fix: bound HTTP intake and response lifetimes

Cargo.lock

@@ -8,12 +8,24 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "bitflags"
+version = "2.13.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3ded4057c258ba199e2d26386d3af3780957ecaee6c4ef4041c6b4b8b97c0b06"
+
 [[package]]
 name = "bytes"
 version = "1.12.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "fc652a48c352aef3ea3aed32080501cf3ef6ed5da78602a020c991775b0aff04"
 
+[[package]]
+name = "cfg-if"
+version = "1.0.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
+
 [[package]]
 name = "displaydoc"
 version = "0.2.7"
@@ -31,6 +43,22 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "877a4ace8713b0bcf2a4e7eec82529c029f1d0619886d18145fea96c3ffe5c0f"
 
+[[package]]
+name = "errno"
+version = "0.3.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
+dependencies = [
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "fastrand"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da7c62ceae207dd37ea5b845da6a0696c799f85e97da1ab5b7910be3c1c80223"
+
 [[package]]
 name = "form_urlencoded"
 version = "1.2.2"
@@ -40,6 +68,17 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "getrandom"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "300e883d756b2e4ec94e02791f39b04b522276138852cfc41d9fb7e904106099"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "r-efi",
+]
+
 [[package]]
 name = "glob"
 version = "0.3.4"
@@ -182,6 +221,18 @@ version = "1.0.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f42a60cbdf9a97f5d2305f08a87dc4e09308d1276d28c869c684d7777685682"
 
+[[package]]
+name = "libc"
+version = "0.2.189"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3eaf3ede3fee6db1a4c2ee091bf8a8b4dccdc6d17f656fb07896ee72867612f2"
+
+[[package]]
+name = "linux-raw-sys"
+version = "0.12.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a66949e030da00e8c7d4434b251670a91556f4144941d37452769c25d58a53"
+
 [[package]]
 name = "litemap"
 version = "0.8.3"
@@ -194,6 +245,12 @@ version = "2.8.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
 
+[[package]]
+name = "once_cell"
+version = "1.21.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9f7c3e4beb33f85d45ae3e3a1792185706c8e16d043238c593331cc7cd313b50"
+
 [[package]]
 name = "percent-encoding"
 version = "2.3.2"
@@ -227,6 +284,25 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "r-efi"
+version = "6.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f8dcc9c7d52a811697d2151c701e0d08956f92b0e24136cf4cf27b57a6a0d9bf"
+
+[[package]]
+name = "rustix"
+version = "1.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "891efababe418670775f199f0d233d84843c227a0949a883ce15b37c78d6629d"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
 [[package]]
 name = "serde"
 version = "1.0.229"
@@ -329,6 +405,19 @@ version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "876fef147edbcbddc8ac5cbbba92c7b86519e314e86638596c09673b2ed01e7f"
 
+[[package]]
+name = "tempfile"
+version = "3.27.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32497e9a4c7b38532efcdebeef879707aa9f794296a4f0244f6f69e9bc8574bd"
+dependencies = [
+ "fastrand",
+ "getrandom",
+ "once_cell",
+ "rustix",
+ "windows-sys",
+]
+
 [[package]]
 name = "termcolor"
 version = "1.4.1"
@@ -456,6 +545,19 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b97319f7b8343df12cc98938e5c3eb436064524c8d2b4e30a1d3a36eecdf81"
 
+[[package]]
+name = "wip-fs-server"
+version = "0.1.0"
+dependencies = [
+ "http",
+ "rustix",
+ "tempfile",
+ "wip-host",
+ "wip-https",
+ "wip-interface",
+ "wip-protocol",
+]
+
 [[package]]
 name = "wip-host"
 version = "0.1.0"

README.md

@@ -5,12 +5,18 @@ Rust building blocks for the Web Interface Protocol (WIP).
 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 Rust
-interface-authoring facade, a request-scoped host runtime, and a private
+interface-authoring facade, a request-scoped host runtime, a bounded Linux
-public-API conformance consumer. The repository root is not itself a package.
+filesystem projection server, and a private public-API conformance consumer. The
+repository root is not itself a package.
 
 ## Crate graph and responsibilities
 
 ```text
+wip-fs-server (request-time filesystem projection and loopback listener)
+├── wip-https                 standard routes/codecs/envelopes/batching
+├── wip-host                  request-scoped publication and dispatch
+└── wip-interface             macro-generated filesystem capabilities
+
 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
@@ -29,7 +35,8 @@ wip-public-api-example (workspace-only executable, integration tests, doctest)
 | `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-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-host` | Opaque interface registration, explicit object membership, validator checks, interface-qualified dispatch against one host-owned instance, and descriptor-guided argument decoding inside that same resolution boundary. | Backend atomicity, global object lookup, or network serving. |
+| `wip-fs-server` | Linux directory-handle-confined request-time projection, bounded BFS trees and file operations, standard `wip-https` dispatch/batch handling, and a loopback HTTP binary for TLS-proxy or explicit development use. | A new wire profile, implicit symlink following, non-loopback cleartext, authentication policy, or filesystem-wide preregistration. |
 | `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
@@ -238,6 +245,17 @@ rolled back. Without that proof, post-invocation failures remain
 comparison and backend commit atomic and return a validator describing the state
 that becomes committed.
 
+## Filesystem projection server
+
+[`crates/wip-fs-server`](crates/wip-fs-server) contains the practical server
+binary and its full security model, configuration, curl walkthrough, and
+resource/failure semantics. It resolves every object from current filesystem
+state, uses pinned directory-relative handles without following symlinks, omits
+non-UTF-8 backend names, performs bounded breadth-first tree discovery, and
+publishes validator-protected replacement only in explicit read-write mode.
+The built-in cleartext listener is loopback-only: production HTTPS is explicitly
+delegated to a reverse proxy, while local plain HTTP requires an opt-in flag.
+
 ## Validation
 
 Enter the dev shell and run the acceptance commands exactly:

crates/wip-fs-server/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "wip-fs-server"
+version = "0.1.0"
+edition = "2024"
+description = "Request-time filesystem projection server for WIP over HTTPS"
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+publish = false
+
+[dependencies]
+http = "1"
+rustix = { version = "1.1", features = ["fs"] }
+wip-host = { path = "../wip-host" }
+wip-https = { path = "../wip-https" }
+wip-interface = { path = "../wip-interface" }
+wip-protocol = { path = "../wip-protocol" }
+
+[dev-dependencies]
+tempfile = "3"

crates/wip-fs-server/README.md

@@ -0,0 +1,148 @@
+# wip-fs-server
+
+`wip-fs-server` projects one configured Linux filesystem directory onto WIP
+Worldspace `/` at request time. It does not register the filesystem contents or
+keep one object instance per entry. It uses `wip-host` for publication and typed
+operation dispatch and uses the standard `wip-https` routes, JSON codecs,
+envelopes, batching, and HTTP status mapping.
+
+## Security model
+
+- The effective root is opened once as a directory capability. Root path
+  components must be real directories (symlink components are rejected), and the
+  displayed effective root is read back from that same pinned descriptor. Every
+  request is resolved segment-by-segment with directory-relative, `O_NOFOLLOW`
+  handles.
+- Symlinks are projected as links and are never followed. Their stored target is
+  available only through the `SymlinkInspect.read_link` application operation.
+- Regular files, directories, symlinks, and unsupported entry types have distinct
+  public descriptions and capability sets.
+- WIP names are Unicode. Linux names that are not valid UTF-8 are deliberately
+  not published; valid UTF-8 names map byte-for-byte and therefore cannot collide.
+  Unicode paths containing backend-invalid NUL bytes are likewise treated as
+  unpublished rather than as backend failures.
+- No object `ref` is issued. This avoids claiming representation identity for
+  hard links or path-specific names. Regular files and symlinks receive an opaque
+  validator containing filesystem identity plus protected metadata; replacing a
+  path therefore does not preserve its validator.
+- Protocol metadata and errors never contain the backend absolute path. Startup
+  prints only the explicitly configured effective root and security-sensitive
+  modes.
+- The built-in listener is cleartext and loopback-only. Production deployments
+  must pass `--behind-tls-proxy` and terminate HTTPS at a trusted reverse proxy.
+  Plain development HTTP requires the explicit `--development-http` flag.
+
+The implementation currently targets Linux because it uses `O_PATH`,
+directory-relative descriptor traversal, and `/proc/self/fd` to reopen the same
+pinned backend object without resolving the untrusted Worldspace path twice.
+
+## Run
+
+Read-only behind a TLS-terminating reverse proxy:
+
+```console
+cargo run -p wip-fs-server -- \
+  --root /srv/public-files \
+  --listen 127.0.0.1:8443 \
+  --base-path /wip \
+  --behind-tls-proxy
+```
+
+Local development with the write capability deliberately enabled:
+
+```console
+cargo run -p wip-fs-server -- \
+  --root ./example-files \
+  --listen 127.0.0.1:8080 \
+  --base-path /wip \
+  --development-http \
+  --read-write
+```
+
+The server reports the effective root, `ReadOnly`/`ReadWrite` mode, transport
+mode, endpoint, and actual listen address. It does not enumerate the root.
+
+## Standard interactions
+
+The following examples use development HTTP for readability. The JSON is the
+standard `wip-https` profile; validators and operation `Bytes` are base64 body
+fields, never `ETag` or `If-Match` headers.
+
+Fetch root:
+
+```console
+curl -sS -X POST http://127.0.0.1:8080/wip/v1/fetch \
+  -H 'Content-Type: application/json' -H 'Accept: application/json' \
+  --data '{"path":"/"}'
+```
+
+Fetch a bounded tree (the root counts toward `limit`):
+
+```console
+curl -sS -X POST http://127.0.0.1:8080/wip/v1/fetch_tree \
+  -H 'Content-Type: application/json' -H 'Accept: application/json' \
+  --data '{"path":"/","depth":2,"limit":100}'
+```
+
+A regular-file fetch returns the opaque read interface reference and an object
+validator. Retrieve that descriptor with:
+
+```console
+curl -sS -X POST http://127.0.0.1:8080/wip/v1/fetch_interface \
+  -H 'Content-Type: application/json' -H 'Accept: application/json' \
+  --data '{"interface":"<read-interface-from-fetch>"}'
+```
+
+Then call a bounded range read:
+
+```console
+curl -sS -X POST http://127.0.0.1:8080/wip/v1/call_operation \
+  -H 'Content-Type: application/json' -H 'Accept: application/json' \
+  --data '{
+    "target":{"path":"/notes.txt","validator":"<base64-validator>"},
+    "interface":{"reference":"<read-interface>"},
+    "operation":"read",
+    "arguments":{"offset":0,"length":4096}
+  }'
+```
+
+In `--read-write` mode a second regular-file interface declares `replace`.
+Writes require the current object validator and return the post-write validator:
+
+```console
+curl -sS -X POST http://127.0.0.1:8080/wip/v1/call_operation \
+  -H 'Content-Type: application/json' -H 'Accept: application/json' \
+  --data '{
+    "target":{"path":"/notes.txt","validator":"<base64-validator>"},
+    "interface":{"reference":"<write-interface>"},
+    "operation":"replace",
+    "arguments":{"contents":"dXBkYXRlZA=="}
+  }'
+```
+
+`fetch`, `fetch_tree`, and `fetch_interface` can also be combined through the
+standard `POST /wip/v1/batch` route. `call_operation` is never batchable.
+
+## Resource and failure behavior
+
+`ResourceLimits` bounds request/response bytes, HTTP request-head bytes, JSON
+nesting, batch items, file read/write bytes, tree depth/node count, pinned handles,
+and active connections/requests. One absolute request deadline covers header and
+body intake, dispatch, cooperative filesystem work, and response transmission;
+stalled clients are closed and cannot occupy a worker beyond that bound. Workers
+accept connections directly, so the listener never moves more than the configured
+concurrency into active userspace service. Advisory file-lock acquisition uses a
+nonblocking loop and checks the same deadline/cancellation rather than allowing a
+contended lock to stall a worker. Tree traversal is breadth-first and opens only
+requested entries. Once a limit or depth boundary is reached it reads only far
+enough to
+prove whether an additional visible child exists, so `truncated` is true only
+when something was actually omitted. I/O failure and cancellation remain errors,
+not clean exhaustion.
+
+Whole-file replacement compares the request validator against the identity and
+state of the same pinned file handle used for the write. Failures before mutation
+carry a `NotCommitted` guarantee and map to `Internal` or
+`ResourceLimitExceeded`; a failure after truncation/write begins maps to
+`OperationOutcomeUnknown`. The server and Clients do not automatically retry
+side-effecting operations.

