fix: align protocol model with canonical WIP

Cargo.lock

@@ -238,6 +238,15 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "23b97319f7b8343df12cc98938e5c3eb436064524c8d2b4e30a1d3a36eecdf81"
 
+[[package]]
+name = "wip-host"
+version = "0.1.0"
+dependencies = [
+ "trybuild",
+ "wip-interface",
+ "wip-protocol",
+]
+
 [[package]]
 name = "wip-interface"
 version = "0.1.0"

Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     ".",
+    "crates/wip-host",
     "crates/wip-interface",
     "crates/wip-interface-macros",
     "crates/wip-protocol",

README.md

@@ -65,3 +65,35 @@ The supported interface slice is deliberately non-generic: public traits,
 `&self`, named parameters, and `OperationResult<T>`. Generic traits or methods,
 associated items, custom lifetimes, inheritance, default method bodies, and
 other receiver forms are rejected at their source spans.
+
+## Host publication and dispatch
+
+Applications use `wip-host` to register generated definitions and explicitly
+choose the ordered interface set for each object publication:
+
+```rust,ignore
+let mut interfaces = wip_host::InterfaceRegistry::new();
+let messenger = interfaces.register(MessengerDefinition, None)?;
+
+let published = wip_host::PublishedObject::new(request_scoped_object)
+    .expose(&messenger)?;
+let protocol_object = published.protocol_object();
+```
+
+`expose` compiles only when the object implements the generated definition's
+interface trait. Implementing a trait does not expose it automatically, empty
+interface sets are valid, insertion order is preserved, and duplicate
+references are rejected. Registry references are opaque; descriptor names and
+Rust type names are not used as wire identity.
+
+Dispatch is qualified by interface reference and operation name. The host checks
+current object identity and validator policy, current interface membership,
+interface validator, descriptor operation, arguments, and result while retaining
+the selected object and registered artifact. Host-private fields and backend
+handles are never projected by `WipObject`.
+
+Providers remain responsible for backend atomicity. Enter a transaction, lock,
+stable-handle scope, or conditional-update primitive before constructing and
+dispatching the request-scoped `PublishedObject`, and retain it until dispatch
+returns. The runtime never validates one object and then resolves a second
+snapshot, but it cannot make an arbitrary external backend atomic by itself.

crates/wip-host/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "wip-host"
+version = "0.1.0"
+edition = "2024"
+description = "Host-side object publication and operation dispatch for WIP"
+license = "MIT OR Apache-2.0"
+
+[dependencies]
+wip-interface = { path = "../wip-interface" }
+wip-protocol = { path = "../wip-protocol" }
+
+[dev-dependencies]
+trybuild = "1"

