for(&FetchInterfaceRequest {
+                interface: self.reference.0.clone(),
+            })
+            .map_err(|_| ProtocolError {
+                code: ProtocolErrorCode::Internal,
+                message: "Host produced an invalid interface response".into(),
+            })?;
+        Ok(response)
    }
 }

@@ -397,26 +532,29 @@ impl<T: WipObject> PublishedObject<T> {

    fn dispatch_resolved(
        &self,
+        context: &ExecutionContext,
        request: CallRequest,
        authorize: impl FnOnce(&T, &InterfaceRef, &str) -> bool,
-    ) -> Result<CallResult, CallError> {
+    ) -> OperationAttempt {
+        let pre_dispatch_failure =
+            |kind, message: &str| OperationAttempt::NotStarted(CallError::new(kind, message));
        let current_object_validator = self.implementation.validator();
        if let Some(supplied) = request.target.validator.as_deref()
            && current_object_validator.map(Validator::as_bytes) != Some(supplied)
        {
-            return Err(CallError::new(
+            return pre_dispatch_failure(
                CallErrorKind::ValidatorMismatch,
                "object validator does not match current object state",
-            ));
+            );
        }

        let Some(bound) = self.interfaces.iter().find(|bound| {
            bound.artifact.reference.as_str() == request.interface.reference.as_str()
        }) else {
-            return Err(CallError::new(
+            return pre_dispatch_failure(
                CallErrorKind::InterfaceMismatch,
                "interface is not a member of the current object publication",
-            ));
+            );
        };

        match (
@@ -424,16 +562,16 @@ impl<T: WipObject> PublishedObject<T> {
            request.interface.validator.as_deref(),
        ) {
            (Some(_), None) => {
-                return Err(CallError::new(
+                return pre_dispatch_failure(
                    CallErrorKind::InterfaceValidatorRequired,
                    "registered interface requires a validator",
-                ));
+                );
            }
            (expected, Some(actual)) if expected.map(Validator::as_bytes) != Some(actual) => {
-                return Err(CallError::new(
+                return pre_dispatch_failure(
                    CallErrorKind::InterfaceValidatorMismatch,
                    "interface validator does not match the registered descriptor",
-                ));
+                );
            }
            _ => {}
        }
@@ -445,10 +583,10 @@ impl<T: WipObject> PublishedObject<T> {
            .iter()
            .any(|operation| operation.name == request.operation)
        {
-            return Err(CallError::new(
+            return pre_dispatch_failure(
                CallErrorKind::OperationNotFound,
-                format!("operation `{}` is not declared", request.operation),
-            ));
+                &format!("operation `{}` is not declared", request.operation),
+            );
        }

        if request.target.validator.is_none()
@@ -456,45 +594,67 @@ impl<T: WipObject> PublishedObject<T> {
                .implementation
                .requires_validator(&bound.artifact.reference, &request.operation)
        {
-            return Err(CallError::new(
+            return pre_dispatch_failure(
                CallErrorKind::ValidatorRequired,
                "this operation requires an object validator",
-            ));
+            );
        }

-        bound
+        if let Err(error) = bound
            .artifact
            .descriptor
            .validate_arguments(&request.operation, &request.arguments)
-            .map_err(|error| CallError::new(CallErrorKind::InvalidArguments, error.to_string()))?;
+        {
+            return pre_dispatch_failure(CallErrorKind::InvalidArguments, &error.to_string());
+        }

        if !authorize(
            &self.implementation,
            &bound.artifact.reference,
            &request.operation,
        ) {
-            return Err(CallError::new(
+            return pre_dispatch_failure(
                CallErrorKind::PermissionDenied,
                "operation is not permitted for this caller",
-            ));
+            );
        }

-        let value = (bound.dispatch)(&self.implementation, &request.operation, request.arguments)
-            .map_err(CallError::from_dispatch)?;
+        if let Err(error) = context.preflight() {
+            return OperationAttempt::NotStarted(error);
+        }

-        bound
+        let value =
+            match (bound.dispatch)(&self.implementation, &request.operation, request.arguments) {
+                Ok(value) => value,
+                Err(
+                    error @ (DispatchError::UnknownOperation(_)
+                    | DispatchError::InvalidArguments(_)
+                    | DispatchError::Decode(_)),
+                ) => return OperationAttempt::NotStarted(CallError::from_pre_dispatch(error)),
+                Err(error) => {
+                    return OperationAttempt::Started(Err(OperationFailure::from_dispatch(error)));
+                }
+            };
+
+        if bound
            .artifact
            .descriptor
            .validate_result(&request.operation, &value)
-            .map_err(|error| CallError::new(CallErrorKind::InvalidResult, error.to_string()))?;
+            .is_err()
+        {
+            return OperationAttempt::Started(Err(OperationFailure::internal(
+                EffectGuarantee::Unknown,
+                "operation implementation produced an invalid result",
+            )));
+        }

-        Ok(CallResult {
+        OperationAttempt::Started(Ok(CallResult {
            result: value,
            validator: self
                .implementation
                .validator()
                .map(|validator| validator.0.clone()),
-        })
+        }))
    }

    /// Consumes the publication and returns its host-private implementation.
@@ -504,24 +664,158 @@ impl<T: WipObject> PublishedObject<T> {
    }
 }

+/// A post-invocation failure awaiting final provider effect disposition.
+///
+/// Providers may upgrade an unknown failure with [`confirm_rollback`](Self::confirm_rollback)
+/// only after the backend transaction has definitely rolled back. Diagnostics are
+/// intentionally generic and safe for protocol exposure.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct OperationFailure {
+    kind: HostErrorKind,
+    effect_guarantee: EffectGuarantee,
+    message: String,
+}
+
+impl OperationFailure {
+    fn internal(effect_guarantee: EffectGuarantee, message: impl Into<String>) -> Self {
+        Self {
+            kind: HostErrorKind::Internal,
+            effect_guarantee,
+            message: bounded_message(message.into()),
+        }
+    }
+
+    fn from_dispatch(error: DispatchError) -> Self {
+        match error {
+            DispatchError::Host(error) => Self {
+                kind: error.kind(),
+                effect_guarantee: error.effect_guarantee(),
+                message: match error.kind() {
+                    HostErrorKind::Internal => "operation implementation failed".into(),
+                    HostErrorKind::ResourceLimitExceeded => {
+                        "operation resource limit was exceeded".into()
+                    }
+                },
+            },
+            DispatchError::Panic => Self::internal(
+                EffectGuarantee::Unknown,
+                "operation implementation panicked",
+            ),
+            DispatchError::Encode(_) => Self::internal(
+                EffectGuarantee::Unknown,
+                "operation result could not be encoded",
+            ),
+            DispatchError::InvalidResult(_) => Self::internal(
+                EffectGuarantee::Unknown,
+                "operation implementation produced an invalid result",
+            ),
+            DispatchError::UnknownOperation(_)
+            | DispatchError::InvalidArguments(_)
+            | DispatchError::Decode(_) => {
+                unreachable!("pre-dispatch failures are classified before OperationFailure")
+            }
+        }
+    }
+
+    /// Returns the Host failure category used when effects are not committed.
+    #[must_use]
+    pub fn kind(&self) -> HostErrorKind {
+        self.kind
+    }
+
+    /// Returns the current effect guarantee.
+    #[must_use]
+    pub fn effect_guarantee(&self) -> EffectGuarantee {
+        self.effect_guarantee
+    }
+
+    /// Confirms that the provider rolled back all operation effects.
+    ///
+    /// Calling this method is a semantic assertion by the provider and must occur
+    /// only after its atomic backend boundary has completed rollback.
+    #[must_use]
+    pub fn confirm_rollback(mut self) -> Self {
+        self.effect_guarantee = EffectGuarantee::NotCommitted;
+        self
+    }
+}
+
+/// Dispatch progress returned to the provider's atomic execution boundary.
+#[derive(Debug)]
+pub enum OperationAttempt {
+    /// A canonical precondition failed and typed implementation code did not run.
+    NotStarted(CallError),
+    /// Typed implementation invocation began, with either a result or a typed
+    /// post-invocation failure.
+    Started(Result<CallResult, OperationFailure>),
+}
+
+impl OperationAttempt {
+    /// Marks a post-invocation failure as fully rolled back.
+    ///
+    /// Successful attempts and pre-dispatch failures are returned unchanged.
+    #[must_use]
+    pub fn confirm_rollback(self) -> Self {
+        match self {
+            Self::Started(Err(error)) => Self::Started(Err(error.confirm_rollback())),
+            other => other,
+        }
+    }
+}
+
+/// Result of one provider resolution or execution boundary.
+#[derive(Debug)]
+pub enum ProviderResult<T> {
+    /// The path resolved and the provider callback completed.
+    Found(T),
+    /// The path is not currently published to this caller.
+    NotFound,
+    /// Provider or backend execution failed.
+    ///
+    /// During `call_operation`, the embedded effect guarantee determines whether
+    /// the failure is safe to expose as `Internal`/`ResourceLimitExceeded` or must
+    /// become `OperationOutcomeUnknown`.
+    Failure(HostError),
+}
+
 /// A request-scoped Worldspace resolver and execution boundary.
 ///
 /// `with_object` must resolve the current object at `path` exactly once and pass
 /// a publication that pins its current interface set, implementations, and
-/// backend target for the duration of `operation`. Implementations may hold a
-/// transaction or lock around the callback. Returning `None` means the path is
-/// not published to the caller. The borrowed publication cannot escape the
-/// callback, so the default call path cannot outlive that provider boundary.
+/// backend target for the duration of `operation`. The execution context is the
+/// runtime-neutral carrier for cancellation, deadline, and resource controls.
+/// The borrowed publication cannot escape the callback.
+///
+/// Providers that can roll back mutable operations should override
+/// [`ObjectProvider::execute_operation`], hold their transaction across the
+/// callback, and call [`OperationAttempt::confirm_rollback`] only after rollback
+/// succeeds. The default boundary conservatively preserves unknown outcomes.
 pub trait ObjectProvider {
    /// Host-private object type produced by this provider.
    type Object: WipObject;

-    /// Runs an operation against the single object snapshot resolved at `path`.
+    /// Runs a callback against the single object snapshot resolved at `path`.
    fn with_object<R>(
        &self,
+        context: &ExecutionContext,
        path: &str,
        operation: impl FnOnce(&PublishedObject<Self::Object>) -> R,
-    ) -> Option<R>;
+    ) -> ProviderResult<R>;
+
+    /// Runs one operation attempt inside the provider's atomic backend boundary.
+    ///
+    /// The default implementation delegates to [`ObjectProvider::with_object`]
+    /// and therefore does not add a rollback guarantee. Transactional providers
+    /// can override this method, inspect the returned [`OperationAttempt`], roll
+    /// back a failed started attempt, and return its confirmed form.
+    fn execute_operation(
+        &self,
+        context: &ExecutionContext,
+        path: &str,
+        operation: impl FnOnce(&PublishedObject<Self::Object>) -> OperationAttempt,
+    ) -> ProviderResult<OperationAttempt> {
+        self.with_object(context, path, operation)
+    }

    /// Decides whether a declared operation may execute for the current caller.
    ///
@@ -540,16 +834,43 @@ pub trait ObjectProvider {

    /// Fetches the canonical object projection currently published at `path`.
    fn fetch(&self, path: &str) -> Result<Object, CallError> {
+        self.fetch_with_context(&ExecutionContext::default(), path)
+    }
+
+    /// Fetches an object while propagating runtime execution controls.
+    fn fetch_with_context(
+        &self,
+        context: &ExecutionContext,
+        path: &str,
+    ) -> Result<Object, CallError> {
        wip_protocol::validate_path(path)
            .map_err(|error| CallError::new(CallErrorKind::InvalidRequest, error.to_string()))?;
-        self.with_object(path, PublishedObject::protocol_object)
-            .ok_or_else(|| CallError::new(CallErrorKind::NotFound, "target path is not published"))
-            .and_then(|object| {
-                object.validate_at_path(path).map_err(|error| {
-                    CallError::new(CallErrorKind::InvalidResult, error.to_string())
-                })?;
-                Ok(object)
-            })
+        let resolved = catch_unwind(AssertUnwindSafe(|| {
+            self.with_object(context, path, PublishedObject::protocol_object)
+        }))
+        .map_err(|_| {
+            CallError::new(
+                CallErrorKind::Internal,
+                "provider panicked while fetching an object",
+            )
+        })?;
+        let object = match resolved {
+            ProviderResult::Found(object) => object,
+            ProviderResult::NotFound => {
+                return Err(CallError::new(
+                    CallErrorKind::NotFound,
+                    "target path is not published",
+                ));
+            }
+            ProviderResult::Failure(error) => return Err(CallError::from_read_failure(error)),
+        };
+        object.validate_at_path(path).map_err(|_| {
+            CallError::new(
+                CallErrorKind::Internal,
+                "Host produced an invalid object response",
+            )
+        })?;
+        Ok(object)
    }

    /// Resolves and executes a canonical path-targeted operation request.
@@ -559,17 +880,47 @@ pub trait ObjectProvider {
    /// supplied object validator mismatch, membership, interface validator
    /// requirement and mismatch, operation existence, object validator
    /// requirement, arguments, then authorization. No failed precondition
-    /// invokes the provider callback or typed implementation.
+    /// invokes typed implementation code.
    fn call_operation(&self, request: CallRequest) -> Result<CallResult, CallError> {
+        self.call_operation_with_context(&ExecutionContext::default(), request)
+    }
+
+    /// Executes an operation while propagating cancellation, deadline, and
+    /// resource-budget controls to the provider and runtime preflight check.
+    fn call_operation_with_context(
+        &self,
+        context: &ExecutionContext,
+        request: CallRequest,
+    ) -> Result<CallResult, CallError> {
        wip_protocol::validate_path(&request.target.path)
            .map_err(|error| CallError::new(CallErrorKind::InvalidRequest, error.to_string()))?;
        let path = request.target.path.clone();
-        self.with_object(&path, |publication| {
-            publication.dispatch_resolved(request, |object, interface, operation| {
-                self.authorize(&path, object, interface, operation)
+        let execution = catch_unwind(AssertUnwindSafe(|| {
+            self.execute_operation(context, &path, |publication| {
+                publication.dispatch_resolved(context, request, |object, interface, operation| {
+                    self.authorize(&path, object, interface, operation)
+                })
            })
-        })
-        .ok_or_else(|| CallError::new(CallErrorKind::NotFound, "target path is not published"))?
+        }));
+
+        let execution = execution.map_err(|_| {
+            CallError::from_operation_failure(OperationFailure::internal(
+                EffectGuarantee::Unknown,
+                "provider execution panicked",
+            ))
+        })?;
+        match execution {
+            ProviderResult::Found(OperationAttempt::NotStarted(error)) => Err(error),
+            ProviderResult::Found(OperationAttempt::Started(Ok(result))) => Ok(result),
+            ProviderResult::Found(OperationAttempt::Started(Err(error))) => {
+                Err(CallError::from_operation_failure(error))
+            }
+            ProviderResult::NotFound => Err(CallError::new(
+                CallErrorKind::NotFound,
+                "target path is not published",
+            )),
+            ProviderResult::Failure(error) => Err(CallError::from_host_failure(error)),
+        }
    }
 }

@@ -594,7 +945,7 @@ impl Display for PublicationError {

 impl Error for PublicationError {}

-/// Stable host dispatch failure kind.
+/// Stable Host dispatch failure kind.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum CallErrorKind {
    /// The request is structurally invalid.
@@ -607,8 +958,13 @@ pub enum CallErrorKind {
    OperationNotFound,
    /// Supplied named values do not satisfy the operation declaration.
    InvalidArguments,
-    /// The encoded implementation result violates its declaration.
-    InvalidResult,
+    /// A bounded cancellation, deadline, or resource limit was exceeded and the
+    /// operation effects are guaranteed not committed.
+    ResourceLimitExceeded,
+    /// The Host failed and operation effects are guaranteed not committed.
+    Internal,
+    /// The Host cannot guarantee whether operation effects were committed.
+    OperationOutcomeUnknown,
    /// This operation requires a validator and the call omitted it.
    ValidatorRequired,
    /// The supplied object validator is stale or belongs to another object.
@@ -619,11 +975,9 @@ pub enum CallErrorKind {
    InterfaceValidatorMismatch,
    /// The operation is declared but not authorized for the caller.
    PermissionDenied,
-    /// The typed implementation reported a host/backend failure.
-    Implementation,
 }

-/// A dispatch failure with a stable kind and non-normative diagnostic.
+/// A dispatch failure with a stable kind and bounded non-normative diagnostic.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct CallError {
    kind: CallErrorKind,
@@ -634,11 +988,11 @@ impl CallError {
    fn new(kind: CallErrorKind, message: impl Into<String>) -> Self {
        Self {
            kind,
-            message: message.into(),
+            message: bounded_message(message.into()),
        }
    }

-    fn from_dispatch(error: DispatchError) -> Self {
+    fn from_pre_dispatch(error: DispatchError) -> Self {
        match error {
            DispatchError::UnknownOperation(operation) => Self::new(
                CallErrorKind::OperationNotFound,
@@ -647,34 +1001,63 @@ impl CallError {
            DispatchError::InvalidArguments(error) => {
                Self::new(CallErrorKind::InvalidArguments, error.to_string())
            }
-            DispatchError::Decode(error) => {
-                Self::new(CallErrorKind::InvalidArguments, error.to_string())
-            }
-            DispatchError::Host(error) => {
-                Self::new(CallErrorKind::Implementation, error.to_string())
-            }
-            DispatchError::Encode(error) => {
-                Self::new(CallErrorKind::InvalidResult, error.to_string())
-            }
-            DispatchError::InvalidResult(error) => {
-                Self::new(CallErrorKind::InvalidResult, error.to_string())
+            DispatchError::Decode(_) => Self::new(
+                CallErrorKind::InvalidArguments,
+                "operation arguments could not be decoded",
+            ),
+            DispatchError::Host(_)
+            | DispatchError::Panic
+            | DispatchError::Encode(_)
+            | DispatchError::InvalidResult(_) => {
+                unreachable!("post-invocation failure used as a pre-dispatch failure")
            }
        }
    }

+    fn from_read_failure(error: HostError) -> Self {
+        match error.kind() {
+            HostErrorKind::Internal => Self::new(
+                CallErrorKind::Internal,
+                "provider failed while fetching data",
+            ),
+            HostErrorKind::ResourceLimitExceeded => Self::new(
+                CallErrorKind::ResourceLimitExceeded,
+                "provider resource limit was exceeded while fetching data",
+            ),
+        }
+    }
+
+    fn from_host_failure(error: HostError) -> Self {
+        let kind = classified_host_kind(error.kind(), error.effect_guarantee());
+        let message = match error.kind() {
+            HostErrorKind::Internal => "provider execution failed",
+            HostErrorKind::ResourceLimitExceeded => {
+                "provider execution resource limit was exceeded"
+            }
+        };
+        Self::new(kind, message)
+    }
+
+    fn from_operation_failure(error: OperationFailure) -> Self {
+        Self::new(
+            classified_host_kind(error.kind, error.effect_guarantee),
+            error.message,
+        )
+    }
+
    /// Returns the stable failure kind.
    #[must_use]
    pub fn kind(&self) -> CallErrorKind {
        self.kind
    }

-    /// Returns the human-readable diagnostic.
+    /// Returns the bounded protocol-safe human-readable diagnostic.
    #[must_use]
    pub fn message(&self) -> &str {
        &self.message
    }

-    /// Maps this host failure to the canonical protocol error taxonomy.
+    /// Maps this Host failure to the canonical protocol error taxonomy.
    #[must_use]
    pub fn protocol_error(&self) -> ProtocolError {
        let code = match self.kind {
@@ -683,7 +1066,9 @@ impl CallError {
            CallErrorKind::InterfaceMismatch => ProtocolErrorCode::InterfaceMismatch,
            CallErrorKind::OperationNotFound => ProtocolErrorCode::OperationNotFound,
            CallErrorKind::InvalidArguments => ProtocolErrorCode::InvalidArguments,
-            CallErrorKind::InvalidResult => ProtocolErrorCode::InvalidResult,
+            CallErrorKind::ResourceLimitExceeded => ProtocolErrorCode::ResourceLimitExceeded,
+            CallErrorKind::Internal => ProtocolErrorCode::Internal,
+            CallErrorKind::OperationOutcomeUnknown => ProtocolErrorCode::OperationOutcomeUnknown,
            CallErrorKind::ValidatorRequired => ProtocolErrorCode::ValidatorRequired,
            CallErrorKind::ValidatorMismatch => ProtocolErrorCode::ValidatorMismatch,
            CallErrorKind::InterfaceValidatorRequired => {
@@ -693,7 +1078,6 @@ impl CallError {
                ProtocolErrorCode::InterfaceValidatorMismatch
            }
            CallErrorKind::PermissionDenied => ProtocolErrorCode::PermissionDenied,
-            CallErrorKind::Implementation => ProtocolErrorCode::Internal,
        };
        ProtocolError {
            code,
@@ -702,6 +1086,30 @@ impl CallError {
    }
 }

+fn classified_host_kind(kind: HostErrorKind, effect_guarantee: EffectGuarantee) -> CallErrorKind {
+    match effect_guarantee {
+        EffectGuarantee::Unknown => CallErrorKind::OperationOutcomeUnknown,
+        EffectGuarantee::NotCommitted => match kind {
+            HostErrorKind::Internal => CallErrorKind::Internal,
+            HostErrorKind::ResourceLimitExceeded => CallErrorKind::ResourceLimitExceeded,
+        },
+    }
+}
+
+const MAX_PROTOCOL_MESSAGE_BYTES: usize = 512;
+
+fn bounded_message(mut message: String) -> String {
+    if message.len() <= MAX_PROTOCOL_MESSAGE_BYTES {
+        return message;
+    }
+    let mut end = MAX_PROTOCOL_MESSAGE_BYTES;
+    while !message.is_char_boundary(end) {
+        end -= 1;
+    }
+    message.truncate(end);
+    message
+}
+
 impl Display for CallError {
    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
        write!(
@@ -1,13 +1,16 @@
 use std::cell::Cell;
 use std::collections::BTreeMap;
 use std::rc::Rc;
+use std::time::{Duration, Instant};

 use wip_host::{
-    CallError, CallErrorKind, CallRequest, InterfaceRef, InterfaceRegistry, InterfaceTarget,
-    ObjectProvider, PublishedObject, RegisteredInterface, Target, Validator, WipObject,
+    CallError, CallErrorKind, CallRequest, CancellationToken, ExecutionContext, InterfaceRef,
+    InterfaceRegistry, InterfaceTarget, ObjectProvider, OperationAttempt, ProviderResult,
+    PublishedObject, RegisteredInterface, Target, Validator, WipObject,
 };
 use wip_interface::{
-    CodecError, HostError, OperationResult, TypeDeclaration, TypeExpr, Value, WipType, interface,
+    CodecError, EffectGuarantee, HostError, OperationResult, TypeDeclaration, TypeExpr, Value,
+    WipType, interface,
 };
 use wip_protocol::ProtocolErrorCode;

@@ -39,6 +42,24 @@ pub trait Hidden {
 pub trait Broken {
    /// Returns a deliberately invalid encoded value.
    fn broken(&self) -> OperationResult<BadValue>;
+
+    /// Produces a result codec failure after implementation invocation.
+    fn encode_failure(&self) -> OperationResult<EncodeFailure>;
+
+    /// Panics after implementation invocation begins.
+    fn panic_after_call(&self) -> OperationResult<String>;
+
+    /// Reports an internal failure without an effect guarantee.
+    fn unknown_internal(&self) -> OperationResult<String>;
+
+    /// Reports an internal failure with a non-commit guarantee.
+    fn safe_internal(&self) -> OperationResult<String>;
+
+    /// Reports a resource failure without an effect guarantee.
+    fn unknown_resource(&self) -> OperationResult<String>;
+
+    /// Reports a resource failure with a non-commit guarantee.
+    fn safe_resource(&self) -> OperationResult<String>;
 }

 #[derive(Debug)]
@@ -60,6 +81,25 @@ impl WipType for BadValue {
    }
 }

+#[derive(Debug)]
+pub struct EncodeFailure;
+
+impl WipType for EncodeFailure {
+    fn type_expr() -> TypeExpr {
+        TypeExpr::String
+    }
+
+    fn collect_declarations(_: &mut Vec<TypeDeclaration>) {}
+
+    fn encode(self) -> Result<Value, CodecError> {
+        Err(CodecError::new("private://backend/result could not encode"))
+    }
+
+    fn decode(_: Value) -> Result<Self, CodecError> {
+        Ok(Self)
+    }
+}
+
 struct Document {
    name: String,
    description: Option<String>,
@@ -135,7 +175,10 @@ impl Reader for Document {

    fn fail(&self) -> OperationResult<String> {
        self.record_call();
-        Err(HostError::new("backend unavailable"))
+        Err(HostError::internal(
+            "backend unavailable",
+            EffectGuarantee::Unknown,
+        ))
    }
 }

@@ -158,6 +201,48 @@ impl Broken for Document {
        self.record_call();
        Ok(BadValue)
    }
+
+    fn encode_failure(&self) -> OperationResult<EncodeFailure> {
+        self.record_call();
+        Ok(EncodeFailure)
+    }
+
+    fn panic_after_call(&self) -> OperationResult<String> {
+        self.record_call();
+        panic!("private://backend panic with credential=secret")
+    }
+
+    fn unknown_internal(&self) -> OperationResult<String> {
+        self.record_call();
+        Err(HostError::internal(
+            "private://backend/path credential=secret",
+            EffectGuarantee::Unknown,
+        ))
+    }
+
+    fn safe_internal(&self) -> OperationResult<String> {
+        self.record_call();
+        Err(HostError::internal(
+            "private://backend/path credential=secret",
+            EffectGuarantee::NotCommitted,
+        ))
+    }
+
+    fn unknown_resource(&self) -> OperationResult<String> {
+        self.record_call();
+        Err(HostError::resource_limit(
+            "private scheduler deadline details",
+            EffectGuarantee::Unknown,
+        ))
+    }
+
+    fn safe_resource(&self) -> OperationResult<String> {
+        self.record_call();
+        Err(HostError::resource_limit(
+            "private scheduler deadline details",
+            EffectGuarantee::NotCommitted,
+        ))
+    }
 }

 struct TestProvider {
@@ -169,6 +254,11 @@ struct TestProvider {
    authorization_checks: Cell<usize>,
    deny: Cell<bool>,
    switched: Cell<bool>,
+    confirm_rollback: Cell<bool>,
+    provider_failure: Cell<Option<(bool, EffectGuarantee)>>,
+    observed_budget: Cell<Option<u64>>,
+    observed_deadline: Cell<Option<Instant>>,
+    observed_cancelled: Cell<bool>,
 }

 impl TestProvider {
@@ -186,6 +276,11 @@ impl TestProvider {
            authorization_checks: Cell::new(0),
            deny: Cell::new(false),
            switched: Cell::new(false),
+            confirm_rollback: Cell::new(false),
+            provider_failure: Cell::new(None),
+            observed_budget: Cell::new(None),
+            observed_deadline: Cell::new(None),
+            observed_cancelled: Cell::new(false),
        }
    }
 }
@@ -195,9 +290,14 @@ impl ObjectProvider for TestProvider {

    fn with_object<R>(
        &self,
+        context: &ExecutionContext,
        path: &str,
        operation: impl FnOnce(&PublishedObject<Self::Object>) -> R,
-    ) -> Option<R> {
+    ) -> ProviderResult<R> {
+        self.observed_budget.set(context.resource_budget());
+        self.observed_deadline.set(context.deadline());
+        self.observed_cancelled
+            .set(context.cancellation().is_cancelled());
        self.resolutions.set(self.resolutions.get() + 1);
        let (document, interfaces) = match path {
            "/document" => (
@@ -235,11 +335,15 @@ impl ObjectProvider for TestProvider {
                )
            }
            "/empty" => (Document::open("empty", None, Rc::clone(&self.calls)), 0),
+            "/invalid-object" => (
+                Document::open("wrong-name", None, Rc::clone(&self.calls)),
+                0,
+            ),
            "/broken" => (
                Document::open("broken", Some("broken-ref"), Rc::clone(&self.calls)),
                3,
            ),
-            _ => return None,
+            _ => return ProviderResult::NotFound,
        };

        let publication = PublishedObject::new(document);
@@ -253,7 +357,32 @@ impl ObjectProvider for TestProvider {
            3 => publication.expose(&self.broken).unwrap(),
            _ => unreachable!(),
        };
-        Some(operation(&publication))
+        ProviderResult::Found(operation(&publication))
+    }
+
+    fn execute_operation(
+        &self,
+        context: &ExecutionContext,
+        path: &str,
+        operation: impl FnOnce(&PublishedObject<Self::Object>) -> OperationAttempt,
+    ) -> ProviderResult<OperationAttempt> {
+        let result = self.with_object(context, path, operation);
+        if let Some((resource, guarantee)) = self.provider_failure.get() {
+            let error = if resource {
+                HostError::resource_limit("private provider scheduler state", guarantee)
+            } else {
+                HostError::internal("private provider transaction path", guarantee)
+            };
+            return ProviderResult::Failure(error);
+        }
+        if self.confirm_rollback.get() {
+            match result {
+                ProviderResult::Found(attempt) => ProviderResult::Found(attempt.confirm_rollback()),
+                other => other,
+            }
+        } else {
+            result
+        }
    }

    fn authorize(&self, _: &str, _: &Document, _: &InterfaceRef, _: &str) -> bool {
@@ -316,12 +445,21 @@ fn registry_returns_atomic_canonical_observation_without_rewriting_descriptor()
    assert_eq!(observation.reference, *reference);
    assert_eq!(observation.descriptor, ReaderDefinition::descriptor());
    assert_eq!(observation.validator, Some(Validator::new(b"schema-v1")));
-    let response = observation.protocol_response();
+    let response = observation.protocol_response().unwrap();
    assert_eq!(response.interface, reference.as_str());
    assert_eq!(response.descriptor, ReaderDefinition::descriptor());
    assert_eq!(response.validator.as_deref(), Some(b"schema-v1".as_slice()));
    response.descriptor.validate().unwrap();