crates/wip-fs-server/src/interfaces.rs

@@ -0,0 +1,43 @@
+//! Filesystem capability interfaces published by the projection.
+
+use wip_interface as wip;
+
+/// Bounded reads from a regular file.
+#[wip::interface]
+pub trait FileRead {
+    /// Reads bytes from the current regular file.
+    ///
+    /// # Returns
+    /// At most the configured read limit, beginning at `offset`.
+    fn read(
+        &self,
+        /// Byte offset; omitted means zero.
+        offset: Option<u64>,
+        /// Requested byte count; omitted means the rest of the file.
+        length: Option<u64>,
+    ) -> wip::OperationResult<wip::Bytes>;
+}
+
+/// Inspection operations for a symbolic link itself.
+#[wip::interface]
+pub trait SymlinkInspect {
+    /// Reads the link payload without following it.
+    ///
+    /// # Returns
+    /// The platform path bytes stored in the symbolic link.
+    fn read_link(&self) -> wip::OperationResult<wip::Bytes>;
+}
+
+/// Explicitly enabled mutation of a regular file.
+#[wip::interface]
+pub trait FileWrite {
+    /// Replaces the current regular file contents through its pinned handle.
+    ///
+    /// # Returns
+    /// Unit after the new bytes have been written and synchronized.
+    fn replace(
+        &self,
+        /// Complete replacement contents.
+        contents: wip::Bytes,
+    ) -> wip::OperationResult<()>;
+}

crates/wip-fs-server/src/lib.rs

@@ -0,0 +1,191 @@
+//! Request-time filesystem projection served through the standard WIP HTTPS binding.
+//!
+//! This crate deliberately keeps the boundaries visible:
+//!
+//! - [`wip_protocol`] owns logical requests and responses;
+//! - [`wip_host`] owns object publication, validators, and typed dispatch;
+//! - [`wip_https`] owns routes, JSON, envelopes, batching, and status mapping;
+//! - this crate owns the filesystem capability boundary and the real HTTP listener.
+//!
+//! TLS is terminated by an explicitly configured reverse proxy. The built-in
+//! listener accepts cleartext only on loopback, either behind that proxy or when
+//! [`TransportSecurity::DevelopmentHttp`] is deliberately selected.
+
+#![deny(missing_docs)]
+
+mod interfaces;
+mod projection;
+mod server;
+
+use std::net::{IpAddr, Ipv4Addr, SocketAddr};
+use std::path::PathBuf;
+use std::time::Duration;
+
+pub use interfaces::{FileRead, FileWrite, SymlinkInspect};
+pub use server::{BoundServer, ServerBuildError, WipFsServer};
+
+/// Filesystem capabilities published by regular files.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AccessMode {
+    /// Publish bounded reads only.
+    ReadOnly,
+    /// Also publish validator-protected whole-file replacement.
+    ReadWrite,
+}
+
+/// How HTTPS is provided for the endpoint.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum TransportSecurity {
+    /// A trusted reverse proxy terminates TLS and forwards to the loopback listener.
+    ReverseProxyTls,
+    /// Cleartext HTTP is deliberately enabled for local development only.
+    DevelopmentHttp,
+}
+
+/// Bounded resource policy applied by the HTTP adapter and filesystem provider.
+#[derive(Debug, Clone, Copy)]
+pub struct ResourceLimits {
+    /// Standard JSON, body-size, nesting, and batch limits.
+    pub wire: wip_https::Limits,
+    /// Maximum bytes returned by one file read.
+    pub max_file_read_bytes: usize,
+    /// Maximum bytes accepted by one file replacement.
+    pub max_file_write_bytes: usize,
+    /// Maximum accepted `fetch_tree` depth.
+    pub max_tree_depth: u32,
+    /// Maximum accepted `fetch_tree` node count, including its root.
+    pub max_tree_nodes: u32,
+    /// Maximum simultaneously pinned projected filesystem handles.
+    pub max_open_handles: usize,
+    /// Maximum bytes accepted for one HTTP request head, including its terminator.
+    pub max_http_header_bytes: usize,
+    /// Maximum requests executing concurrently.
+    pub max_concurrent_requests: usize,
+    /// End-to-end deadline for HTTP intake, dispatch, and response transmission.
+    pub request_timeout: Duration,
+}
+
+impl Default for ResourceLimits {
+    fn default() -> Self {
+        Self {
+            wire: wip_https::Limits::new(256 * 1024, 2 * 1024 * 1024, 64, 64)
+                .expect("default wire limits are nonzero"),
+            max_file_read_bytes: 1024 * 1024,
+            max_file_write_bytes: 1024 * 1024,
+            max_tree_depth: 32,
+            max_tree_nodes: 1024,
+            max_open_handles: 2048,
+            max_http_header_bytes: 16 * 1024,
+            max_concurrent_requests: 32,
+            request_timeout: Duration::from_secs(30),
+        }
+    }
+}
+
+/// Complete listener and projection configuration.
+#[derive(Debug, Clone)]
+pub struct ServerConfig {
+    /// Filesystem directory projected as Worldspace `/`.
+    pub root: PathBuf,
+    /// Loopback socket used by the built-in cleartext listener.
+    pub listen: SocketAddr,
+    /// URL path prefix below which standard `v1/*` routes are mounted.
+    pub endpoint_base_path: String,
+    /// Read-only or explicit read-write publication mode.
+    pub access: AccessMode,
+    /// TLS termination or explicit development HTTP policy.
+    pub transport_security: TransportSecurity,
+    /// Request, operation, traversal, and concurrency bounds.
+    pub limits: ResourceLimits,
+}
+
+impl ServerConfig {
+    /// Builds a secure-by-default configuration for `root`.
+    ///
+    /// The listener defaults to an ephemeral loopback port, read-only access,
+    /// and TLS termination delegated to a reverse proxy.
+    #[must_use]
+    pub fn for_root(root: impl Into<PathBuf>) -> Self {
+        Self {
+            root: root.into(),
+            listen: SocketAddr::new(IpAddr::V4(Ipv4Addr::LOCALHOST), 0),
+            endpoint_base_path: "/wip".into(),
+            access: AccessMode::ReadOnly,
+            transport_security: TransportSecurity::ReverseProxyTls,
+            limits: ResourceLimits::default(),
+        }
+    }
+
+    pub(crate) fn validate(&self) -> Result<(), ConfigError> {
+        if !self.listen.ip().is_loopback() {
+            return Err(ConfigError::NonLoopbackCleartext);
+        }
+        if !valid_base_path(&self.endpoint_base_path) {
+            return Err(ConfigError::InvalidBasePath);
+        }
+        if self.limits.max_file_read_bytes == 0
+            || self.limits.max_file_write_bytes == 0
+            || self.limits.max_tree_nodes == 0
+            || self.limits.max_open_handles == 0
+            || self.limits.max_http_header_bytes == 0
+            || self.limits.max_concurrent_requests == 0
+            || self.limits.request_timeout.is_zero()
+        {
+            return Err(ConfigError::ZeroLimit);
+        }
+        if self.limits.max_open_handles < self.limits.max_tree_nodes as usize {
+            return Err(ConfigError::InsufficientHandles);
+        }
+        if self.limits.wire.max_response_bytes() < 512 {
+            return Err(ConfigError::ResponseLimitTooSmall);
+        }
+        Ok(())
+    }
+
+    pub(crate) fn endpoint(&self) -> Result<wip_https::Endpoint, ConfigError> {
+        let endpoint = format!("https://localhost{}", self.endpoint_base_path);
+        wip_https::Endpoint::parse(&endpoint).map_err(|_| ConfigError::InvalidBasePath)
+    }
+}
+
+/// Invalid server configuration.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ConfigError {
+    /// The cleartext built-in listener was exposed beyond loopback.
+    NonLoopbackCleartext,
+    /// The endpoint prefix is not an absolute canonical URL path.
+    InvalidBasePath,
+    /// A resource limit is zero.
+    ZeroLimit,
+    /// Tree nodes could exhaust the configured handle ceiling by construction.
+    InsufficientHandles,
+    /// The response limit cannot reliably carry a bounded protocol error envelope.
+    ResponseLimitTooSmall,
+}
+
+impl std::fmt::Display for ConfigError {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        formatter.write_str(match self {
+            Self::NonLoopbackCleartext => "the built-in cleartext listener must bind to loopback",
+            Self::InvalidBasePath => {
+                "endpoint base path must be absolute, canonical, and query-free"
+            }
+            Self::ZeroLimit => "all resource limits and the request timeout must be nonzero",
+            Self::InsufficientHandles => "max_open_handles must cover max_tree_nodes",
+            Self::ResponseLimitTooSmall => "max_response_bytes must be at least 512",
+        })
+    }
+}
+
+impl std::error::Error for ConfigError {}
+
+fn valid_base_path(path: &str) -> bool {
+    path.starts_with('/')
+        && !path.contains('?')
+        && !path.contains('#')
+        && !path.contains("//")
+        && !path
+            .split('/')
+            .any(|segment| segment == "." || segment == "..")
+        && (path == "/" || !path.ends_with('/'))
+}

crates/wip-fs-server/src/main.rs

@@ -0,0 +1,83 @@
+use std::error::Error;
+use std::net::SocketAddr;
+use std::path::PathBuf;
+
+use wip_fs_server::{AccessMode, ServerConfig, TransportSecurity, WipFsServer};
+
+fn main() -> Result<(), Box<dyn Error>> {
+    let mut root: Option<PathBuf> = None;
+    let mut listen: SocketAddr = "127.0.0.1:8443".parse()?;
+    let mut base_path = "/wip".to_owned();
+    let mut access = AccessMode::ReadOnly;
+    let mut security = None;
+    let mut arguments = std::env::args().skip(1);
+    while let Some(argument) = arguments.next() {
+        match argument.as_str() {
+            "--root" => root = Some(PathBuf::from(required_value(&mut arguments, "--root")?)),
+            "--listen" => listen = required_value(&mut arguments, "--listen")?.parse()?,
+            "--base-path" => base_path = required_value(&mut arguments, "--base-path")?,
+            "--read-write" => access = AccessMode::ReadWrite,
+            "--development-http" => {
+                set_security(&mut security, TransportSecurity::DevelopmentHttp)?
+            }
+            "--behind-tls-proxy" => {
+                set_security(&mut security, TransportSecurity::ReverseProxyTls)?
+            }
+            "--help" | "-h" => {
+                print_help();
+                return Ok(());
+            }
+            unknown => return Err(format!("unknown argument `{unknown}`; use --help").into()),
+        }
+    }
+
+    let root = root.ok_or("--root is required")?;
+    let transport_security =
+        security.ok_or("select exactly one of --behind-tls-proxy or --development-http")?;
+    let mut config = ServerConfig::for_root(root);
+    config.listen = listen;
+    config.endpoint_base_path = base_path;
+    config.access = access;
+    config.transport_security = transport_security;
+
+    let server = WipFsServer::new(config)?;
+    let effective_root = server.effective_root().to_owned();
+    let endpoint = server.endpoint().clone();
+    let bound = server.bind()?;
+    eprintln!(
+        "wip-fs-server root={} access={access:?} transport={transport_security:?} endpoint={} listen={}",
+        effective_root.display(),
+        endpoint,
+        bound.local_addr()
+    );
+    bound.serve()?;
+    Ok(())
+}
+
+fn required_value(
+    arguments: &mut impl Iterator<Item = String>,
+    option: &str,
+) -> Result<String, Box<dyn Error>> {
+    arguments
+        .next()
+        .ok_or_else(|| format!("{option} requires a value").into())
+}
+
+fn set_security(
+    security: &mut Option<TransportSecurity>,
+    value: TransportSecurity,
+) -> Result<(), Box<dyn Error>> {
+    if security.replace(value).is_some() {
+        Err("select only one transport-security mode".into())
+    } else {
+        Ok(())
+    }
+}
+
+fn print_help() {
+    println!(
+        "Usage: wip-fs-server --root PATH [--listen 127.0.0.1:8443] \\\n         [--base-path /wip] [--read-write] \\\n         (--behind-tls-proxy | --development-http)\n\n\
+         The built-in listener is cleartext and loopback-only. In production, \
+         select --behind-tls-proxy and terminate HTTPS at a trusted reverse proxy."