crates/wip-host/src/lib.rs

@@ -0,0 +1,630 @@
+//! Host-side publication and operation dispatch for Web Interface Protocol objects.
+//!
+//! # Responsibility boundaries
+//!
+//! [`InterfaceRegistry::register`] validates and freezes a generated interface
+//! descriptor, assigns an opaque [`InterfaceRef`], and makes the same descriptor
+//! observation available to clients and dispatch. [`PublishedObject::expose`]
+//! explicitly combines a request-scoped Rust object with a registered interface;
+//! its [`InterfaceImplementation`] bound proves at compile time that the object
+//! implements that interface. Implementing a Rust trait alone never publishes it,
+//! and a publication with no interfaces is valid.
+//!
+//! [`PublishedObject::dispatch`] selects by `(InterfaceRef, operation name)`,
+//! checks object and interface validators, current membership, the frozen
+//! descriptor, and then invokes the matching generated typed dispatcher on the
+//! same object instance. Arguments and results cross the protocol [`Value`]
+//! boundary only through generated validation and codecs. Rust fields that are
+//! not returned by [`WipObject`] are host-private and are never serialized by
+//! this crate.
+//!
+//! The call method is deliberately an execution boundary rather than a global
+//! object registry: a provider may resolve and publish an object per request and
+//! drop it afterward. The provider must enter any backend-specific transaction,
+//! lock, stable-handle scope, or conditional-update primitive *before* creating
+//! or dispatching the publication and retain it until dispatch returns. This
+//! crate keeps validator checks, descriptor and implementation selection, and
+//! invocation in one borrow of that publication; it does not claim that an
+//! arbitrary backend stays stable, and it never reopens a path or resolves a
+//! second implementation snapshot after validation.
+
+#![deny(missing_docs)]
+
+use std::any::TypeId;
+use std::collections::{HashMap, HashSet};
+use std::error::Error;
+use std::fmt::{self, Display, Formatter};
+use std::marker::PhantomData;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicU64, Ordering};
+
+use wip_interface::DispatchError;
+pub use wip_interface::{InterfaceDefinition, InterfaceImplementation};
+pub use wip_protocol;
+use wip_protocol::{
+    InterfaceDescriptor, NamedValue, Object, ObjectId, OperationCall, OperationTarget,
+    ProtocolError, ProtocolErrorCategory, ValidationError, Value,
+};
+
+/// Opaque bytes used as a conditional execution precondition.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct Validator(Vec<u8>);
+
+impl Validator {
+    /// Creates a validator without assigning meaning to its bytes.
+    #[must_use]
+    pub fn new(bytes: impl Into<Vec<u8>>) -> Self {
+        Self(bytes.into())
+    }
+
+    /// Returns the opaque bytes for transport encoding or comparison.
+    #[must_use]
+    pub fn as_bytes(&self) -> &[u8] {
+        &self.0
+    }
+}
+
+/// Opaque host-assigned reference to one registered interface artifact.
+#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct InterfaceRef(String);
+
+impl InterfaceRef {
+    /// Returns the opaque reference for a protocol transport.
+    #[must_use]
+    pub fn as_str(&self) -> &str {
+        &self.0
+    }
+}
+
+/// An immutable observation returned for an opaque interface reference.
+#[derive(Debug, Clone, PartialEq)]
+pub struct InterfaceObservation {
+    /// Opaque reference selected by published objects and operation calls.
+    pub reference: InterfaceRef,
+    /// Optional validator. Its presence makes it a required call precondition.
+    pub validator: Option<Validator>,
+    /// Validated descriptor frozen when the interface was registered.
+    pub descriptor: InterfaceDescriptor,
+}
+
+#[derive(Debug)]
+struct InterfaceArtifact {
+    reference: InterfaceRef,
+    validator: Option<Validator>,
+    descriptor: InterfaceDescriptor,
+}
+
+/// A typed registration token for a generated interface definition.
+///
+/// Tokens can be reused by any number of request-scoped objects. They expose an
+/// opaque reference, not the Rust type name or an address.
+pub struct RegisteredInterface<D> {
+    artifact: Arc<InterfaceArtifact>,
+    definition: PhantomData<fn() -> D>,
+}
+
+impl<D> Clone for RegisteredInterface<D> {
+    fn clone(&self) -> Self {
+        Self {
+            artifact: Arc::clone(&self.artifact),
+            definition: PhantomData,
+        }
+    }
+}
+
+impl<D> RegisteredInterface<D> {
+    /// Returns the opaque protocol reference assigned by the registry.
+    #[must_use]
+    pub fn reference(&self) -> &InterfaceRef {
+        &self.artifact.reference
+    }
+}
+
+/// Registry of validated, immutable interface artifacts.
+///
+/// This registry stores interface definitions, not object instances. Generated
+/// definitions are registered explicitly and receive process-local opaque
+/// references. A validator-free artifact is immutable for the lifetime of its
+/// reference; a validator-bearing artifact requires that exact validator on a
+/// call. Re-registering a definition is rejected instead of silently changing
+/// the descriptor associated with an existing reference.
+#[derive(Debug)]
+pub struct InterfaceRegistry {
+    namespace: u64,
+    next_reference: u64,
+    definitions: HashSet<TypeId>,
+    artifacts: HashMap<InterfaceRef, Arc<InterfaceArtifact>>,
+}
+
+static NEXT_REGISTRY_NAMESPACE: AtomicU64 = AtomicU64::new(1);
+
+impl Default for InterfaceRegistry {
+    fn default() -> Self {
+        Self {
+            namespace: NEXT_REGISTRY_NAMESPACE.fetch_add(1, Ordering::Relaxed),
+            next_reference: 0,
+            definitions: HashSet::new(),
+            artifacts: HashMap::new(),
+        }
+    }
+}
+
+impl InterfaceRegistry {
+    /// Creates an empty interface registry.
+    #[must_use]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Registers and freezes one generated interface definition.
+    ///
+    /// `validator` should be present when the host intends the reference to
+    /// represent a versioned descriptor. Its presence makes the same value a
+    /// mandatory precondition for dispatch. Registration finalizes the
+    /// descriptor's protocol `name` to the assigned opaque reference so it
+    /// corresponds directly to [`Object::interfaces`].
+    pub fn register<D>(
+        &mut self,
+        _definition: D,
+        validator: Option<Validator>,
+    ) -> Result<RegisteredInterface<D>, RegistrationError>
+    where
+        D: InterfaceDefinition + 'static,
+    {
+        let definition = TypeId::of::<D>();
+        if self.definitions.contains(&definition) {
+            return Err(RegistrationError::AlreadyRegistered);
+        }
+
+        let mut descriptor = D::descriptor();
+        descriptor
+            .validate()
+            .map_err(RegistrationError::InvalidDescriptor)?;
+
+        let reference = InterfaceRef(format!(
+            "wip-interface:{}:{}",
+            self.namespace, self.next_reference
+        ));
+        // The protocol model currently carries the interface identifier in the
+        // descriptor's `name` field. Finalize that identity to the same opaque
+        // reference placed on published objects; the generated Rust trait name
+        // is registration-local metadata, not wire identity.
+        descriptor.name = reference.0.clone();
+        self.next_reference = self
+            .next_reference
+            .checked_add(1)
+            .ok_or(RegistrationError::ReferenceSpaceExhausted)?;
+        let artifact = Arc::new(InterfaceArtifact {
+            reference: reference.clone(),
+            validator,
+            descriptor,
+        });
+        self.definitions.insert(definition);
+        self.artifacts.insert(reference, Arc::clone(&artifact));
+
+        Ok(RegisteredInterface {
+            artifact,
+            definition: PhantomData,
+        })
+    }
+
+    /// Observes the descriptor and optional validator for an opaque reference.
+    #[must_use]
+    pub fn observe(&self, reference: &InterfaceRef) -> Option<InterfaceObservation> {
+        self.artifacts
+            .get(reference)
+            .map(|artifact| InterfaceObservation {
+                reference: artifact.reference.clone(),
+                validator: artifact.validator.clone(),
+                descriptor: artifact.descriptor.clone(),
+            })
+    }
+}
+
+/// Failure while registering a generated interface definition.
+#[derive(Debug)]
+pub enum RegistrationError {
+    /// The same generated definition was already assigned a reference.
+    AlreadyRegistered,
+    /// The generated descriptor is structurally invalid.
+    InvalidDescriptor(ValidationError),
+    /// The registry cannot assign another opaque reference.
+    ReferenceSpaceExhausted,
+}
+
+impl Display for RegistrationError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::AlreadyRegistered => {
+                formatter.write_str("interface definition already registered")
+            }
+            Self::InvalidDescriptor(error) => {
+                write!(formatter, "invalid interface descriptor: {error}")
+            }
+            Self::ReferenceSpaceExhausted => {
+                formatter.write_str("interface reference space exhausted")
+            }
+        }
+    }
+}
+
+impl Error for RegistrationError {
+    fn source(&self) -> Option<&(dyn Error + 'static)> {
+        match self {
+            Self::InvalidDescriptor(error) => Some(error),
+            Self::AlreadyRegistered | Self::ReferenceSpaceExhausted => None,
+        }
+    }
+}
+
+/// Public metadata and conditional-execution policy for a host-private object.
+///
+/// Only values returned by this trait are projected into protocol metadata.
+/// Backend handles, filesystem paths, credentials, and other private fields on
+/// the implementing type are neither inspected nor serialized.
+pub trait WipObject {
+    /// Returns the current logical identity of this object.
+    fn id(&self) -> ObjectId;
+
+    /// Returns the current opaque object validator, if any.
+    fn validator(&self) -> Option<&Validator> {
+        None
+    }
+
+    /// Whether a call must include the current object validator.
+    fn requires_validator(&self) -> bool {
+        false
+    }
+}
+
+type DispatchFn<T> = fn(&T, &str, Vec<NamedValue>) -> Result<Option<Value>, DispatchError>;
+
+struct BoundInterface<T> {
+    artifact: Arc<InterfaceArtifact>,
+    dispatch: DispatchFn<T>,
+}
+
+/// A host-private object instance combined with an explicit ordered interface set.
+///
+/// The instance is owned by this value and can therefore be request-scoped. No
+/// global or pre-populated object registry is required.
+pub struct PublishedObject<T: WipObject> {
+    implementation: T,
+    interfaces: Vec<BoundInterface<T>>,
+}
+
+impl<T: WipObject> PublishedObject<T> {
+    /// Starts a publication with no exposed interfaces.
+    #[must_use]
+    pub fn new(implementation: T) -> Self {
+        Self {
+            implementation,
+            interfaces: Vec::new(),
+        }
+    }
+
+    /// Explicitly exposes a registered generated interface in insertion order.
+    ///
+    /// The `InterfaceImplementation<T>` bound is generated only when `T`
+    /// implements the corresponding Rust interface trait. Duplicate opaque
+    /// references are rejected.
+    pub fn expose<D>(mut self, interface: &RegisteredInterface<D>) -> Result<Self, PublicationError>