+    let mut invalid_observation = registry.fetch_interface(reference.as_str()).unwrap();
+    let duplicate_operation = invalid_observation.descriptor.operations[0].clone();
+    invalid_observation
+        .descriptor
+        .operations
+        .push(duplicate_operation);
+    let invalid_response = invalid_observation.protocol_response().unwrap_err();
+    assert_eq!(invalid_response.code, ProtocolErrorCode::Internal);
+
    let error = registry.fetch_interface("unknown").unwrap_err();
    assert_eq!(error.code, ProtocolErrorCode::InterfaceNotFound);
 }
@@ -624,9 +762,15 @@ fn immutable_interface_rejects_a_supplied_validator() {
 }

 #[test]
-fn invalid_results_and_backend_failures_keep_distinct_protocol_codes() {
+fn invalid_host_responses_and_uncertain_operation_failures_use_canonical_codes() {
    let (_, provider, _) = registry_and_provider();

+    assert_failure(
+        provider.fetch("/invalid-object").unwrap_err(),
+        CallErrorKind::Internal,
+        ProtocolErrorCode::Internal,
+    );
+
    assert_failure(
        provider
            .call_operation(request(
@@ -638,8 +782,8 @@ fn invalid_results_and_backend_failures_keep_distinct_protocol_codes() {
                BTreeMap::new(),
            ))
            .unwrap_err(),
-        CallErrorKind::InvalidResult,
-        ProtocolErrorCode::InvalidResult,
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
    );
    assert_failure(
        provider
@@ -652,7 +796,190 @@ fn invalid_results_and_backend_failures_keep_distinct_protocol_codes() {
                BTreeMap::new(),
            ))
            .unwrap_err(),
-        CallErrorKind::Implementation,
-        ProtocolErrorCode::Internal,
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
    );
 }
+
+fn call_broken(provider: &TestProvider, operation: &str) -> CallError {
+    provider
+        .call_operation(request(
+            "/broken",
+            None,
+            provider.broken.reference(),
+            None,
+            operation,
+            BTreeMap::new(),
+        ))
+        .unwrap_err()
+}
+
+#[test]
+fn typed_implementation_failures_map_only_with_a_non_commit_guarantee() {
+    let (_, provider, _) = registry_and_provider();
+
+    let unknown_internal = call_broken(&provider, "unknown_internal");
+    assert_failure(
+        unknown_internal.clone(),
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
+    );
+    assert!(!unknown_internal.message().contains("private://"));
+    assert!(
+        !unknown_internal
+            .protocol_error()
+            .message
+            .contains("credential")
+    );
+
+    assert_failure(
+        call_broken(&provider, "safe_internal"),
+        CallErrorKind::Internal,
+        ProtocolErrorCode::Internal,
+    );
+    assert_failure(
+        call_broken(&provider, "unknown_resource"),
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
+    );
+    assert_failure(
+        call_broken(&provider, "safe_resource"),
+        CallErrorKind::ResourceLimitExceeded,
+        ProtocolErrorCode::ResourceLimitExceeded,
+    );
+}
+
+#[test]
+fn post_invocation_result_and_panic_failures_require_provider_rollback() {
+    for operation in ["broken", "encode_failure", "panic_after_call"] {
+        let (_, provider, _) = registry_and_provider();
+        let error = call_broken(&provider, operation);
+        assert_failure(
+            error.clone(),
+            CallErrorKind::OperationOutcomeUnknown,
+            ProtocolErrorCode::OperationOutcomeUnknown,
+        );
+        assert!(!error.message().contains("private://"));
+        assert!(!error.message().contains("credential"));
+
+        provider.confirm_rollback.set(true);
+        assert_failure(
+            call_broken(&provider, operation),
+            CallErrorKind::Internal,
+            ProtocolErrorCode::Internal,
+        );
+    }
+}
+
+#[test]
+fn provider_failures_after_invocation_use_the_provider_effect_guarantee() {
+    let (_, provider, _) = registry_and_provider();
+
+    provider
+        .provider_failure
+        .set(Some((false, EffectGuarantee::Unknown)));
+    assert_failure(
+        call_broken(&provider, "safe_internal"),
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
+    );
+
+    provider
+        .provider_failure
+        .set(Some((false, EffectGuarantee::NotCommitted)));
+    let internal = call_broken(&provider, "unknown_internal");
+    assert_failure(
+        internal.clone(),
+        CallErrorKind::Internal,
+        ProtocolErrorCode::Internal,
+    );
+    assert!(!internal.message().contains("transaction"));
+
+    provider
+        .provider_failure
+        .set(Some((true, EffectGuarantee::Unknown)));
+    assert_failure(
+        call_broken(&provider, "safe_resource"),
+        CallErrorKind::OperationOutcomeUnknown,
+        ProtocolErrorCode::OperationOutcomeUnknown,
+    );
+
+    provider
+        .provider_failure
+        .set(Some((true, EffectGuarantee::NotCommitted)));
+    assert_failure(
+        call_broken(&provider, "unknown_resource"),
+        CallErrorKind::ResourceLimitExceeded,
+        ProtocolErrorCode::ResourceLimitExceeded,
+    );
+}
+
+#[test]
+fn execution_context_is_propagated_and_preflight_prevents_invocation() {
+    let (_, provider, _) = registry_and_provider();
+    let deadline = Instant::now() + Duration::from_secs(60);
+    let context = ExecutionContext::new()
+        .with_deadline(deadline)
+        .with_resource_budget(17);
+
+    provider
+        .call_operation_with_context(
+            &context,
+            request(
+                "/open",
+                None,
+                provider.reader.reference(),
+                Some(b"schema-v1"),
+                "label",
+                BTreeMap::new(),
+            ),
+        )
+        .unwrap();
+    assert_eq!(provider.observed_deadline.get(), Some(deadline));
+    assert_eq!(provider.observed_budget.get(), Some(17));
+    assert!(!provider.observed_cancelled.get());
+
+    let calls = provider.calls.get();
+    let cancellation = CancellationToken::new();
+    cancellation.cancel();
+    let cancelled = ExecutionContext::new().with_cancellation(cancellation);
+    assert_failure(
+        provider
+            .call_operation_with_context(
+                &cancelled,
+                request(
+                    "/open",
+                    None,
+                    provider.reader.reference(),
+                    Some(b"schema-v1"),
+                    "label",
+                    BTreeMap::new(),
+                ),
+            )
+            .unwrap_err(),
+        CallErrorKind::ResourceLimitExceeded,
+        ProtocolErrorCode::ResourceLimitExceeded,
+    );
+    assert_eq!(provider.calls.get(), calls);
+    assert!(provider.observed_cancelled.get());
+
+    let expired = ExecutionContext::new().with_deadline(Instant::now() - Duration::from_secs(1));
+    assert_failure(
+        provider
+            .call_operation_with_context(
+                &expired,
+                request(
+                    "/open",
+                    None,
+                    provider.reader.reference(),
+                    Some(b"schema-v1"),
+                    "label",
+                    BTreeMap::new(),
+                ),
+            )
+            .unwrap_err(),
+        CallErrorKind::ResourceLimitExceeded,
+        ProtocolErrorCode::ResourceLimitExceeded,
+    );
+    assert_eq!(provider.calls.get(), calls);
+}
@@ -0,0 +1,14 @@
+[package]
+name = "wip-https"
+version = "0.1.0"
+edition = "2024"
+description = "Framework-independent standard WIP over HTTPS v1 binding"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+base64 = "0.22"
+http = "1"
+serde = "1"
+serde_json = "1"
+url = "2"
+wip-protocol = { path = "../wip-protocol" }
@@ -0,0 +1,596 @@
+use std::collections::{BTreeMap, BTreeSet};
+
+use http::header::{ACCEPT, CONTENT_TYPE};
+use http::{Method, Request, Response, StatusCode};
+use serde_json::{Map, Value as Json};
+use wip_protocol::{
+    FetchInterfaceRequest, FetchInterfaceResponse, FetchRequest, FetchResponse, FetchTreeRequest,
+    FetchTreeResponse, INTERFACE_FORMAT_V1, ProtocolError, ProtocolErrorCode, ProtocolInteraction,
+};
+
+use crate::response::{self, DecodedResponse};
+use crate::{
+    BodyKind, ClientResponseError, CodecError, EncodeHttpError, Endpoint, InvalidResponseKind,
+    JSON_CONTENT_TYPE, Limits, ResourceLimitKind, Route, is_json_content_type, json,
+};
+
+/// A retrieval method accepted by the standard v1 batch endpoint.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BatchMethod {
+    /// Fetch one object.
+    Fetch,
+    /// Fetch one bounded tree.
+    FetchTree,
+    /// Fetch one interface descriptor.
+    FetchInterface,
+}
+
+impl BatchMethod {
+    fn name(self) -> &'static str {
+        match self {
+            Self::Fetch => "fetch",
+            Self::FetchTree => "fetch_tree",
+            Self::FetchInterface => "fetch_interface",
+        }
+    }
+
+    fn interaction(self) -> ProtocolInteraction {
+        match self {
+            Self::Fetch => ProtocolInteraction::Fetch,
+            Self::FetchTree => ProtocolInteraction::FetchTree,
+            Self::FetchInterface => ProtocolInteraction::FetchInterface,
+        }
+    }
+}
+
+/// One retrieval interaction accepted by the standard v1 batch endpoint.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum BatchRequestKind {
+    /// Fetch one object.
+    Fetch(FetchRequest),
+    /// Fetch one bounded tree.
+    FetchTree(FetchTreeRequest),
+    /// Fetch one interface descriptor.
+    FetchInterface(FetchInterfaceRequest),
+    /// A known method whose `arguments` are not a valid logical request.
+    Invalid {
+        /// Method that was successfully identified from the item envelope.
+        method: BatchMethod,
+        /// Item-local `invalid_request` to return without rejecting other items.
+        error: ProtocolError,
+    },
+}
+
+impl BatchRequestKind {
+    fn interaction(&self) -> ProtocolInteraction {
+        match self {
+            Self::Fetch(_) => ProtocolInteraction::Fetch,
+            Self::FetchTree(_) => ProtocolInteraction::FetchTree,
+            Self::FetchInterface(_) => ProtocolInteraction::FetchInterface,
+            Self::Invalid { method, .. } => method.interaction(),
+        }
+    }
+}
+
+/// One uniquely identified batch subrequest.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct BatchRequestItem {
+    /// Identifier used only to correlate the corresponding subresponse.
+    pub id: String,
+    /// Retrieval interaction and arguments.
+    pub request: BatchRequestKind,
+}
+
+/// A standard v1 batch request.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct BatchRequest {
+    /// Independent subrequests. Identifiers must be unique.
+    pub requests: Vec<BatchRequestItem>,
+}
+
+/// Successful result of one batch item.
+#[derive(Debug, Clone, PartialEq)]
+pub enum BatchSuccess {
+    /// Successful `fetch` result.
+    Fetch(FetchResponse),
+    /// Successful `fetch_tree` result.
+    FetchTree(FetchTreeResponse),
+    /// Successful `fetch_interface` result.
+    FetchInterface(FetchInterfaceResponse),
+}
+
+/// One batch subresponse, correlated by `id` rather than array position.
+#[derive(Debug, Clone, PartialEq)]
+pub struct BatchResponseItem {
+    /// Identifier copied from its subrequest.
+    pub id: String,
+    /// Direct interaction result or canonical item-local protocol failure.
+    pub outcome: Result<BatchSuccess, ProtocolError>,
+}
+
+/// A valid standard v1 batch response.
+#[derive(Debug, Clone, PartialEq)]
+pub struct BatchResponse {
+    /// Exactly one response for each requested identifier, in any order.
+    pub responses: Vec<BatchResponseItem>,
+}
+
+fn validate_ids<'a>(ids: impl Iterator<Item = &'a str>, maximum: usize) -> Result<(), CodecError> {
+    let mut seen = BTreeSet::new();
+    let mut count = 0;
+    for id in ids {
+        count += 1;
+        if !seen.insert(id) {
+            return Err(CodecError::DuplicateBatchId { id: id.into() });
+        }
+    }
+    if count > maximum {
+        return Err(CodecError::TooManyBatchItems {
+            actual: count,
+            maximum,
+        });
+    }
+    Ok(())
+}
+
+fn request_item_to_json(item: &BatchRequestItem) -> Result<Json, CodecError> {
+    let (method, arguments) = match &item.request {
+        BatchRequestKind::Fetch(value) => ("fetch", json::fetch_request_to_json(value)),
+        BatchRequestKind::FetchTree(value) => {
+            ("fetch_tree", json::fetch_tree_request_to_json(value))
+        }
+        BatchRequestKind::FetchInterface(value) => (
+            "fetch_interface",
+            json::fetch_interface_request_to_json(value),
+        ),
+        BatchRequestKind::Invalid { .. } => {
+            return Err(CodecError::InvalidField {
+                field: "requests".into(),
+                reason: "item-local invalid requests cannot be encoded as client requests".into(),
+            });
+        }
+    };
+    Ok(serde_json::json!({"id": item.id, "method": method, "arguments": arguments}))
+}
+
+fn request_to_json(request: &BatchRequest, limits: Limits) -> Result<Json, CodecError> {
+    validate_ids(
+        request.requests.iter().map(|item| item.id.as_str()),
+        limits.max_batch_items,
+    )?;
+    for item in &request.requests {
+        match &item.request {
+            BatchRequestKind::Fetch(value) => value.validate()?,
+            BatchRequestKind::FetchTree(value) => value.validate()?,
+            BatchRequestKind::FetchInterface(_) | BatchRequestKind::Invalid { .. } => {}
+        }
+    }
+    let requests = request
+        .requests
+        .iter()
+        .map(request_item_to_json)
+        .collect::<Result<Vec<_>, _>>()?;
+    Ok(serde_json::json!({"requests": requests}))
+}
+
+fn request_from_json(value: &Json, limits: Limits) -> Result<BatchRequest, CodecError> {
+    let fields = exact_object(value, "batch", &["requests"])?;
+    let values = array(required(fields, "requests")?, "requests")?;
+    if values.len() > limits.max_batch_items {
+        return Err(CodecError::TooManyBatchItems {
+            actual: values.len(),
+            maximum: limits.max_batch_items,
+        });
+    }
+    let mut requests = Vec::with_capacity(values.len());
+    for (index, value) in values.iter().enumerate() {
+        let field = format!("requests[{index}]");
+        let fields = exact_object(value, &field, &["id", "method", "arguments"])?;
+        let id = string(required(fields, "id")?, &format!("{field}.id"))?;
+        let method_name = string(required(fields, "method")?, &format!("{field}.method"))?;
+        let arguments = required(fields, "arguments")?;
+        let method = match method_name.as_str() {
+            "fetch" => BatchMethod::Fetch,
+            "fetch_tree" => BatchMethod::FetchTree,
+            "fetch_interface" => BatchMethod::FetchInterface,
+            _ => {
+                return Err(CodecError::InvalidField {
+                    field: format!("{field}.method"),
+                    reason: "batch supports only fetch, fetch_tree, and fetch_interface".into(),
+                });
+            }
+        };
+        let decoded = match method {
+            BatchMethod::Fetch => {
+                json::fetch_request_from_json(arguments).map(BatchRequestKind::Fetch)
+            }
+            BatchMethod::FetchTree => {
+                json::fetch_tree_request_from_json(arguments).map(BatchRequestKind::FetchTree)
+            }
+            BatchMethod::FetchInterface => json::fetch_interface_request_from_json(arguments)
+                .map(BatchRequestKind::FetchInterface),
+        };
+        let request = decoded.unwrap_or_else(|error| BatchRequestKind::Invalid {
+            method,
+            error: ProtocolError {
+                code: ProtocolErrorCode::InvalidRequest,
+                message: format!("invalid {} arguments: {error}", method.name()),
+            },
+        });
+        requests.push(BatchRequestItem { id, request });
+    }
+    validate_ids(
+        requests.iter().map(|item| item.id.as_str()),
+        limits.max_batch_items,
+    )?;
+    Ok(BatchRequest { requests })
+}
+
+/// Encodes a batch request using `POST v1/batch`.
+pub fn encode_batch_request(
+    endpoint: &Endpoint,
+    value: &BatchRequest,
+    limits: Limits,
+) -> Result<Request<Vec<u8>>, EncodeHttpError> {
+    let body = json::serialize(&request_to_json(value, limits)?, BodyKind::Request, limits)?;
+    Ok(Request::builder()
+        .method(Method::POST)
+        .uri(endpoint.route(Route::Batch).as_str())
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(ACCEPT, "application/json")
+        .body(body)?)
+}
+
+/// Decodes and validates a batch request body.
+pub fn decode_batch_request(body: &[u8], limits: Limits) -> Result<BatchRequest, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    request_from_json(&value, limits)
+}
+
+fn success_to_json(success: &BatchSuccess) -> Json {
+    match success {
+        BatchSuccess::Fetch(value) => json::object_to_json(value),
+        BatchSuccess::FetchTree(value) => json::fetch_tree_response_to_json(value),
+        BatchSuccess::FetchInterface(value) => json::fetch_interface_response_to_json(value),
+    }
+}
+
+fn response_to_json(
+    request: &BatchRequest,
+    response: &BatchResponse,
+    limits: Limits,
+) -> Result<Json, CodecError> {
+    correlate(request, response, limits)?;
+    Ok(serde_json::json!({
+        "responses": response.responses.iter().map(|item| {
+            let mut fields = Map::new();
+            fields.insert("id".into(), Json::String(item.id.clone()));
+            match &item.outcome {
+                Ok(success) => { fields.insert("result".into(), success_to_json(success)); }
+                Err(error) => { fields.insert("error".into(), response::item_error_to_json(error)); }
+            }
+            Json::Object(fields)
+        }).collect::<Vec<_>>()
+    }))
+}
+
+fn correlate(
+    request: &BatchRequest,
+    response: &BatchResponse,
+    limits: Limits,
+) -> Result<(), CodecError> {
+    validate_ids(
+        request.requests.iter().map(|item| item.id.as_str()),
+        limits.max_batch_items,
+    )?;
+    validate_ids(
+        response.responses.iter().map(|item| item.id.as_str()),
+        limits.max_batch_items,
+    )?;
+    let requested: BTreeMap<&str, &BatchRequestKind> = request
+        .requests
+        .iter()
+        .map(|item| (item.id.as_str(), &item.request))
+        .collect();
+    for item in &response.responses {
+        let Some(kind) = requested.get(item.id.as_str()) else {
+            return Err(CodecError::UnexpectedBatchId {
+                id: item.id.clone(),
+            });
+        };
+        match (&item.outcome, *kind) {
+            (Ok(BatchSuccess::Fetch(value)), BatchRequestKind::Fetch(request)) => {
+                request.validate_response(value)?;
+            }
+            (Ok(BatchSuccess::FetchTree(value)), BatchRequestKind::FetchTree(request)) => {
+                value.validate_for(request)?;
+            }
+            (
+                Ok(BatchSuccess::FetchInterface(value)),
+                BatchRequestKind::FetchInterface(request),
+            ) => {
+                value.validate_for(request)?;
+            }
+            (
+                Err(error),
+                BatchRequestKind::Invalid {
+                    error: expected, ..
+                },
+            ) if error == expected => {}
+            (Err(error), kind)
+                if !matches!(kind, BatchRequestKind::Invalid { .. })
+                    && error.code.is_allowed_for(kind.interaction()) => {}
+            _ => {
+                return Err(CodecError::BatchInteractionMismatch {
+                    id: item.id.clone(),
+                });
+            }
+        }
+    }
+    for item in &request.requests {
+        if !response.responses.iter().any(|other| other.id == item.id) {
+            return Err(CodecError::MissingBatchId {
+                id: item.id.clone(),
+            });
+        }
+    }
+    Ok(())
+}
+
+/// Encodes a valid batch response. Item failures remain inside HTTP 200.
+pub fn encode_batch_response(
+    request: &BatchRequest,
+    value: &BatchResponse,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    let body = json::serialize(
+        &response_to_json(request, value, limits)?,
+        BodyKind::Response,
+        limits,
+    )?;
+    Ok(Response::builder()
+        .status(StatusCode::OK)
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .body(body)?)
+}
+
+/// Encodes a top-level batch-envelope failure.
+///
+/// Item-local failures belong in [`BatchResponseItem`]. Only failures that can
+/// reject the batch envelope before item execution are accepted here. A
+/// resource-limit failure defaults to the logical-limit status; use
+/// [`encode_batch_resource_limit_error_response`] when the concrete class is
+/// known.
+pub fn encode_batch_error_response(
+    error: &ProtocolError,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    if !matches!(
+        error.code,
+        ProtocolErrorCode::InvalidRequest
+            | ProtocolErrorCode::ResourceLimitExceeded
+            | ProtocolErrorCode::Internal
+    ) {
+        return Err(CodecError::InvalidField {
+            field: "error.code".into(),
+            reason: "code is not valid for a top-level batch failure".into(),
+        }
+        .into());
+    }
+    let body = json::serialize(&response::error_to_json(error), BodyKind::Response, limits)?;
+    Ok(Response::builder()
+        .status(response::status_for_error(error.code))
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .body(body)?)
+}
+
+/// Encodes a class-specific top-level batch `resource_limit_exceeded` failure.
+pub fn encode_batch_resource_limit_error_response(
+    error: &ProtocolError,
+    kind: ResourceLimitKind,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    if error.code != ProtocolErrorCode::ResourceLimitExceeded {
+        return Err(CodecError::InvalidField {
+            field: "error.code".into(),
+            reason: "resource-limit encoder requires resource_limit_exceeded".into(),
+        }
+        .into());
+    }
+    let body = json::serialize(&response::error_to_json(error), BodyKind::Response, limits)?;
+    Ok(Response::builder()
+        .status(response::status_for_resource_limit(kind))
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .body(body)?)
+}
+
+fn response_from_json(
+    value: &Json,
+    request: &BatchRequest,
+    limits: Limits,
+) -> Result<BatchResponse, CodecError> {
+    let fields = exact_object(value, "batch", &["responses"])?;
+    let values = array(required(fields, "responses")?, "responses")?;
+    if values.len() > limits.max_batch_items {
+        return Err(CodecError::TooManyBatchItems {
+            actual: values.len(),
+            maximum: limits.max_batch_items,
+        });
+    }
+    let requested: BTreeMap<&str, &BatchRequestKind> = request
+        .requests
+        .iter()
+        .map(|item| (item.id.as_str(), &item.request))
+        .collect();
+    let mut responses = Vec::with_capacity(values.len());
+    for (index, value) in values.iter().enumerate() {
+        let field = format!("responses[{index}]");
+        let fields = object(value, &field)?;
+        for name in fields.keys() {
+            if !["id", "result", "error"].contains(&name.as_str()) {
+                return Err(CodecError::UnknownField {
+                    field: format!("{field}.{name}"),
+                });
+            }
+        }
+        let id = string(required(fields, "id")?, &format!("{field}.id"))?;
+        let Some(kind) = requested.get(id.as_str()) else {
+            return Err(CodecError::UnexpectedBatchId { id });
+        };
+        let outcome = match (fields.get("result"), fields.get("error")) {
+            (Some(_), Some(_)) | (None, None) => {
+                return Err(CodecError::InvalidField {
+                    field,
+                    reason: "batch item must contain exactly one of result or error".into(),
+                });
+            }
+            (None, Some(error)) => {
+                let error = response::item_error_from_json(error)?;
+                match kind {
+                    BatchRequestKind::Invalid {
+                        error: expected, ..
+                    } if error == *expected => {}
+                    BatchRequestKind::Invalid { .. } => {
+                        return Err(CodecError::BatchInteractionMismatch { id });
+                    }
+                    kind if error.code.is_allowed_for(kind.interaction()) => {}
+                    _ => return Err(CodecError::BatchInteractionMismatch { id }),
+                }
+                Err(error)
+            }
+            (Some(result), None) => Ok(match kind {
+                BatchRequestKind::Fetch(request) => {
+                    let value = json::object_from_json(result, "result")?;
+                    request.validate_response(&value)?;
+                    BatchSuccess::Fetch(value)
+                }
+                BatchRequestKind::FetchTree(request) => {
+                    let value = json::fetch_tree_response_from_json(result)?;
+                    value.validate_for(request)?;
+                    BatchSuccess::FetchTree(value)
+                }
+                BatchRequestKind::FetchInterface(request) => {
+                    let value = json::fetch_interface_response_from_json(result)?;
+                    value.validate_for(request)?;
+                    BatchSuccess::FetchInterface(value)
+                }
+                BatchRequestKind::Invalid { .. } => {
+                    return Err(CodecError::BatchInteractionMismatch { id });
+                }
+            }),
+        };
+        responses.push(BatchResponseItem { id, outcome });
+    }
+    let response = BatchResponse { responses };
+    correlate(request, &response, limits)?;
+    Ok(response)
+}
+
+/// Decodes a batch response, including item-local failures within HTTP 200.
+pub fn decode_batch_response<B: AsRef<[u8]>>(
+    request: &BatchRequest,
+    value: &Response<B>,
+    limits: Limits,
+) -> Result<DecodedResponse<BatchResponse>, ClientResponseError> {
+    let valid_content_type = value
+        .headers()
+        .get(CONTENT_TYPE)
+        .and_then(|value| value.to_str().ok())
+        .is_some_and(is_json_content_type);
+    if !valid_content_type {
+        if value.status().is_success() {
+            return Err(ClientResponseError::invalid(
+                InvalidResponseKind::InvalidBatch,
+                "missing or non-UTF-8 application/json Content-Type",
+            ));
+        }
+        return Err(response::transport_failure(value.status()));
+    }
+    let decoded = response::decode(
+        value.status(),
+        value.body().as_ref(),
+        ProtocolInteraction::Fetch,
+        limits,
+        |json| response_from_json(json, request, limits),
+    )
+    .map_err(|error| match error {
+        ClientResponseError::InvalidResponse { detail, .. } => {
+            ClientResponseError::invalid(InvalidResponseKind::InvalidBatch, detail)
+        }
+        other => other,
+    })?;
+    if let DecodedResponse::ProtocolFailure { error, .. } = &decoded
+        && !matches!(
+            error.code,
+            ProtocolErrorCode::InvalidRequest
+                | ProtocolErrorCode::ResourceLimitExceeded
+                | ProtocolErrorCode::Internal
+        )
+    {
+        return Err(ClientResponseError::invalid(
+            InvalidResponseKind::InvalidBatch,
+            "protocol code is not valid for a top-level batch failure",
+        ));
+    }
+    if let DecodedResponse::Success(success) = &decoded {
+        for item in &success.responses {
+            if let Ok(BatchSuccess::FetchInterface(interface)) = &item.outcome
+                && interface.descriptor.format != INTERFACE_FORMAT_V1
+            {
+                return Err(ClientResponseError::UnsupportedDescriptorFormat {
+                    format: interface.descriptor.format.clone(),
+                });
+            }
+        }
+    }
+    Ok(decoded)
+}
+
+fn object<'a>(value: &'a Json, field: &str) -> Result<&'a Map<String, Json>, CodecError> {
+    value.as_object().ok_or_else(|| CodecError::InvalidField {
+        field: field.into(),
+        reason: "expected object".into(),
+    })
+}
+
+fn exact_object<'a>(
+    value: &'a Json,
+    field: &str,
+    allowed: &[&str],
+) -> Result<&'a Map<String, Json>, CodecError> {
+    let fields = object(value, field)?;
+    for name in fields.keys() {
+        if !allowed.contains(&name.as_str()) {
+            return Err(CodecError::UnknownField {
+                field: format!("{field}.{name}"),
+            });
+        }
+    }
+    Ok(fields)
+}
+
+fn required<'a>(fields: &'a Map<String, Json>, name: &str) -> Result<&'a Json, CodecError> {
+    fields
+        .get(name)
+        .ok_or_else(|| CodecError::MissingField { field: name.into() })
+}
+
+fn string(value: &Json, field: &str) -> Result<String, CodecError> {
+    value
+        .as_str()
+        .map(str::to_owned)
+        .ok_or_else(|| CodecError::InvalidField {
+            field: field.into(),
+            reason: "expected string".into(),
+        })
+}
+
+fn array<'a>(value: &'a Json, field: &str) -> Result<&'a [Json], CodecError> {
+    value
+        .as_array()
+        .map(Vec::as_slice)
+        .ok_or_else(|| CodecError::InvalidField {
+            field: field.into(),
+            reason: "expected array".into(),
+        })
+}
@@ -0,0 +1,661 @@
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+
+use http::header::{ACCEPT, CONTENT_TYPE};
+use http::{HeaderMap, Method, Request, Response, StatusCode};
+use wip_protocol::{
+    CallOperationRequest, CallOperationResponse, FetchInterfaceRequest, FetchInterfaceResponse,
+    FetchRequest, FetchResponse, FetchTreeRequest, FetchTreeResponse, INTERFACE_FORMAT_V1,
+    InterfaceDescriptor, InterfaceTarget, ProtocolError, ProtocolInteraction, Target,
+};
+
+use crate::response::{self, DecodedResponse};
+use crate::{
+    BodyKind, ClientResponseError, CodecError, Endpoint, InvalidResponseKind, JSON_CONTENT_TYPE,
+    Limits, ResourceLimitKind, Route, json,
+};
+
+fn request(
+    endpoint: &Endpoint,
+    route: Route,
+    body: Vec<u8>,
+) -> Result<Request<Vec<u8>>, http::Error> {
+    Request::builder()
+        .method(Method::POST)
+        .uri(endpoint.route(route).as_str())
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(ACCEPT, "application/json")
+        .body(body)
+}
+
+fn response(status: StatusCode, body: Vec<u8>) -> Result<Response<Vec<u8>>, http::Error> {
+    Response::builder()
+        .status(status)
+        .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .body(body)
+}
+
+fn require_response_content_type<B>(response: &Response<B>) -> Result<(), ClientResponseError> {
+    let valid = response
+        .headers()
+        .get(CONTENT_TYPE)
+        .and_then(|value| value.to_str().ok())
+        .is_some_and(is_json_content_type);
+    if valid {
+        Ok(())
+    } else if response.status().is_success() {
+        Err(ClientResponseError::invalid(
+            InvalidResponseKind::InvalidSuccessBody,
+            "missing or non-UTF-8 application/json Content-Type",
+        ))
+    } else {
+        Err(response::transport_failure(response.status()))
+    }
+}
+
+fn is_utf8_charset(value: &str) -> bool {
+    let value = value.trim();
+    value.eq_ignore_ascii_case("utf-8")
+        || value
+            .strip_prefix('"')
+            .and_then(|value| value.strip_suffix('"'))
+            .is_some_and(|value| value.eq_ignore_ascii_case("utf-8"))
+}
+
+/// Returns whether a Content-Type value denotes UTF-8 `application/json`.
+///
+/// The charset parameter is optional because JSON exchanged by this binding is
+/// always UTF-8; when present, its value must be `utf-8`. Other parameters are
+/// rejected so intermediaries cannot silently select another representation.
+#[must_use]
+pub fn is_json_content_type(value: &str) -> bool {
+    let mut parts = value.split(';');
+    if !parts
+        .next()
+        .is_some_and(|media| media.trim().eq_ignore_ascii_case("application/json"))
+    {
+        return false;
+    }
+    let mut saw_charset = false;
+    for parameter in parts {
+        let Some((name, value)) = parameter.trim().split_once('=') else {
+            return false;
+        };
+        if !name.trim().eq_ignore_ascii_case("charset") || !is_utf8_charset(value) || saw_charset {
+            return false;
+        }
+        saw_charset = true;
+    }
+    true
+}
+
+fn accepts_json(headers: &HeaderMap) -> bool {
+    let mut present = false;
+    let mut best_match: Option<((u8, u8), f32)> = None;
+    for value in headers.get_all(ACCEPT) {
+        present = true;
+        let Ok(value) = value.to_str() else {
+            continue;
+        };
+        for range in value.split(',') {
+            let mut parts = range.split(';');
+            let media_range = parts.next().unwrap_or_default().trim();
+            let mut quality = 1.0_f32;
+            let mut saw_quality = false;
+            let mut saw_charset = false;
+            let mut media_parameter_count = 0;
+            let mut valid = true;
+            for parameter in parts {
+                let parameter = parameter.trim();
+                let (name, value) = parameter
+                    .split_once('=')
+                    .map_or((parameter, None), |(name, value)| {
+                        (name.trim(), Some(value))
+                    });
+                if name.is_empty() {
+                    valid = false;
+                    break;
+                }
+                if saw_quality {
+                    // Parameters after q are Accept extensions and do not
+                    // constrain the selected representation.
+                    continue;
+                }
+                if name.eq_ignore_ascii_case("q") {
+                    let Some(value) = value else {
+                        valid = false;
+                        break;
+                    };
+                    saw_quality = true;
+                    match value.trim().parse::<f32>() {
+                        Ok(value) if (0.0..=1.0).contains(&value) => quality = value,
+                        _ => {
+                            valid = false;
+                            break;
+                        }
+                    }
+                } else {
+                    let Some(value) = value else {
+                        valid = false;
+                        break;
+                    };
+                    if !name.eq_ignore_ascii_case("charset")
+                        || !is_utf8_charset(value)
+                        || saw_charset
+                    {
+                        valid = false;
+                        break;
+                    }
+                    saw_charset = true;
+                    media_parameter_count += 1;
+                }
+            }
+            let media_specificity = if media_range.eq_ignore_ascii_case("application/json") {
+                Some(2)
+            } else if media_range.eq_ignore_ascii_case("application/*") {
+                Some(1)
+            } else if media_range == "*/*" {
+                Some(0)
+            } else {
+                None
+            };
+            if valid && let Some(media_specificity) = media_specificity {
+                let specificity = (media_specificity, media_parameter_count);
+                match best_match {
+                    Some((best_specificity, _)) if best_specificity > specificity => {}
+                    Some((best_specificity, best_quality)) if best_specificity == specificity => {
+                        best_match = Some((specificity, best_quality.max(quality)));
+                    }
+                    _ => best_match = Some((specificity, quality)),
+                }
+            }
+        }
+    }
+    if present {
+        best_match.is_some_and(|(_, quality)| quality > 0.0)
+    } else {
+        true
+    }
+}
+
+/// A failure while validating inbound HTTP request metadata.
+#[derive(Debug)]
+pub enum RequestMetadataError {
+    /// The method or route does not match the selected WIP interaction.
+    InvalidRequest(CodecError),
+    /// The request body does not use UTF-8 `application/json`.
+    UnsupportedMediaType,
+    /// The request's `Accept` metadata excludes `application/json`.
+    NotAcceptable,
+}
+
+impl RequestMetadataError {
+    /// Returns the HTTP status for this metadata failure.
+    #[must_use]
+    pub const fn status(&self) -> StatusCode {
+        match self {
+            Self::InvalidRequest(_) => StatusCode::BAD_REQUEST,
+            Self::UnsupportedMediaType => StatusCode::UNSUPPORTED_MEDIA_TYPE,
+            Self::NotAcceptable => StatusCode::NOT_ACCEPTABLE,
+        }
+    }
+}
+
+impl Display for RequestMetadataError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidRequest(error) => error.fmt(formatter),
+            Self::UnsupportedMediaType => {
+                formatter.write_str("expected UTF-8 application/json Content-Type")
+            }
+            Self::NotAcceptable => formatter.write_str("request does not accept application/json"),
+        }
+    }
+}
+
+impl Error for RequestMetadataError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            Self::InvalidRequest(error) => Some(error),
+            Self::UnsupportedMediaType | Self::NotAcceptable => None,
+        }
+    }
+}
+
+/// Validates mandatory HTTP metadata for an inbound WIP request.
+///
+/// Both absolute-form and origin-form request URIs are accepted, but the path
+/// must exactly equal the selected endpoint route and a query is forbidden.
+/// Unsupported content negotiation is reported as a Transport Binding metadata
+/// failure rather than a Core `invalid_request`.
+pub fn validate_http_request<B>(
+    endpoint: &Endpoint,
+    route: Route,
+    value: &Request<B>,
+) -> Result<(), RequestMetadataError> {
+    if value.method() != Method::POST {
+        return Err(RequestMetadataError::InvalidRequest(
+            CodecError::InvalidField {
+                field: "method".into(),
+                reason: "standard WIP routes require POST".into(),
+            },
+        ));
+    }
+    let expected = endpoint.route(route);
+    if value.uri().path() != expected.path() || value.uri().query().is_some() {
+        return Err(RequestMetadataError::InvalidRequest(
+            CodecError::InvalidField {
+                field: "route".into(),
+                reason: "request URI does not match the selected standard route".into(),
+            },
+        ));
+    }
+    let valid_content_type = value
+        .headers()
+        .get(CONTENT_TYPE)
+        .and_then(|value| value.to_str().ok())
+        .is_some_and(is_json_content_type);
+    if !valid_content_type {
+        return Err(RequestMetadataError::UnsupportedMediaType);
+    }
+    if !accepts_json(value.headers()) {
+        return Err(RequestMetadataError::NotAcceptable);
+    }
+    Ok(())
+}
+
+/// Encodes a `fetch` HTTP request.
+pub fn encode_fetch_request(
+    endpoint: &Endpoint,
+    value: &FetchRequest,
+    limits: Limits,
+) -> Result<Request<Vec<u8>>, EncodeHttpError> {
+    value.validate().map_err(CodecError::from)?;
+    let body = json::serialize(
+        &json::fetch_request_to_json(value),
+        BodyKind::Request,
+        limits,
+    )?;
+    Ok(request(endpoint, Route::Fetch, body)?)
+}
+
+/// Decodes a `fetch` request body.
+pub fn decode_fetch_request(body: &[u8], limits: Limits) -> Result<FetchRequest, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    json::fetch_request_from_json(&value)
+}
+
+/// Encodes a `fetch_tree` HTTP request.
+pub fn encode_fetch_tree_request(
+    endpoint: &Endpoint,
+    value: &FetchTreeRequest,
+    limits: Limits,
+) -> Result<Request<Vec<u8>>, EncodeHttpError> {
+    value.validate().map_err(CodecError::from)?;
+    let body = json::serialize(
+        &json::fetch_tree_request_to_json(value),
+        BodyKind::Request,
+        limits,
+    )?;
+    Ok(request(endpoint, Route::FetchTree, body)?)
+}
+
+/// Decodes a `fetch_tree` request body.
+pub fn decode_fetch_tree_request(
+    body: &[u8],
+    limits: Limits,
+) -> Result<FetchTreeRequest, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    json::fetch_tree_request_from_json(&value)
+}
+
+/// Encodes a `fetch_interface` HTTP request.
+pub fn encode_fetch_interface_request(
+    endpoint: &Endpoint,
+    value: &FetchInterfaceRequest,
+    limits: Limits,
+) -> Result<Request<Vec<u8>>, EncodeHttpError> {
+    let body = json::serialize(
+        &json::fetch_interface_request_to_json(value),
+        BodyKind::Request,
+        limits,
+    )?;
+    Ok(request(endpoint, Route::FetchInterface, body)?)
+}
+
+/// Decodes a `fetch_interface` request body.
+pub fn decode_fetch_interface_request(
+    body: &[u8],
+    limits: Limits,
+) -> Result<FetchInterfaceRequest, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    json::fetch_interface_request_from_json(&value)
+}
+
+/// Descriptor-independent fields needed to resolve a `call_operation` request.
+///
+/// A Host decodes this metadata first, fixes the current interface descriptor,
+/// then passes the same body and descriptor to [`decode_call_operation_request`].
+/// This preserves canonical path/interface/operation lookup and error precedence
+/// without treating unvalidated argument JSON as a logical [`wip_protocol::Value`].
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CallOperationMetadata {
+    /// Path and optional object-state precondition.
+    pub target: Target,
+    /// Interface reference and optional interface precondition.
+    pub interface: InterfaceTarget,
+    /// Operation name used to select a declaration.
+    pub operation: String,
+}
+
+impl CallOperationMetadata {
+    /// Decodes the descriptor-bound request and verifies that routing metadata
+    /// still matches the values used to resolve `descriptor`.
+    pub fn decode_request(
+        &self,
+        body: &[u8],
+        descriptor: &InterfaceDescriptor,
+        limits: Limits,
+    ) -> Result<CallOperationRequest, CodecError> {
+        let request = decode_call_operation_request(body, descriptor, limits)?;
+        if request.target != self.target
+            || request.interface != self.interface
+            || request.operation != self.operation
+        {
+            return Err(CodecError::InvalidField {
+                field: "request".into(),
+                reason: "call metadata changed after descriptor resolution".into(),
+            });
+        }
+        Ok(request)
+    }
+}
+
+/// Decodes descriptor-independent `call_operation` routing metadata.
+pub fn decode_call_operation_metadata(
+    body: &[u8],
+    limits: Limits,
+) -> Result<CallOperationMetadata, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    let (target, interface, operation) = json::call_request_metadata_from_json(&value)?;
+    Ok(CallOperationMetadata {
+        target,
+        interface,
+        operation,
+    })
+}
+
+/// Encodes a descriptor-bound `call_operation` HTTP request.
+pub fn encode_call_operation_request(
+    endpoint: &Endpoint,
+    value: &CallOperationRequest,
+    descriptor: &InterfaceDescriptor,
+    limits: Limits,