+    );
+}

crates/wip-fs-server/src/server.rs

@@ -0,0 +1,747 @@
+use std::io::{Read, Write};
+use std::net::{SocketAddr, TcpListener, TcpStream};
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use http::{Request, Response, StatusCode};
+use wip_host::{ExecutionContext, ObjectProvider};
+use wip_https::{
+    BatchRequestKind, BatchResponse, BatchResponseItem, BatchSuccess, CodecError, EncodeHttpError,
+    Endpoint, RequestMetadataError, ResourceLimitKind, Route, decode_batch_request,
+    decode_call_operation_metadata, decode_fetch_interface_request, decode_fetch_request,
+    decode_fetch_tree_request, encode_batch_error_response,
+    encode_batch_resource_limit_error_response, encode_batch_response,
+    encode_call_operation_response, encode_fetch_interface_response, encode_fetch_response,
+    encode_fetch_tree_response, encode_protocol_error_response,
+    encode_resource_limit_error_response, validate_http_request,
+};
+use wip_protocol::{ProtocolError, ProtocolErrorCode, ProtocolInteraction};
+
+use crate::projection::Projection;
+use crate::{ConfigError, ServerConfig};
+
+/// Filesystem projection and framework-neutral standard WIP request adapter.
+pub struct WipFsServer {
+    config: ServerConfig,
+    endpoint: Endpoint,
+    effective_root: std::path::PathBuf,
+    projection: Arc<Projection>,
+}
+
+impl WipFsServer {
+    /// Validates configuration and opens the configured directory capability.
+    pub fn new(config: ServerConfig) -> Result<Self, ServerBuildError> {
+        config.validate()?;
+        let endpoint = config.endpoint()?;
+        let projection = Projection::open(&config.root, config.access, config.limits)?;
+        let effective_root = projection.effective_root()?;
+        Ok(Self {
+            config,
+            endpoint,
+            effective_root,
+            projection: Arc::new(projection),
+        })
+    }
+
+    /// Returns the canonical effective filesystem root opened by the server.
+    #[must_use]
+    pub fn effective_root(&self) -> &std::path::Path {
+        &self.effective_root
+    }
+
+    /// Returns the configured transport endpoint prefix.
+    #[must_use]
+    pub fn endpoint(&self) -> &Endpoint {
+        &self.endpoint
+    }
+
+    /// Handles one already-buffered HTTP request with the standard `wip-https` codecs.
+    ///
+    /// Listener integrations must enforce the same body limit while collecting bytes.
+    #[must_use]
+    pub fn handle_http(&self, request: Request<Vec<u8>>) -> Response<Vec<u8>> {
+        self.handle_http_with_deadline(request, Instant::now() + self.config.limits.request_timeout)
+    }
+
+    fn handle_http_with_deadline(
+        &self,
+        request: Request<Vec<u8>>,
+        deadline: Instant,
+    ) -> Response<Vec<u8>> {
+        let Some(route) = self.route(request.uri().path()) else {
+            return empty_response(StatusCode::NOT_FOUND);
+        };
+        if let Err(error) = validate_http_request(&self.endpoint, route, &request) {
+            return self.metadata_error(route, error);
+        }
+        let context = ExecutionContext::new()
+            .with_deadline(deadline)
+            .with_resource_budget(u64::from(self.config.limits.max_tree_nodes));
+        match route {
+            Route::Fetch => self.fetch(request.body(), &context),
+            Route::FetchTree => self.fetch_tree(request.body(), &context),
+            Route::FetchInterface => self.fetch_interface(request.body()),
+            Route::CallOperation => self.call_operation(request.body(), &context),
+            Route::Batch => self.batch(request.body(), &context),
+        }
+    }
+
+    /// Binds the built-in bounded loopback HTTP listener.
+    ///
+    /// The listener is cleartext by design. Configuration must explicitly state
+    /// whether TLS is terminated by a reverse proxy or development HTTP is in use.
+    pub fn bind(self) -> Result<BoundServer, ServerBuildError> {
+        let listener = TcpListener::bind(self.config.listen)
+            .map_err(|error| ServerBuildError::Listener(error.to_string()))?;
+        listener
+            .set_nonblocking(true)
+            .map_err(|error| ServerBuildError::Listener(error.to_string()))?;
+        let local_addr = listener
+            .local_addr()
+            .map_err(|error| ServerBuildError::Listener(error.to_string()))?;
+        Ok(BoundServer {
+            local_addr,
+            service: Arc::new(self),
+            listener: Arc::new(listener),
+        })
+    }
+
+    fn route(&self, path: &str) -> Option<Route> {
+        [
+            Route::Fetch,
+            Route::FetchTree,
+            Route::FetchInterface,
+            Route::CallOperation,
+            Route::Batch,
+        ]
+        .into_iter()
+        .find(|route| self.endpoint.route(*route).path() == path)
+    }
+
+    fn fetch(&self, body: &[u8], context: &ExecutionContext) -> Response<Vec<u8>> {
+        let request = match decode_fetch_request(body, self.config.limits.wire) {
+            Ok(request) => request,
+            Err(error) => return self.codec_error(ProtocolInteraction::Fetch, error),
+        };
+        match self
+            .projection
+            .fetch_with_context(context, &request.path)
+            .map_err(|error| error.protocol_error())
+        {
+            Ok(object) => encode_fetch_response(&request, &object, self.config.limits.wire)
+                .unwrap_or_else(|error| self.read_encode_error(ProtocolInteraction::Fetch, error)),
+            Err(error) => self.protocol_error(ProtocolInteraction::Fetch, &error, None),
+        }
+    }
+
+    fn fetch_tree(&self, body: &[u8], context: &ExecutionContext) -> Response<Vec<u8>> {
+        let request = match decode_fetch_tree_request(body, self.config.limits.wire) {
+            Ok(request) => request,
+            Err(error) => return self.codec_error(ProtocolInteraction::FetchTree, error),
+        };
+        match self.projection.fetch_tree(context, &request) {
+            Ok(tree) => encode_fetch_tree_response(&request, &tree, self.config.limits.wire)
+                .unwrap_or_else(|error| {
+                    self.read_encode_error(ProtocolInteraction::FetchTree, error)
+                }),
+            Err(error) => self.protocol_error(ProtocolInteraction::FetchTree, &error, None),
+        }
+    }
+
+    fn fetch_interface(&self, body: &[u8]) -> Response<Vec<u8>> {
+        let request = match decode_fetch_interface_request(body, self.config.limits.wire) {
+            Ok(request) => request,
+            Err(error) => return self.codec_error(ProtocolInteraction::FetchInterface, error),
+        };
+        match self.projection.fetch_interface(&request) {
+            Ok(interface) => {
+                encode_fetch_interface_response(&request, &interface, self.config.limits.wire)
+                    .unwrap_or_else(|error| {
+                        self.read_encode_error(ProtocolInteraction::FetchInterface, error)
+                    })
+            }
+            Err(error) => self.protocol_error(ProtocolInteraction::FetchInterface, &error, None),
+        }
+    }
+
+    fn call_operation(&self, body: &[u8], context: &ExecutionContext) -> Response<Vec<u8>> {
+        let metadata = match decode_call_operation_metadata(body, self.config.limits.wire) {
+            Ok(metadata) => metadata,
+            Err(error) => return self.codec_error(ProtocolInteraction::CallOperation, error),
+        };
+        let may_commit = metadata.operation == "replace";
+        let decoded = std::sync::Mutex::new(None);
+        let execution = self.projection.call_operation_with_context_and_decoder(
+            context,
+            metadata.target.clone(),
+            metadata.interface.clone(),
+            metadata.operation.clone(),
+            |descriptor| {
+                let request = metadata.decode_request(body, descriptor, self.config.limits.wire)?;
+                let arguments = request.arguments.clone();
+                *decoded.lock().unwrap_or_else(|error| error.into_inner()) =
+                    Some((request, descriptor.clone()));
+                Ok::<_, CodecError>(arguments)
+            },
+        );
+        match execution.map_err(|error| error.protocol_error()) {
+            Ok(result) => {
+                let Some((request, descriptor)) = decoded
+                    .into_inner()
+                    .unwrap_or_else(|error| error.into_inner())
+                else {
+                    let error = ProtocolError {
+                        code: if may_commit {
+                            ProtocolErrorCode::OperationOutcomeUnknown
+                        } else {
+                            ProtocolErrorCode::Internal
+                        },
+                        message: "operation completed without response metadata".into(),
+                    };
+                    return self.protocol_error(ProtocolInteraction::CallOperation, &error, None);
+                };
+                encode_call_operation_response(
+                    &request,
+                    &descriptor,
+                    &result,
+                    self.config.limits.wire,
+                )
+                .unwrap_or_else(|encode_error| {
+                    if !may_commit {
+                        return self
+                            .read_encode_error(ProtocolInteraction::CallOperation, encode_error);
+                    }
+                    // Replacement may already be committed, so a response
+                    // encoding failure cannot carry a non-commit guarantee.
+                    let error = ProtocolError {
+                        code: ProtocolErrorCode::OperationOutcomeUnknown,
+                        message: "operation completed but its response could not be encoded".into(),
+                    };
+                    self.protocol_error(ProtocolInteraction::CallOperation, &error, None)
+                })
+            }
+            Err(error) => self.protocol_error(ProtocolInteraction::CallOperation, &error, None),
+        }
+    }
+
+    fn batch(&self, body: &[u8], context: &ExecutionContext) -> Response<Vec<u8>> {
+        let request = match decode_batch_request(body, self.config.limits.wire) {
+            Ok(request) => request,
+            Err(error) => return self.batch_codec_error(error),
+        };
+        let responses = request
+            .requests
+            .iter()
+            .map(|item| {
+                let outcome = match &item.request {
+                    BatchRequestKind::Fetch(request) => self
+                        .projection
+                        .fetch_with_context(context, &request.path)
+                        .map(BatchSuccess::Fetch)
+                        .map_err(|error| error.protocol_error()),
+                    BatchRequestKind::FetchTree(request) => self
+                        .projection
+                        .fetch_tree(context, request)
+                        .map(BatchSuccess::FetchTree),
+                    BatchRequestKind::FetchInterface(request) => self
+                        .projection
+                        .fetch_interface(request)
+                        .map(BatchSuccess::FetchInterface),
+                    BatchRequestKind::Invalid { error, .. } => Err(error.clone()),
+                };
+                BatchResponseItem {
+                    id: item.id.clone(),
+                    outcome,
+                }
+            })
+            .collect();
+        let response = BatchResponse { responses };
+        encode_batch_response(&request, &response, self.config.limits.wire).unwrap_or_else(
+            |error| match error {
+                EncodeHttpError::Codec(codec) => self.batch_codec_error(codec),
+                EncodeHttpError::Http(_) => self.batch_top_error(&internal_error(), None),
+            },
+        )
+    }
+
+    fn metadata_error(&self, route: Route, error: RequestMetadataError) -> Response<Vec<u8>> {
+        match error {
+            RequestMetadataError::InvalidRequest(_) => self.protocol_error(
+                interaction(route),
+                &ProtocolError {
+                    code: ProtocolErrorCode::InvalidRequest,
+                    message: "invalid HTTP request metadata".into(),
+                },
+                None,
+            ),
+            RequestMetadataError::UnsupportedMediaType => {
+                empty_response(StatusCode::UNSUPPORTED_MEDIA_TYPE)
+            }
+            RequestMetadataError::NotAcceptable => empty_response(StatusCode::NOT_ACCEPTABLE),
+        }
+    }
+
+    fn codec_error(
+        &self,
+        interaction: ProtocolInteraction,
+        error: CodecError,
+    ) -> Response<Vec<u8>> {
+        if let Some(kind) = error.resource_limit_kind() {
+            self.protocol_error(interaction, &resource_error(), Some(kind))
+        } else {
+            self.protocol_error(
+                interaction,
+                &ProtocolError {
+                    code: ProtocolErrorCode::InvalidRequest,
+                    message: "malformed WIP request".into(),
+                },
+                None,
+            )
+        }
+    }
+
+    fn batch_codec_error(&self, error: CodecError) -> Response<Vec<u8>> {
+        if let Some(kind) = error.resource_limit_kind() {
+            self.batch_top_error(&resource_error(), Some(kind))
+        } else {
+            self.batch_top_error(
+                &ProtocolError {
+                    code: ProtocolErrorCode::InvalidRequest,
+                    message: "malformed WIP batch request".into(),
+                },
+                None,
+            )
+        }
+    }
+
+    fn read_encode_error(
+        &self,
+        interaction: ProtocolInteraction,
+        error: EncodeHttpError,
+    ) -> Response<Vec<u8>> {
+        match error {
+            EncodeHttpError::Codec(codec) if codec.resource_limit_kind().is_some() => {
+                self.protocol_error(interaction, &resource_error(), codec.resource_limit_kind())
+            }
+            _ => self.protocol_error(interaction, &internal_error(), None),
+        }
+    }
+
+    fn protocol_error(
+        &self,
+        interaction: ProtocolInteraction,
+        error: &ProtocolError,
+        resource_kind: Option<ResourceLimitKind>,
+    ) -> Response<Vec<u8>> {
+        let encoded = match resource_kind {
+            Some(kind) => encode_resource_limit_error_response(
+                interaction,
+                error,
+                kind,
+                self.config.limits.wire,
+            ),
+            None => encode_protocol_error_response(interaction, error, self.config.limits.wire),
+        };
+        encoded.unwrap_or_else(|_| empty_response(StatusCode::INTERNAL_SERVER_ERROR))
+    }
+
+    fn batch_top_error(
+        &self,
+        error: &ProtocolError,
+        resource_kind: Option<ResourceLimitKind>,
+    ) -> Response<Vec<u8>> {
+        let encoded = match resource_kind {
+            Some(kind) => {
+                encode_batch_resource_limit_error_response(error, kind, self.config.limits.wire)
+            }
+            None => encode_batch_error_response(error, self.config.limits.wire),
+        };
+        encoded.unwrap_or_else(|_| empty_response(StatusCode::INTERNAL_SERVER_ERROR))
+    }
+}
+
+/// Bound real HTTP listener for a [`WipFsServer`].