+    where
+        D: InterfaceImplementation<T>,
+    {
+        if self
+            .interfaces
+            .iter()
+            .any(|bound| bound.artifact.reference == interface.artifact.reference)
+        {
+            return Err(PublicationError::DuplicateInterface(
+                interface.artifact.reference.clone(),
+            ));
+        }
+
+        self.interfaces.push(BoundInterface {
+            artifact: Arc::clone(&interface.artifact),
+            dispatch: D::dispatch,
+        });
+        Ok(self)
+    }
+
+    /// Returns the host-private implementation without projecting its fields.
+    #[must_use]
+    pub fn implementation(&self) -> &T {
+        &self.implementation
+    }
+
+    /// Builds the protocol object metadata with interface insertion order intact.
+    #[must_use]
+    pub fn protocol_object(&self) -> Object {
+        let object = Object {
+            id: self.implementation.id(),
+            interfaces: self
+                .interfaces
+                .iter()
+                .map(|bound| bound.artifact.reference.0.clone())
+                .collect(),
+        };
+        debug_assert!(object.validate().is_ok());
+        object
+    }
+
+    /// Dispatches one qualified operation against this current publication.
+    ///
+    /// Preconditions are checked before generated operation code runs. The
+    /// selected artifact and function pointer are borrowed once and are not
+    /// resolved again after validator checks.
+    pub fn dispatch(&self, request: CallRequest) -> Result<CallResult, CallError> {
+        if request.object != self.implementation.id() {
+            return Err(CallError::new(
+                CallErrorKind::ObjectNotFound,
+                "call target does not identify this published object",
+            ));
+        }
+
+        let current_object_validator = self.implementation.validator();
+        match request.object_validator.as_ref() {
+            Some(supplied) if Some(supplied) != current_object_validator => {
+                return Err(CallError::new(
+                    CallErrorKind::ValidatorMismatch,
+                    "object validator does not match current object state",
+                ));
+            }
+            None if self.implementation.requires_validator() => {
+                return Err(CallError::new(
+                    CallErrorKind::ValidatorRequired,
+                    "this object requires a validator",
+                ));
+            }
+            _ => {}
+        }
+
+        let Some(bound) = self
+            .interfaces
+            .iter()
+            .find(|bound| bound.artifact.reference == request.interface.reference)
+        else {
+            return Err(CallError::new(
+                CallErrorKind::InterfaceMismatch,
+                "interface is not a member of the current object publication",
+            ));
+        };
+
+        match (
+            bound.artifact.validator.as_ref(),
+            request.interface.validator.as_ref(),
+        ) {
+            (Some(_), None) => {
+                return Err(CallError::new(
+                    CallErrorKind::InterfaceValidatorRequired,
+                    "registered interface requires a validator",
+                ));
+            }
+            (expected, Some(actual)) if expected != Some(actual) => {
+                return Err(CallError::new(
+                    CallErrorKind::InterfaceValidatorMismatch,
+                    "interface validator does not match the registered descriptor",
+                ));
+            }
+            _ => {}
+        }
+
+        if !bound
+            .artifact
+            .descriptor
+            .operations
+            .iter()
+            .any(|operation| operation.name == request.operation)
+        {
+            return Err(CallError::new(
+                CallErrorKind::OperationNotFound,
+                format!("operation `{}` is not declared", request.operation),
+            ));
+        }
+
+        bound
+            .artifact
+            .descriptor
+            .validate_call(&OperationCall {
+                target: OperationTarget {
+                    object: request.object.clone(),
+                    interface: bound.artifact.descriptor.name.clone(),
+                    operation: request.operation.clone(),
+                },
+                arguments: request.arguments.clone(),
+            })
+            .map_err(|error| CallError::new(CallErrorKind::InvalidArguments, error.to_string()))?;
+
+        let value = (bound.dispatch)(&self.implementation, &request.operation, request.arguments)
+            .map_err(CallError::from_dispatch)?;
+
+        bound
+            .artifact
+            .descriptor
+            .validate_return(&request.operation, value.as_ref())
+            .map_err(|error| CallError::new(CallErrorKind::InvalidResult, error.to_string()))?;
+
+        Ok(CallResult {
+            value,
+            validator: self.implementation.validator().cloned(),
+        })
+    }
+
+    /// Consumes the publication and returns its host-private implementation.
+    #[must_use]
+    pub fn into_inner(self) -> T {
+        self.implementation
+    }
+}
+
+/// Failure to construct an explicit object publication.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum PublicationError {
+    /// The same opaque interface reference was exposed more than once.
+    DuplicateInterface(InterfaceRef),
+}
+
+impl Display for PublicationError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::DuplicateInterface(reference) => write!(
+                formatter,
+                "interface `{}` is already exposed by this object",
+                reference.as_str()
+            ),
+        }
+    }
+}
+
+impl Error for PublicationError {}
+
+/// Interface portion of a qualified operation target.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct InterfaceTarget {
+    /// Opaque reference selected from the current object's interface set.
+    pub reference: InterfaceRef,
+    /// Validator copied from the descriptor observation, when one was present.
+    pub validator: Option<Validator>,
+}
+
+/// One transport-independent request to a published object operation.
+#[derive(Debug, Clone, PartialEq)]
+pub struct CallRequest {
+    /// Current logical object identity.
+    pub object: ObjectId,
+    /// Optional current object-state precondition.
+    pub object_validator: Option<Validator>,
+    /// Qualified interface reference and descriptor precondition.
+    pub interface: InterfaceTarget,
+    /// Operation name within the selected interface descriptor.
+    pub operation: String,
+    /// Named protocol arguments.
+    pub arguments: Vec<NamedValue>,
+}
+
+/// Successful host dispatch result.
+#[derive(Debug, Clone, PartialEq)]
+pub struct CallResult {
+    /// Encoded application value, or `None` for a no-return operation.
+    pub value: Option<Value>,
+    /// Object validator observed after the implementation returned.
+    pub validator: Option<Validator>,
+}
+
+/// Stable host dispatch failure kind.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CallErrorKind {
+    /// The call names a different or unavailable object.
+    ObjectNotFound,
+    /// The selected interface is not exposed by the current object.
+    InterfaceMismatch,
+    /// The operation is absent from the selected descriptor.
+    OperationNotFound,
+    /// Supplied named values do not satisfy the operation declaration.
+    InvalidArguments,
+    /// The encoded implementation result violates its declaration.
+    InvalidResult,
+    /// This object requires a validator and the call omitted it.
+    ValidatorRequired,
+    /// The supplied object validator is stale or belongs to another object.
+    ValidatorMismatch,
+    /// The selected mutable interface requires its observed validator.
+    InterfaceValidatorRequired,
+    /// The supplied interface validator does not identify the current descriptor.
+    InterfaceValidatorMismatch,
+    /// The typed implementation reported a host/backend failure.
+    Implementation,
+}
+
+/// A dispatch failure with a stable kind and non-normative diagnostic.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct CallError {
+    kind: CallErrorKind,
+    message: String,
+}
+
+impl CallError {
+    fn new(kind: CallErrorKind, message: impl Into<String>) -> Self {
+        Self {
+            kind,
+            message: message.into(),
+        }
+    }
+
+    fn from_dispatch(error: DispatchError) -> Self {
+        match error {
+            DispatchError::UnknownOperation(operation) => Self::new(
+                CallErrorKind::OperationNotFound,
+                format!("operation `{operation}` is not declared"),
+            ),
+            DispatchError::InvalidArguments(error) => {
+                Self::new(CallErrorKind::InvalidArguments, error.to_string())
+            }
+            DispatchError::Decode(error) => {
+                Self::new(CallErrorKind::InvalidArguments, error.to_string())
+            }
+            DispatchError::Host(error) => {
+                Self::new(CallErrorKind::Implementation, error.to_string())
+            }
+            DispatchError::Encode(error) => {
+                Self::new(CallErrorKind::InvalidResult, error.to_string())
+            }
+            DispatchError::InvalidResult(error) => {
+                Self::new(CallErrorKind::InvalidResult, error.to_string())
+            }
+        }
+    }
+
+    /// Returns the stable failure kind.
+    #[must_use]
+    pub fn kind(&self) -> CallErrorKind {
+        self.kind
+    }
+
+    /// Returns the human-readable diagnostic.
+    #[must_use]
+    pub fn message(&self) -> &str {
+        &self.message
+    }
+
+    /// Maps this host failure to the existing protocol error taxonomy.
+    ///
+    /// Validator details remain available through [`CallError::kind`], while
+    /// the current protocol model represents conditional-request failures as
+    /// `InvalidRequest`. Result/codec and implementation failures are internal,
+    /// because exposing malformed host output as an application failure would
+    /// be unsafe.
+    #[must_use]
+    pub fn protocol_error(&self) -> ProtocolError {
+        let category = match self.kind {
+            CallErrorKind::ObjectNotFound => ProtocolErrorCategory::ObjectNotFound,
+            CallErrorKind::InterfaceMismatch => ProtocolErrorCategory::InterfaceNotFound,
+            CallErrorKind::OperationNotFound => ProtocolErrorCategory::OperationNotFound,
+            CallErrorKind::InvalidArguments => ProtocolErrorCategory::InvalidArguments,
+            CallErrorKind::ValidatorRequired
+            | CallErrorKind::ValidatorMismatch
+            | CallErrorKind::InterfaceValidatorRequired
+            | CallErrorKind::InterfaceValidatorMismatch => ProtocolErrorCategory::InvalidRequest,
+            CallErrorKind::InvalidResult | CallErrorKind::Implementation => {
+                ProtocolErrorCategory::Internal
+            }
+        };
+        ProtocolError {
+            category,
+            message: self.message.clone(),
+        }
+    }
+}
+
+impl Display for CallError {
+    fn fmt(&self, formatter: &mut Formatter<'_>) -> fmt::Result {
+        write!(
+            formatter,
+            "host dispatch failed ({:?}): {}",
+            self.kind, self.message
+        )
+    }
+}
+
+impl Error for CallError {}