+) -> Result<Request<Vec<u8>>, EncodeHttpError> {
+    let value = json::call_request_to_json(value, descriptor)?;
+    let body = json::serialize(&value, BodyKind::Request, limits)?;
+    Ok(request(endpoint, Route::CallOperation, body)?)
+}
+
+/// Decodes a descriptor-bound `call_operation` request body.
+pub fn decode_call_operation_request(
+    body: &[u8],
+    descriptor: &InterfaceDescriptor,
+    limits: Limits,
+) -> Result<CallOperationRequest, CodecError> {
+    let value = json::parse(body, BodyKind::Request, limits)?;
+    json::call_request_from_json(&value, descriptor)
+}
+
+/// Encodes a successful `fetch` response as a direct body with HTTP 200.
+pub fn encode_fetch_response(
+    request_value: &FetchRequest,
+    value: &FetchResponse,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    request_value
+        .validate_response(value)
+        .map_err(CodecError::from)?;
+    let body = json::serialize(&json::object_to_json(value), BodyKind::Response, limits)?;
+    Ok(response(StatusCode::OK, body)?)
+}
+
+/// Decodes and classifies a `fetch` client response.
+pub fn decode_fetch_response<B: AsRef<[u8]>>(
+    request_value: &FetchRequest,
+    value: &Response<B>,
+    limits: Limits,
+) -> Result<DecodedResponse<FetchResponse>, ClientResponseError> {
+    require_response_content_type(value)?;
+    response::decode(
+        value.status(),
+        value.body().as_ref(),
+        ProtocolInteraction::Fetch,
+        limits,
+        |json| {
+            let object = json::object_from_json(json, "response")?;
+            request_value.validate_response(&object)?;
+            Ok(object)
+        },
+    )
+}
+
+/// Encodes a successful `fetch_tree` response as a direct body with HTTP 200.
+pub fn encode_fetch_tree_response(
+    request_value: &FetchTreeRequest,
+    value: &FetchTreeResponse,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    value
+        .validate_for(request_value)
+        .map_err(CodecError::from)?;
+    let body = json::serialize(
+        &json::fetch_tree_response_to_json(value),
+        BodyKind::Response,
+        limits,
+    )?;
+    Ok(response(StatusCode::OK, body)?)
+}
+
+/// Decodes and classifies a `fetch_tree` client response.
+pub fn decode_fetch_tree_response<B: AsRef<[u8]>>(
+    request_value: &FetchTreeRequest,
+    value: &Response<B>,
+    limits: Limits,
+) -> Result<DecodedResponse<FetchTreeResponse>, ClientResponseError> {
+    require_response_content_type(value)?;
+    response::decode(
+        value.status(),
+        value.body().as_ref(),
+        ProtocolInteraction::FetchTree,
+        limits,
+        |json| {
+            let tree = json::fetch_tree_response_from_json(json)?;
+            tree.validate_for(request_value)?;
+            Ok(tree)
+        },
+    )
+}
+
+/// Encodes a successful `fetch_interface` response as a direct body with HTTP 200.
+pub fn encode_fetch_interface_response(
+    request_value: &FetchInterfaceRequest,
+    value: &FetchInterfaceResponse,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    value
+        .validate_for(request_value)
+        .map_err(CodecError::from)?;
+    let body = json::serialize(
+        &json::fetch_interface_response_to_json(value),
+        BodyKind::Response,
+        limits,
+    )?;
+    Ok(response(StatusCode::OK, body)?)
+}
+
+/// Decodes and classifies a `fetch_interface` client response.
+pub fn decode_fetch_interface_response<B: AsRef<[u8]>>(
+    request_value: &FetchInterfaceRequest,
+    value: &Response<B>,
+    limits: Limits,
+) -> Result<DecodedResponse<FetchInterfaceResponse>, ClientResponseError> {
+    require_response_content_type(value)?;
+    let decoded = response::decode(
+        value.status(),
+        value.body().as_ref(),
+        ProtocolInteraction::FetchInterface,
+        limits,
+        |json| {
+            let interface = json::fetch_interface_response_from_json(json)?;
+            interface.validate_for(request_value)?;
+            Ok(interface)
+        },
+    )?;
+    if let DecodedResponse::Success(success) = &decoded
+        && success.descriptor.format != INTERFACE_FORMAT_V1
+    {
+        return Err(ClientResponseError::UnsupportedDescriptorFormat {
+            format: success.descriptor.format.clone(),
+        });
+    }
+    Ok(decoded)
+}
+
+/// Encodes a successful `call_operation` response as a direct body with HTTP 200.
+pub fn encode_call_operation_response(
+    request_value: &CallOperationRequest,
+    descriptor: &InterfaceDescriptor,
+    value: &CallOperationResponse,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    let json = json::call_response_to_json(value, descriptor, &request_value.operation)?;
+    let body = json::serialize(&json, BodyKind::Response, limits)?;
+    Ok(response(StatusCode::OK, body)?)
+}
+
+/// Decodes and classifies a descriptor-bound `call_operation` client response.
+pub fn decode_call_operation_response<B: AsRef<[u8]>>(
+    request_value: &CallOperationRequest,
+    descriptor: &InterfaceDescriptor,
+    value: &Response<B>,
+    limits: Limits,
+) -> Result<DecodedResponse<CallOperationResponse>, ClientResponseError> {
+    require_response_content_type(value)?;
+    response::decode(
+        value.status(),
+        value.body().as_ref(),
+        ProtocolInteraction::CallOperation,
+        limits,
+        |json| json::call_response_from_json(json, descriptor, &request_value.operation),
+    )
+}
+
+fn validate_protocol_error(
+    interaction: ProtocolInteraction,
+    error: &ProtocolError,
+) -> Result<(), CodecError> {
+    if !error.code.is_allowed_for(interaction) {
+        return Err(CodecError::InvalidField {
+            field: "error.code".into(),
+            reason: format!(
+                "code `{}` is not allowed for {interaction:?}",
+                response::error_code_name(error.code)
+            ),
+        });
+    }
+    Ok(())
+}
+
+fn encode_protocol_error_with_status(
+    interaction: ProtocolInteraction,
+    error: &ProtocolError,
+    status: StatusCode,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    validate_protocol_error(interaction, error)?;
+    let body = json::serialize(&response::error_to_json(error), BodyKind::Response, limits)?;
+    Ok(response(status, body)?)
+}
+
+/// Encodes a canonical Host error envelope using its standard HTTP status.
+///
+/// The code must be allowed for `interaction`. This API accepts only
+/// [`ProtocolError`], so client-local `InvalidResponse` and
+/// `UnsupportedDescriptorFormat` classifications cannot be emitted as Host
+/// error envelopes. Resource-limit errors use the logical-limit status; callers
+/// that know the concrete limit class should use
+/// [`encode_resource_limit_error_response`].
+pub fn encode_protocol_error_response(
+    interaction: ProtocolInteraction,
+    error: &ProtocolError,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    encode_protocol_error_with_status(
+        interaction,
+        error,
+        response::status_for_error(error.code),
+        limits,
+    )
+}
+
+/// Encodes a `resource_limit_exceeded` envelope with its class-specific status.
+pub fn encode_resource_limit_error_response(
+    interaction: ProtocolInteraction,
+    error: &ProtocolError,
+    kind: ResourceLimitKind,
+    limits: Limits,
+) -> Result<Response<Vec<u8>>, EncodeHttpError> {
+    if error.code != wip_protocol::ProtocolErrorCode::ResourceLimitExceeded {
+        return Err(CodecError::InvalidField {
+            field: "error.code".into(),
+            reason: "resource-limit encoder requires resource_limit_exceeded".into(),
+        }
+        .into());
+    }
+    encode_protocol_error_with_status(
+        interaction,
+        error,
+        response::status_for_resource_limit(kind),
+        limits,
+    )
+}
+
+/// Failure while building an outbound framework-neutral HTTP message.
+#[derive(Debug)]
+pub enum EncodeHttpError {
+    /// JSON or protocol encoding failed.
+    Codec(CodecError),
+    /// The framework-neutral HTTP message builder rejected the URI or headers.
+    Http(http::Error),
+}
+
+impl std::fmt::Display for EncodeHttpError {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Codec(error) => error.fmt(formatter),
+            Self::Http(error) => error.fmt(formatter),
+        }
+    }
+}
+
+impl std::error::Error for EncodeHttpError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Codec(error) => Some(error),
+            Self::Http(error) => Some(error),
+        }
+    }
+}
+
+impl From<CodecError> for EncodeHttpError {
+    fn from(value: CodecError) -> Self {
+        Self::Codec(value)
+    }
+}
+
+impl From<http::Error> for EncodeHttpError {
+    fn from(value: http::Error) -> Self {
+        Self::Http(value)
+    }
+}
@@ -0,0 +1,156 @@
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+
+use url::Url;
+
+/// The media type emitted for every WIP request and every response with a body.
+pub const JSON_CONTENT_TYPE: &str = "application/json; charset=utf-8";
+
+/// A fixed standard WIP over HTTPS v1 route.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub enum Route {
+    /// Fetch one object.
+    Fetch,
+    /// Fetch a bounded object tree.
+    FetchTree,
+    /// Fetch an interface descriptor.
+    FetchInterface,
+    /// Call one operation.
+    CallOperation,
+    /// Package independent retrieval interactions.
+    Batch,
+}
+
+impl Route {
+    /// Returns the RFC 3986 relative reference used below an endpoint prefix.
+    #[must_use]
+    pub const fn relative_reference(self) -> &'static str {
+        match self {
+            Self::Fetch => "v1/fetch",
+            Self::FetchTree => "v1/fetch_tree",
+            Self::FetchInterface => "v1/fetch_interface",
+            Self::CallOperation => "v1/call_operation",
+            Self::Batch => "v1/batch",
+        }
+    }
+}
+
+/// A canonical absolute HTTPS base URL whose path always ends in `/`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Endpoint(Url);
+
+impl Endpoint {
+    /// Parses and canonicalizes an endpoint.
+    ///
+    /// The input must be an absolute HTTPS URL without a query or fragment. Its
+    /// path is an endpoint prefix, not a Worldspace path. A trailing slash is
+    /// appended when absent so RFC 3986 relative-reference resolution preserves
+    /// the final prefix segment.
+    pub fn parse(input: &str) -> Result<Self, EndpointError> {
+        let mut url = Url::parse(input).map_err(EndpointError::InvalidUrl)?;
+        if url.scheme() != "https" {
+            return Err(EndpointError::NotHttps);
+        }
+        if url.cannot_be_a_base() || url.host_str().is_none() {
+            return Err(EndpointError::NotAbsoluteBase);
+        }
+        if url.query().is_some() {
+            return Err(EndpointError::HasQuery);
+        }
+        if url.fragment().is_some() {
+            return Err(EndpointError::HasFragment);
+        }
+        if !url.path().ends_with('/') {
+            let path = format!("{}/", url.path());
+            url.set_path(&path);
+        }
+        Ok(Self(url))
+    }
+
+    /// Returns the canonical base URL.
+    #[must_use]
+    pub fn as_url(&self) -> &Url {
+        &self.0
+    }
+
+    /// Resolves one fixed v1 route below this endpoint prefix.
+    #[must_use]
+    pub fn route(&self, route: Route) -> Url {
+        self.0
+            .join(route.relative_reference())
+            .expect("fixed relative WIP routes are valid URL references")
+    }
+
+    /// Recognizes an exact standard route below this endpoint.
+    ///
+    /// Query strings, fragments, additional path segments, and Worldspace paths
+    /// are not route components and therefore never match.
+    #[must_use]
+    pub fn recognize(&self, candidate: &Url) -> Option<Route> {
+        const ROUTES: [Route; 5] = [
+            Route::Fetch,
+            Route::FetchTree,
+            Route::FetchInterface,
+            Route::CallOperation,
+            Route::Batch,
+        ];
+        if candidate.query().is_some() || candidate.fragment().is_some() {
+            return None;
+        }
+        ROUTES
+            .into_iter()
+            .find(|route| self.route(*route) == *candidate)
+    }
+}
+
+impl Display for Endpoint {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        self.0.fmt(formatter)
+    }
+}
+
+impl TryFrom<&str> for Endpoint {
+    type Error = EndpointError;
+
+    fn try_from(value: &str) -> Result<Self, Self::Error> {
+        Self::parse(value)
+    }
+}
+
+/// Why an endpoint is not a valid standard WIP HTTPS base.
+#[derive(Debug)]
+pub enum EndpointError {
+    /// URL parsing failed.
+    InvalidUrl(url::ParseError),
+    /// The URL scheme is not `https`.
+    NotHttps,
+    /// The URL is not a hierarchical absolute URL with an authority.
+    NotAbsoluteBase,
+    /// A query component was supplied.
+    HasQuery,
+    /// A fragment component was supplied.
+    HasFragment,
+}
+
+impl Display for EndpointError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::InvalidUrl(error) => write!(formatter, "invalid endpoint URL: {error}"),
+            Self::NotHttps => formatter.write_str("WIP endpoint must use HTTPS"),
+            Self::NotAbsoluteBase => {
+                formatter.write_str("WIP endpoint must be an absolute base URL")
+            }
+            Self::HasQuery => formatter.write_str("WIP endpoint must not contain a query"),
+            Self::HasFragment => formatter.write_str("WIP endpoint must not contain a fragment"),
+        }
+    }
+}
+
+impl Error for EndpointError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            Self::InvalidUrl(error) => Some(error),
+            _ => None,
+        }
+    }
+}
@@ -0,0 +1,255 @@
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+
+/// Caller-selected hard limits applied before or while decoding JSON.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Limits {
+    /// Largest accepted request body in bytes.
+    pub(crate) max_request_bytes: usize,
+    /// Largest accepted response body in bytes.
+    pub(crate) max_response_bytes: usize,
+    /// Largest accepted JSON container nesting depth.
+    pub(crate) max_nesting: usize,
+    /// Largest accepted number of batch items.
+    pub(crate) max_batch_items: usize,
+}
+
+impl Limits {
+    /// Creates a nonzero limit set.
+    pub fn new(
+        max_request_bytes: usize,
+        max_response_bytes: usize,
+        max_nesting: usize,
+        max_batch_items: usize,
+    ) -> Result<Self, LimitConfigurationError> {
+        if max_request_bytes == 0 {
+            return Err(LimitConfigurationError::ZeroRequestBytes);
+        }
+        if max_response_bytes == 0 {
+            return Err(LimitConfigurationError::ZeroResponseBytes);
+        }
+        if max_nesting == 0 {
+            return Err(LimitConfigurationError::ZeroNesting);
+        }
+        if max_batch_items == 0 {
+            return Err(LimitConfigurationError::ZeroBatchItems);
+        }
+        Ok(Self {
+            max_request_bytes,
+            max_response_bytes,
+            max_nesting,
+            max_batch_items,
+        })
+    }
+
+    /// Returns the request body byte limit.
+    #[must_use]
+    pub const fn max_request_bytes(self) -> usize {
+        self.max_request_bytes
+    }
+
+    /// Returns the response body byte limit.
+    #[must_use]
+    pub const fn max_response_bytes(self) -> usize {
+        self.max_response_bytes
+    }
+
+    /// Returns the JSON container nesting limit.
+    #[must_use]
+    pub const fn max_nesting(self) -> usize {
+        self.max_nesting
+    }
+
+    /// Returns the batch item count limit.
+    #[must_use]
+    pub const fn max_batch_items(self) -> usize {
+        self.max_batch_items
+    }
+}
+
+/// Why a [`Limits`] configuration is not bounded.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum LimitConfigurationError {
+    /// Request-byte limit was zero.
+    ZeroRequestBytes,
+    /// Response-byte limit was zero.
+    ZeroResponseBytes,
+    /// Nesting limit was zero.
+    ZeroNesting,
+    /// Batch-item limit was zero.
+    ZeroBatchItems,
+}
+
+impl Display for LimitConfigurationError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        formatter.write_str(match self {
+            Self::ZeroRequestBytes => "request byte limit must be nonzero",
+            Self::ZeroResponseBytes => "response byte limit must be nonzero",
+            Self::ZeroNesting => "nesting limit must be nonzero",
+            Self::ZeroBatchItems => "batch item limit must be nonzero",
+        })
+    }
+}
+
+impl Error for LimitConfigurationError {}
+
+/// Whether a body is being decoded as a request or response.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum BodyKind {
+    /// An inbound server request.
+    Request,
+    /// An inbound client response.
+    Response,
+}
+
+/// The class of a resource limit exceeded by a wire representation.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ResourceLimitKind {
+    /// A request or response representation exceeded its byte-size limit.
+    RepresentationBytes,
+    /// A logical limit such as nesting depth, batch count, or collection size was exceeded.
+    Logical,
+}
+
+/// A malformed or locally disallowed wire representation.
+#[derive(Debug)]
+pub enum CodecError {
+    /// The body exceeds its configured byte limit.
+    BodyTooLarge {
+        /// Actual body size.
+        actual: usize,
+        /// Configured maximum.
+        maximum: usize,
+    },
+    /// JSON syntax is invalid.
+    InvalidJson(serde_json::Error),
+    /// A JSON container exceeds the configured nesting depth.
+    NestingTooDeep {
+        /// Configured maximum.
+        maximum: usize,
+    },
+    /// A required field is absent.
+    MissingField {
+        /// Field name.
+        field: String,
+    },
+    /// An undeclared field is present.
+    UnknownField {
+        /// Field name.
+        field: String,
+    },
+    /// A field has an invalid JSON type or semantic representation.
+    InvalidField {
+        /// Field name or value location.
+        field: String,
+        /// Stable human-readable reason.
+        reason: String,
+    },
+    /// An optional field was represented by JSON null rather than omission.
+    NullOptionalField {
+        /// Field name.
+        field: String,
+    },
+    /// Base64 is not canonical RFC 4648 Section 4 encoding.
+    InvalidBase64 {
+        /// Field name or value location.
+        field: String,
+    },
+    /// Logical protocol validation rejected the decoded representation.
+    ProtocolValidation(wip_protocol::ValidationError),
+    /// The batch exceeds its configured item count.
+    TooManyBatchItems {
+        /// Actual item count.
+        actual: usize,
+        /// Configured maximum.
+        maximum: usize,
+    },
+    /// Batch item identifiers are not unique.
+    DuplicateBatchId {
+        /// Repeated identifier.
+        id: String,
+    },
+    /// A response contains a batch identifier that was not requested.
+    UnexpectedBatchId {
+        /// Unexpected identifier.
+        id: String,
+    },
+    /// A response omitted a requested batch identifier.
+    MissingBatchId {
+        /// Missing identifier.
+        id: String,
+    },
+    /// A batch item result does not match its requested interaction.
+    BatchInteractionMismatch {
+        /// Item identifier.
+        id: String,
+    },
+}
+
+impl CodecError {
+    /// Classifies this failure when it represents a canonical resource limit.
+    #[must_use]
+    pub const fn resource_limit_kind(&self) -> Option<ResourceLimitKind> {
+        match self {
+            Self::BodyTooLarge { .. } => Some(ResourceLimitKind::RepresentationBytes),
+            Self::NestingTooDeep { .. } | Self::TooManyBatchItems { .. } => {
+                Some(ResourceLimitKind::Logical)
+            }
+            _ => None,
+        }
+    }
+}
+
+impl Display for CodecError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::BodyTooLarge { actual, maximum } => {
+                write!(formatter, "body has {actual} bytes; maximum is {maximum}")
+            }
+            Self::InvalidJson(error) => write!(formatter, "invalid JSON: {error}"),
+            Self::NestingTooDeep { maximum } => {
+                write!(formatter, "JSON nesting exceeds maximum {maximum}")
+            }
+            Self::MissingField { field } => write!(formatter, "missing field `{field}`"),
+            Self::UnknownField { field } => write!(formatter, "unknown field `{field}`"),
+            Self::InvalidField { field, reason } => {
+                write!(formatter, "invalid field `{field}`: {reason}")
+            }
+            Self::NullOptionalField { field } => {
+                write!(
+                    formatter,
+                    "optional field `{field}` must be omitted instead of null"
+                )
+            }
+            Self::InvalidBase64 { field } => {
+                write!(formatter, "field `{field}` is not canonical base64")
+            }
+            Self::ProtocolValidation(error) => error.fmt(formatter),
+            Self::TooManyBatchItems { actual, maximum } => {
+                write!(formatter, "batch has {actual} items; maximum is {maximum}")
+            }
+            Self::DuplicateBatchId { id } => write!(formatter, "duplicate batch id `{id}`"),
+            Self::UnexpectedBatchId { id } => write!(formatter, "unexpected batch id `{id}`"),
+            Self::MissingBatchId { id } => write!(formatter, "missing batch id `{id}`"),
+            Self::BatchInteractionMismatch { id } => {
+                write!(formatter, "batch result does not match request `{id}`")
+            }
+        }
+    }
+}
+
+impl Error for CodecError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            Self::InvalidJson(error) => Some(error),
+            Self::ProtocolValidation(error) => Some(error),
+            _ => None,
+        }
+    }
+}
+
+impl From<wip_protocol::ValidationError> for CodecError {
+    fn from(value: wip_protocol::ValidationError) -> Self {
+        Self::ProtocolValidation(value)
+    }
+}
@@ -0,0 +1,67 @@
+//! Framework-independent standard WIP over HTTPS v1 binding.
+//!
+//! This crate owns endpoint and route derivation, UTF-8 JSON encoding, canonical
+//! success and error response handling, HTTP status mapping, descriptor-guided
+//! operation-value conversion, and retrieval batching. It deliberately performs
+//! no I/O and depends on no server framework, TLS implementation, filesystem
+//! projection, client cache, or presentation layer.
+//!
+//! Logical values remain owned by [`wip_protocol`]. Validators and `Bytes` are
+//! encoded in JSON bodies using canonical RFC 4648 Section 4 base64; this crate
+//! does not infer WIP validator semantics from `ETag` or `If-Match`.
+//!
+//! ```
+//! use wip_https::{Endpoint, Limits, encode_fetch_request};
+//! use wip_protocol::FetchRequest;
+//!
+//! let endpoint = Endpoint::parse("https://example.test/api/wip")?;
+//! let limits = Limits::new(64 * 1024, 1024 * 1024, 64, 100)?;
+//! let request = encode_fetch_request(
+//!     &endpoint,
+//!     &FetchRequest { path: "/items/123".into() },
+//!     limits,
+//! )?;
+//! assert_eq!(request.uri(), "https://example.test/api/wip/v1/fetch");
+//! assert_eq!(request.method(), http::Method::POST);
+//! # Ok::<(), Box<dyn std::error::Error>>(())
+//! ```
+
+#![deny(missing_docs)]
+
+mod batch;
+mod codec;
+mod endpoint;
+mod error;
+mod json;
+mod response;
+
+pub use batch::{
+    BatchMethod, BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse,
+    BatchResponseItem, BatchSuccess, decode_batch_request, decode_batch_response,
+    encode_batch_error_response, encode_batch_request, encode_batch_resource_limit_error_response,
+    encode_batch_response,
+};
+pub use codec::{
+    CallOperationMetadata, EncodeHttpError, RequestMetadataError, decode_call_operation_metadata,
+    decode_call_operation_request, decode_call_operation_response, decode_fetch_interface_request,
+    decode_fetch_interface_response, decode_fetch_request, decode_fetch_response,
+    decode_fetch_tree_request, decode_fetch_tree_response, encode_call_operation_request,
+    encode_call_operation_response, encode_fetch_interface_request,
+    encode_fetch_interface_response, encode_fetch_request, encode_fetch_response,
+    encode_fetch_tree_request, encode_fetch_tree_response, encode_protocol_error_response,
+    encode_resource_limit_error_response, is_json_content_type, validate_http_request,
+};
+pub use endpoint::{Endpoint, EndpointError, JSON_CONTENT_TYPE, Route};
+pub use error::{BodyKind, CodecError, LimitConfigurationError, Limits, ResourceLimitKind};
+pub use response::{
+    ClientResponseError, DecodedResponse, InvalidResponseKind, StatusMismatch,
+    TransportBindingFailure, TransportFailureKind, error_code_name, status_for_error,
+    status_for_resource_limit,
+};
+
+/// Framework-neutral HTTP types used by this binding's public API.
+pub use http;
+/// URL type used by [`Endpoint`].
+pub use url;
+/// Transport-independent logical protocol model used by this binding.
+pub use wip_protocol;
@@ -0,0 +1,365 @@
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+
+use http::StatusCode;
+use serde_json::{Map, Value as Json};
+use wip_protocol::{ProtocolError, ProtocolErrorCode, ProtocolInteraction};
+
+use crate::{BodyKind, CodecError, Limits, ResourceLimitKind, json};
+
+/// A successfully classified client response.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum DecodedResponse<T> {
+    /// A successful direct response body.
+    Success(T),
+    /// A canonical Host protocol failure.
+    ProtocolFailure {
+        /// The authoritative protocol error decoded from the envelope.
+        error: ProtocolError,
+        /// A diagnostic when the HTTP status differs from the canonical mapping.
+        status_mismatch: Option<StatusMismatch>,
+    },
+}
+
+/// Diagnostic evidence that HTTP metadata disagrees with a valid error envelope.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct StatusMismatch {
+    /// Status received from the peer.
+    pub actual: StatusCode,
+    /// Canonical status for the envelope's protocol code.
+    pub expected: StatusCode,
+}
+
+/// Class of non-protocol HTTP failure returned without a valid WIP envelope.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TransportFailureKind {
+    /// HTTP 401, commonly emitted by authentication infrastructure.
+    AuthenticationRequired,
+    /// HTTP 403, commonly emitted by endpoint policy or infrastructure.
+    EndpointForbidden,
+    /// Another non-success HTTP response without a WIP error envelope.
+    HttpStatus,
+}
+
+/// A non-success HTTP response that is not a valid WIP protocol failure.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TransportBindingFailure {
+    /// HTTP status returned by the peer or intermediary.
+    pub status: StatusCode,
+    /// Coarse classification which does not invent a protocol error code.
+    pub kind: TransportFailureKind,
+}
+
+/// Why a response violates the WIP v1 response contract.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum InvalidResponseKind {
+    /// A 2xx response contained an error envelope.
+    ErrorEnvelopeOnSuccessStatus,
+    /// A non-2xx response contained a valid success body.
+    SuccessBodyOnErrorStatus,
+    /// A valid error envelope used a code forbidden for the interaction.
+    DisallowedProtocolCode,
+    /// A valid success body used a 2xx status other than canonical HTTP 200.
+    NonCanonicalSuccessStatus,
+    /// A 2xx body was malformed or semantically invalid.
+    InvalidSuccessBody,
+    /// A batch response did not correlate exactly with its request.
+    InvalidBatch,
+}
+
+/// A local failure while classifying or validating a peer response.
+#[derive(Debug)]
+pub enum ClientResponseError {
+    /// The HTTP exchange failed outside the protocol envelope.
+    TransportBinding(TransportBindingFailure),
+    /// The peer supplied a contradictory or invalid WIP response.
+    InvalidResponse {
+        /// Stable response-failure category.
+        kind: InvalidResponseKind,
+        /// Bounded diagnostic from local decoding.
+        detail: String,
+    },
+    /// The descriptor is structurally valid but uses an unsupported format.
+    UnsupportedDescriptorFormat {
+        /// Format identifier received from the Host.
+        format: String,
+    },
+}
+
+impl ClientResponseError {
+    pub(crate) fn invalid(kind: InvalidResponseKind, detail: impl Into<String>) -> Self {
+        Self::InvalidResponse {
+            kind,
+            detail: detail.into(),
+        }
+    }
+}
+
+impl Display for ClientResponseError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::TransportBinding(failure) => write!(
+                formatter,
+                "transport binding failure ({:?}, HTTP {})",
+                failure.kind, failure.status
+            ),
+            Self::InvalidResponse { kind, detail } => {
+                write!(formatter, "invalid WIP response ({kind:?}): {detail}")
+            }
+            Self::UnsupportedDescriptorFormat { format } => {
+                write!(
+                    formatter,
+                    "unsupported interface descriptor format `{format}`"
+                )
+            }
+        }
+    }
+}
+
+impl Error for ClientResponseError {}
+
+/// Returns the canonical HTTP status for a wire-level protocol error.
+///
+/// [`ProtocolErrorCode::ResourceLimitExceeded`] defaults to the logical-limit
+/// status. Use [`status_for_resource_limit`] when the concrete limit class is
+/// known.
+#[must_use]
+pub const fn status_for_error(code: ProtocolErrorCode) -> StatusCode {
+    match code {
+        ProtocolErrorCode::InvalidRequest => StatusCode::BAD_REQUEST,
+        ProtocolErrorCode::NotFound | ProtocolErrorCode::InterfaceNotFound => StatusCode::NOT_FOUND,
+        ProtocolErrorCode::InterfaceMismatch => StatusCode::CONFLICT,
+        ProtocolErrorCode::OperationNotFound => StatusCode::NOT_FOUND,
+        ProtocolErrorCode::InvalidArguments => StatusCode::UNPROCESSABLE_ENTITY,
+        ProtocolErrorCode::ValidatorRequired | ProtocolErrorCode::InterfaceValidatorRequired => {
+            StatusCode::PRECONDITION_REQUIRED
+        }
+        ProtocolErrorCode::ValidatorMismatch | ProtocolErrorCode::InterfaceValidatorMismatch => {
+            StatusCode::PRECONDITION_FAILED
+        }
+        ProtocolErrorCode::PermissionDenied => StatusCode::FORBIDDEN,
+        ProtocolErrorCode::ResourceLimitExceeded => StatusCode::UNPROCESSABLE_ENTITY,
+        ProtocolErrorCode::Internal | ProtocolErrorCode::OperationOutcomeUnknown => {
+            StatusCode::INTERNAL_SERVER_ERROR
+        }
+    }
+}
+
+/// Returns the canonical HTTP status for a concrete resource-limit class.
+#[must_use]
+pub const fn status_for_resource_limit(kind: ResourceLimitKind) -> StatusCode {
+    match kind {
+        ResourceLimitKind::RepresentationBytes => StatusCode::PAYLOAD_TOO_LARGE,
+        ResourceLimitKind::Logical => StatusCode::UNPROCESSABLE_ENTITY,
+    }
+}
+
+fn status_matches_error(status: StatusCode, code: ProtocolErrorCode) -> bool {
+    match code {
+        ProtocolErrorCode::ResourceLimitExceeded => {
+            status == StatusCode::PAYLOAD_TOO_LARGE || status == StatusCode::UNPROCESSABLE_ENTITY
+        }
+        _ => status == status_for_error(code),
+    }
+}
+
+/// Returns the stable snake-case wire spelling of a protocol code.
+#[must_use]
+pub const fn error_code_name(code: ProtocolErrorCode) -> &'static str {
+    match code {
+        ProtocolErrorCode::InvalidRequest => "invalid_request",
+        ProtocolErrorCode::NotFound => "not_found",
+        ProtocolErrorCode::InterfaceNotFound => "interface_not_found",
+        ProtocolErrorCode::InterfaceMismatch => "interface_mismatch",
+        ProtocolErrorCode::OperationNotFound => "operation_not_found",
+        ProtocolErrorCode::InvalidArguments => "invalid_arguments",
+        ProtocolErrorCode::ValidatorRequired => "validator_required",
+        ProtocolErrorCode::ValidatorMismatch => "validator_mismatch",
+        ProtocolErrorCode::InterfaceValidatorRequired => "interface_validator_required",
+        ProtocolErrorCode::InterfaceValidatorMismatch => "interface_validator_mismatch",
+        ProtocolErrorCode::PermissionDenied => "permission_denied",
+        ProtocolErrorCode::ResourceLimitExceeded => "resource_limit_exceeded",
+        ProtocolErrorCode::Internal => "internal",
+        ProtocolErrorCode::OperationOutcomeUnknown => "operation_outcome_unknown",
+    }
+}
+
+fn error_code_from_name(name: &str) -> Option<ProtocolErrorCode> {
+    Some(match name {
+        "invalid_request" => ProtocolErrorCode::InvalidRequest,
+        "not_found" => ProtocolErrorCode::NotFound,
+        "interface_not_found" => ProtocolErrorCode::InterfaceNotFound,
+        "interface_mismatch" => ProtocolErrorCode::InterfaceMismatch,
+        "operation_not_found" => ProtocolErrorCode::OperationNotFound,
+        "invalid_arguments" => ProtocolErrorCode::InvalidArguments,
+        "validator_required" => ProtocolErrorCode::ValidatorRequired,
+        "validator_mismatch" => ProtocolErrorCode::ValidatorMismatch,
+        "interface_validator_required" => ProtocolErrorCode::InterfaceValidatorRequired,
+        "interface_validator_mismatch" => ProtocolErrorCode::InterfaceValidatorMismatch,
+        "permission_denied" => ProtocolErrorCode::PermissionDenied,
+        "resource_limit_exceeded" => ProtocolErrorCode::ResourceLimitExceeded,
+        "internal" => ProtocolErrorCode::Internal,
+        "operation_outcome_unknown" => ProtocolErrorCode::OperationOutcomeUnknown,
+        _ => return None,
+    })
+}
+
+pub(crate) fn error_to_json(error: &ProtocolError) -> Json {
+    serde_json::json!({
+        "error": {
+            "code": error_code_name(error.code),
+            "message": error.message,
+        }
+    })
+}
+
+pub(crate) fn item_error_to_json(error: &ProtocolError) -> Json {
+    serde_json::json!({
+        "code": error_code_name(error.code),
+        "message": error.message,
+    })
+}
+
+pub(crate) fn item_error_from_json(value: &Json) -> Result<ProtocolError, CodecError> {
+    let fields = value
+        .as_object()
+        .ok_or_else(|| invalid_field("error", "expected object"))?;
+    exact(fields, &["code", "message"], "error")?;
+    let code_name = required_string(fields, "code")?;
+    let code = error_code_from_name(code_name)
+        .ok_or_else(|| invalid_field("error.code", "unknown protocol error code"))?;
+    let message = required_string(fields, "message")?.to_owned();
+    Ok(ProtocolError { code, message })
+}
+
+fn envelope_error_from_json(value: &Json) -> Result<Option<ProtocolError>, CodecError> {
+    let Some(fields) = value.as_object() else {
+        return Ok(None);
+    };
+    if fields.len() != 1 || !fields.contains_key("error") {
+        return Ok(None);
+    }
+    item_error_from_json(&fields["error"]).map(Some)
+}
+
+fn exact(fields: &Map<String, Json>, allowed: &[&str], parent: &str) -> Result<(), CodecError> {
+    for name in fields.keys() {
+        if !allowed.contains(&name.as_str()) {
+            return Err(CodecError::UnknownField {
+                field: format!("{parent}.{name}"),
+            });
+        }
+    }
+    for name in allowed {
+        if !fields.contains_key(*name) {
+            return Err(CodecError::MissingField {
+                field: format!("{parent}.{name}"),
+            });
+        }
+    }
+    Ok(())
+}
+
+fn required_string<'a>(fields: &'a Map<String, Json>, name: &str) -> Result<&'a str, CodecError> {
+    fields
+        .get(name)
+        .and_then(Json::as_str)
+        .ok_or_else(|| invalid_field(&format!("error.{name}"), "expected string"))
+}
+
+fn invalid_field(field: &str, reason: &str) -> CodecError {
+    CodecError::InvalidField {
+        field: field.into(),
+        reason: reason.into(),
+    }
+}
+
+pub(crate) fn decode<T>(
+    status: StatusCode,
+    body: &[u8],
+    interaction: ProtocolInteraction,
+    limits: Limits,
+    success: impl FnOnce(&Json) -> Result<T, CodecError>,
+) -> Result<DecodedResponse<T>, ClientResponseError> {
+    let value = match json::parse(body, BodyKind::Response, limits) {
+        Ok(value) => value,
+        Err(_) if !status.is_success() => {
+            return Err(transport_failure(status));
+        }
+        Err(error) => {
+            return Err(ClientResponseError::invalid(
+                InvalidResponseKind::InvalidSuccessBody,
+                error.to_string(),
+            ));
+        }
+    };
+
+    match envelope_error_from_json(&value) {
+        Ok(Some(error)) => {
+            if status.is_success() {
+                return Err(ClientResponseError::invalid(
+                    InvalidResponseKind::ErrorEnvelopeOnSuccessStatus,
+                    "protocol error envelope carried by a success status",
+                ));
+            }
+            if !error.code.is_allowed_for(interaction) {
+                return Err(ClientResponseError::invalid(
+                    InvalidResponseKind::DisallowedProtocolCode,
+                    format!(
+                        "code `{}` is not allowed for {interaction:?}",
+                        error_code_name(error.code)
+                    ),
+                ));
+            }
+            let expected = status_for_error(error.code);
+            let status_mismatch =
+                (!status_matches_error(status, error.code)).then_some(StatusMismatch {
+                    actual: status,
+                    expected,
+                });
+            Ok(DecodedResponse::ProtocolFailure {
+                error,
+                status_mismatch,
+            })
+        }
+        Err(_) if !status.is_success() => Err(transport_failure(status)),
+        Err(error) => Err(ClientResponseError::invalid(
+            InvalidResponseKind::InvalidSuccessBody,
+            error.to_string(),
+        )),
+        Ok(None) if status == StatusCode::OK => success(&value)
+            .map(DecodedResponse::Success)
+            .map_err(|error| {
+                ClientResponseError::invalid(
+                    InvalidResponseKind::InvalidSuccessBody,
+                    error.to_string(),
+                )
+            }),
+        Ok(None) if status.is_success() => match success(&value) {
+            Ok(_) => Err(ClientResponseError::invalid(
+                InvalidResponseKind::NonCanonicalSuccessStatus,
+                format!("success body carried by non-canonical HTTP {status}"),
+            )),
+            Err(error) => Err(ClientResponseError::invalid(
+                InvalidResponseKind::InvalidSuccessBody,
+                error.to_string(),
+            )),
+        },
+        Ok(None) => match success(&value) {
+            Ok(_) => Err(ClientResponseError::invalid(
+                InvalidResponseKind::SuccessBodyOnErrorStatus,
+                "valid success body carried by a non-success status",
+            )),
+            Err(_) => Err(transport_failure(status)),
+        },
+    }
+}
+
+pub(crate) fn transport_failure(status: StatusCode) -> ClientResponseError {
+    let kind = match status {
+        StatusCode::UNAUTHORIZED => TransportFailureKind::AuthenticationRequired,
+        StatusCode::FORBIDDEN => TransportFailureKind::EndpointForbidden,
+        _ => TransportFailureKind::HttpStatus,
+    };
+    ClientResponseError::TransportBinding(TransportBindingFailure { status, kind })
+}
@@ -0,0 +1,353 @@
+use wip_https::http::StatusCode;
+use wip_https::wip_protocol::{
+    FetchInterfaceRequest, FetchInterfaceResponse, FetchRequest, INTERFACE_FORMAT_V1,
+    InterfaceDescriptor, Object, ProtocolError, ProtocolErrorCode,
+};
+use wip_https::{
+    BatchMethod, BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse,
+    BatchResponseItem, BatchSuccess, ClientResponseError, DecodedResponse, Endpoint,
+    InvalidResponseKind, Limits, ResourceLimitKind, decode_batch_request, decode_batch_response,
+    encode_batch_error_response, encode_batch_request, encode_batch_resource_limit_error_response,
+    encode_batch_response,
+};
+
+fn limits() -> Limits {
+    Limits::new(100_000, 100_000, 64, 4).unwrap()
+}
+
+fn request() -> BatchRequest {
+    BatchRequest {
+        requests: vec![
+            BatchRequestItem {
+                id: "object".into(),
+                request: BatchRequestKind::Fetch(FetchRequest {
+                    path: "/item".into(),
+                }),
+            },
+            BatchRequestItem {
+                id: "interface".into(),
+                request: BatchRequestKind::FetchInterface(FetchInterfaceRequest {
+                    interface: "interface-v1".into(),
+                }),
+            },
+        ],
+    }
+}
+
+#[test]
+fn batch_round_trips_by_unique_id_with_item_failures_and_validators() {
+    let request = request();
+    let endpoint = Endpoint::parse("https://example.test/wip").unwrap();
+    let encoded_request = encode_batch_request(&endpoint, &request, limits()).unwrap();
+    assert_eq!(encoded_request.uri().path(), "/wip/v1/batch");
+    assert_eq!(encoded_request.headers()["accept"], "application/json");
+    assert_eq!(
+        decode_batch_request(encoded_request.body(), limits()).unwrap(),
+        request
+    );
+
+    let response = BatchResponse {
+        responses: vec![
+            BatchResponseItem {
+                id: "interface".into(),
+                outcome: Err(ProtocolError {
+                    code: ProtocolErrorCode::InterfaceNotFound,
+                    message: "gone".into(),
+                }),
+            },
+            BatchResponseItem {
+                id: "object".into(),
+                outcome: Ok(BatchSuccess::Fetch(Object {
+                    name: "item".into(),
+                    description: None,
+                    interfaces: vec![],
+                    r#ref: None,
+                    validator: Some(vec![0, 1, 2, 255]),
+                })),
+            },
+        ],
+    };
+    let encoded = encode_batch_response(&request, &response, limits()).unwrap();
+    assert_eq!(encoded.status(), StatusCode::OK);
+    assert!(
+        std::str::from_utf8(encoded.body())
+            .unwrap()
+            .contains("AAEC/w==")
+    );
+    assert_eq!(
+        decode_batch_response(&request, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(response)
+    );
+}
+
+#[test]
+fn batch_interface_validator_round_trips_in_item_body() {
+    let request = BatchRequest {
+        requests: vec![BatchRequestItem {
+            id: "interface".into(),
+            request: BatchRequestKind::FetchInterface(FetchInterfaceRequest {
+                interface: "interface-v1".into(),
+            }),
+        }],
+    };
+    let response = BatchResponse {
+        responses: vec![BatchResponseItem {
+            id: "interface".into(),
+            outcome: Ok(BatchSuccess::FetchInterface(FetchInterfaceResponse {
+                interface: "interface-v1".into(),
+                descriptor: InterfaceDescriptor {
+                    format: INTERFACE_FORMAT_V1.into(),
+                    documentation: None,
+                    types: vec![],
+                    operations: vec![],
+                },
+                validator: Some(vec![255, 254, 253]),
+            })),
+        }],
+    };
+    let encoded = encode_batch_response(&request, &response, limits()).unwrap();