+pub struct BoundServer {
+    local_addr: SocketAddr,
+    service: Arc<WipFsServer>,
+    listener: Arc<TcpListener>,
+}
+
+impl BoundServer {
+    /// Returns the actual bound loopback address, including an assigned port.
+    #[must_use]
+    pub fn local_addr(&self) -> SocketAddr {
+        self.local_addr
+    }
+
+    /// Serves requests with a fixed worker count until `shutdown` becomes true.
+    ///
+    /// Workers accept connections directly, so at most
+    /// `max_concurrent_requests` sockets are active in userspace. Each connection
+    /// is closed after one request and shares one absolute deadline across HTTP
+    /// intake, dispatch, and response transmission.
+    pub fn serve_until(&self, shutdown: Arc<AtomicBool>) -> Result<(), std::io::Error> {
+        let mut workers = Vec::with_capacity(self.service.config.limits.max_concurrent_requests);
+        for _ in 0..self.service.config.limits.max_concurrent_requests {
+            let listener = Arc::clone(&self.listener);
+            let service = Arc::clone(&self.service);
+            let shutdown = Arc::clone(&shutdown);
+            workers.push(thread::spawn(move || {
+                while !shutdown.load(Ordering::Acquire) {
+                    match listener.accept() {
+                        Ok((stream, _)) => serve_connection(&service, stream),
+                        Err(error) if error.kind() == std::io::ErrorKind::WouldBlock => {
+                            thread::sleep(Duration::from_millis(5));
+                        }
+                        Err(error) if error.kind() == std::io::ErrorKind::Interrupted => {}
+                        Err(error) => return Err(error),
+                    }
+                }
+                Ok(())
+            }));
+        }
+        for worker in workers {
+            worker
+                .join()
+                .map_err(|_| std::io::Error::other("HTTP worker panicked"))??;
+        }
+        Ok(())
+    }
+
+    /// Serves until the process is terminated.
+    pub fn serve(&self) -> Result<(), std::io::Error> {
+        self.serve_until(Arc::new(AtomicBool::new(false)))
+    }
+}
+
+#[derive(Debug)]
+struct ParsedRequestHead {
+    method: http::Method,
+    target: String,
+    headers: Vec<(http::header::HeaderName, http::HeaderValue)>,
+    content_length: usize,
+}
+
+#[derive(Debug)]
+enum IntakeError {
+    Timeout,
+    HeaderTooLarge,
+    PayloadTooLarge { target: String },
+    BadRequest,
+    Socket,
+}
+
+fn serve_connection(service: &WipFsServer, mut stream: TcpStream) {
+    let _ = stream.set_nonblocking(false);
+    let started = Instant::now();
+    let deadline = started
+        .checked_add(service.config.limits.request_timeout)
+        .unwrap_or(started);
+    let response = match read_http_request(
+        &mut stream,
+        service.config.limits.max_http_header_bytes,
+        service.config.limits.wire.max_request_bytes(),
+        deadline,
+    ) {
+        Ok(request) => Some(service.handle_http_with_deadline(request, deadline)),
+        Err(IntakeError::HeaderTooLarge) => {
+            Some(empty_response(StatusCode::REQUEST_HEADER_FIELDS_TOO_LARGE))
+        }
+        Err(IntakeError::PayloadTooLarge { target }) => {
+            Some(payload_too_large_response(service, &target))
+        }
+        Err(IntakeError::BadRequest) => Some(empty_response(StatusCode::BAD_REQUEST)),
+        Err(IntakeError::Timeout | IntakeError::Socket) => None,
+    };
+    if let Some(response) = response {
+        let _ = write_http_response(&mut stream, &response, deadline);
+    }
+    let _ = stream.shutdown(std::net::Shutdown::Both);
+}
+
+fn read_http_request(
+    stream: &mut TcpStream,
+    maximum_header: usize,
+    maximum_body: usize,
+    deadline: Instant,
+) -> Result<Request<Vec<u8>>, IntakeError> {
+    let mut received = Vec::with_capacity(maximum_header.min(8 * 1024));
+    let header_end = loop {
+        if let Some(position) = received.windows(4).position(|window| window == b"\r\n\r\n") {
+            let end = position + 4;
+            if end > maximum_header {
+                return Err(IntakeError::HeaderTooLarge);
+            }
+            break end;
+        }
+        if received.len() >= maximum_header {
+            return Err(IntakeError::HeaderTooLarge);
+        }
+        let mut chunk = [0_u8; 4 * 1024];
+        let available = (maximum_header - received.len()).min(chunk.len());
+        let count = read_with_deadline(stream, &mut chunk[..available], deadline)?;
+        if count == 0 {
+            return Err(IntakeError::BadRequest);
+        }
+        received.extend_from_slice(&chunk[..count]);
+    };
+
+    let parsed = parse_request_head(&received[..header_end])?;
+    if parsed.content_length > maximum_body {
+        return Err(IntakeError::PayloadTooLarge {
+            target: parsed.target,
+        });
+    }
+    let mut body = Vec::with_capacity(parsed.content_length);
+    let buffered = &received[header_end..];
+    body.extend_from_slice(&buffered[..buffered.len().min(parsed.content_length)]);
+    while body.len() < parsed.content_length {
+        let mut chunk = [0_u8; 8 * 1024];
+        let wanted = (parsed.content_length - body.len()).min(chunk.len());
+        let count = read_with_deadline(stream, &mut chunk[..wanted], deadline)?;
+        if count == 0 {
+            return Err(IntakeError::BadRequest);
+        }
+        body.extend_from_slice(&chunk[..count]);
+    }
+
+    let mut builder = Request::builder().method(parsed.method).uri(parsed.target);
+    for (name, value) in parsed.headers {
+        builder = builder.header(name, value);
+    }
+    builder.body(body).map_err(|_| IntakeError::BadRequest)
+}
+
+fn parse_request_head(bytes: &[u8]) -> Result<ParsedRequestHead, IntakeError> {
+    let text = std::str::from_utf8(bytes).map_err(|_| IntakeError::BadRequest)?;
+    let mut lines = text
+        .strip_suffix("\r\n\r\n")
+        .ok_or(IntakeError::BadRequest)?
+        .split("\r\n");
+    let mut request_line = lines
+        .next()
+        .ok_or(IntakeError::BadRequest)?
+        .split_ascii_whitespace();
+    let method = request_line.next().ok_or(IntakeError::BadRequest)?;
+    let target = request_line.next().ok_or(IntakeError::BadRequest)?;
+    let version = request_line.next().ok_or(IntakeError::BadRequest)?;
+    if request_line.next().is_some()
+        || !matches!(version, "HTTP/1.0" | "HTTP/1.1")
+        || !target.starts_with('/')
+    {
+        return Err(IntakeError::BadRequest);
+    }
+    let method =
+        http::Method::from_bytes(method.as_bytes()).map_err(|_| IntakeError::BadRequest)?;
+    let _: http::Uri = target.parse().map_err(|_| IntakeError::BadRequest)?;
+
+    let mut headers = Vec::new();
+    let mut content_length = None;
+    for line in lines {
+        if line.is_empty() || line.starts_with([' ', '\t']) {
+            return Err(IntakeError::BadRequest);
+        }
+        let (name, value) = line.split_once(':').ok_or(IntakeError::BadRequest)?;
+        let name = http::header::HeaderName::from_bytes(name.as_bytes())
+            .map_err(|_| IntakeError::BadRequest)?;
+        let value =
+            http::HeaderValue::from_str(value.trim()).map_err(|_| IntakeError::BadRequest)?;
+        if name == http::header::CONTENT_LENGTH {
+            if content_length.is_some() {
+                return Err(IntakeError::BadRequest);
+            }
+            content_length = Some(
+                value
+                    .to_str()
+                    .ok()
+                    .and_then(|value| value.parse::<usize>().ok())
+                    .ok_or(IntakeError::BadRequest)?,
+            );
+        }
+        if name == http::header::TRANSFER_ENCODING {
+            return Err(IntakeError::BadRequest);
+        }
+        headers.push((name, value));
+    }
+
+    Ok(ParsedRequestHead {
+        method,
+        target: target.to_owned(),
+        headers,
+        content_length: content_length.unwrap_or(0),
+    })
+}
+
+fn read_with_deadline(
+    stream: &mut TcpStream,
+    buffer: &mut [u8],
+    deadline: Instant,
+) -> Result<usize, IntakeError> {
+    let remaining = deadline
+        .checked_duration_since(Instant::now())
+        .ok_or(IntakeError::Timeout)?;
+    stream
+        .set_read_timeout(Some(remaining.max(Duration::from_millis(1))))
+        .map_err(|_| IntakeError::Socket)?;
+    stream.read(buffer).map_err(|error| match error.kind() {
+        std::io::ErrorKind::TimedOut | std::io::ErrorKind::WouldBlock => IntakeError::Timeout,
+        _ => IntakeError::Socket,
+    })
+}
+
+fn payload_too_large_response(service: &WipFsServer, target: &str) -> Response<Vec<u8>> {
+    let route = service.route(target.split('?').next().unwrap_or_default());
+    route.map_or_else(
+        || empty_response(StatusCode::PAYLOAD_TOO_LARGE),
+        |route| {
+            if route == Route::Batch {
+                service.batch_top_error(
+                    &resource_error(),
+                    Some(ResourceLimitKind::RepresentationBytes),
+                )
+            } else {
+                service.protocol_error(
+                    interaction(route),
+                    &resource_error(),
+                    Some(ResourceLimitKind::RepresentationBytes),
+                )
+            }
+        },
+    )
+}
+
+fn write_http_response(
+    stream: &mut TcpStream,
+    response: &Response<Vec<u8>>,
+    deadline: Instant,
+) -> Result<(), std::io::Error> {
+    let mut encoded = Vec::new();
+    write!(
+        encoded,
+        "HTTP/1.1 {} {}\r\n",
+        response.status().as_u16(),
+        response.status().canonical_reason().unwrap_or("")
+    )?;
+    for (name, value) in response.headers() {
+        if name == http::header::CONTENT_LENGTH
+            || name == http::header::CONNECTION
+            || name == http::header::TRANSFER_ENCODING
+        {
+            continue;
+        }
+        encoded.extend_from_slice(name.as_str().as_bytes());
+        encoded.extend_from_slice(b": ");
+        encoded.extend_from_slice(value.as_bytes());
+        encoded.extend_from_slice(b"\r\n");
+    }
+    write!(
+        encoded,
+        "Content-Length: {}\r\nConnection: close\r\n\r\n",
+        response.body().len()
+    )?;
+    encoded.extend_from_slice(response.body());
+    write_all_with_deadline(stream, &encoded, deadline)
+}
+
+fn write_all_with_deadline(
+    stream: &mut TcpStream,
+    mut bytes: &[u8],
+    deadline: Instant,
+) -> Result<(), std::io::Error> {
+    while !bytes.is_empty() {
+        let remaining = deadline
+            .checked_duration_since(Instant::now())
+            .ok_or_else(|| {
+                std::io::Error::new(std::io::ErrorKind::TimedOut, "request timed out")
+            })?;
+        stream.set_write_timeout(Some(remaining.max(Duration::from_millis(1))))?;
+        match stream.write(bytes) {
+            Ok(0) => {
+                return Err(std::io::Error::new(
+                    std::io::ErrorKind::WriteZero,
+                    "socket closed",
+                ));
+            }
+            Ok(count) => bytes = &bytes[count..],
+            Err(error) if error.kind() == std::io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+    stream.flush()
+}
+
+fn interaction(route: Route) -> ProtocolInteraction {
+    match route {
+        Route::Fetch => ProtocolInteraction::Fetch,
+        Route::FetchTree => ProtocolInteraction::FetchTree,
+        Route::FetchInterface => ProtocolInteraction::FetchInterface,
+        Route::CallOperation => ProtocolInteraction::CallOperation,
+        Route::Batch => ProtocolInteraction::Fetch,
+    }
+}
+
+fn resource_error() -> ProtocolError {
+    ProtocolError {
+        code: ProtocolErrorCode::ResourceLimitExceeded,
+        message: "configured resource limit exceeded".into(),
+    }
+}
+
+fn internal_error() -> ProtocolError {
+    ProtocolError {
+        code: ProtocolErrorCode::Internal,
+        message: "filesystem server failed".into(),
+    }
+}
+
+fn empty_response(status: StatusCode) -> Response<Vec<u8>> {
+    Response::builder()
+        .status(status)
+        .body(Vec::new())
+        .expect("static status builds an HTTP response")
+}
+
+/// Failure while validating, opening, or binding the server.