crates/wip-host/tests/compile_fail.rs

@@ -0,0 +1,5 @@
+#[test]
+fn rejects_exposing_an_unimplemented_interface() {
+    let tests = trybuild::TestCases::new();
+    tests.compile_fail("tests/ui/unimplemented_interface.rs");
+}

crates/wip-host/tests/host.rs

@@ -0,0 +1,497 @@
+use std::cell::{Cell, RefCell};
+
+use wip_host::{
+    CallErrorKind, CallRequest, InterfaceRegistry, InterfaceTarget, PublishedObject, Validator,
+    WipObject,
+};
+use wip_interface::{
+    CodecError, HostError, NamedValue, OperationResult, TypeDeclaration, TypeExpr, Value, WipType,
+    interface,
+};
+use wip_protocol::{ObjectId, ProtocolErrorCategory};
+
+#[interface]
+pub trait Reader {
+    /// Returns the reader-qualified label.
+    fn label(&self) -> OperationResult<String>;
+
+    /// Adds two integers.
+    fn add(&self, left: i64, right: i64) -> OperationResult<i64>;
+}
+
+#[interface]
+pub trait Writer {
+    /// Returns the writer-qualified label.
+    fn label(&self) -> OperationResult<String>;
+}
+
+#[interface]
+pub trait Hidden {
+    /// Returns a hidden value.
+    fn hidden(&self) -> OperationResult<String>;
+}
+
+#[interface]
+pub trait Broken {
+    /// Returns a deliberately invalid encoded value.
+    fn broken(&self) -> OperationResult<BadValue>;
+}
+
+#[derive(Debug)]
+pub struct BadValue;
+
+impl WipType for BadValue {
+    fn type_expr() -> TypeExpr {
+        TypeExpr::Integer
+    }
+
+    fn collect_declarations(_: &mut Vec<TypeDeclaration>) {}
+
+    fn encode(self) -> Result<Value, CodecError> {
+        Ok(Value::String("not an integer".into()))
+    }
+
+    fn decode(_: Value) -> Result<Self, CodecError> {
+        Ok(Self)
+    }
+}
+
+struct Document {
+    id: String,
+    validator: Option<Validator>,
+    require_validator: bool,
+    calls: Cell<usize>,
+    private_backend_handle: RefCell<String>,
+}
+
+impl Document {
+    fn new(id: &str) -> Self {
+        Self {
+            id: id.into(),
+            validator: None,
+            require_validator: false,
+            calls: Cell::new(0),
+            private_backend_handle: RefCell::new("/private/backend/path".into()),
+        }
+    }
+
+    fn strict(id: &str, validator: &[u8]) -> Self {
+        Self {
+            id: id.into(),
+            validator: Some(Validator::new(validator)),
+            require_validator: true,
+            calls: Cell::new(0),
+            private_backend_handle: RefCell::new("secret-handle".into()),
+        }
+    }
+
+    fn record_call(&self) {
+        self.calls.set(self.calls.get() + 1);
+    }
+}
+
+impl WipObject for Document {
+    fn id(&self) -> ObjectId {
+        ObjectId(self.id.clone())
+    }
+
+    fn validator(&self) -> Option<&Validator> {
+        self.validator.as_ref()
+    }
+
+    fn requires_validator(&self) -> bool {
+        self.require_validator
+    }
+}
+
+impl Reader for Document {
+    fn label(&self) -> OperationResult<String> {
+        self.record_call();
+        Ok("reader".into())
+    }
+
+    fn add(&self, left: i64, right: i64) -> OperationResult<i64> {
+        self.record_call();
+        Ok(left + right)
+    }
+}
+
+impl Writer for Document {
+    fn label(&self) -> OperationResult<String> {
+        self.record_call();
+        Ok("writer".into())
+    }
+}
+
+impl Hidden for Document {
+    fn hidden(&self) -> OperationResult<String> {
+        self.record_call();
+        Ok("hidden".into())
+    }
+}
+
+impl Broken for Document {
+    fn broken(&self) -> OperationResult<BadValue> {
+        self.record_call();
+        Ok(BadValue)
+    }
+}
+
+fn request(
+    object: &str,
+    object_validator: Option<&[u8]>,
+    reference: &wip_host::InterfaceRef,
+    interface_validator: Option<&[u8]>,
+    operation: &str,
+    arguments: Vec<NamedValue>,
+) -> CallRequest {
+    CallRequest {
+        object: ObjectId(object.into()),
+        object_validator: object_validator.map(Validator::new),
+        interface: InterfaceTarget {
+            reference: reference.clone(),
+            validator: interface_validator.map(Validator::new),
+        },
+        operation: operation.into(),
+        arguments,
+    }
+}
+
+#[test]
+fn registry_exposes_opaque_validated_descriptor_observations() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+
+    assert_ne!(reader.reference().as_str(), "Reader");
+    let observation = registry.observe(reader.reference()).unwrap();
+    assert_eq!(observation.reference, *reader.reference());
+    assert_eq!(observation.descriptor.name, reader.reference().as_str());
+    assert_eq!(observation.validator, None);
+    observation.descriptor.validate().unwrap();
+
+    assert!(registry.register(ReaderDefinition, None).is_err());
+
+    let mut other_registry = InterfaceRegistry::new();
+    let other_reader = other_registry.register(ReaderDefinition, None).unwrap();
+    assert_ne!(reader.reference(), other_reader.reference());
+}
+
+#[test]
+fn publication_is_explicit_ordered_qualified_and_request_scoped() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+    let writer = registry.register(WriterDefinition, None).unwrap();
+    let _hidden = registry.register(HiddenDefinition, None).unwrap();
+
+    let publication = PublishedObject::new(Document::new("document-1"))
+        .expose(&writer)
+        .unwrap()
+        .expose(&reader)
+        .unwrap();
+
+    let object = publication.protocol_object();
+    assert_eq!(
+        object.interfaces,
+        vec![
+            writer.reference().as_str().to_owned(),
+            reader.reference().as_str().to_owned()
+        ]
+    );
+    wip_protocol::InterfaceObservation {
+        object: object.clone(),
+        descriptors: vec![
+            registry.observe(writer.reference()).unwrap().descriptor,
+            registry.observe(reader.reference()).unwrap().descriptor,
+        ],
+    }
+    .validate()
+    .unwrap();
+    assert!(!format!("{object:?}").contains("private/backend/path"));
+
+    let writer_result = publication
+        .dispatch(request(
+            "document-1",
+            None,
+            writer.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap();
+    let reader_result = publication
+        .dispatch(request(
+            "document-1",
+            None,
+            reader.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap();
+    assert_eq!(writer_result.value, Some(Value::String("writer".into())));
+    assert_eq!(reader_result.value, Some(Value::String("reader".into())));
+    assert_eq!(publication.implementation().calls.get(), 2);
+    assert_eq!(
+        publication
+            .implementation()
+            .private_backend_handle
+            .borrow()
+            .as_str(),
+        "/private/backend/path"
+    );
+}
+
+#[test]
+fn implemented_but_unexposed_interface_is_not_a_member() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+    let hidden = registry.register(HiddenDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::new("document-2"))
+        .expose(&reader)
+        .unwrap();
+
+    let error = publication
+        .dispatch(request(
+            "document-2",
+            None,
+            hidden.reference(),
+            None,
+            "hidden",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(error.kind(), CallErrorKind::InterfaceMismatch);
+    assert_eq!(
+        error.protocol_error().category,
+        ProtocolErrorCategory::InterfaceNotFound
+    );
+    assert_eq!(publication.implementation().calls.get(), 0);
+}
+
+#[test]
+fn zero_interface_objects_are_valid() {
+    let publication = PublishedObject::new(Document::new("empty"));
+    let object = publication.protocol_object();
+    assert_eq!(object.id, ObjectId("empty".into()));
+    assert!(object.interfaces.is_empty());
+    object.validate().unwrap();
+}
+
+#[test]
+fn duplicate_exposure_is_rejected_without_reordering() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::new("duplicate"))
+        .expose(&reader)
+        .unwrap();
+    let error = match publication.expose(&reader) {
+        Ok(_) => panic!("duplicate exposure unexpectedly succeeded"),
+        Err(error) => error,
+    };
+    assert!(error.to_string().contains(reader.reference().as_str()));
+}
+
+#[test]
+fn operation_and_argument_failures_are_mapped_without_execution() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::new("validation"))
+        .expose(&reader)
+        .unwrap();
+
+    let missing = publication
+        .dispatch(request(
+            "validation",
+            None,
+            reader.reference(),
+            None,
+            "missing",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(missing.kind(), CallErrorKind::OperationNotFound);
+    assert_eq!(
+        missing.protocol_error().category,
+        ProtocolErrorCategory::OperationNotFound
+    );
+
+    let invalid = publication
+        .dispatch(request(
+            "validation",
+            None,
+            reader.reference(),
+            None,
+            "add",
+            vec![NamedValue {
+                name: "left".into(),
+                value: Value::String("wrong".into()),
+            }],
+        ))
+        .unwrap_err();
+    assert_eq!(invalid.kind(), CallErrorKind::InvalidArguments);
+    assert_eq!(
+        invalid.protocol_error().category,
+        ProtocolErrorCategory::InvalidArguments
+    );
+    assert_eq!(publication.implementation().calls.get(), 0);
+}
+
+#[test]
+fn invalid_implementation_result_is_internal_and_not_returned() {
+    let mut registry = InterfaceRegistry::new();
+    let broken = registry.register(BrokenDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::new("broken"))
+        .expose(&broken)
+        .unwrap();
+
+    let error = publication
+        .dispatch(request(
+            "broken",
+            None,
+            broken.reference(),
+            None,
+            "broken",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(error.kind(), CallErrorKind::InvalidResult);
+    assert_eq!(
+        error.protocol_error().category,
+        ProtocolErrorCategory::Internal
+    );
+    assert_eq!(publication.implementation().calls.get(), 1);
+}
+
+#[test]
+fn object_validator_missing_and_mismatch_are_distinct_and_prevent_execution() {
+    let mut registry = InterfaceRegistry::new();
+    let reader = registry.register(ReaderDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::strict("strict", b"object-v1"))
+        .expose(&reader)
+        .unwrap();
+
+    let missing = publication
+        .dispatch(request(
+            "strict",
+            None,
+            reader.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(missing.kind(), CallErrorKind::ValidatorRequired);
+
+    let mismatch = publication
+        .dispatch(request(
+            "strict",
+            Some(b"stale"),
+            reader.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(mismatch.kind(), CallErrorKind::ValidatorMismatch);
+    assert_eq!(publication.implementation().calls.get(), 0);
+
+    let result = publication
+        .dispatch(request(
+            "strict",
+            Some(b"object-v1"),
+            reader.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap();
+    assert_eq!(result.validator, Some(Validator::new(b"object-v1")));
+    assert_eq!(publication.implementation().calls.get(), 1);
+}
+
+#[test]
+fn interface_validator_missing_and_mismatch_are_distinct_and_prevent_execution() {
+    let mut registry = InterfaceRegistry::new();
+    let writer = registry
+        .register(WriterDefinition, Some(Validator::new(b"schema-v1")))
+        .unwrap();
+    let publication = PublishedObject::new(Document::new("mutable-interface"))
+        .expose(&writer)
+        .unwrap();
+
+    let observation = registry.observe(writer.reference()).unwrap();
+    assert_eq!(observation.validator, Some(Validator::new(b"schema-v1")));
+
+    let missing = publication
+        .dispatch(request(
+            "mutable-interface",
+            None,
+            writer.reference(),
+            None,
+            "label",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(missing.kind(), CallErrorKind::InterfaceValidatorRequired);
+
+    let mismatch = publication
+        .dispatch(request(
+            "mutable-interface",
+            None,
+            writer.reference(),
+            Some(b"schema-v0"),
+            "label",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(mismatch.kind(), CallErrorKind::InterfaceValidatorMismatch);
+    assert_eq!(publication.implementation().calls.get(), 0);
+
+    let result = publication
+        .dispatch(request(
+            "mutable-interface",
+            None,
+            writer.reference(),
+            Some(b"schema-v1"),
+            "label",
+            vec![],
+        ))
+        .unwrap();
+    assert_eq!(result.value, Some(Value::String("writer".into())));
+}
+
+#[test]
+fn host_failures_map_to_internal_without_becoming_domain_values() {
+    #[interface]
+    pub trait Failing {
+        /// Always fails in the host implementation.
+        fn fail(&self) -> OperationResult<String>;
+    }
+
+    impl Failing for Document {
+        fn fail(&self) -> OperationResult<String> {
+            Err(HostError::new("backend unavailable"))
+        }
+    }
+
+    let mut registry = InterfaceRegistry::new();
+    let failing = registry.register(FailingDefinition, None).unwrap();
+    let publication = PublishedObject::new(Document::new("failure"))
+        .expose(&failing)
+        .unwrap();
+    let error = publication
+        .dispatch(request(
+            "failure",
+            None,
+            failing.reference(),
+            None,
+            "fail",
+            vec![],
+        ))
+        .unwrap_err();
+    assert_eq!(error.kind(), CallErrorKind::Implementation);
+    assert_eq!(
+        error.protocol_error().category,
+        ProtocolErrorCategory::Internal
+    );
+}