+    assert!(
+        std::str::from_utf8(encoded.body())
+            .unwrap()
+            .contains("//79")
+    );
+    assert_eq!(
+        decode_batch_response(&request, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(response)
+    );
+}
+
+#[test]
+fn malformed_known_method_arguments_are_item_local() {
+    let body = br#"{
+        "requests": [
+            {"id":"valid","method":"fetch","arguments":{"path":"/item"}},
+            {"id":"invalid","method":"fetch_tree","arguments":{"path":"/","depth":"deep","limit":1}}
+        ]
+    }"#;
+    let decoded = decode_batch_request(body, limits()).unwrap();
+    assert!(matches!(
+        decoded.requests[0].request,
+        BatchRequestKind::Fetch(_)
+    ));
+    let invalid = match &decoded.requests[1].request {
+        BatchRequestKind::Invalid { method, error } => {
+            assert_eq!(*method, BatchMethod::FetchTree);
+            assert_eq!(error.code, ProtocolErrorCode::InvalidRequest);
+            error.clone()
+        }
+        other => panic!("expected item-local invalid request, got {other:?}"),
+    };
+
+    let response = BatchResponse {
+        responses: vec![
+            BatchResponseItem {
+                id: "valid".into(),
+                outcome: Ok(BatchSuccess::Fetch(Object {
+                    name: "item".into(),
+                    description: None,
+                    interfaces: vec![],
+                    r#ref: None,
+                    validator: None,
+                })),
+            },
+            BatchResponseItem {
+                id: "invalid".into(),
+                outcome: Err(invalid),
+            },
+        ],
+    };
+    let encoded = encode_batch_response(&decoded, &response, limits()).unwrap();
+    assert_eq!(encoded.status(), StatusCode::OK);
+    assert_eq!(
+        decode_batch_response(&decoded, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(response)
+    );
+}
+
+#[test]
+fn invalid_batch_envelopes_are_rejected_at_top_level() {
+    assert!(decode_batch_request(br#"{}"#, limits()).is_err());
+
+    let malformed_item = br#"{
+        "requests": [
+            {"id":"item","method":"fetch","arguments":{"path":"/"},"extra":true}
+        ]
+    }"#;
+    assert!(decode_batch_request(malformed_item, limits()).is_err());
+
+    let duplicate = br#"{
+        "requests": [
+            {"id":"same","method":"fetch","arguments":{"path":"/a"}},
+            {"id":"same","method":"fetch","arguments":{"path":"/b"}}
+        ]
+    }"#;
+    assert!(decode_batch_request(duplicate, limits()).is_err());
+
+    let operation = br#"{
+        "requests": [
+            {"id":"call","method":"call_operation","arguments":{}}
+        ]
+    }"#;
+    assert!(decode_batch_request(operation, limits()).is_err());
+
+    let too_many = Limits::new(100_000, 100_000, 64, 1).unwrap();
+    assert!(decode_batch_request(duplicate, too_many).is_err());
+}
+
+#[test]
+fn batch_resource_limits_use_413_or_422_and_never_429() {
+    let error = ProtocolError {
+        code: ProtocolErrorCode::ResourceLimitExceeded,
+        message: "bounded".into(),
+    };
+    for (kind, status) in [
+        (
+            ResourceLimitKind::RepresentationBytes,
+            StatusCode::PAYLOAD_TOO_LARGE,
+        ),
+        (ResourceLimitKind::Logical, StatusCode::UNPROCESSABLE_ENTITY),
+    ] {
+        let encoded = encode_batch_resource_limit_error_response(&error, kind, limits()).unwrap();
+        assert_eq!(encoded.status(), status);
+        assert_ne!(encoded.status(), StatusCode::TOO_MANY_REQUESTS);
+        assert_eq!(
+            decode_batch_response(&request(), &encoded, limits()).unwrap(),
+            DecodedResponse::ProtocolFailure {
+                error: error.clone(),
+                status_mismatch: None,
+            }
+        );
+    }
+}
+
+#[test]
+fn batch_success_body_requires_exactly_http_200() {
+    let request = request();
+    let response = BatchResponse {
+        responses: vec![
+            BatchResponseItem {
+                id: "object".into(),
+                outcome: Ok(BatchSuccess::Fetch(Object {
+                    name: "item".into(),
+                    description: None,
+                    interfaces: vec![],
+                    r#ref: None,
+                    validator: None,
+                })),
+            },
+            BatchResponseItem {
+                id: "interface".into(),
+                outcome: Err(ProtocolError {
+                    code: ProtocolErrorCode::InterfaceNotFound,
+                    message: "gone".into(),
+                }),
+            },
+        ],
+    };
+    let encoded = encode_batch_response(&request, &response, limits()).unwrap();
+    for status in [StatusCode::CREATED, StatusCode::ACCEPTED] {
+        let mut noncanonical = encoded.clone();
+        *noncanonical.status_mut() = status;
+        assert!(matches!(
+            decode_batch_response(&request, &noncanonical, limits()).unwrap_err(),
+            ClientResponseError::InvalidResponse { .. }
+        ));
+    }
+}
+
+#[test]
+fn top_level_batch_errors_use_the_batch_allowed_code_set() {
+    let invalid = ProtocolError {
+        code: ProtocolErrorCode::InvalidRequest,
+        message: "bad envelope".into(),
+    };
+    let encoded = encode_batch_error_response(&invalid, limits()).unwrap();
+    assert_eq!(
+        decode_batch_response(&request(), &encoded, limits()).unwrap(),
+        DecodedResponse::ProtocolFailure {
+            error: invalid,
+            status_mismatch: None,
+        }
+    );
+
+    let not_found = wip_https::http::Response::builder()
+        .status(StatusCode::NOT_FOUND)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(br#"{"error":{"code":"not_found","message":"not a batch failure"}}"#.to_vec())
+        .unwrap();
+    assert!(matches!(
+        decode_batch_response(&request(), &not_found, limits()).unwrap_err(),
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::InvalidBatch,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn unsupported_batch_descriptor_waits_for_envelope_correlation() {
+    let duplicate = wip_https::http::Response::builder()
+        .status(StatusCode::OK)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(
+            br#"{"responses":[{"id":"interface","result":{"interface":"interface-v1","descriptor":{"format":"wip-interface/2","future":true}}},{"id":"interface","result":{"interface":"interface-v1","descriptor":{"format":"wip-interface/2"}}}]}"#
+                .to_vec(),
+        )
+        .unwrap();
+    assert!(matches!(
+        decode_batch_response(&request(), &duplicate, limits()).unwrap_err(),
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::InvalidBatch,
+            ..
+        }
+    ));
+
+    let missing = wip_https::http::Response::builder()
+        .status(StatusCode::OK)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(
+            br#"{"responses":[{"id":"interface","result":{"interface":"interface-v1","descriptor":{"format":"wip-interface/2"}}}]}"#
+                .to_vec(),
+        )
+        .unwrap();
+    assert!(matches!(
+        decode_batch_response(&request(), &missing, limits()).unwrap_err(),
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::InvalidBatch,
+            ..
+        }
+    ));
+
+    let request = BatchRequest {
+        requests: vec![BatchRequestItem {
+            id: "interface".into(),
+            request: BatchRequestKind::FetchInterface(FetchInterfaceRequest {
+                interface: "interface-v1".into(),
+            }),
+        }],
+    };
+    assert!(matches!(
+        decode_batch_response(&request, &missing, limits()).unwrap_err(),
+        ClientResponseError::UnsupportedDescriptorFormat { format }
+            if format == "wip-interface/2"
+    ));
+}
+
+#[test]
+fn batch_response_must_have_exactly_the_requested_ids() {
+    let request = request();
+    let missing = BatchResponse {
+        responses: vec![BatchResponseItem {
+            id: "object".into(),
+            outcome: Ok(BatchSuccess::Fetch(Object {
+                name: "item".into(),
+                description: None,
+                interfaces: vec![],
+                r#ref: None,
+                validator: None,
+            })),
+        }],
+    };
+    assert!(encode_batch_response(&request, &missing, limits()).is_err());
+}
@@ -0,0 +1,508 @@
+use std::collections::BTreeMap;
+
+use wip_https::http::StatusCode;
+use wip_https::wip_protocol::{
+    CallOperationRequest, CallOperationResponse, Documentation, EnumCase, FetchInterfaceRequest,
+    FetchInterfaceResponse, FetchRequest, FetchTreeRequest, FetchTreeResponse, FieldDeclaration,
+    INTERFACE_FORMAT_V1, InterfaceDescriptor, InterfaceTarget, MAX_SAFE_INTEGER, Object,
+    ObjectTreeNode, OperationDeclaration, ParameterDeclaration, ReturnDeclaration, Target,
+    TypeDeclaration, TypeExpr, UnionCase, Value,
+};
+use wip_https::{
+    ClientResponseError, CodecError, DecodedResponse, Endpoint, InvalidResponseKind, Limits,
+    ResourceLimitKind, decode_call_operation_metadata, decode_call_operation_request,
+    decode_call_operation_response, decode_fetch_interface_request,
+    decode_fetch_interface_response, decode_fetch_request, decode_fetch_response,
+    decode_fetch_tree_request, decode_fetch_tree_response, encode_call_operation_request,
+    encode_call_operation_response, encode_fetch_interface_request,
+    encode_fetch_interface_response, encode_fetch_request, encode_fetch_response,
+    encode_fetch_tree_request, encode_fetch_tree_response,
+};
+
+fn limits() -> Limits {
+    Limits::new(1_000_000, 1_000_000, 100, 100).unwrap()
+}
+
+fn endpoint() -> Endpoint {
+    Endpoint::parse("https://example.test/wip").unwrap()
+}
+
+fn object(name: &str, validator: &[u8]) -> Object {
+    Object {
+        name: name.into(),
+        description: Some("description".into()),
+        interfaces: vec!["interface-v1".into()],
+        r#ref: Some(format!("object:{name}")),
+        validator: Some(validator.to_vec()),
+    }
+}
+
+fn descriptor() -> InterfaceDescriptor {
+    InterfaceDescriptor {
+        format: INTERFACE_FORMAT_V1.into(),
+        documentation: Some(Documentation {
+            summary: "Codec fixture".into(),
+            details: None,
+        }),
+        types: vec![TypeDeclaration {
+            name: "Pair".into(),
+            documentation: None,
+            definition: TypeExpr::Record {
+                fields: vec![
+                    FieldDeclaration {
+                        name: "required".into(),
+                        required: true,
+                        documentation: None,
+                        r#type: TypeExpr::String,
+                    },
+                    FieldDeclaration {
+                        name: "optional".into(),
+                        required: false,
+                        documentation: None,
+                        r#type: TypeExpr::String,
+                    },
+                    FieldDeclaration {
+                        name: "optional_json".into(),
+                        required: false,
+                        documentation: None,
+                        r#type: TypeExpr::Json,
+                    },
+                ],
+            },
+        }],
+        operations: vec![OperationDeclaration {
+            name: "everything".into(),
+            documentation: None,
+            parameters: vec![
+                parameter("unit", TypeExpr::Unit),
+                parameter("boolean", TypeExpr::Boolean),
+                parameter("integer", TypeExpr::Integer),
+                parameter("number", TypeExpr::Number),
+                parameter("string", TypeExpr::String),
+                parameter("bytes", TypeExpr::Bytes),
+                parameter("entry", TypeExpr::Entry),
+                parameter(
+                    "list",
+                    TypeExpr::List {
+                        items: Box::new(TypeExpr::Integer),
+                    },
+                ),
+                parameter(
+                    "record",
+                    TypeExpr::Named {
+                        name: "Pair".into(),
+                    },
+                ),
+                parameter(
+                    "enum",
+                    TypeExpr::Enum {
+                        cases: vec![EnumCase {
+                            name: "ready".into(),
+                            documentation: None,
+                        }],
+                    },
+                ),
+                parameter(
+                    "union",
+                    TypeExpr::Union {
+                        cases: vec![
+                            UnionCase {
+                                name: "empty".into(),
+                                documentation: None,
+                                payload: None,
+                            },
+                            UnionCase {
+                                name: "found".into(),
+                                documentation: None,
+                                payload: Some(TypeExpr::Entry),
+                            },
+                        ],
+                    },
+                ),
+                parameter("json", TypeExpr::Json),
+            ],
+            returns: ReturnDeclaration {
+                documentation: None,
+                r#type: TypeExpr::Bytes,
+            },
+        }],
+    }
+}
+
+fn parameter(name: &str, r#type: TypeExpr) -> ParameterDeclaration {
+    ParameterDeclaration {
+        name: name.into(),
+        required: true,
+        documentation: None,
+        r#type,
+    }
+}
+
+fn record(fields: impl IntoIterator<Item = (&'static str, Value)>) -> Value {
+    Value::Record(
+        fields
+            .into_iter()
+            .map(|(name, value)| (name.into(), value))
+            .collect(),
+    )
+}
+
+fn call_request() -> CallOperationRequest {
+    CallOperationRequest {
+        target: Target {
+            path: "/items/123".into(),
+            validator: Some(vec![0, 1, 2, 255]),
+        },
+        interface: InterfaceTarget {
+            reference: "interface-v1".into(),
+            validator: Some(vec![9, 8, 7]),
+        },
+        operation: "everything".into(),
+        arguments: BTreeMap::from([
+            ("unit".into(), Value::Unit),
+            ("boolean".into(), Value::Boolean(true)),
+            ("integer".into(), Value::Integer(MAX_SAFE_INTEGER)),
+            ("number".into(), Value::Number(1.5)),
+            ("string".into(), Value::String("text".into())),
+            ("bytes".into(), Value::Bytes(vec![0, 1, 2, 255])),
+            ("entry".into(), Value::String("/items/123".into())),
+            (
+                "list".into(),
+                Value::List(vec![Value::Integer(1), Value::Integer(2)]),
+            ),
+            (
+                "record".into(),
+                record([("required", Value::String("present".into()))]),
+            ),
+            ("enum".into(), Value::String("ready".into())),
+            (
+                "union".into(),
+                record([
+                    ("$case", Value::String("found".into())),
+                    ("value", Value::String("/items/123".into())),
+                ]),
+            ),
+            (
+                "json".into(),
+                record([
+                    ("null", Value::Unit),
+                    ("number", Value::Integer(2)),
+                    ("path_like", Value::String("/not-an-entry".into())),
+                ]),
+            ),
+        ]),
+    }
+}
+
+#[test]
+fn every_single_interaction_request_accepts_json() {
+    let fetch =
+        encode_fetch_request(&endpoint(), &FetchRequest { path: "/".into() }, limits()).unwrap();
+    let fetch_tree = encode_fetch_tree_request(
+        &endpoint(),
+        &FetchTreeRequest {
+            path: "/".into(),
+            depth: 1,
+            limit: 1,
+        },
+        limits(),
+    )
+    .unwrap();
+    let fetch_interface = encode_fetch_interface_request(
+        &endpoint(),
+        &FetchInterfaceRequest {
+            interface: "interface-v1".into(),
+        },
+        limits(),
+    )
+    .unwrap();
+    let call = encode_call_operation_request(&endpoint(), &call_request(), &descriptor(), limits())
+        .unwrap();
+
+    for request in [fetch, fetch_tree, fetch_interface, call] {
+        assert_eq!(request.headers()["accept"], "application/json");
+    }
+}
+
+#[test]
+fn fetch_round_trips_direct_body_and_body_validator() {
+    let request = FetchRequest {
+        path: "/items/123".into(),
+    };
+    let encoded_request = encode_fetch_request(&endpoint(), &request, limits()).unwrap();
+    assert_eq!(encoded_request.uri().path(), "/wip/v1/fetch");
+    assert_eq!(
+        decode_fetch_request(encoded_request.body(), limits()).unwrap(),
+        request
+    );
+
+    let expected = object("123", &[0, 1, 2, 255]);
+    let encoded = encode_fetch_response(&request, &expected, limits()).unwrap();
+    assert_eq!(encoded.status(), StatusCode::OK);
+    assert_eq!(
+        decode_fetch_response(&request, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(expected)
+    );
+    assert!(encoded.headers().get("etag").is_none());
+}
+
+#[test]
+fn tree_and_interface_round_trip_nested_logical_models() {
+    let tree_request = FetchTreeRequest {
+        path: "/items".into(),
+        depth: 1,
+        limit: 2,
+    };
+    let encoded_request = encode_fetch_tree_request(&endpoint(), &tree_request, limits()).unwrap();
+    assert_eq!(
+        decode_fetch_tree_request(encoded_request.body(), limits()).unwrap(),
+        tree_request
+    );
+    let tree = FetchTreeResponse {
+        root: ObjectTreeNode {
+            object: object("items", b"root-validator"),
+            children: vec![ObjectTreeNode {
+                object: object("123", b"child-validator"),
+                children: vec![],
+            }],
+        },
+        truncated: false,
+    };
+    let encoded = encode_fetch_tree_response(&tree_request, &tree, limits()).unwrap();
+    assert_eq!(
+        decode_fetch_tree_response(&tree_request, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(tree)
+    );
+
+    let interface_request = FetchInterfaceRequest {
+        interface: "interface-v1".into(),
+    };
+    let encoded_request =
+        encode_fetch_interface_request(&endpoint(), &interface_request, limits()).unwrap();
+    assert_eq!(
+        decode_fetch_interface_request(encoded_request.body(), limits()).unwrap(),
+        interface_request
+    );
+    let interface = FetchInterfaceResponse {
+        interface: interface_request.interface.clone(),
+        descriptor: descriptor(),
+        validator: Some(vec![4, 5, 6, 255]),
+    };
+    let encoded =
+        encode_fetch_interface_response(&interface_request, &interface, limits()).unwrap();
+    assert_eq!(
+        decode_fetch_interface_response(&interface_request, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(interface)
+    );
+}
+
+#[test]
+fn descriptor_guided_values_and_validators_round_trip_both_directions() {
+    let descriptor = descriptor();
+    let request = call_request();
+    let encoded =
+        encode_call_operation_request(&endpoint(), &request, &descriptor, limits()).unwrap();
+    let body = std::str::from_utf8(encoded.body()).unwrap();
+    assert!(body.contains("AAEC/w=="));
+    let metadata = decode_call_operation_metadata(encoded.body(), limits()).unwrap();
+    assert_eq!(metadata.target, request.target);
+    assert_eq!(metadata.interface, request.interface);
+    assert_eq!(metadata.operation, request.operation);
+    assert_eq!(
+        metadata
+            .decode_request(encoded.body(), &descriptor, limits())
+            .unwrap(),
+        request
+    );
+    let mut changed_route = request.clone();
+    changed_route.target.path = "/items/other".into();
+    let changed =
+        encode_call_operation_request(&endpoint(), &changed_route, &descriptor, limits()).unwrap();
+    assert!(
+        metadata
+            .decode_request(changed.body(), &descriptor, limits())
+            .is_err()
+    );
+
+    let mut null_json_request = request.clone();
+    null_json_request
+        .arguments
+        .insert("json".into(), Value::Unit);
+    null_json_request.arguments.insert(
+        "record".into(),
+        record([
+            ("required", Value::String("present".into())),
+            ("optional_json", Value::Unit),
+        ]),
+    );
+    let null_json =
+        encode_call_operation_request(&endpoint(), &null_json_request, &descriptor, limits())
+            .unwrap();
+    assert_eq!(
+        decode_call_operation_request(null_json.body(), &descriptor, limits()).unwrap(),
+        null_json_request
+    );
+
+    let expected = CallOperationResponse {
+        result: Value::Bytes(vec![255, 0, 1]),
+        validator: Some(vec![3, 2, 1, 0]),
+    };
+    let encoded =
+        encode_call_operation_response(&request, &descriptor, &expected, limits()).unwrap();
+    assert!(
+        std::str::from_utf8(encoded.body())
+            .unwrap()
+            .contains("/wAB")
+    );
+    assert_eq!(
+        decode_call_operation_response(&request, &descriptor, &encoded, limits()).unwrap(),
+        DecodedResponse::Success(expected)
+    );
+}
+
+#[test]
+fn malformed_unknown_null_and_noncanonical_base64_are_rejected() {
+    let limits = limits();
+    assert!(decode_fetch_request(br#"{"path":"/","extra":true}"#, limits).is_err());
+    assert!(decode_fetch_request(br#"{"path":"relative","path":"/"}"#, limits).is_err());
+
+    let request = call_request();
+    let descriptor = descriptor();
+    let body = serde_json::to_vec(&serde_json::json!({
+        "target": {"path": "/items/123", "validator": null},
+        "interface": {"reference": "interface-v1"},
+        "operation": "everything",
+        "arguments": {}
+    }))
+    .unwrap();
+    assert!(decode_call_operation_request(&body, &descriptor, limits).is_err());
+
+    let mut json: serde_json::Value = serde_json::from_slice(
+        encode_call_operation_request(&endpoint(), &request, &descriptor, limits)
+            .unwrap()
+            .body(),
+    )
+    .unwrap();
+    json["arguments"]["bytes"] = serde_json::Value::String("AAEC_w==".into());
+    assert!(
+        decode_call_operation_request(&serde_json::to_vec(&json).unwrap(), &descriptor, limits)
+            .is_err()
+    );
+}
+
+#[test]
+fn caller_limits_bound_bytes_and_nesting() {
+    let tiny = Limits::new(8, 8, 2, 1).unwrap();
+    let too_large = decode_fetch_request(br#"{"path":"/long"}"#, tiny).unwrap_err();
+    assert!(matches!(&too_large, CodecError::BodyTooLarge { .. }));
+    assert_eq!(
+        too_large.resource_limit_kind(),
+        Some(ResourceLimitKind::RepresentationBytes)
+    );
+
+    let nested = br#"{"path":[[["/"]]]}"#;
+    let nesting_limited = Limits::new(1024, 1024, 2, 1).unwrap();
+    let too_deep = decode_fetch_request(nested, nesting_limited).unwrap_err();
+    assert!(matches!(&too_deep, CodecError::NestingTooDeep { .. }));
+    assert_eq!(
+        too_deep.resource_limit_kind(),
+        Some(ResourceLimitKind::Logical)
+    );
+
+    let outbound_limited = Limits::new(1_000_000, 1_000_000, 1, 10).unwrap();
+    assert!(
+        encode_call_operation_request(
+            &endpoint(),
+            &call_request(),
+            &descriptor(),
+            outbound_limited,
+        )
+        .is_err()
+    );
+    assert!(
+        encode_fetch_response(
+            &FetchRequest {
+                path: "/item".into(),
+            },
+            &object("item", b"validator"),
+            outbound_limited,
+        )
+        .is_err()
+    );
+}
+
+#[test]
+fn unsupported_descriptor_format_is_client_local() {
+    let request = FetchInterfaceRequest {
+        interface: "interface-v1".into(),
+    };
+    let mut interface = FetchInterfaceResponse {
+        interface: request.interface.clone(),
+        descriptor: descriptor(),
+        validator: None,
+    };
+    interface.descriptor.format = "future-format".into();
+    let response = encode_fetch_interface_response(&request, &interface, limits()).unwrap();
+    let error = decode_fetch_interface_response(&request, &response, limits()).unwrap_err();
+    assert!(matches!(
+        error,
+        ClientResponseError::UnsupportedDescriptorFormat { .. }
+    ));
+
+    let future_shape = wip_https::http::Response::builder()
+        .status(StatusCode::OK)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(
+            br#"{"interface":"interface-v1","descriptor":{"format":"wip-interface/2","future_shape":true}}"#
+                .to_vec(),
+        )
+        .unwrap();
+    assert!(matches!(
+        decode_fetch_interface_response(&request, &future_shape, limits()).unwrap_err(),
+        ClientResponseError::UnsupportedDescriptorFormat { format }
+            if format == "wip-interface/2"
+    ));
+
+    for malformed in [
+        br#"{"interface":"wrong","descriptor":{"format":"wip-interface/2"}}"#.as_slice(),
+        br#"{"interface":"interface-v1","descriptor":{"format":"wip-interface/2"},"validator":null}"#
+            .as_slice(),
+    ] {
+        let response = wip_https::http::Response::builder()
+            .status(StatusCode::OK)
+            .header("content-type", "application/json; charset=utf-8")
+            .body(malformed.to_vec())
+            .unwrap();
+        assert!(matches!(
+            decode_fetch_interface_response(&request, &response, limits()).unwrap_err(),
+            ClientResponseError::InvalidResponse {
+                kind: InvalidResponseKind::InvalidSuccessBody,
+                ..
+            }
+        ));
+    }
+}
+
+#[test]
+fn invalid_success_is_classified_as_invalid_response() {
+    let response = wip_https::http::Response::builder()
+        .status(StatusCode::OK)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(br#"{"name":"wrong","interfaces":[]}"#.to_vec())
+        .unwrap();
+    let error = decode_fetch_response(
+        &FetchRequest {
+            path: "/expected".into(),
+        },
+        &response,
+        limits(),
+    )
+    .unwrap_err();
+    assert!(matches!(
+        error,
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::InvalidSuccessBody,
+            ..
+        }
+    ));
+}
@@ -0,0 +1,304 @@
+use wip_https::http::{Response, StatusCode};
+use wip_https::wip_protocol::{
+    FetchRequest, ProtocolError, ProtocolErrorCode, ProtocolInteraction,
+};
+use wip_https::{
+    ClientResponseError, DecodedResponse, InvalidResponseKind, Limits, ResourceLimitKind,
+    TransportFailureKind, decode_fetch_response, encode_protocol_error_response,
+    encode_resource_limit_error_response, error_code_name, is_json_content_type, status_for_error,
+    status_for_resource_limit,
+};
+
+fn limits() -> Limits {
+    Limits::new(64 * 1024, 64 * 1024, 32, 16).unwrap()
+}
+
+fn request() -> FetchRequest {
+    FetchRequest { path: "/".into() }
+}
+
+fn response(status: StatusCode, body: impl Into<Vec<u8>>) -> Response<Vec<u8>> {
+    Response::builder()
+        .status(status)
+        .header("content-type", "application/json; charset=utf-8")
+        .body(body.into())
+        .unwrap()
+}
+
+#[test]
+fn content_type_accepts_only_utf8_json_syntax() {
+    assert!(is_json_content_type("application/json"));
+    assert!(is_json_content_type("Application/JSON; Charset=\"UTF-8\""));
+    assert!(!is_json_content_type("application/json; charset=utf-16"));
+    assert!(!is_json_content_type("application/json; charset=\"utf-8"));
+    assert!(!is_json_content_type("application/json; charset=utf-8\""));
+    assert!(!is_json_content_type("application/json; profile=other"));
+}
+
+#[test]
+fn every_protocol_code_has_stable_name_and_status() {
+    let expected = [
+        (
+            ProtocolErrorCode::InvalidRequest,
+            "invalid_request",
+            StatusCode::BAD_REQUEST,
+        ),
+        (
+            ProtocolErrorCode::NotFound,
+            "not_found",
+            StatusCode::NOT_FOUND,
+        ),
+        (
+            ProtocolErrorCode::InterfaceNotFound,
+            "interface_not_found",
+            StatusCode::NOT_FOUND,
+        ),
+        (
+            ProtocolErrorCode::InterfaceMismatch,
+            "interface_mismatch",
+            StatusCode::CONFLICT,
+        ),
+        (
+            ProtocolErrorCode::OperationNotFound,
+            "operation_not_found",
+            StatusCode::NOT_FOUND,
+        ),
+        (
+            ProtocolErrorCode::InvalidArguments,
+            "invalid_arguments",
+            StatusCode::UNPROCESSABLE_ENTITY,
+        ),
+        (
+            ProtocolErrorCode::ValidatorRequired,
+            "validator_required",
+            StatusCode::PRECONDITION_REQUIRED,
+        ),
+        (
+            ProtocolErrorCode::ValidatorMismatch,
+            "validator_mismatch",
+            StatusCode::PRECONDITION_FAILED,
+        ),
+        (
+            ProtocolErrorCode::InterfaceValidatorRequired,
+            "interface_validator_required",
+            StatusCode::PRECONDITION_REQUIRED,
+        ),
+        (
+            ProtocolErrorCode::InterfaceValidatorMismatch,
+            "interface_validator_mismatch",
+            StatusCode::PRECONDITION_FAILED,
+        ),
+        (
+            ProtocolErrorCode::PermissionDenied,
+            "permission_denied",
+            StatusCode::FORBIDDEN,
+        ),
+        (
+            ProtocolErrorCode::ResourceLimitExceeded,
+            "resource_limit_exceeded",
+            StatusCode::UNPROCESSABLE_ENTITY,
+        ),
+        (
+            ProtocolErrorCode::Internal,
+            "internal",
+            StatusCode::INTERNAL_SERVER_ERROR,
+        ),
+        (
+            ProtocolErrorCode::OperationOutcomeUnknown,
+            "operation_outcome_unknown",
+            StatusCode::INTERNAL_SERVER_ERROR,
+        ),
+    ];
+    assert_eq!(expected.len(), ProtocolErrorCode::ALL.len());
+    for (code, name, status) in expected {
+        assert_eq!(error_code_name(code), name);
+        assert_eq!(status_for_error(code), status);
+    }
+}
+
+#[test]
+fn resource_limit_statuses_encode_and_decode_by_concrete_limit_class() {
+    let error = ProtocolError {
+        code: ProtocolErrorCode::ResourceLimitExceeded,
+        message: "bounded".into(),
+    };
+    let cases = [
+        (
+            ResourceLimitKind::RepresentationBytes,
+            StatusCode::PAYLOAD_TOO_LARGE,
+        ),
+        (ResourceLimitKind::Logical, StatusCode::UNPROCESSABLE_ENTITY),
+    ];
+    for (kind, status) in cases {
+        assert_eq!(status_for_resource_limit(kind), status);
+        let encoded = encode_resource_limit_error_response(
+            ProtocolInteraction::Fetch,
+            &error,
+            kind,
+            limits(),
+        )
+        .unwrap();
+        assert_eq!(encoded.status(), status);
+        assert_eq!(
+            decode_fetch_response(&request(), &encoded, limits()).unwrap(),
+            DecodedResponse::ProtocolFailure {
+                error: error.clone(),
+                status_mismatch: None,
+            }
+        );
+    }
+
+    let default =
+        encode_protocol_error_response(ProtocolInteraction::Fetch, &error, limits()).unwrap();
+    assert_eq!(default.status(), StatusCode::UNPROCESSABLE_ENTITY);
+    assert_ne!(default.status(), StatusCode::TOO_MANY_REQUESTS);
+}
+
+#[test]
+fn rate_limit_status_without_protocol_envelope_stays_transport_failure() {
+    let response = Response::builder()
+        .status(StatusCode::TOO_MANY_REQUESTS)
+        .body(b"rate limited".to_vec())
+        .unwrap();
+    assert!(matches!(
+        decode_fetch_response(&request(), &response, limits()).unwrap_err(),
+        ClientResponseError::TransportBinding(failure)
+            if failure.status == StatusCode::TOO_MANY_REQUESTS
+                && failure.kind == TransportFailureKind::HttpStatus
+    ));
+}
+
+#[test]
+fn valid_success_body_requires_exactly_http_200() {
+    let success_body = br#"{"name":"","interfaces":[]}"#;
+    for status in [StatusCode::CREATED, StatusCode::ACCEPTED] {
+        assert!(matches!(
+            decode_fetch_response(&request(), &response(status, success_body), limits())
+                .unwrap_err(),
+            ClientResponseError::InvalidResponse {
+                kind: InvalidResponseKind::NonCanonicalSuccessStatus,
+                ..
+            }
+        ));
+    }
+}
+
+#[test]
+fn server_encoder_rejects_codes_disallowed_for_the_interaction() {
+    let error = ProtocolError {
+        code: ProtocolErrorCode::InterfaceNotFound,
+        message: "not valid for fetch".into(),
+    };
+    assert!(encode_protocol_error_response(ProtocolInteraction::Fetch, &error, limits()).is_err());
+}
+
+#[test]
+fn valid_envelope_code_is_authoritative_when_status_mismatches() {
+    let error = ProtocolError {
+        code: ProtocolErrorCode::NotFound,
+        message: "missing".into(),
+    };
+    let mut encoded =
+        encode_protocol_error_response(ProtocolInteraction::Fetch, &error, limits()).unwrap();
+    *encoded.status_mut() = StatusCode::IM_A_TEAPOT;
+
+    assert_eq!(
+        decode_fetch_response(&request(), &encoded, limits()).unwrap(),
+        DecodedResponse::ProtocolFailure {
+            error,
+            status_mismatch: Some(wip_https::StatusMismatch {
+                actual: StatusCode::IM_A_TEAPOT,
+                expected: StatusCode::NOT_FOUND,
+            }),
+        }
+    );
+}
+
+#[test]
+fn envelope_and_status_contradictions_are_invalid_responses() {
+    let error_body = br#"{"error":{"code":"not_found","message":"missing"}}"#;
+    let on_success =
+        decode_fetch_response(&request(), &response(StatusCode::OK, error_body), limits())
+            .unwrap_err();
+    assert!(matches!(
+        on_success,
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::ErrorEnvelopeOnSuccessStatus,
+            ..
+        }
+    ));
+
+    let success_body = br#"{"name":"","interfaces":[]}"#;
+    let on_error = decode_fetch_response(
+        &request(),
+        &response(StatusCode::BAD_GATEWAY, success_body),
+        limits(),
+    )
+    .unwrap_err();
+    assert!(matches!(
+        on_error,
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::SuccessBodyOnErrorStatus,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn disallowed_protocol_code_is_invalid_instead_of_reclassified() {
+    let body = br#"{"error":{"code":"interface_not_found","message":"wrong interaction"}}"#;
+    let error = decode_fetch_response(&request(), &response(StatusCode::NOT_FOUND, body), limits())
+        .unwrap_err();
+    assert!(matches!(
+        error,
+        ClientResponseError::InvalidResponse {
+            kind: InvalidResponseKind::DisallowedProtocolCode,
+            ..
+        }
+    ));
+}
+
+#[test]
+fn proxy_authentication_and_endpoint_failures_stay_transport_failures() {
+    let cases = [
+        (
+            StatusCode::BAD_GATEWAY,
+            TransportFailureKind::HttpStatus,
+            b"proxy failure".as_slice(),
+        ),
+        (
+            StatusCode::UNAUTHORIZED,
+            TransportFailureKind::AuthenticationRequired,
+            b"login required".as_slice(),
+        ),
+        (
+            StatusCode::FORBIDDEN,
+            TransportFailureKind::EndpointForbidden,
+            b"denied".as_slice(),
+        ),
+    ];
+    for (status, expected_kind, body) in cases {
+        let response = Response::builder()
+            .status(status)
+            .body(body.to_vec())
+            .unwrap();
+        let error = decode_fetch_response(&request(), &response, limits()).unwrap_err();
+        assert!(matches!(
+            error,
+            ClientResponseError::TransportBinding(failure)
+                if failure.status == status && failure.kind == expected_kind
+        ));
+    }
+}
+
+#[test]
+fn malformed_non_success_envelope_is_transport_binding_failure() {
+    let malformed = response(
+        StatusCode::BAD_GATEWAY,
+        br#"{"error":{"code":"not_found","message":null}}"#,
+    );
+    assert!(matches!(
+        decode_fetch_response(&request(), &malformed, limits()).unwrap_err(),
+        ClientResponseError::TransportBinding(_)
+    ));
+}
@@ -0,0 +1,127 @@
+use wip_https::http::{Method, Request, StatusCode};
+use wip_https::{Endpoint, RequestMetadataError, Route, validate_http_request};
+
+#[test]
+fn endpoint_is_https_absolute_queryless_and_canonical() {
+    let endpoint = Endpoint::parse("https://example.test/root/prefix").unwrap();
+    assert_eq!(endpoint.to_string(), "https://example.test/root/prefix/");
+
+    let expected = [
+        (Route::Fetch, "https://example.test/root/prefix/v1/fetch"),
+        (
+            Route::FetchTree,
+            "https://example.test/root/prefix/v1/fetch_tree",
+        ),
+        (
+            Route::FetchInterface,
+            "https://example.test/root/prefix/v1/fetch_interface",
+        ),
+        (
+            Route::CallOperation,
+            "https://example.test/root/prefix/v1/call_operation",
+        ),
+        (Route::Batch, "https://example.test/root/prefix/v1/batch"),
+    ];
+    for (route, url) in expected {
+        assert_eq!(endpoint.route(route).as_str(), url);
+        assert_eq!(
+            endpoint.recognize(&wip_https::url::Url::parse(url).unwrap()),
+            Some(route)
+        );
+    }
+    assert_eq!(
+        endpoint.recognize(
+            &wip_https::url::Url::parse("https://example.test/root/prefix/v1/fetch?path=/items")
+                .unwrap()
+        ),
+        None
+    );
+}
+
+#[test]
+fn routes_never_mix_worldspace_paths_into_endpoint_prefixes() {
+    let endpoint = Endpoint::parse("https://example.test/wip/%E4%B8%96%E7%95%8C/").unwrap();
+    let route = endpoint.route(Route::Fetch);
+    assert_eq!(route.path(), "/wip/%E4%B8%96%E7%95%8C/v1/fetch");
+    assert!(!route.as_str().contains("items"));
+}
+
+#[test]
+fn inbound_http_metadata_enforces_post_route_and_json() {
+    let endpoint = Endpoint::parse("https://example.test/wip").unwrap();
+    let valid = Request::builder()
+        .method(Method::POST)
+        .uri("/wip/v1/fetch")
+        .header("content-type", "application/json; charset=utf-8")
+        .body(Vec::<u8>::new())
+        .unwrap();
+    assert!(validate_http_request(&endpoint, Route::Fetch, &valid).is_ok());
+
+    let wrong_method = Request::builder()
+        .method(Method::GET)
+        .uri("/wip/v1/fetch")
+        .header("content-type", "application/json")
+        .body(Vec::<u8>::new())
+        .unwrap();
+    assert!(validate_http_request(&endpoint, Route::Fetch, &wrong_method).is_err());
+
+    let wrong_route = Request::builder()
+        .method(Method::POST)
+        .uri("/wip/v1/fetch_tree")
+        .header("content-type", "application/json")
+        .body(Vec::<u8>::new())
+        .unwrap();
+    assert!(validate_http_request(&endpoint, Route::Fetch, &wrong_route).is_err());
+
+    for accept in [
+        "text/plain, */*;q=1, application/json;q=0",
+        "application/json; charset=utf-16",
+        "application/json; profile=future",
+    ] {
+        let incompatible_accept = Request::builder()
+            .method(Method::POST)
+            .uri("/wip/v1/fetch")
+            .header("content-type", "application/json")
+            .header("accept", accept)
+            .body(Vec::<u8>::new())
+            .unwrap();
+        let error =
+            validate_http_request(&endpoint, Route::Fetch, &incompatible_accept).unwrap_err();
+        assert!(matches!(&error, RequestMetadataError::NotAcceptable));
+        assert_eq!(error.status(), StatusCode::NOT_ACCEPTABLE);
+    }
+
+    for accept in [
+        "application/json; charset=UTF-8",
+        "application/json; q=1; profile=accept-extension",
+    ] {
+        let compatible_accept = Request::builder()
+            .method(Method::POST)
+            .uri("/wip/v1/fetch")
+            .header("content-type", "application/json")
+            .header("accept", accept)
+            .body(Vec::<u8>::new())
+            .unwrap();
+        assert!(validate_http_request(&endpoint, Route::Fetch, &compatible_accept).is_ok());
+    }
+
+    let unsupported_media_type = Request::builder()
+        .method(Method::POST)
+        .uri("/wip/v1/fetch")
+        .header("content-type", "text/plain")
+        .header("accept", "application/json")
+        .body(Vec::<u8>::new())
+        .unwrap();
+    let error =
+        validate_http_request(&endpoint, Route::Fetch, &unsupported_media_type).unwrap_err();
+    assert!(matches!(&error, RequestMetadataError::UnsupportedMediaType));
+    assert_eq!(error.status(), StatusCode::UNSUPPORTED_MEDIA_TYPE);
+}
+
+#[test]
+fn invalid_endpoint_components_are_rejected() {
+    assert!(Endpoint::parse("http://example.test/wip").is_err());
+    assert!(Endpoint::parse("/relative").is_err());
+    assert!(Endpoint::parse("https://example.test/wip?q=1").is_err());
+    assert!(Endpoint::parse("https://example.test/wip#fragment").is_err());
+}
@@ -647,14 +647,17 @@ fn dispatch_arm(operation: &Operation) -> TokenStream2 {
            .map_err(::wip_interface::DispatchError::InvalidArguments)?;
            let decoded = #arguments_ident::decode(arguments)
                .map_err(::wip_interface::DispatchError::Decode)?;
-            let result = implementation.#method_ident(#(#arguments),*)
-                .map_err(::wip_interface::DispatchError::Host)?;
-            let encoded = #arguments_ident::encode_result(result)
-                .map_err(::wip_interface::DispatchError::Encode)?;
-            descriptor
-                .validate_result(#operation_name, &encoded)
-                .map_err(::wip_interface::DispatchError::InvalidResult)?;
-            ::std::result::Result::Ok(encoded)
+            ::std::panic::catch_unwind(::std::panic::AssertUnwindSafe(|| {
+                let result = implementation.#method_ident(#(#arguments),*)
+                    .map_err(::wip_interface::DispatchError::Host)?;
+                let encoded = #arguments_ident::encode_result(result)
+                    .map_err(::wip_interface::DispatchError::Encode)?;
+                descriptor
+                    .validate_result(#operation_name, &encoded)
+                    .map_err(::wip_interface::DispatchError::InvalidResult)?;
+                ::std::result::Result::Ok(encoded)
+            }))
+            .map_err(|_| ::wip_interface::DispatchError::Panic)?
        }
    }
 }
@@ -46,8 +46,10 @@
 //! `Option<T>` is supported only directly as a record field or operation
 //! parameter. It means omission, not a null value. A domain failure belongs in
 //! an application return enum/union and is returned as `Ok(value)`.
-//! [`HostError`] is reserved for host/runtime failure, so the required
-//! [`OperationResult`] convention keeps those two failure classes distinct.
+//! [`HostError`] is reserved for host/runtime failure and requires an explicit
+//! [`HostErrorKind`] plus [`EffectGuarantee`]. The required [`OperationResult`]
+//! convention therefore keeps domain failures separate from runtime failures and
+//! makes outcome uncertainty visible to Host dispatch.
 //!
 //! # Migration to canonical values
 //!
@@ -139,29 +141,107 @@ pub trait InterfaceImplementation<T>: InterfaceDefinition {
 /// `Err(HostError)` means the host or runtime could not perform the operation.
 pub type OperationResult<T> = Result<T, HostError>;