+#[derive(Debug)]
+pub enum ServerBuildError {
+    /// Configuration is unsafe or unbounded.
+    Config(ConfigError),
+    /// The root capability could not be opened.
+    Io(std::io::Error),
+    /// The listener could not be bound.
+    Listener(String),
+}
+
+impl std::fmt::Display for ServerBuildError {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Config(error) => write!(formatter, "invalid server configuration: {error}"),
+            Self::Io(error) => write!(formatter, "filesystem root could not be opened: {error}"),
+            Self::Listener(error) => write!(formatter, "HTTP listener could not be bound: {error}"),
+        }
+    }
+}
+
+impl std::error::Error for ServerBuildError {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        match self {
+            Self::Config(error) => Some(error),
+            Self::Io(error) => Some(error),
+            Self::Listener(_) => None,
+        }
+    }
+}
+
+impl From<ConfigError> for ServerBuildError {
+    fn from(value: ConfigError) -> Self {
+        Self::Config(value)
+    }
+}
+
+impl From<std::io::Error> for ServerBuildError {
+    fn from(value: std::io::Error) -> Self {
+        Self::Io(value)
+    }
+}

crates/wip-fs-server/tests/end_to_end.rs

@@ -0,0 +1,478 @@
+use std::collections::BTreeMap;
+use std::io::{Read, Write};
+use std::net::{SocketAddr, TcpStream};
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::thread;
+use std::time::{Duration, Instant};
+
+use tempfile::tempdir;
+use wip_fs_server::{AccessMode, ServerConfig, TransportSecurity, WipFsServer};
+use wip_https::{
+    BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse, BatchSuccess, DecodedResponse,
+    Endpoint, JSON_CONTENT_TYPE, Limits, Route, decode_batch_request, decode_batch_response,
+    decode_call_operation_response, decode_fetch_interface_response, decode_fetch_response,
+    decode_fetch_tree_response, encode_batch_request, encode_call_operation_request,
+    encode_fetch_interface_request, encode_fetch_request, encode_fetch_tree_request,
+};
+use wip_protocol::{
+    CallOperationRequest, FetchInterfaceRequest, FetchRequest, FetchTreeRequest, InterfaceTarget,
+    ProtocolErrorCode, Target, Value,
+};
+
+#[test]
+fn real_listener_serves_four_core_interactions_batch_and_write() {
+    let temporary = tempdir().expect("temporary root");
+    std::fs::write(temporary.path().join("hello.txt"), b"hello world").expect("write file");
+    std::fs::create_dir(temporary.path().join("nested")).expect("create directory");
+
+    let mut config = ServerConfig::for_root(temporary.path());
+    config.access = AccessMode::ReadWrite;
+    config.transport_security = TransportSecurity::DevelopmentHttp;
+    let limits = config.limits.wire;
+    let bound = Arc::new(
+        WipFsServer::new(config)
+            .expect("build server")
+            .bind()
+            .expect("bind"),
+    );
+    let address = bound.local_addr();
+    let shutdown = Arc::new(AtomicBool::new(false));
+    let worker = {
+        let bound = Arc::clone(&bound);
+        let shutdown = Arc::clone(&shutdown);
+        thread::spawn(move || bound.serve_until(shutdown))
+    };
+    let endpoint = Endpoint::parse(&format!("https://localhost:{}/wip", address.port()))
+        .expect("client endpoint");
+
+    let file_request = FetchRequest {
+        path: "/hello.txt".into(),
+    };
+    let response = exchange(
+        address,
+        encode_fetch_request(&endpoint, &file_request, limits).expect("encode fetch"),
+    );
+    let file =
+        success(decode_fetch_response(&file_request, &response, limits).expect("decode fetch"));
+    assert_eq!(file.name, "hello.txt");
+    assert_eq!(file.interfaces.len(), 2);
+    assert!(file.validator.is_some());
+
+    let tree_request = FetchTreeRequest {
+        path: "/".into(),
+        depth: 1,
+        limit: 10,
+    };
+    let response = exchange(
+        address,
+        encode_fetch_tree_request(&endpoint, &tree_request, limits).expect("encode tree"),
+    );
+    let tree =
+        success(decode_fetch_tree_response(&tree_request, &response, limits).expect("decode tree"));
+    assert!(!tree.truncated);
+    assert_eq!(tree.root.children.len(), 2);
+
+    let read_interface_request = FetchInterfaceRequest {
+        interface: file.interfaces[0].clone(),
+    };
+    let response = exchange(
+        address,
+        encode_fetch_interface_request(&endpoint, &read_interface_request, limits)
+            .expect("encode interface fetch"),
+    );
+    let read_interface = success(
+        decode_fetch_interface_response(&read_interface_request, &response, limits)
+            .expect("decode interface"),
+    );
+    assert_eq!(read_interface.descriptor.operations[0].name, "read");
+
+    let read_request = CallOperationRequest {
+        target: Target {
+            path: "/hello.txt".into(),
+            validator: file.validator.clone(),
+        },
+        interface: InterfaceTarget {
+            reference: file.interfaces[0].clone(),
+            validator: None,
+        },
+        operation: "read".into(),
+        arguments: BTreeMap::from([
+            ("offset".into(), Value::Integer(6)),
+            ("length".into(), Value::Integer(5)),
+        ]),
+    };
+    let response = exchange(
+        address,
+        encode_call_operation_request(&endpoint, &read_request, &read_interface.descriptor, limits)
+            .expect("encode read call"),
+    );
+    let read = success(
+        decode_call_operation_response(
+            &read_request,
+            &read_interface.descriptor,
+            &response,
+            limits,
+        )
+        .expect("decode read call"),
+    );
+    assert_eq!(read.result, Value::Bytes(b"world".to_vec()));
+
+    let batch_request = BatchRequest {
+        requests: vec![
+            BatchRequestItem {
+                id: "root".into(),
+                request: BatchRequestKind::Fetch(FetchRequest { path: "/".into() }),
+            },
+            BatchRequestItem {
+                id: "tree".into(),
+                request: BatchRequestKind::FetchTree(FetchTreeRequest {
+                    path: "/nested".into(),
+                    depth: 1,
+                    limit: 4,
+                }),
+            },
+            BatchRequestItem {
+                id: "interface".into(),
+                request: BatchRequestKind::FetchInterface(read_interface_request.clone()),
+            },
+        ],
+    };
+    let response = exchange(
+        address,
+        encode_batch_request(&endpoint, &batch_request, limits).expect("encode batch"),
+    );
+    let batch =
+        success(decode_batch_response(&batch_request, &response, limits).expect("decode batch"));
+    assert_batch_successes(&batch);
+
+    let write_interface_request = FetchInterfaceRequest {
+        interface: file.interfaces[1].clone(),
+    };
+    let response = exchange(
+        address,
+        encode_fetch_interface_request(&endpoint, &write_interface_request, limits)
+            .expect("encode write interface fetch"),
+    );
+    let write_interface = success(
+        decode_fetch_interface_response(&write_interface_request, &response, limits)
+            .expect("decode write interface"),
+    );
+    let write_request = CallOperationRequest {
+        target: Target {
+            path: "/hello.txt".into(),
+            validator: file.validator,
+        },
+        interface: InterfaceTarget {
+            reference: file.interfaces[1].clone(),
+            validator: None,
+        },
+        operation: "replace".into(),
+        arguments: BTreeMap::from([("contents".into(), Value::Bytes(b"updated".to_vec()))]),
+    };
+    let response = exchange(
+        address,
+        encode_call_operation_request(
+            &endpoint,
+            &write_request,
+            &write_interface.descriptor,
+            limits,
+        )
+        .expect("encode write call"),
+    );
+    let write = success(
+        decode_call_operation_response(
+            &write_request,
+            &write_interface.descriptor,
+            &response,
+            limits,
+        )
+        .expect("decode write call"),
+    );
+    assert!(write.validator.is_some());
+    assert_eq!(
+        std::fs::read(temporary.path().join("hello.txt")).expect("read updated file"),
+        b"updated"
+    );
+
+    shutdown.store(true, Ordering::Release);
+    worker
+        .join()
+        .expect("join listener")
+        .expect("listener exits cleanly");
+}
+
+#[test]
+fn stalled_request_body_times_out_and_releases_the_only_worker() {
+    let temporary = tempdir().expect("temporary root");
+    let mut config = ServerConfig::for_root(temporary.path());
+    config.transport_security = TransportSecurity::DevelopmentHttp;
+    config.limits.max_concurrent_requests = 1;
+    config.limits.request_timeout = Duration::from_millis(200);
+    let limits = config.limits.wire;
+    let bound = Arc::new(
+        WipFsServer::new(config)
+            .expect("build server")
+            .bind()
+            .expect("bind"),
+    );
+    let address = bound.local_addr();
+    let shutdown = Arc::new(AtomicBool::new(false));
+    let worker = {
+        let bound = Arc::clone(&bound);
+        let shutdown = Arc::clone(&shutdown);
+        thread::spawn(move || bound.serve_until(shutdown))
+    };
+
+    let mut stalled = TcpStream::connect(address).expect("connect stalled client");
+    stalled
+        .set_read_timeout(Some(Duration::from_secs(1)))
+        .expect("set stalled read timeout");
+    write!(
+        stalled,
+        "POST /wip/v1/fetch HTTP/1.1\r\nHost: localhost\r\nContent-Type: application/json\r\nAccept: application/json\r\nContent-Length: 100\r\n\r\n{{"
+    )
+    .expect("write partial request");
+    stalled.flush().expect("flush partial request");
+    thread::sleep(Duration::from_millis(25));
+
+    let endpoint = Endpoint::parse(&format!("https://localhost:{}/wip", address.port()))
+        .expect("client endpoint");
+    let fetch = FetchRequest { path: "/".into() };
+    let started = Instant::now();
+    let response = exchange(
+        address,
+        encode_fetch_request(&endpoint, &fetch, limits).expect("encode fetch"),
+    );
+    let _root = success(decode_fetch_response(&fetch, &response, limits).expect("decode fetch"));
+    assert!(
+        started.elapsed() < Duration::from_secs(1),
+        "the valid request remained starved after the intake deadline"
+    );
+
+    let mut byte = [0_u8; 1];
+    match stalled.read(&mut byte) {
+        Ok(0) => {}
+        Err(error)
+            if matches!(
+                error.kind(),
+                std::io::ErrorKind::ConnectionReset
+                    | std::io::ErrorKind::ConnectionAborted
+                    | std::io::ErrorKind::BrokenPipe
+            ) => {}
+        outcome => panic!("stalled connection was not closed after its deadline: {outcome:?}"),
+    }
+
+    shutdown.store(true, Ordering::Release);
+    worker
+        .join()
+        .expect("join listener")
+        .expect("listener exits cleanly");
+}
+
+#[test]
+fn batch_keeps_known_malformed_arguments_item_local() {
+    let temporary = tempdir().expect("temporary root");
+    let config = ServerConfig::for_root(temporary.path());
+    let limits = config.limits.wire;
+    let server = WipFsServer::new(config).expect("build server");
+    let endpoint = Endpoint::parse("https://localhost/wip").expect("endpoint");
+    let body = br#"{"requests":[{"id":"ok","method":"fetch","arguments":{"path":"/"}},{"id":"bad","method":"fetch_tree","arguments":{"path":"/","depth":"bad","limit":1}}]}"#;
+    let logical = decode_batch_request(body, limits).expect("decode item-local invalid request");
+    assert!(matches!(
+        logical.requests[1].request,
+        BatchRequestKind::Invalid { .. }
+    ));
+    let request = http::Request::builder()
+        .method(http::Method::POST)
+        .uri(endpoint.route(Route::Batch).as_str())
+        .header(http::header::CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(http::header::ACCEPT, "application/json")
+        .body(body.to_vec())
+        .expect("build request");
+    let response = server.handle_http(request);
+    let batch = success(
+        decode_batch_response(&logical, &response, limits).expect("decode mixed batch response"),
+    );
+    assert!(matches!(
+        batch.responses[0].outcome,
+        Ok(BatchSuccess::Fetch(_))
+    ));
+    assert!(batch.responses[1].outcome.is_err());
+}
+
+#[test]
+fn call_argument_decoding_does_not_mask_missing_target() {
+    let temporary = tempdir().expect("temporary root");
+    let config = ServerConfig::for_root(temporary.path());
+    let server = WipFsServer::new(config).expect("build server");
+    let endpoint = Endpoint::parse("https://localhost/wip").expect("endpoint");