crates/wip-host/tests/ui/unimplemented_interface.rs

@@ -0,0 +1,22 @@
+use wip_host::{InterfaceRegistry, PublishedObject, WipObject};
+use wip_interface::{OperationResult, interface};
+use wip_protocol::ObjectId;
+
+#[interface]
+pub trait Search {
+    fn search(&self) -> OperationResult<String>;
+}
+
+struct Object;
+
+impl WipObject for Object {
+    fn id(&self) -> ObjectId {
+        ObjectId("object".into())
+    }
+}
+
+fn main() {
+    let mut registry = InterfaceRegistry::new();
+    let search = registry.register(SearchDefinition, None).unwrap();
+    let _published = PublishedObject::new(Object).expose(&search).unwrap();
+}

crates/wip-host/tests/ui/unimplemented_interface.stderr

@@ -0,0 +1,34 @@
+error[E0277]: the trait bound `Object: Search` is not satisfied
+  --> tests/ui/unimplemented_interface.rs:21:58
+   |
+21 |     let _published = PublishedObject::new(Object).expose(&search).unwrap();
+   |                                                   ------ ^^^^^^^ unsatisfied trait bound
+   |                                                   |
+   |                                                   required by a bound introduced by this call
+   |
+help: the trait `Search` is not implemented for `Object`
+  --> tests/ui/unimplemented_interface.rs:10:1
+   |
+10 | struct Object;
+   | ^^^^^^^^^^^^^
+help: this trait has no implementations, consider adding one
+  --> tests/ui/unimplemented_interface.rs:6:1
+   |
+ 6 | pub trait Search {
+   | ^^^^^^^^^^^^^^^^
+note: required for `SearchDefinition` to implement `InterfaceImplementation<Object>`
+  --> tests/ui/unimplemented_interface.rs:5:1
+   |
+ 5 | #[interface]
+   | ^^^^^^^^^^^^
+ 6 | pub trait Search {
+   |           ^^^^^^
+note: required by a bound in `PublishedObject::<T>::expose`
+  --> src/lib.rs
+   |
+   |     pub fn expose<D>(mut self, interface: &RegisteredInterface<D>) -> Result<Self, PublicationError>
+   |            ------ required by a bound in this associated function
+   |     where
+   |         D: InterfaceImplementation<T>,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `PublishedObject::<T>::expose`
+   = note: this error originates in the attribute macro `interface` (in Nightly builds, run with -Z macro-backtrace for more info)

crates/wip-interface-macros/src/lib.rs

@@ -170,14 +170,8 @@ fn expand_interface(attribute: TokenStream2, item: ItemTrait) -> syn::Result<Tok
             }
         }
 
-        impl #definition_ident {
-            /// Builds the interface descriptor generated from the trait declaration.
-            pub fn descriptor() -> ::wip_interface::wip_protocol::InterfaceDescriptor {
-                <Self as ::wip_interface::InterfaceDefinition>::descriptor()
-            }
-
-            /// Dispatches one validated logical operation call to a typed implementation.
-            pub fn dispatch<T: #trait_ident>(
+        impl<T: #trait_ident> ::wip_interface::InterfaceImplementation<T> for #definition_ident {
+            fn dispatch(
                 implementation: &T,
                 operation: &str,
                 arguments: ::std::vec::Vec<::wip_interface::wip_protocol::NamedValue>,
@@ -197,6 +191,29 @@ fn expand_interface(attribute: TokenStream2, item: ItemTrait) -> syn::Result<Tok
             }
         }
 