-/// A host/runtime failure, kept separate from the operation's application
+/// Whether an operation failure proves that no effects were committed.
+///
+/// This guarantee is consumed by Host dispatch when choosing a protocol failure:
+/// only [`NotCommitted`](Self::NotCommitted) failures may become `Internal` or
+/// `ResourceLimitExceeded`; [`Unknown`](Self::Unknown) failures must become
+/// `OperationOutcomeUnknown`.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum EffectGuarantee {
+    /// The operation was not invoked, or every effect was rolled back.
+    NotCommitted,
+    /// The operation may have committed effects.
+    Unknown,
+}
+
+/// Host/runtime failure category used when effects are known not to be committed.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum HostErrorKind {
+    /// The Host or backend encountered an internal failure.
+    Internal,
+    /// A cancellation, deadline, or bounded resource limit was exceeded.
+    ResourceLimitExceeded,
+}
+
+/// A typed host/runtime failure, kept separate from the operation's application
 /// return type.
+///
+/// The effect guarantee is mandatory. Host runtimes must ignore the diagnostic
+/// when producing a wire response; it is bounded here for local observability but
+/// can still contain backend-private information.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct HostError {
+    kind: HostErrorKind,
+    effect_guarantee: EffectGuarantee,
    message: String,
 }

 impl HostError {
-    /// Creates a host failure with a human-readable diagnostic.
+    /// Creates an internal Host failure with an explicit effect guarantee.
    #[must_use]
-    pub fn new(message: impl Into<String>) -> Self {
+    pub fn internal(message: impl Into<String>, effect_guarantee: EffectGuarantee) -> Self {
+        Self::new(HostErrorKind::Internal, effect_guarantee, message)
+    }
+
+    /// Creates a resource-limit Host failure with an explicit effect guarantee.
+    #[must_use]
+    pub fn resource_limit(message: impl Into<String>, effect_guarantee: EffectGuarantee) -> Self {
+        Self::new(
+            HostErrorKind::ResourceLimitExceeded,
+            effect_guarantee,
+            message,
+        )
+    }
+
+    fn new(
+        kind: HostErrorKind,
+        effect_guarantee: EffectGuarantee,
+        message: impl Into<String>,
+    ) -> Self {
        Self {
-            message: message.into(),
+            kind,
+            effect_guarantee,
+            message: bounded_diagnostic(message.into()),
        }
    }