+    let body = br#"{"target":{"path":"/missing"},"interface":{"reference":"unknown"},"operation":"missing","arguments":{"bytes":"not-base64"}}"#;
+    let request = http::Request::builder()
+        .method(http::Method::POST)
+        .uri(endpoint.route(Route::CallOperation).as_str())
+        .header(http::header::CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(http::header::ACCEPT, "application/json")
+        .body(body.to_vec())
+        .expect("build request");
+    let response = server.handle_http(request);
+    assert_eq!(response.status(), http::StatusCode::NOT_FOUND);
+    assert!(
+        std::str::from_utf8(response.body())
+            .expect("UTF-8 error")
+            .contains("\"not_found\"")
+    );
+}
+
+#[test]
+fn backend_invalid_unicode_path_is_not_found_not_internal() {
+    let temporary = tempdir().expect("temporary root");
+    let config = ServerConfig::for_root(temporary.path());
+    let limits = config.limits.wire;
+    let server = WipFsServer::new(config).expect("build server");
+    let endpoint = Endpoint::parse("https://localhost/wip").expect("endpoint");
+    let request = FetchRequest {
+        path: "/bad\0name".into(),
+    };
+    let response = server
+        .handle_http(encode_fetch_request(&endpoint, &request, limits).expect("encode fetch"));
+    assert_eq!(response.status(), http::StatusCode::NOT_FOUND);
+    match decode_fetch_response(&request, &response, limits).expect("decode missing response") {
+        DecodedResponse::ProtocolFailure { error, .. } => {
+            assert_eq!(error.code, ProtocolErrorCode::NotFound);
+        }
+        DecodedResponse::Success(_) => panic!("backend-invalid path must not resolve"),
+    }
+}
+
+#[test]
+fn read_response_size_failure_preserves_non_commit_guarantee() {
+    let temporary = tempdir().expect("temporary root");
+    std::fs::write(temporary.path().join("large"), vec![b'x'; 2_000]).expect("write file");
+    let mut config = ServerConfig::for_root(temporary.path());
+    config.limits.wire = Limits::new(4_096, 1_024, 64, 64).expect("wire limits");
+    let limits = config.limits.wire;
+    let server = WipFsServer::new(config).expect("build server");
+    let endpoint = Endpoint::parse("https://localhost/wip").expect("endpoint");
+
+    let fetch_request = FetchRequest {
+        path: "/large".into(),
+    };
+    let response = server.handle_http(
+        encode_fetch_request(&endpoint, &fetch_request, limits).expect("encode fetch"),
+    );
+    let file =
+        success(decode_fetch_response(&fetch_request, &response, limits).expect("decode fetch"));
+    let interface_request = FetchInterfaceRequest {
+        interface: file.interfaces[0].clone(),
+    };
+    let response = server.handle_http(
+        encode_fetch_interface_request(&endpoint, &interface_request, limits)
+            .expect("encode interface fetch"),
+    );
+    let interface = success(
+        decode_fetch_interface_response(&interface_request, &response, limits)
+            .expect("decode interface"),
+    );
+    let call = CallOperationRequest {
+        target: Target {
+            path: "/large".into(),
+            validator: file.validator,
+        },
+        interface: InterfaceTarget {
+            reference: file.interfaces[0].clone(),
+            validator: None,
+        },
+        operation: "read".into(),
+        arguments: BTreeMap::from([("length".into(), Value::Integer(1_500))]),
+    };
+    let response = server.handle_http(
+        encode_call_operation_request(&endpoint, &call, &interface.descriptor, limits)
+            .expect("encode read call"),
+    );
+    assert_eq!(response.status(), http::StatusCode::PAYLOAD_TOO_LARGE);
+    match decode_call_operation_response(&call, &interface.descriptor, &response, limits)
+        .expect("decode resource failure")
+    {
+        DecodedResponse::ProtocolFailure { error, .. } => {
+            assert_eq!(error.code, ProtocolErrorCode::ResourceLimitExceeded);
+        }
+        DecodedResponse::Success(_) => panic!("oversized read response must fail"),
+    }
+}
+
+fn assert_batch_successes(batch: &BatchResponse) {
+    assert_eq!(batch.responses.len(), 3);
+    assert!(matches!(
+        batch.responses[0].outcome,
+        Ok(BatchSuccess::Fetch(_))
+    ));
+    assert!(matches!(
+        batch.responses[1].outcome,
+        Ok(BatchSuccess::FetchTree(_))
+    ));
+    assert!(matches!(
+        batch.responses[2].outcome,
+        Ok(BatchSuccess::FetchInterface(_))
+    ));
+}
+
+fn success<T>(response: DecodedResponse<T>) -> T {
+    match response {
+        DecodedResponse::Success(value) => value,
+        DecodedResponse::ProtocolFailure { error, .. } => panic!("protocol failure: {error}"),
+    }
+}
+
+fn exchange(address: SocketAddr, request: http::Request<Vec<u8>>) -> http::Response<Vec<u8>> {
+    let mut stream = TcpStream::connect(address).expect("connect listener");
+    stream
+        .set_read_timeout(Some(Duration::from_secs(5)))
+        .expect("set read timeout");
+    let path = request
+        .uri()
+        .path_and_query()
+        .map_or("/", |value| value.as_str());
+    write!(
+        stream,
+        "{} {} HTTP/1.1\r\nHost: localhost\r\nConnection: close\r\n",
+        request.method(),
+        path
+    )
+    .expect("write request line");
+    for (name, value) in request.headers() {
+        write!(
+            stream,
+            "{}: {}\r\n",
+            name,
+            value.to_str().expect("ASCII request header")
+        )
+        .expect("write header");
+    }
+    write!(stream, "Content-Length: {}\r\n\r\n", request.body().len())
+        .expect("write content length");
+    stream.write_all(request.body()).expect("write body");
+    stream.flush().expect("flush request");
+
+    let mut raw = Vec::new();
+    stream.read_to_end(&mut raw).expect("read response");
+    let split = raw
+        .windows(4)
+        .position(|window| window == b"\r\n\r\n")
+        .expect("HTTP response header");
+    let head = std::str::from_utf8(&raw[..split]).expect("UTF-8 response head");
+    let mut lines = head.split("\r\n");
+    let status = lines
+        .next()
+        .and_then(|line| line.split_whitespace().nth(1))
+        .and_then(|status| status.parse::<u16>().ok())
+        .expect("response status");
+    let mut builder = http::Response::builder().status(status);
+    for line in lines {
+        let (name, value) = line.split_once(':').expect("response header");
+        builder = builder.header(name, value.trim());
+    }
+    builder
+        .body(raw[split + 4..].to_vec())
+        .expect("build response")
+}

crates/wip-host/src/lib.rs

@@ -535,11 +535,36 @@ impl<T: WipObject> PublishedObject<T> {
         context: &ExecutionContext,
         request: CallRequest,
         authorize: impl FnOnce(&T, &InterfaceRef, &str) -> bool,
+    ) -> OperationAttempt {
+        let CallRequest {
+            target,
+            interface,
+            operation,
+            arguments,
+        } = request;
+        self.dispatch_resolved_with_decoder(
+            context,
+            target,
+            interface,
+            operation,
+            |_| Ok::<_, std::convert::Infallible>(arguments),
+            authorize,
+        )
+    }
+
+    fn dispatch_resolved_with_decoder<E>(
+        &self,
+        context: &ExecutionContext,
+        target: Target,
+        interface: InterfaceTarget,
+        operation: String,
+        decode_arguments: impl FnOnce(&InterfaceDescriptor) -> Result<BTreeMap<String, Value>, E>,
+        authorize: impl FnOnce(&T, &InterfaceRef, &str) -> bool,
     ) -> 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()
+        if let Some(supplied) = target.validator.as_deref()
             && current_object_validator.map(Validator::as_bytes) != Some(supplied)
         {
             return pre_dispatch_failure(
@@ -548,9 +573,11 @@ impl<T: WipObject> PublishedObject<T> {
             );
         }
 
-        let Some(bound) = self.interfaces.iter().find(|bound| {
+        let Some(bound) = self
-            bound.artifact.reference.as_str() == request.interface.reference.as_str()
+            .interfaces
-        }) else {
+            .iter()
+            .find(|bound| bound.artifact.reference.as_str() == interface.reference.as_str())
+        else {
             return pre_dispatch_failure(
                 CallErrorKind::InterfaceMismatch,
                 "interface is not a member of the current object publication",
@@ -559,7 +586,7 @@ impl<T: WipObject> PublishedObject<T> {
 
         match (
             bound.artifact.validator.as_ref(),
-            request.interface.validator.as_deref(),
+            interface.validator.as_deref(),
         ) {
             (Some(_), None) => {
                 return pre_dispatch_failure(
@@ -581,18 +608,18 @@ impl<T: WipObject> PublishedObject<T> {
             .descriptor
             .operations
             .iter()
-            .any(|operation| operation.name == request.operation)
+            .any(|declared| declared.name == operation)
         {
             return pre_dispatch_failure(
                 CallErrorKind::OperationNotFound,
-                &format!("operation `{}` is not declared", request.operation),
+                &format!("operation `{operation}` is not declared"),
             );
         }
 
-        if request.target.validator.is_none()
+        if target.validator.is_none()
             && self
                 .implementation
-                .requires_validator(&bound.artifact.reference, &request.operation)
+                .requires_validator(&bound.artifact.reference, &operation)
         {
             return pre_dispatch_failure(
                 CallErrorKind::ValidatorRequired,
@@ -600,19 +627,24 @@ impl<T: WipObject> PublishedObject<T> {
             );
         }
 
+        let arguments = match decode_arguments(&bound.artifact.descriptor) {
+            Ok(arguments) => arguments,
+            Err(_) => {
+                return pre_dispatch_failure(
+                    CallErrorKind::InvalidArguments,
+                    "operation arguments could not be decoded",
+                );
+            }
+        };
         if let Err(error) = bound
             .artifact
             .descriptor
-            .validate_arguments(&request.operation, &request.arguments)
+            .validate_arguments(&operation, &arguments)
         {
             return pre_dispatch_failure(CallErrorKind::InvalidArguments, &error.to_string());
         }
 
-        if !authorize(
+        if !authorize(&self.implementation, &bound.artifact.reference, &operation) {
-            &self.implementation,
-            &bound.artifact.reference,
-            &request.operation,
-        ) {
             return pre_dispatch_failure(
                 CallErrorKind::PermissionDenied,
                 "operation is not permitted for this caller",
@@ -623,23 +655,22 @@ impl<T: WipObject> PublishedObject<T> {
             return OperationAttempt::NotStarted(error);
         }
 
-        let value =
+        let value = match (bound.dispatch)(&self.implementation, &operation, arguments) {
-            match (bound.dispatch)(&self.implementation, &request.operation, request.arguments) {
+            Ok(value) => value,
-                Ok(value) => value,
+            Err(
-                Err(
+                error @ (DispatchError::UnknownOperation(_)
-                    error @ (DispatchError::UnknownOperation(_)
+                | DispatchError::InvalidArguments(_)
-                    | DispatchError::InvalidArguments(_)
+                | DispatchError::Decode(_)),
-                    | DispatchError::Decode(_)),
+            ) => return OperationAttempt::NotStarted(CallError::from_pre_dispatch(error)),
-                ) => return OperationAttempt::NotStarted(CallError::from_pre_dispatch(error)),
+            Err(error) => {
-                Err(error) => {
+                return OperationAttempt::Started(Err(OperationFailure::from_dispatch(error)));
-                    return OperationAttempt::Started(Err(OperationFailure::from_dispatch(error)));
+            }
-                }
+        };
-            };
 
         if bound
             .artifact
             .descriptor
-            .validate_result(&request.operation, &value)
+            .validate_result(&operation, &value)
             .is_err()
         {
             return OperationAttempt::Started(Err(OperationFailure::internal(
@@ -922,6 +953,62 @@ pub trait ObjectProvider {
             ProviderResult::Failure(error) => Err(CallError::from_host_failure(error)),
         }
     }
+
+    /// Resolves one operation target and decodes its arguments only after all
+    /// descriptor-independent canonical preconditions have succeeded.