+        impl #definition_ident {
+            /// Builds the interface descriptor generated from the trait declaration.
+            pub fn descriptor() -> ::wip_interface::wip_protocol::InterfaceDescriptor {
+                <Self as ::wip_interface::InterfaceDefinition>::descriptor()
+            }
+
+            /// Dispatches one validated logical operation call to a typed implementation.
+            pub fn dispatch<T: #trait_ident>(
+                implementation: &T,
+                operation: &str,
+                arguments: ::std::vec::Vec<::wip_interface::wip_protocol::NamedValue>,
+            ) -> ::std::result::Result<
+                ::std::option::Option<::wip_interface::wip_protocol::Value>,
+                ::wip_interface::DispatchError,
+            > {
+                <Self as ::wip_interface::InterfaceImplementation<T>>::dispatch(
+                    implementation,
+                    operation,
+                    arguments,
+                )
+            }
+        }
+
         #(#argument_items)*
     })
 }

crates/wip-interface/src/lib.rs

@@ -92,6 +92,21 @@ pub trait InterfaceDefinition {
     fn descriptor() -> InterfaceDescriptor;
 }
 
+/// Typed dispatch implemented by every generated interface companion.
+///
+/// `T` must implement the Rust interface trait associated with this definition.
+/// Host runtimes use this bound when an interface is explicitly exposed, so an
+/// object that does not implement that interface is rejected at compile time.
+pub trait InterfaceImplementation<T>: InterfaceDefinition {
+    /// Validates, decodes, and dispatches one operation to `implementation`,
+    /// then encodes and validates its result.
+    fn dispatch(
+        implementation: &T,
+        operation: &str,
+        arguments: Vec<NamedValue>,
+    ) -> Result<Option<Value>, DispatchError>;
+}
+
 /// Result convention required for generated interface operations.
 ///
 /// `Ok(T)` is an application result, including domain-failure union cases.

crates/wip-protocol/src/error.rs

@@ -8,79 +8,65 @@ pub enum NameNamespace {
     TypeDeclaration,
     /// Operations in an interface descriptor.
     Operation,
-    /// Fields in a record declaration.
+    /// Fields in an inline or named record type.
     Field,
     /// Parameters in an operation declaration.
     Parameter,
-    /// Variants in an enum declaration.
-    EnumVariant,
-    /// Variants in a union declaration.
-    UnionVariant,
-    /// Fields supplied in a record value.
-    RecordValueField,
-    /// Arguments supplied in an operation call.
-    Argument,
-    /// Members in a logical JSON object.
-    JsonMember,
-    /// Descriptors in an interface observation.
-    InterfaceDescriptor,
+    /// Cases in an enum type.
+    EnumCase,
+    /// Cases in a union type.
+    UnionCase,
+    /// Child object names beneath one tree node.
+    ChildObject,
 }
 
-/// Structural kind of a logical protocol value.
+/// Structural kind of a schema-neutral logical value.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum ValueKind {
-    /// String value.
-    String,
+    /// Unit value.
+    Unit,
     /// Boolean value.
     Boolean,
     /// Integer value.
     Integer,
     /// Floating-point number value.
     Number,
+    /// String value.
+    String,
     /// Byte sequence.
     Bytes,
-    /// List value.
-    List,
-    /// Key/value entry.
-    Entry,
     /// Record value.
     Record,
-    /// Enum value.
-    Enum,
-    /// Tagged-union value.
-    Union,
-    /// Logical JSON value.
-    Json,
+    /// List value.
+    List,
 }
 
 /// A typed segment identifying a declaration or value location.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum PathSegment {
-    /// Interface descriptor.
-    Interface(String),
+    /// Descriptor root.
+    Descriptor,
     /// Named type declaration.
     Declaration(String),
     /// Operation declaration or call.
     Operation(String),
     /// Record field declaration or value.
     Field(String),
-    /// Operation parameter declaration or argument.
+    /// Operation parameter or argument.
     Parameter(String),
-    /// Enum or union variant.
-    Variant(String),
-    /// List or JSON array index.
+    /// Enum or union case.
+    Case(String),
+    /// List index.
     Index(usize),
-    /// Entry key.
-    EntryKey,
-    /// Entry value.
-    EntryValue,
     /// Operation return value.
     Return,
-    /// JSON object member.
-    JsonMember(String),
+    /// Object at a Worldspace path.
+    Object(String),
+    /// Child object in a tree response.
+    Child(String),
 }
 
-/// Machine-readable reason why protocol validation failed.
+/// Machine-readable reason why logical protocol validation failed.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ValidationErrorKind {
     /// A name occurred more than once in one namespace.
@@ -117,11 +103,15 @@ pub enum ValidationErrorKind {
         /// Missing field name.
         name: String,
     },
-    /// An enum or union value selected an undeclared variant.
-    UnknownVariant {
-        /// Unknown variant name.
+    /// An enum or union selected an undeclared case.
+    UnknownCase {
+        /// Unknown case name.
         name: String,
     },
+    /// A payload-bearing union case omitted `value`.
+    MissingUnionPayload,
+    /// A payload-free union case supplied `value`.
+    UnexpectedUnionPayload,
     /// An operation call contains an undeclared argument.
     UnknownParameter {
         /// Unknown parameter name.
@@ -132,44 +122,66 @@ pub enum ValidationErrorKind {
         /// Missing parameter name.
         name: String,
     },
-    /// An integer is outside the JavaScript-lossless range.
+    /// An operation is not declared by the descriptor.
+    UnknownOperation {
+        /// Unknown operation name.
+        name: String,
+    },
+    /// An integer is outside the interoperable safe range.
     IntegerOutOfRange {
         /// Rejected integer.
         value: i64,
     },
     /// A numeric value is NaN or infinite.
     NonFiniteNumber,
+    /// A JSON-interpreted value tree contains protocol bytes.
+    BytesInJson,
+    /// An object name is not a valid root or non-root path segment.
+    InvalidObjectName {
+        /// Rejected object name.
+        name: String,
+    },
     /// An object's ordered interface set contains a duplicate.
     DuplicateInterface {
-        /// Duplicate interface name.
-        name: String,
+        /// Duplicate opaque interface reference.
+        reference: String,
     },
-    /// An observation omits a descriptor named by its object.
-    MissingInterfaceDescriptor {
-        /// Missing interface name.
-        name: String,
+    /// A string is not a canonical absolute Worldspace path.
+    InvalidPath {
+        /// Rejected path.
+        path: String,
     },
-    /// An observation contains a descriptor not named by its object.
-    UnexpectedInterfaceDescriptor {
-        /// Unexpected interface name.
-        name: String,
-    },
-    /// A call targets an interface other than the descriptor being used.
-    InterfaceMismatch {
-        /// Descriptor interface name.
+    /// An object name does not match the path where it was observed.
+    ObjectNameMismatch {
+        /// Name required by the observation path.
         expected: String,
-        /// Call target interface name.
+        /// Name supplied by the object.
         actual: String,
     },
-    /// An operation is not declared by the interface.
-    UnknownOperation {
-        /// Unknown operation name.
-        name: String,
+    /// Equivalent ref/validator observations disagree on object representation.
+    InconsistentObjectObservation {
+        /// Shared opaque object reference.
+        reference: String,
+    },
+    /// A `fetch_tree` request used a zero limit.
+    ZeroTreeLimit,
+    /// A tree response exceeds the requested maximum depth.
+    TreeDepthExceeded {
+        /// Requested maximum depth.
+        maximum: u32,
+    },
+    /// A tree response exceeds the requested maximum node count.
+    TreeLimitExceeded {
+        /// Requested maximum node count.
+        limit: u32,
+    },
+    /// A response refers to a different interface than its request.
+    InterfaceResponseMismatch {
+        /// Requested opaque reference.
+        expected: String,
+        /// Returned opaque reference.
+        actual: String,
     },
-    /// A no-return operation produced a value.
-    UnexpectedReturnValue,
-    /// An operation with a return declaration produced no value.
-    MissingReturnValue,
 }
 