-    /// Returns the diagnostic message.
+    /// Returns the typed Host failure category.
+    #[must_use]
+    pub fn kind(&self) -> HostErrorKind {
+        self.kind
+    }
+
+    /// Returns the operation-effect guarantee attached by the implementation.
+    #[must_use]
+    pub fn effect_guarantee(&self) -> EffectGuarantee {
+        self.effect_guarantee
+    }
+
+    /// Returns the bounded local diagnostic message.
+    ///
+    /// Host runtimes must not place this value in protocol responses because it
+    /// can contain backend paths, credentials, or other private details.
    #[must_use]
    pub fn message(&self) -> &str {
        &self.message
    }
 }

+const MAX_DIAGNOSTIC_BYTES: usize = 512;
+
+fn bounded_diagnostic(mut message: String) -> String {
+    if message.len() <= MAX_DIAGNOSTIC_BYTES {
+        return message;
+    }
+    let mut end = MAX_DIAGNOSTIC_BYTES;
+    while !message.is_char_boundary(end) {
+        end -= 1;
+    }
+    message.truncate(end);
+    message
+}
+
 impl Display for HostError {
    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
        formatter.write_str(&self.message)
@@ -241,12 +321,59 @@ pub enum DispatchError {
    Decode(CodecError),
    /// The implementation reported a host/runtime failure.
    Host(HostError),
+    /// The implementation panicked after invocation began.
+    ///
+    /// Panic payloads are deliberately discarded because they can contain
+    /// backend-private diagnostics.
+    Panic,
    /// The Rust result could not be encoded.
    Encode(CodecError),
    /// The encoded result did not match the generated declaration.
    InvalidResult(wip_protocol::ValidationError),
 }

+/// Whether generated dispatch failed before or after typed implementation
+/// invocation began.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum DispatchPhase {
+    /// Typed implementation code was not invoked.
+    BeforeInvocation,
+    /// Typed implementation invocation began, so effects require an explicit
+    /// non-commit or rollback guarantee.
+    AfterInvocation,
+}
+
+impl DispatchError {
+    /// Returns the execution phase in which this dispatch failure occurred.
+    #[must_use]
+    pub fn phase(&self) -> DispatchPhase {
+        match self {
+            Self::UnknownOperation(_) | Self::InvalidArguments(_) | Self::Decode(_) => {
+                DispatchPhase::BeforeInvocation
+            }
+            Self::Host(_) | Self::Panic | Self::Encode(_) | Self::InvalidResult(_) => {
+                DispatchPhase::AfterInvocation
+            }
+        }
+    }
+
+    /// Returns a post-invocation effect guarantee when the implementation
+    /// supplied one.
+    ///
+    /// Panic, encode, and result-validation failures default to `Unknown` until
+    /// a provider confirms rollback. Pre-invocation failures return `None`.
+    #[must_use]
+    pub fn effect_guarantee(&self) -> Option<EffectGuarantee> {
+        match self {
+            Self::UnknownOperation(_) | Self::InvalidArguments(_) | Self::Decode(_) => None,
+            Self::Host(error) => Some(error.effect_guarantee()),
+            Self::Panic | Self::Encode(_) | Self::InvalidResult(_) => {
+                Some(EffectGuarantee::Unknown)
+            }
+        }
+    }
+}
+
 impl Display for DispatchError {
    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
        match self {
@@ -256,6 +383,7 @@ impl Display for DispatchError {
            Self::InvalidArguments(error) => write!(formatter, "invalid arguments: {error}"),
            Self::Decode(error) => write!(formatter, "argument decoding failed: {error}"),
            Self::Host(error) => write!(formatter, "host operation failed: {error}"),
+            Self::Panic => formatter.write_str("operation implementation panicked"),
            Self::Encode(error) => write!(formatter, "result encoding failed: {error}"),
            Self::InvalidResult(error) => write!(formatter, "invalid operation result: {error}"),
        }
@@ -265,7 +393,7 @@ impl Display for DispatchError {
 impl Error for DispatchError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match self {
-            Self::UnknownOperation(_) => None,
+            Self::UnknownOperation(_) | Self::Panic => None,
            Self::InvalidArguments(error) | Self::InvalidResult(error) => Some(error),
            Self::Decode(error) | Self::Encode(error) => Some(error),
            Self::Host(error) => Some(error),
@@ -1,7 +1,10 @@
 use std::collections::BTreeMap;

 use wip_interface::wip_protocol::{INTERFACE_FORMAT_V1, TypeExpr, Value};
-use wip_interface::{DispatchError, HostError, OperationResult, WipType, interface};
+use wip_interface::{
+    DispatchError, DispatchPhase, EffectGuarantee, HostError, HostErrorKind, OperationResult,
+    WipType, interface,
+};

 /// Publication request.
 #[derive(Debug, Clone, PartialEq, WipType)]
@@ -66,7 +69,10 @@ impl Catalog for AcceptingCatalog {
    }

    fn host_value(&self) -> OperationResult<String> {
-        Err(HostError::new("backend unavailable"))
+        Err(HostError::internal(
+            "backend unavailable",
+            EffectGuarantee::Unknown,
+        ))
    }
 }

@@ -90,6 +96,26 @@ impl Catalog for RejectingCatalog {
    }
 }

+struct PanickingCatalog;
+
+impl Catalog for PanickingCatalog {
+    fn publish(
+        &self,
+        _request: PublishRequest,
+        _note: Option<String>,
+    ) -> OperationResult<PublishOutcome> {
+        panic!("private panic payload")
+    }
+
+    fn ping(&self) -> OperationResult<()> {
+        panic!("private panic payload")
+    }
+
+    fn host_value(&self) -> OperationResult<String> {
+        panic!("private panic payload")
+    }
+}
+
 fn publish_arguments(with_note: bool) -> BTreeMap<String, Value> {
    let mut arguments = BTreeMap::from([(
        "request".into(),
@@ -203,16 +229,41 @@ fn typed_dispatch_validates_decodes_invokes_encodes_and_validates() {
    let invalid =
        CatalogDefinition::dispatch(&AcceptingCatalog, "publish", BTreeMap::new()).unwrap_err();
    assert!(matches!(invalid, DispatchError::InvalidArguments(_)));
+    assert_eq!(invalid.phase(), DispatchPhase::BeforeInvocation);
+    assert_eq!(invalid.effect_guarantee(), None);

    let host =
        CatalogDefinition::dispatch(&AcceptingCatalog, "host_value", BTreeMap::new()).unwrap_err();
-    assert!(matches!(host, DispatchError::Host(error) if error.message() == "backend unavailable"));
+    assert!(
+        matches!(&host, DispatchError::Host(error) if error.message() == "backend unavailable")
+    );
+    assert_eq!(host.phase(), DispatchPhase::AfterInvocation);
+    assert_eq!(host.effect_guarantee(), Some(EffectGuarantee::Unknown));
+
+    let panic =
+        CatalogDefinition::dispatch(&PanickingCatalog, "host_value", BTreeMap::new()).unwrap_err();
+    assert!(matches!(panic, DispatchError::Panic));
+    assert_eq!(panic.phase(), DispatchPhase::AfterInvocation);
+    assert_eq!(panic.effect_guarantee(), Some(EffectGuarantee::Unknown));
+    assert!(!panic.to_string().contains("private panic payload"));

    let unknown =
        CatalogDefinition::dispatch(&AcceptingCatalog, "missing", BTreeMap::new()).unwrap_err();
    assert!(matches!(unknown, DispatchError::UnknownOperation(name) if name == "missing"));
 }