+    ///
+    /// Transport bindings whose value representation depends on the selected
+    /// interface descriptor should use this method instead of resolving a
+    /// descriptor before [`ObjectProvider::call_operation_with_context`]. The
+    /// callback executes inside the same exact-once provider boundary after
+    /// object/interface validators, membership, operation lookup, and required
+    /// object-validator checks. A callback error becomes `InvalidArguments` and
+    /// typed implementation code is not invoked.
+    fn call_operation_with_context_and_decoder<E>(
+        &self,
+        context: &ExecutionContext,
+        target: Target,
+        interface: InterfaceTarget,
+        operation: String,
+        decode_arguments: impl FnOnce(&InterfaceDescriptor) -> Result<BTreeMap<String, Value>, E>,
+    ) -> Result<CallResult, CallError> {
+        wip_protocol::validate_path(&target.path)
+            .map_err(|error| CallError::new(CallErrorKind::InvalidRequest, error.to_string()))?;
+        let path = target.path.clone();
+        let execution = catch_unwind(AssertUnwindSafe(|| {
+            self.execute_operation(context, &path, |publication| {
+                publication.dispatch_resolved_with_decoder(
+                    context,
+                    target,
+                    interface,
+                    operation,
+                    decode_arguments,
+                    |object, interface, operation| {
+                        self.authorize(&path, object, interface, operation)
+                    },
+                )
+            })
+        }));
+
+        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)),
+        }
+    }
 }
 
 /// Failure to construct an explicit object publication.

crates/wip-host/tests/host.rs

@@ -741,6 +741,89 @@ fn call_failures_follow_canonical_precedence_without_execution() {
     assert_eq!(provider.calls.get(), 0);
 }
 
+#[test]
+fn descriptor_guided_decoder_runs_inside_canonical_resolution_boundary() {
+    let (_, provider, hidden) = registry_and_provider();
+    let decodes = Cell::new(0_u32);
+    let decode_failure = || {
+        decodes.set(decodes.get() + 1);
+        Err::<BTreeMap<String, Value>, _>(())
+    };
+
+    let missing = provider
+        .call_operation_with_context_and_decoder(
+            &ExecutionContext::new(),
+            Target {
+                path: "/missing".into(),
+                validator: Some(b"stale".to_vec()),
+            },
+            InterfaceTarget {
+                reference: hidden.reference().as_str().into(),
+                validator: None,
+            },
+            "missing".into(),
+            |_| decode_failure(),
+        )
+        .unwrap_err();
+    assert_eq!(missing.kind(), CallErrorKind::NotFound);
+    assert_eq!(decodes.get(), 0);
+
+    let stale = provider
+        .call_operation_with_context_and_decoder(
+            &ExecutionContext::new(),
+            Target {
+                path: "/document".into(),
+                validator: Some(b"stale".to_vec()),
+            },
+            InterfaceTarget {
+                reference: hidden.reference().as_str().into(),
+                validator: None,
+            },
+            "hidden".into(),
+            |_| decode_failure(),
+        )
+        .unwrap_err();
+    assert_eq!(stale.kind(), CallErrorKind::ValidatorMismatch);
+    assert_eq!(decodes.get(), 0);
+
+    let mismatch = provider
+        .call_operation_with_context_and_decoder(
+            &ExecutionContext::new(),
+            Target {
+                path: "/document".into(),
+                validator: Some(b"object-v1".to_vec()),
+            },
+            InterfaceTarget {
+                reference: hidden.reference().as_str().into(),
+                validator: None,
+            },
+            "hidden".into(),
+            |_| decode_failure(),
+        )
+        .unwrap_err();
+    assert_eq!(mismatch.kind(), CallErrorKind::InterfaceMismatch);
+    assert_eq!(decodes.get(), 0);
+
+    let invalid_arguments = provider
+        .call_operation_with_context_and_decoder(
+            &ExecutionContext::new(),
+            Target {
+                path: "/document".into(),
+                validator: Some(b"object-v1".to_vec()),
+            },
+            InterfaceTarget {
+                reference: provider.reader.reference().as_str().into(),
+                validator: Some(b"schema-v1".to_vec()),
+            },
+            "add".into(),
+            |_| decode_failure(),
+        )
+        .unwrap_err();
+    assert_eq!(invalid_arguments.kind(), CallErrorKind::InvalidArguments);
+    assert_eq!(decodes.get(), 1);
+    assert_eq!(provider.calls.get(), 0);
+}
+
 #[test]
 fn immutable_interface_rejects_a_supplied_validator() {
     let (_, provider, _) = registry_and_provider();

crates/wip-https/src/batch.rs

@@ -1,6 +1,6 @@
 use std::collections::{BTreeMap, BTreeSet};
 
-use http::header::CONTENT_TYPE;
+use http::header::{ACCEPT, CONTENT_TYPE};
 use http::{Method, Request, Response, StatusCode};
 use serde_json::{Map, Value as Json};
 use wip_protocol::{
@@ -11,9 +11,38 @@ use wip_protocol::{
 use crate::response::{self, DecodedResponse};
 use crate::{
     BodyKind, ClientResponseError, CodecError, EncodeHttpError, Endpoint, InvalidResponseKind,
-    JSON_CONTENT_TYPE, Limits, Route, is_json_content_type, json,
+    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 {
@@ -23,6 +52,13 @@ pub enum BatchRequestKind {
     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 {
@@ -31,6 +67,7 @@ impl BatchRequestKind {
             Self::Fetch(_) => ProtocolInteraction::Fetch,
             Self::FetchTree(_) => ProtocolInteraction::FetchTree,
             Self::FetchInterface(_) => ProtocolInteraction::FetchInterface,
+            Self::Invalid { method, .. } => method.interaction(),
         }
     }
 }
@@ -96,7 +133,7 @@ fn validate_ids<'a>(ids: impl Iterator<Item = &'a str>, maximum: usize) -> Resul
     Ok(())
 }
 
-fn request_item_to_json(item: &BatchRequestItem) -> Json {
+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) => {
@@ -106,8 +143,14 @@ fn request_item_to_json(item: &BatchRequestItem) -> Json {
             "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(),
+            });
+        }
     };
-    serde_json::json!({"id": item.id, "method": method, "arguments": arguments})
+    Ok(serde_json::json!({"id": item.id, "method": method, "arguments": arguments}))
 }
 
 fn request_to_json(request: &BatchRequest, limits: Limits) -> Result<Json, CodecError> {
@@ -119,12 +162,15 @@ fn request_to_json(request: &BatchRequest, limits: Limits) -> Result<Json, Codec
         match &item.request {
             BatchRequestKind::Fetch(value) => value.validate()?,
             BatchRequestKind::FetchTree(value) => value.validate()?,
-            BatchRequestKind::FetchInterface(_) => {}
+            BatchRequestKind::FetchInterface(_) | BatchRequestKind::Invalid { .. } => {}
         }
     }
-    Ok(serde_json::json!({
+    let requests = request
-        "requests": request.requests.iter().map(request_item_to_json).collect::<Vec<_>>()
+        .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> {
@@ -141,16 +187,12 @@ fn request_from_json(value: &Json, limits: Limits) -> Result<BatchRequest, Codec
         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 = string(required(fields, "method")?, &format!("{field}.method"))?;
+        let method_name = string(required(fields, "method")?, &format!("{field}.method"))?;
         let arguments = required(fields, "arguments")?;
-        let request = match method.as_str() {
+        let method = match method_name.as_str() {
-            "fetch" => BatchRequestKind::Fetch(json::fetch_request_from_json(arguments)?),
+            "fetch" => BatchMethod::Fetch,
-            "fetch_tree" => {
+            "fetch_tree" => BatchMethod::FetchTree,
-                BatchRequestKind::FetchTree(json::fetch_tree_request_from_json(arguments)?)
+            "fetch_interface" => BatchMethod::FetchInterface,
-            }
-            "fetch_interface" => BatchRequestKind::FetchInterface(
-                json::fetch_interface_request_from_json(arguments)?,
-            ),
             _ => {
                 return Err(CodecError::InvalidField {
                     field: format!("{field}.method"),
@@ -158,6 +200,23 @@ fn request_from_json(value: &Json, limits: Limits) -> Result<BatchRequest, Codec
                 });
             }
         };
+        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(
@@ -178,6 +237,7 @@ pub fn encode_batch_request(
         .method(Method::POST)
         .uri(endpoint.route(Route::Batch).as_str())
         .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(ACCEPT, "application/json")
         .body(body)?)
 }
 
@@ -238,33 +298,29 @@ fn correlate(
                 id: item.id.clone(),
             });
         };
-        match &item.outcome {
+        match (&item.outcome, *kind) {
-            Ok(BatchSuccess::Fetch(value)) if matches!(kind, BatchRequestKind::Fetch(_)) => {
+            (Ok(BatchSuccess::Fetch(value)), BatchRequestKind::Fetch(request)) => {
-                if let BatchRequestKind::Fetch(request) = kind {
+                request.validate_response(value)?;
-                    request.validate_response(value)?;
-                }
             }
-            Ok(BatchSuccess::FetchTree(value))
+            (Ok(BatchSuccess::FetchTree(value)), BatchRequestKind::FetchTree(request)) => {
-                if matches!(kind, BatchRequestKind::FetchTree(_)) =>
+                value.validate_for(request)?;
-            {
-                if let BatchRequestKind::FetchTree(request) = kind {
-                    value.validate_for(request)?;
-                }
             }
-            Ok(BatchSuccess::FetchInterface(value))
+            (
-                if matches!(kind, BatchRequestKind::FetchInterface(_)) =>
+                Ok(BatchSuccess::FetchInterface(value)),
-            {
+                BatchRequestKind::FetchInterface(request),
-                if let BatchRequestKind::FetchInterface(request) = kind {
+            ) => {
-                    value.validate_for(request)?;
+                value.validate_for(request)?;
-                }
             }
-            Ok(_) => {
+            (
-                return Err(CodecError::BatchInteractionMismatch {
+                Err(error),
-                    id: item.id.clone(),
+                BatchRequestKind::Invalid {
-                });
+                    error: expected, ..
-            }
+                },
-            Err(error) if error.code.is_allowed_for(kind.interaction()) => {}
+            ) if error == expected => {}
-            Err(_) => {
+            (Err(error), kind)
+                if !matches!(kind, BatchRequestKind::Invalid { .. })
+                    && error.code.is_allowed_for(kind.interaction()) => {}
+            _ => {
                 return Err(CodecError::BatchInteractionMismatch {
                     id: item.id.clone(),
                 });
@@ -301,7 +357,10 @@ pub fn encode_batch_response(
 /// 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.