 /// A validation failure with a typed path to the failing location.
@@ -211,30 +223,44 @@ impl Display for ValidationError {
 
 impl Error for ValidationError {}
 
-/// Stable category of an error returned by a protocol host runtime.
+/// Stable protocol failure code returned by a host or produced by a client.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum ProtocolErrorCategory {
+pub enum ProtocolErrorCode {
     /// The request is structurally invalid.
     InvalidRequest,
     /// The target object is not published.
-    ObjectNotFound,
-    /// The target interface is not implemented by the object.
+    NotFound,
+    /// The interface reference is not currently published.
     InterfaceNotFound,
-    /// The target operation is not declared by the interface.
+    /// The selected interface is not on the current object.
+    InterfaceMismatch,
+    /// The selected operation is not declared by the current interface.
     OperationNotFound,
     /// Supplied operation arguments are invalid.
     InvalidArguments,
-    /// The implementation rejected the call for a domain reason.
-    OperationFailed,
+    /// A host result does not satisfy the declaration.
+    InvalidResult,
+    /// The operation requires an object validator and none was supplied.
+    ValidatorRequired,
+    /// The supplied object validator does not match current state.
+    ValidatorMismatch,
+    /// A mutable interface requires its validator and none was supplied.
+    InterfaceValidatorRequired,
+    /// The supplied interface validator does not match the descriptor.
+    InterfaceValidatorMismatch,
+    /// A published operation is not permitted for the caller.
+    PermissionDenied,
+    /// A bounded protocol resource limit was exceeded.
+    ResourceLimitExceeded,
     /// The host encountered an internal failure.
     Internal,
 }
 
-/// Transport-independent protocol failure returned by a host runtime.
+/// Transport-independent protocol failure.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ProtocolError {
-    /// Stable programmatic category.
-    pub category: ProtocolErrorCategory,
-    /// Human-readable diagnostic. Consumers must not branch on this text.
+    /// Stable programmatic code. Consumers must branch on this field.
+    pub code: ProtocolErrorCode,
+    /// Bounded human-readable diagnostic. Consumers must not branch on it.
     pub message: String,
 }

crates/wip-protocol/src/lib.rs

@@ -1,9 +1,32 @@
-//! Transport-independent logical types for the Web Interface Protocol (WIP).
+//! Canonical transport-independent logical types for the Web Interface Protocol.
 //!
-//! This crate deliberately models interface declarations, published objects,
-//! operation calls, and operation results without assigning them HTTP routes,
-//! methods, headers, or JSON envelopes. A transport can encode these values,
-//! but the encoding is outside this crate's contract.
+//! This crate follows the Core Model and `3-protocol.md` without assigning HTTP
+//! routes, methods, headers, URL encodings, or JSON envelopes. The correspondence
+//! between canonical logical concepts and this crate is direct:
+//!
+//! | Canonical protocol concept | Rust API |
+//! | --- | --- |
+//! | Object projection and ordered interface set | [`Object`] |
+//! | Optional object identity / state precondition | `Object::ref` / [`Object::validator`] |
+//! | Interface Descriptor | [`InterfaceDescriptor`] |
+//! | Named declaration and all schema expressions | [`TypeDeclaration`] / [`TypeExpr`] |
+//! | Schema-neutral primitive/composite value | [`Value`] |
+//! | `fetch` | [`FetchRequest`] / [`FetchResponse`] |
+//! | `fetch_tree` | [`FetchTreeRequest`] / [`FetchTreeResponse`] |
+//! | `fetch_interface` | [`FetchInterfaceRequest`] / [`FetchInterfaceResponse`] |
+//! | Object and interface call preconditions | [`Target`] / [`InterfaceTarget`] |
+//! | `call_operation` | [`CallOperationRequest`] / [`CallOperationResponse`] |
+//! | Stable failure taxonomy | [`ProtocolErrorCode`] / [`ProtocolError`] |
+//!
+//! Paths, object refs, interface refs, and validators remain separate concepts.
+//! They are represented by ordinary protocol strings/bytes in the corresponding
+//! fields. In particular, object refs are optional, operation targeting uses a
+//! path, and this crate defines no interaction that fetches an object by ref.
+//!
+//! [`Value`] contains only the canonical raw value kinds. A descriptor interprets
+//! enum values as strings, entries as canonical-path strings, and unions as
+//! records with a `$case` string plus an optional `value` payload. JSON uses the
+//! same value tree (`Unit` is JSON null) and rejects bytes.
 
 #![deny(missing_docs)]
 
@@ -12,19 +35,33 @@ mod model;
 mod validation;
 
 pub use error::{
-    NameNamespace, PathSegment, ProtocolError, ProtocolErrorCategory, ValidationError,
+    NameNamespace, PathSegment, ProtocolError, ProtocolErrorCode, ValidationError,
     ValidationErrorKind, ValueKind,
 };
 pub use model::{
-    Documentation, EnumDeclaration, EnumVariantDeclaration, FieldDeclaration, InterfaceDescriptor,
-    InterfaceObservation, JsonMember, JsonValue, NamedValue, Object, ObjectId, OperationCall,
-    OperationDeclaration, OperationOutcome, OperationResult, OperationTarget, ParameterDeclaration,
-    RecordDeclaration, ReturnDeclaration, TypeDeclaration, TypeExpr, UnionDeclaration,
-    UnionVariantDeclaration, Value,
+    CallOperationRequest, CallOperationResponse, Documentation, EnumCase, FetchInterfaceRequest,
+    FetchInterfaceResponse, FetchRequest, FetchResponse, FetchTreeRequest, FetchTreeResponse,
+    FieldDeclaration, InterfaceDescriptor, InterfaceTarget, Object, ObjectTreeNode,
+    OperationDeclaration, ParameterDeclaration, ProtocolResult, ReturnDeclaration, Target,
+    TypeDeclaration, TypeExpr, UnionCase, Value,
 };
 
-/// Largest integer that is exactly interoperable with a JavaScript `Number`.
+/// Validates a canonical absolute Worldspace path.
+pub fn validate_path(path: &str) -> Result<(), ValidationError> {
+    validation::validate_path(path)
+}
+
+/// Canonical format identifier for the first Interface Descriptor format.
+pub const INTERFACE_FORMAT_V1: &str = "wip-interface/1";
+
+/// Discriminator field used by a union's raw record value.
+pub const UNION_CASE_FIELD: &str = "$case";
+
+/// Optional payload field used by a union's raw record value.
+pub const UNION_VALUE_FIELD: &str = "value";
+
+/// Largest integer exactly interoperable with a JavaScript `Number`.
 pub const MAX_SAFE_INTEGER: i64 = 9_007_199_254_740_991;
 
-/// Smallest integer that is exactly interoperable with a JavaScript `Number`.
+/// Smallest integer exactly interoperable with a JavaScript `Number`.
 pub const MIN_SAFE_INTEGER: i64 = -MAX_SAFE_INTEGER;

crates/wip-protocol/src/model.rs

@@ -1,6 +1,8 @@
+use std::collections::BTreeMap;
+
 use crate::{ProtocolError, ValidationError};
 
-/// Human-readable documentation attached to a protocol declaration.
+/// Human-readable plain-text documentation attached to a protocol declaration.
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub struct Documentation {
     /// A short, self-contained description.
@@ -9,242 +11,194 @@ pub struct Documentation {
     pub details: Option<String>,
 }
 
-/// Stable logical identity of a published object.
-#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct ObjectId(pub String);
-
-/// A published object and the ordered set of interfaces it implements.
+/// The protocol projection currently published at one Worldspace path.
 ///
-/// The vector order is significant. Call [`Object::validate`] before
-/// publication to reject duplicate interface names.
+/// `name` is a path segment, `interfaces` is an ordered set of opaque interface
+/// references, `r#ref` is optional object identity, and `validator` is an
+/// independent optional observation precondition. In particular, neither the
+/// path nor `r#ref` is a mandatory object identifier.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct Object {
-    /// Logical object identity.
-    pub id: ObjectId,
-    /// Interface names in publication order.
+    /// Path-segment name. The root object's name is empty.
+    pub name: String,
+    /// Short public description of the object.
+    pub description: Option<String>,
+    /// Opaque interface references in host publication order.
     pub interfaces: Vec<String>,
-}
-
-/// A complete logical observation of an object and its interface descriptors.
-#[derive(Debug, Clone, PartialEq)]
-pub struct InterfaceObservation {
-    /// Observed object.
-    pub object: Object,
-    /// Descriptors corresponding to `object.interfaces`.
-    pub descriptors: Vec<InterfaceDescriptor>,
+    /// Optional opaque identity within one client-facing Worldspace.
+    pub r#ref: Option<String>,
+    /// Optional opaque validator for the object's observed state.
+    pub validator: Option<Vec<u8>>,
 }
 