+#[test]
+fn host_errors_require_a_typed_kind_and_effect_guarantee() {
+    let internal = HostError::internal("x".repeat(4_096), EffectGuarantee::NotCommitted);
+    assert_eq!(internal.kind(), HostErrorKind::Internal);
+    assert_eq!(internal.effect_guarantee(), EffectGuarantee::NotCommitted);
+    assert!(internal.message().len() <= 512);
+
+    let resource = HostError::resource_limit("deadline", EffectGuarantee::Unknown);
+    assert_eq!(resource.kind(), HostErrorKind::ResourceLimitExceeded);
+    assert_eq!(resource.effect_guarantee(), EffectGuarantee::Unknown);
+}
+
 /// Operations whose distinct source names normalize to the same PascalCase.
 #[interface]
 pub trait DistinctOperations {
@@ -223,10 +223,29 @@ impl Display for ValidationError {

 impl Error for ValidationError {}

-/// Stable protocol failure code returned by a host or produced by a client.
+/// One core interaction whose failure codes form a closed set.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ProtocolInteraction {
+    /// Fetch one object by its Worldspace path.
+    Fetch,
+    /// Fetch a bounded tree of objects.
+    FetchTree,
+    /// Fetch one interface descriptor by its opaque reference.
+    FetchInterface,
+    /// Invoke one operation on a path-targeted object.
+    CallOperation,
+}
+
+/// Stable protocol failure code returned by a host.
+///
+/// This is the complete wire-level code set. A Client treats a malformed success
+/// or failure response, including a code disallowed for its interaction, as a
+/// Client-local `InvalidResponse`. An unsupported descriptor format is likewise
+/// a Client-local `UnsupportedDescriptorFormat`; neither condition is a code a
+/// Host can return.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ProtocolErrorCode {
-    /// The request is structurally invalid.
+    /// The request is structurally invalid before an operation descriptor is fixed.
    InvalidRequest,
    /// The target object is not published.
    NotFound,
@@ -236,10 +255,8 @@ pub enum ProtocolErrorCode {
    InterfaceMismatch,
    /// The selected operation is not declared by the current interface.
    OperationNotFound,
-    /// Supplied operation arguments are invalid.
+    /// Supplied arguments do not match the fixed operation declaration.
    InvalidArguments,
-    /// A host result does not satisfy the declaration.
-    InvalidResult,
    /// The operation requires an object validator and none was supplied.
    ValidatorRequired,
    /// The supplied object validator does not match current state.
@@ -251,9 +268,88 @@ pub enum ProtocolErrorCode {
    /// A published operation is not permitted for the caller.
    PermissionDenied,
    /// A bounded protocol resource limit was exceeded.
+    ///
+    /// For `call_operation`, the Host guarantees that the operation was not run
+    /// or that all of its effects were rolled back.
    ResourceLimitExceeded,
-    /// The host encountered an internal failure.
+    /// The Host encountered an internal failure.
+    ///
+    /// For `call_operation`, the Host guarantees that the operation was not run
+    /// or that all of its effects were rolled back.
    Internal,
+    /// The Host cannot guarantee that the operation was not run or rolled back.
+    ///
+    /// A Client must not automatically retry because the operation may have
+    /// committed effects even though no success response was available.
+    OperationOutcomeUnknown,
+}
+
+impl ProtocolErrorCode {
+    /// Every canonical wire-level error code.
+    pub const ALL: [Self; 14] = [
+        Self::InvalidRequest,
+        Self::NotFound,
+        Self::InterfaceNotFound,
+        Self::InterfaceMismatch,
+        Self::OperationNotFound,
+        Self::InvalidArguments,
+        Self::ValidatorRequired,
+        Self::ValidatorMismatch,
+        Self::InterfaceValidatorRequired,
+        Self::InterfaceValidatorMismatch,
+        Self::PermissionDenied,
+        Self::ResourceLimitExceeded,
+        Self::Internal,
+        Self::OperationOutcomeUnknown,
+    ];
+
+    /// Whether a Host may return this code for `interaction`.
+    ///
+    /// `false` identifies an invalid error response; it does not turn that
+    /// response into another wire-level protocol failure.
+    #[must_use]
+    pub const fn is_allowed_for(self, interaction: ProtocolInteraction) -> bool {
+        use ProtocolErrorCode::{
+            InterfaceMismatch, InterfaceNotFound, InterfaceValidatorMismatch,
+            InterfaceValidatorRequired, Internal, InvalidArguments, InvalidRequest, NotFound,
+            OperationNotFound, OperationOutcomeUnknown, PermissionDenied, ResourceLimitExceeded,
+            ValidatorMismatch, ValidatorRequired,
+        };
+        use ProtocolInteraction::{CallOperation, Fetch, FetchInterface, FetchTree};
+
+        match (interaction, self) {
+            (_, InvalidRequest | ResourceLimitExceeded | Internal) => true,
+            (Fetch | FetchTree, NotFound) => true,
+            (FetchInterface, InterfaceNotFound) => true,
+            (
+                CallOperation,
+                NotFound
+                | InterfaceMismatch
+                | OperationNotFound
+                | InvalidArguments
+                | ValidatorRequired
+                | ValidatorMismatch
+                | InterfaceValidatorRequired
+                | InterfaceValidatorMismatch
+                | PermissionDenied
+                | OperationOutcomeUnknown,
+            ) => true,
+            (
+                _,
+                NotFound
+                | InterfaceNotFound
+                | InterfaceMismatch
+                | OperationNotFound
+                | InvalidArguments
+                | ValidatorRequired
+                | ValidatorMismatch
+                | InterfaceValidatorRequired
+                | InterfaceValidatorMismatch
+                | PermissionDenied
+                | OperationOutcomeUnknown,
+            ) => false,
+        }
+    }
 }

 /// Transport-independent protocol failure.
@@ -16,7 +16,20 @@
 //! | `fetch_interface` | [`FetchInterfaceRequest`] / [`FetchInterfaceResponse`] |
 //! | Object and interface call preconditions | [`Target`] / [`InterfaceTarget`] |
 //! | `call_operation` | [`CallOperationRequest`] / [`CallOperationResponse`] |
-//! | Stable failure taxonomy | [`ProtocolErrorCode`] / [`ProtocolError`] |
+//! | Stable Host failure taxonomy | [`ProtocolErrorCode`] / [`ProtocolError`] |
+//! | Per-interaction allowed failure codes | [`ProtocolInteraction`] / [`ProtocolErrorCode::is_allowed_for`] |
+//!
+//! [`ProtocolErrorCode`] is a closed set of Host-returned wire failures. After a
+//! Client receives a response, an invalid Object, Descriptor, operation result,
+//! malformed error, or error code disallowed by [`ProtocolInteraction`] is a
+//! Client-local `InvalidResponse`, not another wire error. A descriptor whose
+//! `format` is not supported is a Client-local `UnsupportedDescriptorFormat`.
+//!
+//! For `call_operation`, [`ProtocolErrorCode::Internal`] and
+//! [`ProtocolErrorCode::ResourceLimitExceeded`] guarantee that the operation did
+//! not run or that all effects were rolled back. Only
+//! [`ProtocolErrorCode::OperationOutcomeUnknown`] means the Host cannot make that
+//! guarantee; Clients must not automatically retry it.
 //!
 //! Paths, object refs, interface refs, and validators remain separate concepts.
 //! They are represented by ordinary protocol strings/bytes in the corresponding
@@ -35,8 +48,8 @@ mod model;
 mod validation;

 pub use error::{
-    NameNamespace, PathSegment, ProtocolError, ProtocolErrorCode, ValidationError,
-    ValidationErrorKind, ValueKind,
+    NameNamespace, PathSegment, ProtocolError, ProtocolErrorCode, ProtocolInteraction,
+    ValidationError, ValidationErrorKind, ValueKind,
 };
 pub use model::{
    CallOperationRequest, CallOperationResponse, Documentation, EnumCase, FetchInterfaceRequest,
@@ -379,6 +379,9 @@ impl FetchRequest {
    }

    /// Validates an object returned for this request.
+    ///
+    /// Failure means the Client received an invalid success response; it is not a
+    /// Host-returned [`crate::ProtocolErrorCode`].
    pub fn validate_response(&self, response: &FetchResponse) -> Result<(), ValidationError> {
        response.validate_at_path(&self.path)
    }
@@ -393,6 +396,9 @@ impl FetchTreeRequest {

 impl FetchTreeResponse {
    /// Validates tree shape, names, depth, and node limit for `request`.
+    ///
+    /// Failure means the Client received an invalid success response; it is not a
+    /// Host-returned [`crate::ProtocolErrorCode`].
    pub fn validate_for(&self, request: &FetchTreeRequest) -> Result<(), ValidationError> {
        crate::validation::validate_fetch_tree_response(self, request)
    }
@@ -400,6 +406,11 @@ impl FetchTreeResponse {

 impl FetchInterfaceResponse {
    /// Validates request correspondence and descriptor semantics.
+    ///
+    /// Failure means the Client received an invalid success response; it is not a
+    /// Host-returned [`crate::ProtocolErrorCode`]. Descriptor format support is a
+    /// separate Client concern: an otherwise valid descriptor with an unsupported
+    /// `format` is a Client-local `UnsupportedDescriptorFormat`.
    pub fn validate_for(&self, request: &FetchInterfaceRequest) -> Result<(), ValidationError> {
        crate::validation::validate_fetch_interface_response(self, request)
    }
@@ -414,6 +425,9 @@ impl CallOperationRequest {

 impl CallOperationResponse {
    /// Validates this result against the named operation in `descriptor`.
+    ///
+    /// Failure means the Client received an invalid success response; it is not a
+    /// Host-returned [`crate::ProtocolErrorCode`].
    pub fn validate_for(
        &self,
        descriptor: &InterfaceDescriptor,
@@ -5,8 +5,8 @@ use wip_protocol::{
    FetchInterfaceResponse, FetchRequest, FetchTreeRequest, FetchTreeResponse, FieldDeclaration,
    INTERFACE_FORMAT_V1, InterfaceDescriptor, InterfaceTarget, MAX_SAFE_INTEGER, NameNamespace,
    Object, ObjectTreeNode, OperationDeclaration, ParameterDeclaration, PathSegment, ProtocolError,
-    ProtocolErrorCode, ProtocolResult, ReturnDeclaration, Target, TypeDeclaration, TypeExpr,
-    UnionCase, ValidationErrorKind, Value, ValueKind,
+    ProtocolErrorCode, ProtocolInteraction, ProtocolResult, ReturnDeclaration, Target,
+    TypeDeclaration, TypeExpr, UnionCase, ValidationErrorKind, Value, ValueKind,
 };

 fn record(entries: impl IntoIterator<Item = (&'static str, Value)>) -> Value {
@@ -729,24 +729,26 @@ fn fetch_tree_dtos_validate_names_depth_limit_and_siblings() {
 }

 #[test]
-fn protocol_result_and_every_canonical_error_code_are_available() {
-    let codes = [
-        ProtocolErrorCode::InvalidRequest,
-        ProtocolErrorCode::NotFound,
-        ProtocolErrorCode::InterfaceNotFound,
-        ProtocolErrorCode::InterfaceMismatch,
-        ProtocolErrorCode::OperationNotFound,
-        ProtocolErrorCode::InvalidArguments,
-        ProtocolErrorCode::InvalidResult,
-        ProtocolErrorCode::ValidatorRequired,
-        ProtocolErrorCode::ValidatorMismatch,
-        ProtocolErrorCode::InterfaceValidatorRequired,
-        ProtocolErrorCode::InterfaceValidatorMismatch,
-        ProtocolErrorCode::PermissionDenied,
-        ProtocolErrorCode::ResourceLimitExceeded,
-        ProtocolErrorCode::Internal,
-    ];
-    assert_eq!(codes.len(), 14);
+fn protocol_result_exposes_the_exact_canonical_wire_error_codes() {
+    assert_eq!(
+        ProtocolErrorCode::ALL,
+        [
+            ProtocolErrorCode::InvalidRequest,
+            ProtocolErrorCode::NotFound,
+            ProtocolErrorCode::InterfaceNotFound,
+            ProtocolErrorCode::InterfaceMismatch,
+            ProtocolErrorCode::OperationNotFound,
+            ProtocolErrorCode::InvalidArguments,
+            ProtocolErrorCode::ValidatorRequired,
+            ProtocolErrorCode::ValidatorMismatch,
+            ProtocolErrorCode::InterfaceValidatorRequired,
+            ProtocolErrorCode::InterfaceValidatorMismatch,
+            ProtocolErrorCode::PermissionDenied,
+            ProtocolErrorCode::ResourceLimitExceeded,
+            ProtocolErrorCode::Internal,
+            ProtocolErrorCode::OperationOutcomeUnknown,
+        ]
+    );