+/// 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,
@@ -325,6 +384,26 @@ pub fn encode_batch_error_response(
         .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,
@@ -367,8 +446,15 @@ fn response_from_json(
             }
             (None, Some(error)) => {
                 let error = response::item_error_from_json(error)?;
-                if !error.code.is_allowed_for(kind.interaction()) {
+                match kind {
-                    return Err(CodecError::BatchInteractionMismatch { id });
+                    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)
             }
@@ -388,6 +474,9 @@ fn response_from_json(
                     value.validate_for(request)?;
                     BatchSuccess::FetchInterface(value)
                 }
+                BatchRequestKind::Invalid { .. } => {
+                    return Err(CodecError::BatchInteractionMismatch { id });
+                }
             }),
         };
         responses.push(BatchResponseItem { id, outcome });

crates/wip-https/src/codec.rs

@@ -1,5 +1,8 @@
-use http::header::CONTENT_TYPE;
+use std::error::Error;
-use http::{Method, Request, Response, StatusCode};
+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,
@@ -9,7 +12,7 @@ use wip_protocol::{
 use crate::response::{self, DecodedResponse};
 use crate::{
     BodyKind, ClientResponseError, CodecError, Endpoint, InvalidResponseKind, JSON_CONTENT_TYPE,
-    Limits, Route, json,
+    Limits, ResourceLimitKind, Route, json,
 };
 
 fn request(
@@ -21,6 +24,7 @@ fn request(
         .method(Method::POST)
         .uri(endpoint.route(route).as_str())
         .header(CONTENT_TYPE, JSON_CONTENT_TYPE)
+        .header(ACCEPT, "application/json")
         .body(body)
 }
 
@@ -49,6 +53,15 @@ fn require_response_content_type<B>(response: &Response<B>) -> Result<(), Client
     }
 }
 
+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
@@ -68,13 +81,7 @@ pub fn is_json_content_type(value: &str) -> bool {
         let Some((name, value)) = parameter.trim().split_once('=') else {
             return false;
         };
-        let charset = value.trim();
+        if !name.trim().eq_ignore_ascii_case("charset") || !is_utf8_charset(value) || saw_charset {
-        let charset_is_utf8 = charset.eq_ignore_ascii_case("utf-8")
-            || charset
-                .strip_prefix('"')
-                .and_then(|value| value.strip_suffix('"'))
-                .is_some_and(|value| value.eq_ignore_ascii_case("utf-8"));
-        if !name.trim().eq_ignore_ascii_case("charset") || !charset_is_utf8 || saw_charset {
             return false;
         }
         saw_charset = true;
@@ -82,27 +89,166 @@ pub fn is_json_content_type(value: &str) -> bool {
     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<(), CodecError> {
+) -> Result<(), RequestMetadataError> {
     if value.method() != Method::POST {
-        return Err(CodecError::InvalidField {
+        return Err(RequestMetadataError::InvalidRequest(
-            field: "method".into(),
+            CodecError::InvalidField {
-            reason: "standard WIP routes require POST".into(),
+                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(CodecError::InvalidField {
+        return Err(RequestMetadataError::InvalidRequest(
-            field: "route".into(),
+            CodecError::InvalidField {
-            reason: "request URI does not match the selected standard route".into(),
+                field: "route".into(),
-        });
+                reason: "request URI does not match the selected standard route".into(),
+            },
+        ));
     }
     let valid_content_type = value
         .headers()
@@ -110,10 +256,10 @@ pub fn validate_http_request<B>(
         .and_then(|value| value.to_str().ok())
         .is_some_and(is_json_content_type);
     if !valid_content_type {
-        return Err(CodecError::InvalidField {
+        return Err(RequestMetadataError::UnsupportedMediaType);
-            field: "content-type".into(),
+    }
-            reason: "expected UTF-8 application/json".into(),
+    if !accepts_json(value.headers()) {
-        });
+        return Err(RequestMetadataError::NotAcceptable);
     }
     Ok(())
 }
@@ -405,17 +551,10 @@ pub fn decode_call_operation_response<B: AsRef<[u8]>>(
     )
 }
 
-/// Encodes a canonical Host error envelope using its standard HTTP status.
+fn validate_protocol_error(
-///
-/// 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.
-pub fn encode_protocol_error_response(
     interaction: ProtocolInteraction,
     error: &ProtocolError,
-    limits: Limits,
+) -> Result<(), CodecError> {
-) -> Result<Response<Vec<u8>>, EncodeHttpError> {
     if !error.code.is_allowed_for(interaction) {
         return Err(CodecError::InvalidField {
             field: "error.code".into(),
@@ -423,11 +562,63 @@ pub fn encode_protocol_error_response(
                 "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());
     }
-    let body = json::serialize(&response::error_to_json(error), BodyKind::Response, limits)?;
+    encode_protocol_error_with_status(
-    Ok(response(response::status_for_error(error.code), body)?)
+        interaction,
+        error,
+        response::status_for_resource_limit(kind),
+        limits,
+    )
 }
 
 /// Failure while building an outbound framework-neutral HTTP message.

crates/wip-https/src/error.rs

@@ -102,6 +102,15 @@ pub enum BodyKind {
     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 {
@@ -177,6 +186,20 @@ pub enum CodecError {
     },
 }
 
+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 {

crates/wip-https/src/lib.rs

@@ -36,25 +36,27 @@ mod json;
 mod response;
 
 pub use batch::{
-    BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse, BatchResponseItem,
+    BatchMethod, BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse,
-    BatchSuccess, decode_batch_request, decode_batch_response, encode_batch_error_response,
+    BatchResponseItem, BatchSuccess, decode_batch_request, decode_batch_response,
-    encode_batch_request, encode_batch_response,
+    encode_batch_error_response, encode_batch_request, encode_batch_resource_limit_error_response,
+    encode_batch_response,
 };
 pub use codec::{
-    CallOperationMetadata, EncodeHttpError, decode_call_operation_metadata,
+    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,
-    is_json_content_type, validate_http_request,
+    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};
+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.

crates/wip-https/src/response.rs

@@ -5,7 +5,7 @@ use http::StatusCode;
 use serde_json::{Map, Value as Json};
 use wip_protocol::{ProtocolError, ProtocolErrorCode, ProtocolInteraction};
 
-use crate::{BodyKind, CodecError, Limits, json};
+use crate::{BodyKind, CodecError, Limits, ResourceLimitKind, json};
 
 /// A successfully classified client response.
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -59,6 +59,8 @@ pub enum InvalidResponseKind {
     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.
@@ -117,6 +119,10 @@ impl Display for ClientResponseError {
 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 {
@@ -132,13 +138,31 @@ pub const fn status_for_error(code: ProtocolErrorCode) -> StatusCode {
             StatusCode::PRECONDITION_FAILED
         }
         ProtocolErrorCode::PermissionDenied => StatusCode::FORBIDDEN,
-        ProtocolErrorCode::ResourceLimitExceeded => StatusCode::TOO_MANY_REQUESTS,
+        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 {
@@ -288,12 +312,14 @@ pub(crate) fn decode<T>(
                 ));
             }
             let expected = status_for_error(error.code);
-            Ok(DecodedResponse::ProtocolFailure {
+            let status_mismatch =
-                error,
+                (!status_matches_error(status, error.code)).then_some(StatusMismatch {
-                status_mismatch: (status != expected).then_some(StatusMismatch {
                     actual: status,
                     expected,
-                }),
+                });
+            Ok(DecodedResponse::ProtocolFailure {
+                error,
+                status_mismatch,
             })
         }
         Err(_) if !status.is_success() => Err(transport_failure(status)),
@@ -301,16 +327,24 @@ pub(crate) fn decode<T>(
             InvalidResponseKind::InvalidSuccessBody,
             error.to_string(),
         )),
-        Ok(None) if status.is_success() => {
+        Ok(None) if status == StatusCode::OK => success(&value)
-            success(&value)
+            .map(DecodedResponse::Success)
-                .map(DecodedResponse::Success)
+            .map_err(|error| {
-                .map_err(|error| {
+                ClientResponseError::invalid(
-                    ClientResponseError::invalid(
+                    InvalidResponseKind::InvalidSuccessBody,
-                        InvalidResponseKind::InvalidSuccessBody,
+                    error.to_string(),
-                        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,

crates/wip-https/tests/batch.rs

@@ -4,9 +4,10 @@ use wip_https::wip_protocol::{
     InterfaceDescriptor, Object, ProtocolError, ProtocolErrorCode,
 };
 use wip_https::{
-    BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse, BatchResponseItem,
+    BatchMethod, BatchRequest, BatchRequestItem, BatchRequestKind, BatchResponse,
-    BatchSuccess, ClientResponseError, DecodedResponse, Endpoint, InvalidResponseKind, Limits,
+    BatchResponseItem, BatchSuccess, ClientResponseError, DecodedResponse, Endpoint,
-    decode_batch_request, decode_batch_response, encode_batch_error_response, encode_batch_request,
+    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,
 };
 
@@ -39,6 +40,7 @@ fn batch_round_trips_by_unique_id_with_item_failures_and_validators() {
     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
@@ -115,8 +117,65 @@ fn batch_interface_validator_round_trips_in_item_body() {
     );
 }
 
+#[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"}},
@@ -136,6 +195,67 @@ fn invalid_batch_envelopes_are_rejected_at_top_level() {
     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 {

crates/wip-https/tests/codecs.rs

@@ -9,11 +9,12 @@ use wip_https::wip_protocol::{
     TypeDeclaration, TypeExpr, UnionCase, Value,
 };
 use wip_https::{
-    ClientResponseError, DecodedResponse, Endpoint, InvalidResponseKind, Limits,
+    ClientResponseError, CodecError, DecodedResponse, Endpoint, InvalidResponseKind, Limits,
-    decode_call_operation_metadata, decode_call_operation_request, decode_call_operation_response,
+    ResourceLimitKind, decode_call_operation_metadata, decode_call_operation_request,
-    decode_fetch_interface_request, decode_fetch_interface_response, decode_fetch_request,
+    decode_call_operation_response, decode_fetch_interface_request,
-    decode_fetch_response, decode_fetch_tree_request, decode_fetch_tree_response,
+    decode_fetch_interface_response, decode_fetch_request, decode_fetch_response,
-    encode_call_operation_request, encode_call_operation_response, encode_fetch_interface_request,
+    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,
 };
@@ -193,6 +194,36 @@ fn call_request() -> CallOperationRequest {
     }
 }
 
+#[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 {
@@ -362,11 +393,21 @@ fn malformed_unknown_null_and_noncanonical_base64_are_rejected() {
 #[test]
 fn caller_limits_bound_bytes_and_nesting() {
     let tiny = Limits::new(8, 8, 2, 1).unwrap();
-    assert!(decode_fetch_request(br#"{"path":"/long"}"#, tiny).is_err());
+    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();
-    assert!(decode_fetch_request(nested, nesting_limited).is_err());
+    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!(

crates/wip-https/tests/responses.rs

@@ -3,9 +3,10 @@ use wip_https::wip_protocol::{
     FetchRequest, ProtocolError, ProtocolErrorCode, ProtocolInteraction,
 };
 use wip_https::{
-    ClientResponseError, DecodedResponse, InvalidResponseKind, Limits, TransportFailureKind,
+    ClientResponseError, DecodedResponse, InvalidResponseKind, Limits, ResourceLimitKind,
-    decode_fetch_response, encode_protocol_error_response, error_code_name, is_json_content_type,
+    TransportFailureKind, decode_fetch_response, encode_protocol_error_response,
-    status_for_error,
+    encode_resource_limit_error_response, error_code_name, is_json_content_type, status_for_error,
+    status_for_resource_limit,
 };
 
 fn limits() -> Limits {
@@ -95,7 +96,7 @@ fn every_protocol_code_has_stable_name_and_status() {
         (
             ProtocolErrorCode::ResourceLimitExceeded,
             "resource_limit_exceeded",
-            StatusCode::TOO_MANY_REQUESTS,
+            StatusCode::UNPROCESSABLE_ENTITY,
         ),
         (
             ProtocolErrorCode::Internal,
@@ -115,6 +116,73 @@ fn every_protocol_code_has_stable_name_and_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 {

crates/wip-https/tests/routes.rs

@@ -1,5 +1,5 @@
-use wip_https::http::{Method, Request};
+use wip_https::http::{Method, Request, StatusCode};
-use wip_https::{Endpoint, Route, validate_http_request};
+use wip_https::{Endpoint, RequestMetadataError, Route, validate_http_request};
 
 #[test]
 fn endpoint_is_https_absolute_queryless_and_canonical() {
@@ -72,6 +72,50 @@ fn inbound_http_metadata_enforces_post_route_and_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]