    let failure: ProtocolResult<()> = ProtocolResult::Failure(ProtocolError {
        code: ProtocolErrorCode::InvalidArguments,
@@ -758,3 +760,127 @@ fn protocol_result_and_every_canonical_error_code_are_available() {
        ProtocolResult::Success(Value::Unit)
    );
 }
+
+fn assert_allowed_codes(interaction: ProtocolInteraction, expected: &[ProtocolErrorCode]) {
+    let actual: Vec<_> = ProtocolErrorCode::ALL
+        .into_iter()
+        .filter(|code| code.is_allowed_for(interaction))
+        .collect();
+    assert_eq!(actual, expected);
+
+    for code in ProtocolErrorCode::ALL {
+        assert_eq!(
+            code.is_allowed_for(interaction),
+            expected.contains(&code),
+            "unexpected {code:?} validity for {interaction:?}"
+        );
+    }
+}
+
+#[test]
+fn fetch_error_codes_are_exhaustive() {
+    assert_allowed_codes(
+        ProtocolInteraction::Fetch,
+        &[
+            ProtocolErrorCode::InvalidRequest,
+            ProtocolErrorCode::NotFound,
+            ProtocolErrorCode::ResourceLimitExceeded,
+            ProtocolErrorCode::Internal,
+        ],
+    );
+}
+
+#[test]
+fn fetch_tree_error_codes_are_exhaustive() {
+    assert_allowed_codes(
+        ProtocolInteraction::FetchTree,
+        &[
+            ProtocolErrorCode::InvalidRequest,
+            ProtocolErrorCode::NotFound,
+            ProtocolErrorCode::ResourceLimitExceeded,
+            ProtocolErrorCode::Internal,
+        ],
+    );
+}
+
+#[test]
+fn fetch_interface_error_codes_are_exhaustive() {
+    assert_allowed_codes(
+        ProtocolInteraction::FetchInterface,
+        &[
+            ProtocolErrorCode::InvalidRequest,
+            ProtocolErrorCode::InterfaceNotFound,
+            ProtocolErrorCode::ResourceLimitExceeded,
+            ProtocolErrorCode::Internal,
+        ],
+    );
+}
+
+#[test]
+fn call_operation_error_codes_are_exhaustive() {
+    assert_allowed_codes(
+        ProtocolInteraction::CallOperation,
+        &[
+            ProtocolErrorCode::InvalidRequest,
+            ProtocolErrorCode::NotFound,
+            ProtocolErrorCode::InterfaceMismatch,
+            ProtocolErrorCode::OperationNotFound,
+            ProtocolErrorCode::InvalidArguments,
+            ProtocolErrorCode::ValidatorRequired,
+            ProtocolErrorCode::ValidatorMismatch,
+            ProtocolErrorCode::InterfaceValidatorRequired,
+            ProtocolErrorCode::InterfaceValidatorMismatch,
+            ProtocolErrorCode::PermissionDenied,
+            ProtocolErrorCode::ResourceLimitExceeded,
+            ProtocolErrorCode::Internal,
+            ProtocolErrorCode::OperationOutcomeUnknown,
+        ],
+    );
+}
+
+#[test]
+fn invalid_success_payloads_remain_client_local_validation_failures() {
+    let fetch = FetchRequest {
+        path: "/articles/one".into(),
+    };
+    assert!(matches!(
+        fetch.validate_response(&object("other")).unwrap_err().kind,
+        ValidationErrorKind::ObjectNameMismatch { .. }
+    ));
+
+    let interface_request = FetchInterfaceRequest {
+        interface: "catalog-v1".into(),
+    };
+    let mut invalid_descriptor = descriptor();
+    invalid_descriptor
+        .operations
+        .push(invalid_descriptor.operations[0].clone());
+    assert!(matches!(
+        FetchInterfaceResponse {
+            interface: interface_request.interface.clone(),
+            descriptor: invalid_descriptor,
+            validator: None,
+        }
+        .validate_for(&interface_request)
+        .unwrap_err()
+        .kind,
+        ValidationErrorKind::DuplicateName {
+            namespace: NameNamespace::Operation,
+            ..
+        }
+    ));
+
+    assert!(matches!(
+        CallOperationResponse {
+            result: Value::String("not a boolean".into()),
+            validator: None,
+        }
+        .validate_for(&descriptor(), "publish")
+        .unwrap_err()
+        .kind,
+        ValidationErrorKind::TypeMismatch {
+            expected: ValueKind::Boolean,
+            actual: ValueKind::String,
+        }
+    ));
+}
@@ -0,0 +1,12 @@
+[package]
+name = "wip-public-api-example"
+version = "0.1.0"
+edition = "2024"
+description = "Public-only end-to-end conformance consumer for the WIP Rust APIs"
+license = "MIT OR Apache-2.0"
+publish = false
+
+[dependencies]
+wip-host = { path = "../wip-host" }
+wip-interface = { path = "../wip-interface" }
+wip-protocol = { path = "../wip-protocol" }
@@ -0,0 +1,541 @@
+//! Public-only conformance consumer for the WIP Rust crates.
+//!
+//! # Architectural boundary
+//!
+//! This package is an ordinary application consumer. Its direct dependencies are
+//! the public `wip-protocol`, `wip-interface`, and `wip-host` crates; it neither
+//! imports workspace-private modules nor depends on `wip-interface-macros`.
+//! `wip-protocol` owns transport-independent DTOs and schema-neutral values,
+//! while this package owns its application DTOs and interface traits. The
+//! request-scoped implementation, backend handle, authorization policy, and
+//! publication wiring remain host-private. A transport binding would translate
+//! its own wire routes and envelopes to the protocol call DTOs; no HTTP type is
+//! part of an application trait or interface descriptor.
+//!
+//! # Breaking migration exercised here
+//!
+//! The canonical API targets operations by `target.path` rather than a mandatory
+//! object identifier. Object `ref` and object/interface validators are separate,
+//! optional observation fields. Interface references are opaque values observed
+//! separately from descriptors, and descriptors contain neither a Rust trait
+//! name nor an opaque-reference `name` field. Application records, enums,
+//! unions, entry paths, and JSON all encode through the schema-neutral [`Value`]
+//! variants: entries and enums are strings, unions are discriminator records,
+//! and JSON recursively uses ordinary records/lists/primitives. The former
+//! `Entry<K, V>` and semantic `Value::Entry`, `Value::Enum`, `Value::Union`, and
+//! `Value::Json` forms are intentionally unsupported.
+//!
+//! # Supported authoring subset
+//!
+//! Public, non-generic traits use immutable `&self` receivers, owned named
+//! parameters, and explicit `wip::OperationResult<T>` returns. Derived DTOs are
+//! named-field records, all-unit enums, or unions with unit and single-payload
+//! cases. A direct `Option<T>` means field/argument omission, never protocol
+//! null. See `wip-interface` for the complete rejected-syntax list.
+
+#![deny(missing_docs)]
+
+use std::collections::BTreeMap;
+use std::error::Error;
+use std::io;
+
+use wip_host::{
+    CallErrorKind, CallRequest, ExecutionContext, InterfaceRef, InterfaceRegistry, InterfaceTarget,
+    ObjectProvider, ProviderResult, PublishedObject, RegisteredInterface, Target, Validator,
+    WipObject,
+};
+use wip_interface as wip;
+use wip_interface::WipType;
+use wip_protocol::{ProtocolError, ProtocolErrorCode, Value};
+
+const OBJECT_PATH: &str = "/article-service";
+const OBJECT_VALIDATOR: &[u8] = b"object-v1";
+const CATALOG_VALIDATOR: &[u8] = b"catalog-v1";
+
+/// Publication visibility represented as a protocol enum string.
+#[derive(Debug, Clone, PartialEq, Eq, wip::WipType)]
+pub enum Visibility {
+    /// Visible to every authorized caller.
+    Public,
+    /// Visible only inside the application domain.
+    Private,
+}
+
+/// An application-owned request DTO mapped to a protocol record.
+#[derive(Debug, Clone, PartialEq, wip::WipType)]
+pub struct PublishRequest {
+    /// Title of the article to publish.
+    pub title: String,
+    /// Optional article body; omission is distinct from JSON null.
+    pub body: Option<String>,
+    /// Canonical Worldspace path to the source entry.
+    pub source: wip::Entry,
+    /// Application enum represented by a schema-neutral string.
+    pub visibility: Visibility,
+    /// Schema-opaque JSON represented by ordinary protocol values.
+    pub metadata: wip::JsonValue,
+}
+
+/// The application domain result of a publication attempt.
+#[derive(Debug, Clone, PartialEq, Eq, wip::WipType)]
+pub enum PublishOutcome {
+    /// Publication succeeded and returned its application identifier.
+    Published(String),
+    /// An application policy rejected the publication.
+    Rejected(String),
+}
+
+/// Article publication operations.
+#[wip::interface]
+pub trait Catalog {
+    /// Publishes an article or reports an application-domain rejection.
+    ///
+    /// # Returns
+    /// The typed application outcome.
+    fn publish(
+        &self,
+        /// Application publication request.
+        request: PublishRequest,
+    ) -> wip::OperationResult<PublishOutcome>;
+
+    /// Returns the catalog-qualified status.
+    fn status(&self) -> wip::OperationResult<String>;
+
+    /// Demonstrates a rollback-confirmed host/backend failure.
+    fn backend_status(&self) -> wip::OperationResult<String>;
+
+    /// Demonstrates a host/backend failure with an unknown operation outcome.
+    fn uncertain_backend_status(&self) -> wip::OperationResult<String>;
+
+    /// Demonstrates denial after every structural precondition succeeds.
+    fn restricted_status(&self) -> wip::OperationResult<String>;
+}
+
+/// Audit operations exposed by the same object.
+#[wip::interface]
+pub trait Audit {
+    /// Returns the audit-qualified status.
+    fn status(&self) -> wip::OperationResult<String>;
+}
+
+/// A registered but deliberately unexposed interface.
+#[wip::interface]
+pub trait Diagnostics {
+    /// Returns host-private diagnostics when explicitly exposed.
+    fn diagnostics(&self) -> wip::OperationResult<String>;
+}
+
+/// Observable outcomes from the complete public-API scenario.
+#[derive(Debug, Clone, PartialEq)]
+pub struct DemoReport {
+    /// Path-segment name from the canonical object projection.
+    pub object_name: String,
+    /// Optional object identity, distinct from the resolution path.
+    pub object_reference: Option<String>,
+    /// Optional object-state validator.
+    pub object_validator: Option<Vec<u8>>,
+    /// Opaque interface references published by the object, in exposure order.
+    pub published_interfaces: Vec<String>,
+    /// Opaque reference assigned to the catalog descriptor.
+    pub catalog_interface_reference: String,
+    /// Opaque reference assigned to the audit descriptor.
+    pub audit_interface_reference: String,
+    /// Descriptor format observed separately for the catalog reference.
+    pub catalog_descriptor_format: String,
+    /// Descriptor format observed separately for the audit reference.
+    pub audit_descriptor_format: String,
+    /// Typed successful application result decoded from a validated [`Value`].
+    pub published: PublishOutcome,
+    /// Typed application-domain rejection decoded from a validated [`Value`].
+    pub rejected: PublishOutcome,
+    /// Result of the catalog-qualified `status` operation.
+    pub catalog_status: String,
+    /// Result of the audit-qualified `status` operation.
+    pub audit_status: String,
+    /// Stable failure kind produced by the deliberate host/backend failure.
+    pub host_failure: CallErrorKind,
+    /// Protocol failure whose operation effects are guaranteed not committed.
+    pub protocol_failure: ProtocolError,
+    /// Protocol failure whose operation effects cannot be proven absent.
+    pub unknown_protocol_failure: ProtocolError,
+    /// Authorization failure after a fully qualified valid request.
+    pub permission_failure: ProtocolErrorCode,
+    /// Recovery signal for a stale object validator.
+    pub validator_failure: ProtocolErrorCode,
+    /// Failure for a known but unexposed interface reference.
+    pub interface_mismatch: ProtocolErrorCode,
+    /// Failure for an unknown interface observation reference.
+    pub interface_not_found: ProtocolErrorCode,
+    /// First failure for a request with an invalid path and later invalid fields.
+    pub precedence_failure: ProtocolErrorCode,
+}
+
+/// Runs the complete end-to-end conformance example.
+///
+/// The provider resolves the current object from a Worldspace path for each
+/// call. Interface observations remain separate from object projection, and all
+/// successful calls carry independent object and interface validators.
+///
+/// # Errors
+///
+/// Returns an error if registration, observation, path resolution, dispatch, or
+/// application-value decoding fails unexpectedly.
+pub fn run() -> Result<DemoReport, Box<dyn Error>> {
+    let mut registry = InterfaceRegistry::new();
+    let catalog = registry.register(CatalogDefinition, Some(Validator::new(CATALOG_VALIDATOR)))?;
+    let audit = registry.register(AuditDefinition, None)?;
+    let diagnostics = registry.register(DiagnosticsDefinition, None)?;
+    let provider = ApplicationProvider {
+        catalog: catalog.clone(),
+        audit: audit.clone(),
+    };
+
+    let object = provider.fetch(OBJECT_PATH)?;
+    let catalog_response = registry
+        .fetch_interface(
+            object
+                .interfaces
+                .first()
+                .ok_or_else(|| io::Error::other("catalog interface was not published"))?,
+        )?
+        .protocol_response()?;
+    let audit_response = registry
+        .fetch_interface(
+            object
+                .interfaces
+                .get(1)
+                .ok_or_else(|| io::Error::other("audit interface was not published"))?,
+        )?
+        .protocol_response()?;
+
+    let published = dispatch_publish(
+        &provider,
+        catalog.reference(),
+        PublishRequest {
+            title: "Public APIs".into(),
+            body: Some("protocol values in, validated values out".into()),
+            source: wip::Entry::new("/drafts/public-apis")?,
+            visibility: Visibility::Public,
+            metadata: wip::JsonValue::Object(vec![wip::JsonMember {
+                name: "reviewed".into(),
+                value: wip::JsonValue::Boolean(true),
+            }]),
+        },
+    )?;
+    let rejected = dispatch_publish(
+        &provider,
+        catalog.reference(),
+        PublishRequest {
+            title: String::new(),
+            body: None,
+            source: wip::Entry::new("/drafts/untitled")?,
+            visibility: Visibility::Private,
+            metadata: wip::JsonValue::Null,
+        },
+    )?;
+    let catalog_status = dispatch_string(
+        &provider,
+        request(
+            OBJECT_PATH,
+            catalog.reference(),
+            Some(CATALOG_VALIDATOR),
+            "status",
+            BTreeMap::new(),
+        ),
+    )?;
+    let audit_status = dispatch_string(
+        &provider,
+        request(
+            OBJECT_PATH,
+            audit.reference(),
+            None,
+            "status",
+            BTreeMap::new(),
+        ),
+    )?;
+
+    let host_error = provider
+        .call_operation(request(
+            OBJECT_PATH,
+            catalog.reference(),
+            Some(CATALOG_VALIDATOR),
+            "backend_status",
+            BTreeMap::new(),
+        ))
+        .expect_err("backend_status must model a host failure");
+    ensure_kind(&host_error, CallErrorKind::Internal)?;
+    let protocol_failure = host_error.protocol_error();
+
+    let unknown_protocol_failure = provider
+        .call_operation(request(
+            OBJECT_PATH,
+            catalog.reference(),
+            Some(CATALOG_VALIDATOR),
+            "uncertain_backend_status",
+            BTreeMap::new(),
+        ))
+        .expect_err("uncertain_backend_status must preserve an unknown outcome")
+        .protocol_error();
+
+    let permission_failure = provider
+        .call_operation(request(
+            OBJECT_PATH,
+            catalog.reference(),
+            Some(CATALOG_VALIDATOR),
+            "restricted_status",
+            BTreeMap::new(),
+        ))
+        .expect_err("restricted_status must be denied")
+        .protocol_error()
+        .code;
+
+    let validator_failure = provider
+        .call_operation(CallRequest {
+            target: Target {
+                path: OBJECT_PATH.into(),
+                validator: Some(b"stale-object".to_vec()),
+            },
+            interface: InterfaceTarget {
+                reference: diagnostics.reference().as_str().to_owned(),
+                validator: Some(b"stale-interface".to_vec()),
+            },
+            operation: "missing".into(),
+            arguments: BTreeMap::from([("unknown".into(), Value::Unit)]),
+        })
+        .expect_err("the stale object validator must fail first")
+        .protocol_error()
+        .code;
+
+    let interface_mismatch = provider
+        .call_operation(request(
+            OBJECT_PATH,
+            diagnostics.reference(),
+            None,
+            "diagnostics",
+            BTreeMap::new(),
+        ))
+        .expect_err("registered but unexposed interface must not dispatch")
+        .protocol_error()
+        .code;
+
+    let interface_not_found = registry
+        .fetch_interface("missing-interface")
+        .expect_err("unknown interface references must not resolve")
+        .code;
+
+    let precedence_failure = provider
+        .call_operation(CallRequest {
+            target: Target {
+                path: "relative/path".into(),
+                validator: Some(b"stale-object".to_vec()),
+            },
+            interface: InterfaceTarget {
+                reference: diagnostics.reference().as_str().to_owned(),
+                validator: Some(b"stale-interface".to_vec()),
+            },
+            operation: "missing".into(),
+            arguments: BTreeMap::from([("unknown".into(), Value::Unit)]),
+        })
+        .expect_err("invalid path must have canonical precedence")
+        .protocol_error()
+        .code;
+
+    Ok(DemoReport {
+        object_name: object.name,
+        object_reference: object.r#ref,
+        object_validator: object.validator,
+        published_interfaces: object.interfaces,
+        catalog_interface_reference: catalog.reference().as_str().to_owned(),
+        audit_interface_reference: audit.reference().as_str().to_owned(),
+        catalog_descriptor_format: catalog_response.descriptor.format,
+        audit_descriptor_format: audit_response.descriptor.format,
+        published,
+        rejected,
+        catalog_status,
+        audit_status,
+        host_failure: host_error.kind(),
+        protocol_failure,
+        unknown_protocol_failure,
+        permission_failure,
+        validator_failure,
+        interface_mismatch,
+        interface_not_found,
+        precedence_failure,
+    })
+}
+
+fn ensure_kind(error: &wip_host::CallError, expected: CallErrorKind) -> Result<(), io::Error> {
+    if error.kind() == expected {
+        Ok(())
+    } else {
+        Err(io::Error::other(format!(
+            "unexpected host failure kind: {:?}",
+            error.kind()
+        )))
+    }
+}
+
+fn dispatch_publish(
+    provider: &ApplicationProvider,
+    catalog: &InterfaceRef,
+    request_value: PublishRequest,
+) -> Result<PublishOutcome, Box<dyn Error>> {
+    let encoded_request = request_value.encode()?;
+    let result = provider.call_operation(request(
+        OBJECT_PATH,
+        catalog,
+        Some(CATALOG_VALIDATOR),
+        "publish",
+        BTreeMap::from([("request".into(), encoded_request)]),
+    ))?;
+    Ok(PublishOutcome::decode(result.result)?)
+}
+
+fn dispatch_string(
+    provider: &ApplicationProvider,
+    request: CallRequest,
+) -> Result<String, Box<dyn Error>> {
+    let result = provider.call_operation(request)?;
+    Ok(String::decode(result.result)?)
+}
+
+fn request(
+    path: &str,
+    interface: &InterfaceRef,
+    interface_validator: Option<&[u8]>,
+    operation: &str,
+    arguments: BTreeMap<String, Value>,
+) -> CallRequest {
+    CallRequest {
+        target: Target {
+            path: path.into(),
+            validator: Some(OBJECT_VALIDATOR.to_vec()),
+        },
+        interface: InterfaceTarget {
+            reference: interface.as_str().to_owned(),
+            validator: interface_validator.map(<[u8]>::to_vec),
+        },
+        operation: operation.into(),
+        arguments,
+    }
+}
+
+struct ApplicationProvider {
+    catalog: RegisteredInterface<CatalogDefinition>,
+    audit: RegisteredInterface<AuditDefinition>,
+}
+
+impl ObjectProvider for ApplicationProvider {
+    type Object = ApplicationService;
+
+    fn with_object<R>(
+        &self,
+        _context: &ExecutionContext,
+        path: &str,
+        operation: impl FnOnce(&PublishedObject<Self::Object>) -> R,
+    ) -> ProviderResult<R> {
+        if path != OBJECT_PATH {
+            return ProviderResult::NotFound;
+        }
+        let publication = PublishedObject::new(ApplicationService::new())
+            .expose(&self.catalog)
+            .expect("ApplicationService implements Catalog")
+            .expose(&self.audit)
+            .expect("ApplicationService implements Audit");
+        ProviderResult::Found(operation(&publication))
+    }
+
+    fn authorize(
+        &self,
+        _: &str,
+        _: &ApplicationService,
+        _: &InterfaceRef,
+        operation: &str,
+    ) -> bool {
+        operation != "restricted_status"
+    }
+}
+
+struct ApplicationService {
+    object_validator: Validator,
+    backend_connection: String,
+}
+
+impl ApplicationService {
+    fn new() -> Self {
+        Self {
+            object_validator: Validator::new(OBJECT_VALIDATOR),
+            backend_connection: "private://article-database".into(),
+        }
+    }
+}
+
+impl WipObject for ApplicationService {
+    fn name(&self) -> &str {
+        "article-service"
+    }
+
+    fn description(&self) -> Option<&str> {
+        Some("Article publication service")
+    }
+
+    fn reference(&self) -> Option<&str> {
+        Some("article-service-instance")
+    }
+
+    fn validator(&self) -> Option<&Validator> {
+        Some(&self.object_validator)
+    }
+
+    fn requires_validator(&self, _: &InterfaceRef, _: &str) -> bool {
+        true
+    }
+}
+
+impl Catalog for ApplicationService {
+    fn publish(&self, request: PublishRequest) -> wip::OperationResult<PublishOutcome> {
+        if request.title.trim().is_empty() {
+            Ok(PublishOutcome::Rejected("a title is required".into()))
+        } else {
+            Ok(PublishOutcome::Published("article-1".into()))
+        }
+    }
+
+    fn status(&self) -> wip::OperationResult<String> {
+        Ok("catalog-ready".into())
+    }
+
+    fn backend_status(&self) -> wip::OperationResult<String> {
+        if self.backend_connection.starts_with("private://") {
+            Err(wip::HostError::internal(
+                "backend unavailable",
+                wip::EffectGuarantee::NotCommitted,
+            ))
+        } else {
+            Ok("backend-ready".into())
+        }
+    }
+
+    fn uncertain_backend_status(&self) -> wip::OperationResult<String> {
+        Err(wip::HostError::internal(
+            "backend commit acknowledgement unavailable",
+            wip::EffectGuarantee::Unknown,
+        ))
+    }
+
+    fn restricted_status(&self) -> wip::OperationResult<String> {
+        Ok("authorization hook should prevent this call".into())
+    }
+}
+
+impl Audit for ApplicationService {
+    fn status(&self) -> wip::OperationResult<String> {
+        Ok("audit-ready".into())
+    }
+}
+
+impl Diagnostics for ApplicationService {
+    fn diagnostics(&self) -> wip::OperationResult<String> {
+        Ok("host-private".into())
+    }
+}
@@ -0,0 +1,246 @@
+use std::collections::BTreeMap;
+
+use wip_host::CallErrorKind;
+use wip_interface::{Entry, JsonMember, JsonValue, WipType};
+use wip_protocol::{INTERFACE_FORMAT_V1, InterfaceDescriptor, Object, ProtocolErrorCode, Value};
+use wip_public_api_example::{CatalogDefinition, PublishOutcome, PublishRequest, Visibility, run};
+
+#[test]
+fn public_crates_support_the_complete_qualified_end_to_end_scenario() {
+    let report = run().unwrap();
+
+    assert_eq!(report.object_name, "article-service");
+    assert_eq!(
+        report.object_reference.as_deref(),
+        Some("article-service-instance")
+    );
+    assert_eq!(
+        report.object_validator.as_deref(),
+        Some(b"object-v1".as_slice())
+    );
+    assert_eq!(
+        report.published_interfaces,
+        [
+            report.catalog_interface_reference.clone(),
+            report.audit_interface_reference.clone(),
+        ],
+        "interfaces must retain explicit publication order"
+    );
+    assert_ne!(
+        report.catalog_interface_reference, report.audit_interface_reference,
+        "interfaces form an ordered set of distinct opaque references"
+    );
+    assert_eq!(report.catalog_descriptor_format, INTERFACE_FORMAT_V1);
+    assert_eq!(report.audit_descriptor_format, INTERFACE_FORMAT_V1);
+    assert_eq!(
+        report.published,
+        PublishOutcome::Published("article-1".into())
+    );
+    assert_eq!(
+        report.rejected,
+        PublishOutcome::Rejected("a title is required".into())
+    );
+    assert_eq!(report.catalog_status, "catalog-ready");
+    assert_eq!(report.audit_status, "audit-ready");
+}
+
+#[test]
+fn domain_host_permission_and_validator_failures_remain_distinct() {
+    let report = run().unwrap();
+
+    assert!(matches!(report.rejected, PublishOutcome::Rejected(_)));
+    assert_eq!(report.host_failure, CallErrorKind::Internal);
+    assert_eq!(report.protocol_failure.code, ProtocolErrorCode::Internal);
+    assert_eq!(
+        report.unknown_protocol_failure.code,
+        ProtocolErrorCode::OperationOutcomeUnknown
+    );
+    assert_eq!(
+        report.permission_failure,
+        ProtocolErrorCode::PermissionDenied
+    );
+    assert_eq!(
+        report.validator_failure,
+        ProtocolErrorCode::ValidatorMismatch,
+        "validator recovery signals must not collapse to InvalidRequest"
+    );
+}
+
+#[test]
+fn interface_mismatch_is_not_interface_not_found() {
+    let report = run().unwrap();
+
+    assert_eq!(
+        report.interface_mismatch,
+        ProtocolErrorCode::InterfaceMismatch
+    );
+    assert_eq!(
+        report.interface_not_found,
+        ProtocolErrorCode::InterfaceNotFound
+    );
+    assert_ne!(report.interface_mismatch, report.interface_not_found);
+}
+
+#[test]
+fn invalid_path_keeps_canonical_failure_precedence() {
+    let report = run().unwrap();
+
+    assert_eq!(report.precedence_failure, ProtocolErrorCode::InvalidRequest);
+    assert_ne!(report.precedence_failure, report.validator_failure);
+    assert_ne!(report.precedence_failure, report.interface_mismatch);
+}
+
+#[test]
+fn object_fields_keep_path_context_and_optional_ref_separate() {
+    // Listing every field makes this test fail to compile if a mandatory
+    // ObjectId is reintroduced into the canonical object DTO.
+    let object = Object {
+        name: "article".into(),
+        description: None,
+        interfaces: vec!["catalog-ref".into(), "audit-ref".into()],
+        r#ref: None,
+        validator: None,
+    };
+
+    object.validate_at_path("/library/article").unwrap();
+    assert_eq!(object.name, "article");
+    assert_eq!(object.r#ref, None);
+    assert_eq!(object.interfaces, ["catalog-ref", "audit-ref"]);
+}
+
+#[test]
+fn interface_reference_is_observed_separately_from_descriptor_fields() {
+    // An exact destructuring pattern is compile-time coverage that the
+    // descriptor has no trait-name or opaque-reference `name` field.
+    let InterfaceDescriptor {
+        format,
+        documentation,
+        types,
+        operations,
+    } = CatalogDefinition::descriptor();
+
+    assert_eq!(format, INTERFACE_FORMAT_V1);
+    assert!(documentation.is_some());
+    assert!(!types.is_empty());
+    assert_eq!(
+        operations
+            .iter()
+            .map(|operation| operation.name.as_str())
+            .collect::<Vec<_>>(),
+        [
+            "publish",
+            "status",
+            "backend_status",
+            "uncertain_backend_status",
+            "restricted_status",
+        ]
+    );
+}
+
+#[test]
+fn application_record_enum_union_entry_and_json_use_schema_neutral_values() {
+    let request = PublishRequest {
+        title: "Canonical values".into(),
+        body: None,
+        source: Entry::new("/drafts/canonical-values").unwrap(),
+        visibility: Visibility::Public,
+        metadata: JsonValue::Object(vec![
+            JsonMember {
+                name: "tags".into(),
+                value: JsonValue::Array(vec![JsonValue::String("wip".into()), JsonValue::Null]),
+            },
+            JsonMember {
+                name: "ready".into(),
+                value: JsonValue::Boolean(true),
+            },
+        ]),
+    };
+
+    let encoded = request.encode().unwrap();
+    assert_schema_neutral(&encoded);
+    let Value::Record(fields) = encoded else {
+        panic!("derived DTO record must use Value::Record")
+    };
+    assert_eq!(
+        fields.get("title"),
+        Some(&Value::String("Canonical values".into()))
+    );
+    assert!(!fields.contains_key("body"));
+    assert_eq!(
+        fields.get("source"),
+        Some(&Value::String("/drafts/canonical-values".into()))
+    );
+    assert_eq!(
+        fields.get("visibility"),
+        Some(&Value::String("Public".into()))
+    );
+    assert_eq!(
+        fields.get("metadata"),
+        Some(&Value::Record(BTreeMap::from([
+            ("ready".into(), Value::Boolean(true)),
+            (
+                "tags".into(),
+                Value::List(vec![Value::String("wip".into()), Value::Unit])
+            ),
+        ])))
+    );
+
+    let outcome = PublishOutcome::Rejected("policy".into()).encode().unwrap();
+    assert_schema_neutral(&outcome);
+    assert_eq!(
+        outcome,
+        Value::Record(BTreeMap::from([
+            ("$case".into(), Value::String("Rejected".into())),
+            ("value".into(), Value::String("policy".into())),
+        ]))
+    );
+}
+
+#[test]
+fn entry_is_a_validated_canonical_absolute_path_string() {
+    let entry = Entry::new("/articles/one").unwrap();
+    assert_eq!(
+        entry.encode().unwrap(),
+        Value::String("/articles/one".into())
+    );
+
+    for invalid in [
+        "articles/one",
+        "/articles/",
+        "/articles//one",
+        "/articles/./one",
+        "/articles/../one",
+    ] {
+        assert!(
+            Entry::new(invalid).is_err(),
+            "accepted invalid path {invalid}"
+        );
+        assert!(
+            Entry::decode(Value::String(invalid.into())).is_err(),
+            "decoded invalid path {invalid}"
+        );
+    }
+}
+
+fn assert_schema_neutral(value: &Value) {
+    // This exhaustive match is a compile-time regression guard: reintroducing
+    // semantic Entry/Enum/Union/Json variants makes the consumer non-exhaustive.
+    match value {
+        Value::Unit
+        | Value::Boolean(_)
+        | Value::Integer(_)
+        | Value::Number(_)
+        | Value::String(_)
+        | Value::Bytes(_) => {}
+        Value::Record(fields) => {
+            for value in fields.values() {
+                assert_schema_neutral(value);
+            }
+        }
+        Value::List(values) => {
+            for value in values {
+                assert_schema_neutral(value);
+            }
+        }
+    }
+}
@@ -1,360 +0,0 @@
-//! End-to-end use of the public WIP protocol, interface, and host APIs.
-//!
-//! This workspace package defines application DTOs and interfaces with
-//! `wip-interface`, keeps its implementation private, publishes it through a
-//! request-scoped `wip-host` provider, and crosses the call boundary only with
-//! canonical `wip-protocol` values and path targets.
-
-#![deny(missing_docs)]
-
-use std::collections::BTreeMap;
-use std::error::Error;
-use std::io;
-
-use wip_host::{
-    CallErrorKind, CallRequest, InterfaceRef, InterfaceRegistry, InterfaceTarget, ObjectProvider,
-    PublishedObject, RegisteredInterface, Target, Validator, WipObject,
-};
-use wip_interface as wip;
-use wip_interface::WipType;
-use wip_protocol::ProtocolError;
-
-const OBJECT_PATH: &str = "/article-service";
-const OBJECT_VALIDATOR: &[u8] = b"object-v1";
-const CATALOG_VALIDATOR: &[u8] = b"catalog-v1";
-
-/// An application-owned request DTO mapped to a protocol record.
-#[derive(Debug, Clone, PartialEq, Eq, wip::WipType)]
-pub struct PublishRequest {
-    /// Title of the article to publish.
-    pub title: String,
-    /// Optional article body; omission is distinct from JSON null.
-    pub body: Option<String>,
-}
-
-/// The application domain result of a publication attempt.
-#[derive(Debug, Clone, PartialEq, Eq, wip::WipType)]
-pub enum PublishOutcome {
-    /// Publication succeeded and returned its application identifier.
-    Published(String),
-    /// An application policy rejected the publication.
-    Rejected(String),
-}
-
-/// Article publication operations.
-#[wip::interface]
-pub trait Catalog {
-    /// Publishes an article or reports an application-domain rejection.
-    ///
-    /// # Returns
-    /// The typed application outcome.
-    fn publish(
-        &self,
-        /// Application publication request.
-        request: PublishRequest,
-    ) -> wip::OperationResult<PublishOutcome>;
-
-    /// Returns the catalog-qualified status.
-    fn status(&self) -> wip::OperationResult<String>;
-
-    /// Demonstrates a host/backend failure rather than a domain result.
-    fn backend_status(&self) -> wip::OperationResult<String>;
-}
-
-/// Audit operations exposed by the same object.
-#[wip::interface]
-pub trait Audit {
-    /// Returns the audit-qualified status.
-    fn status(&self) -> wip::OperationResult<String>;
-}
-
-/// A registered but deliberately unexposed interface.
-#[wip::interface]
-pub trait Diagnostics {
-    /// Returns host-private diagnostics when explicitly exposed.
-    fn diagnostics(&self) -> wip::OperationResult<String>;
-}
-
-/// Observable outcomes from the complete public-API scenario.
-#[derive(Debug, Clone, PartialEq)]
-pub struct DemoReport {
-    /// Opaque interface references published by the object, in exposure order.
-    pub published_interfaces: Vec<String>,
-    /// Descriptor format observed for the catalog interface.
-    pub catalog_descriptor_format: String,
-    /// Descriptor format observed for the audit interface.
-    pub audit_descriptor_format: String,
-    /// Typed successful application result decoded from a validated `Value`.
-    pub published: PublishOutcome,
-    /// Typed application-domain rejection decoded from a validated `Value`.
-    pub rejected: PublishOutcome,
-    /// Result of the catalog-qualified `status` operation.
-    pub catalog_status: String,
-    /// Result of the audit-qualified `status` operation.
-    pub audit_status: String,
-    /// Stable failure kind produced by the deliberate host/backend failure.
-    pub host_failure: CallErrorKind,
-    /// A protocol-level failure built from the host failure.
-    pub protocol_failure: ProtocolError,
-}
-
-/// Runs the complete end-to-end example.
-///
-/// The provider resolves the current object from a Worldspace path for each
-/// call. Interface observations remain separate from object projection, and all
-/// calls carry independent object and interface validators.
-///
-/// # Errors
-///
-/// Returns an error if registration, observation, path resolution, dispatch, or
-/// application-value decoding fails unexpectedly.
-pub fn run() -> Result<DemoReport, Box<dyn Error>> {
-    let mut registry = InterfaceRegistry::new();
-    let catalog = registry.register(CatalogDefinition, Some(Validator::new(CATALOG_VALIDATOR)))?;
-    let audit = registry.register(AuditDefinition, None)?;
-    let _diagnostics = registry.register(DiagnosticsDefinition, None)?;
-    let provider = ApplicationProvider {
-        catalog: catalog.clone(),
-        audit: audit.clone(),
-    };
-
-    let object = provider.fetch(OBJECT_PATH)?;
-    let catalog_observation = registry.fetch_interface(
-        object
-            .interfaces
-            .first()
-            .ok_or_else(|| io::Error::other("catalog interface was not published"))?,
-    )?;
-    let audit_observation = registry.fetch_interface(
-        object
-            .interfaces
-            .get(1)
-            .ok_or_else(|| io::Error::other("audit interface was not published"))?,
-    )?;
-
-    let published = dispatch_publish(
-        &provider,
-        catalog.reference(),
-        PublishRequest {
-            title: "Public APIs".into(),
-            body: Some("protocol values in, validated values out".into()),
-        },
-    )?;
-    let rejected = dispatch_publish(
-        &provider,
-        catalog.reference(),
-        PublishRequest {
-            title: String::new(),
-            body: None,
-        },
-    )?;
-    let catalog_status = dispatch_string(
-        &provider,
-        request(
-            catalog.reference(),
-            Some(CATALOG_VALIDATOR),
-            "status",
-            BTreeMap::new(),
-        ),
-    )?;
-    let audit_status = dispatch_string(
-        &provider,
-        request(audit.reference(), None, "status", BTreeMap::new()),
-    )?;
-
-    let host_error = provider
-        .call_operation(request(
-            catalog.reference(),
-            Some(CATALOG_VALIDATOR),
-            "backend_status",
-            BTreeMap::new(),
-        ))
-        .unwrap_err();
-    if host_error.kind() != CallErrorKind::Implementation {
-        return Err(io::Error::other(format!(
-            "unexpected host failure kind: {:?}",
-            host_error.kind()
-        ))
-        .into());
-    }
-    let protocol_failure = host_error.protocol_error();
-
-    Ok(DemoReport {
-        published_interfaces: object.interfaces,
-        catalog_descriptor_format: catalog_observation.descriptor.format,
-        audit_descriptor_format: audit_observation.descriptor.format,
-        published,
-        rejected,
-        catalog_status,
-        audit_status,
-        host_failure: host_error.kind(),
-        protocol_failure,
-    })
-}
-
-fn dispatch_publish(
-    provider: &ApplicationProvider,
-    catalog: &InterfaceRef,
-    request_value: PublishRequest,
-) -> Result<PublishOutcome, Box<dyn Error>> {
-    let encoded_request = request_value.encode()?;
-    let result = provider.call_operation(request(
-        catalog,
-        Some(CATALOG_VALIDATOR),
-        "publish",
-        BTreeMap::from([("request".into(), encoded_request)]),
-    ))?;
-    Ok(PublishOutcome::decode(result.result)?)
-}
-
-fn dispatch_string(
-    provider: &ApplicationProvider,
-    request: CallRequest,
-) -> Result<String, Box<dyn Error>> {
-    let result = provider.call_operation(request)?;
-    Ok(String::decode(result.result)?)
-}
-
-fn request(
-    interface: &InterfaceRef,
-    interface_validator: Option<&[u8]>,
-    operation: &str,
-    arguments: BTreeMap<String, wip_protocol::Value>,
-) -> CallRequest {
-    CallRequest {
-        target: Target {
-            path: OBJECT_PATH.into(),
-            validator: Some(OBJECT_VALIDATOR.to_vec()),
-        },
-        interface: InterfaceTarget {
-            reference: interface.as_str().to_owned(),
-            validator: interface_validator.map(<[u8]>::to_vec),
-        },
-        operation: operation.into(),
-        arguments,
-    }
-}
-
-struct ApplicationProvider {
-    catalog: RegisteredInterface<CatalogDefinition>,
-    audit: RegisteredInterface<AuditDefinition>,
-}
-
-impl ObjectProvider for ApplicationProvider {
-    type Object = ApplicationService;
-
-    fn with_object<R>(
-        &self,
-        path: &str,
-        operation: impl FnOnce(&PublishedObject<Self::Object>) -> R,
-    ) -> Option<R> {
-        if path != OBJECT_PATH {
-            return None;
-        }
-        let publication = PublishedObject::new(ApplicationService::new())
-            .expose(&self.catalog)
-            .expect("ApplicationService implements Catalog")
-            .expose(&self.audit)
-            .expect("ApplicationService implements Audit");
-        Some(operation(&publication))
-    }
-}
-
-struct ApplicationService {
-    object_validator: Validator,
-    backend_connection: String,
-}
-
-impl ApplicationService {
-    fn new() -> Self {
-        Self {
-            object_validator: Validator::new(OBJECT_VALIDATOR),
-            backend_connection: "private://article-database".into(),
-        }
-    }
-}
-
-impl WipObject for ApplicationService {
-    fn name(&self) -> &str {
-        "article-service"
-    }
-
-    fn description(&self) -> Option<&str> {
-        Some("Article publication service")
-    }
-
-    fn reference(&self) -> Option<&str> {
-        Some("article-service-instance")
-    }
-
-    fn validator(&self) -> Option<&Validator> {
-        Some(&self.object_validator)
-    }
-
-    fn requires_validator(&self, _: &InterfaceRef, _: &str) -> bool {
-        true
-    }
-}
-
-impl Catalog for ApplicationService {
-    fn publish(&self, request: PublishRequest) -> wip::OperationResult<PublishOutcome> {
-        if request.title.trim().is_empty() {
-            Ok(PublishOutcome::Rejected("a title is required".into()))
-        } else {
-            Ok(PublishOutcome::Published("article-1".into()))
-        }
-    }
-
-    fn status(&self) -> wip::OperationResult<String> {
-        Ok("catalog-ready".into())
-    }
-
-    fn backend_status(&self) -> wip::OperationResult<String> {
-        if self.backend_connection.starts_with("private://") {
-            Err(wip::HostError::new("backend unavailable"))
-        } else {
-            Ok("backend-ready".into())
-        }
-    }
-}
-
-impl Audit for ApplicationService {
-    fn status(&self) -> wip::OperationResult<String> {
-        Ok("audit-ready".into())
-    }
-}
-
-impl Diagnostics for ApplicationService {
-    fn diagnostics(&self) -> wip::OperationResult<String> {
-        Ok("host-private".into())
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use wip_protocol::ProtocolErrorCode;
-
-    #[test]
-    fn unexposed_interfaces_are_membership_failures() {
-        let mut registry = InterfaceRegistry::new();
-        let catalog = registry.register(CatalogDefinition, None).unwrap();
-        let audit = registry.register(AuditDefinition, None).unwrap();
-        let diagnostics = registry.register(DiagnosticsDefinition, None).unwrap();
-        let provider = ApplicationProvider { catalog, audit };
-
-        let error = provider
-            .call_operation(request(
-                diagnostics.reference(),
-                None,
-                "diagnostics",
-                BTreeMap::new(),
-            ))
-            .unwrap_err();
-        assert_eq!(error.kind(), CallErrorKind::InterfaceMismatch);
-        assert_eq!(
-            error.protocol_error().code,
-            ProtocolErrorCode::InterfaceMismatch
-        );
-    }
-}
@@ -1,24 +0,0 @@
-use wip_host::CallErrorKind;
-use wip_protocol::{INTERFACE_FORMAT_V1, ProtocolErrorCode};
-use wip_public_api_example::{PublishOutcome, run};
-
-#[test]
-fn public_crates_support_the_complete_end_to_end_scenario() {
-    let report = run().unwrap();
-
-    assert_eq!(report.published_interfaces.len(), 2);
-    assert_eq!(report.catalog_descriptor_format, INTERFACE_FORMAT_V1);
-    assert_eq!(report.audit_descriptor_format, INTERFACE_FORMAT_V1);
-    assert_eq!(
-        report.published,
-        PublishOutcome::Published("article-1".into())
-    );
-    assert_eq!(
-        report.rejected,
-        PublishOutcome::Rejected("a title is required".into())
-    );
-    assert_eq!(report.catalog_status, "catalog-ready");
-    assert_eq!(report.audit_status, "audit-ready");
-    assert_eq!(report.host_failure, CallErrorKind::Implementation);
-    assert_eq!(report.protocol_failure.code, ProtocolErrorCode::Internal);
-}
Author	SHA1	Message	Date
Hare	e1998fb8fd	fix(client): validate suppressed tree objects	2026-09-30 09:45:53 +09:00
Hare	b4e38fc2c2	fix(client): preserve operation observation ownership	2026-09-30 09:38:28 +09:00
Hare	f207b71f83	fix(client): preserve normalized request ownership	2026-09-30 09:21:44 +09:00
Hare	e5162339e9	fix(client): retain request ownership revisions	2026-09-30 09:09:20 +09:00
Hare	20b3986ab6	fix(client): preserve observation freshness	2026-09-30 08:59:53 +09:00
Hare	2da2a28a67	feat(client): add stateful WIP runtime	2026-09-30 08:46:12 +09:00
Hare	96db3dd6a8	fix: honor Accept media parameters	2026-09-30 07:59:50 +09:00
Hare	625f4c148d	fix(https): align canonical binding semantics	2026-09-30 07:50:51 +09:00
Hare	beeffae9c5	fix: validate HTTPS binding limits and response ordering	2026-09-30 06:43:02 +09:00
Hare	56923c1160	feat: implement WIP over HTTPS v1 binding	2026-09-30 06:32:04 +09:00
Hare	6de58da17d	feat: model operation outcome guarantees	2026-09-30 05:52:38 +09:00
Hare	027555eb4e	fix: align protocol error semantics	2026-09-30 05:26:34 +09:00
Hare	75119f23e5	feat(example): restore virtual workspace conformance	2026-09-29 06:51:05 +09:00