 /// Transport-independent description of one interface.
-#[derive(Debug, Clone, PartialEq)]
+///
+/// Interface identity is supplied by interaction fields such as
+/// [`FetchInterfaceResponse::interface`], not embedded in the descriptor.
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct InterfaceDescriptor {
-    /// Interface name.
-    pub name: String,
+    /// Descriptor format version understood by clients and hosts.
+    pub format: String,
     /// Optional interface documentation.
     pub documentation: Option<Documentation>,
-    /// Named type declarations local to this descriptor.
-    pub declarations: Vec<TypeDeclaration>,
+    /// Named declarations local to this descriptor.
+    pub types: Vec<TypeDeclaration>,
     /// Operations exposed by this interface.
     pub operations: Vec<OperationDeclaration>,
 }
 
-/// A named type declaration local to an interface descriptor.
-#[derive(Debug, Clone, PartialEq)]
-pub enum TypeDeclaration {
-    /// A record declaration.
-    Record(RecordDeclaration),
-    /// An enumeration declaration.
-    Enum(EnumDeclaration),
-    /// A tagged union declaration.
-    Union(UnionDeclaration),
-}
-
-impl TypeDeclaration {
-    /// Returns the descriptor-local declaration name.
-    #[must_use]
-    pub fn name(&self) -> &str {
-        match self {
-            Self::Record(declaration) => &declaration.name,
-            Self::Enum(declaration) => &declaration.name,
-            Self::Union(declaration) => &declaration.name,
-        }
-    }
-}
-
-/// Declaration of a record with named fields.
-#[derive(Debug, Clone, PartialEq)]
-pub struct RecordDeclaration {
+/// A descriptor-local named type declaration.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TypeDeclaration {
     /// Descriptor-local type name.
     pub name: String,
-    /// Optional record documentation.
+    /// Optional type documentation.
     pub documentation: Option<Documentation>,
-    /// Fields in declaration order.
-    pub fields: Vec<FieldDeclaration>,
+    /// Definition associated with `name`.
+    pub definition: TypeExpr,
+}
+
+/// A type expression used by declarations, fields, parameters, and returns.
+///
+/// [`TypeExpr::Named`] references are resolved only within the containing
+/// descriptor. Recursive references, including recursion through lists,
+/// records, and unions, are invalid.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum TypeExpr {
+    /// A value carrying no data.
+    Unit,
+    /// A boolean.
+    Boolean,
+    /// A JavaScript-lossless signed integer.
+    Integer,
+    /// A finite IEEE-754 binary64 number.
+    Number,
+    /// A Unicode string.
+    String,
+    /// An opaque byte sequence.
+    Bytes,
+    /// A schema-opaque JSON-compatible value tree.
+    Json,
+    /// A canonical absolute Worldspace path represented by a string value.
+    Entry,
+    /// A descriptor-local named declaration.
+    Named {
+        /// Referenced declaration name.
+        name: String,
+    },
+    /// A record with named fields.
+    Record {
+        /// Fields in declaration order.
+        fields: Vec<FieldDeclaration>,
+    },
+    /// An ordered list.
+    List {
+        /// Type of every list item.
+        items: Box<TypeExpr>,
+    },
+    /// A closed set of payload-free cases represented by strings.
+    Enum {
+        /// Cases in declaration order.
+        cases: Vec<EnumCase>,
+    },
+    /// A discriminated union represented by a record.
+    Union {
+        /// Cases in declaration order.
+        cases: Vec<UnionCase>,
+    },
 }
 
 /// Declaration of a record field.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct FieldDeclaration {
     /// Field name.
     pub name: String,
+    /// Whether the field must be present.
+    pub required: bool,
     /// Optional field documentation.
     pub documentation: Option<Documentation>,
     /// Field value type.
-    pub ty: TypeExpr,
-    /// Whether the field may be omitted.
-    ///
-    /// Optionality represents absence, not a `null` value.
-    pub optional: bool,
+    pub r#type: TypeExpr,
 }
 
-/// Declaration of an enumeration.
+/// One payload-free enum case.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct EnumDeclaration {
-    /// Descriptor-local type name.
+pub struct EnumCase {
+    /// Case name.
     pub name: String,
-    /// Optional enum documentation.
+    /// Optional case documentation.
     pub documentation: Option<Documentation>,
-    /// Allowed variants in declaration order.
-    pub variants: Vec<EnumVariantDeclaration>,
 }
 
-/// Declaration of one enumeration variant.
+/// One union case with zero or one payload.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct EnumVariantDeclaration {
-    /// Variant name.
+pub struct UnionCase {
+    /// Case name.
     pub name: String,
-    /// Optional variant documentation.
+    /// Optional case documentation.
     pub documentation: Option<Documentation>,
-}
-
-/// Declaration of a tagged union.
-#[derive(Debug, Clone, PartialEq)]
-pub struct UnionDeclaration {
-    /// Descriptor-local type name.
-    pub name: String,
-    /// Optional union documentation.
-    pub documentation: Option<Documentation>,
-    /// Allowed tagged variants in declaration order.
-    pub variants: Vec<UnionVariantDeclaration>,
-}
-
-/// Declaration of one tagged-union variant.
-#[derive(Debug, Clone, PartialEq)]
-pub struct UnionVariantDeclaration {
-    /// Variant tag.
-    pub name: String,
-    /// Optional variant documentation.
-    pub documentation: Option<Documentation>,
-    /// Payload type.
-    pub ty: TypeExpr,
-}
-
-/// A type expression used by fields, parameters, returns, and union payloads.
-///
-/// `Named` references are resolved only within the containing descriptor.
-/// Optional values are represented by the containing field or parameter and
-/// therefore are intentionally not a type expression.
-#[derive(Debug, Clone, PartialEq)]
-pub enum TypeExpr {
-    /// A UTF-8 string.
-    String,
-    /// A boolean.
-    Boolean,
-    /// A JavaScript-lossless integer.
-    Integer,
-    /// A finite IEEE-754 double precision number.
-    Number,
-    /// An opaque byte sequence.
-    Bytes,
-    /// An ordered sequence of values.
-    List(Box<TypeExpr>),
-    /// A key/value entry.
-    Entry {
-        /// Entry key type.
-        key: Box<TypeExpr>,
-        /// Entry value type.
-        value: Box<TypeExpr>,
-    },
-    /// A logical JSON value.
-    Json,
-    /// A descriptor-local named declaration.
-    Named(String),
+    /// Optional payload type.
+    pub payload: Option<TypeExpr>,
 }
 
 /// Declaration of one interface operation.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct OperationDeclaration {
-    /// Operation name, unique within its interface.
+    /// Operation name, unique within its descriptor.
     pub name: String,
     /// Optional operation documentation.
     pub documentation: Option<Documentation>,
     /// Parameters in declaration order.
     pub parameters: Vec<ParameterDeclaration>,
-    /// Return declaration, or `None` for an operation with no return value.
-    pub returns: Option<ReturnDeclaration>,
+    /// Return declaration. No-data operations return [`TypeExpr::Unit`].
+    pub returns: ReturnDeclaration,
 }
 
 /// Declaration of one operation parameter.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ParameterDeclaration {
     /// Parameter name.
     pub name: String,
+    /// Whether the parameter must be present.
+    pub required: bool,
     /// Optional parameter documentation.
     pub documentation: Option<Documentation>,
     /// Parameter value type.
-    pub ty: TypeExpr,
-    /// Whether the parameter may be omitted.
-    ///
-    /// Optionality represents absence, not a `null` value.
-    pub optional: bool,
+    pub r#type: TypeExpr,
 }
 
 /// Declaration of an operation return value.
-#[derive(Debug, Clone, PartialEq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ReturnDeclaration {
     /// Optional return-value documentation.
     pub documentation: Option<Documentation>,
     /// Return value type.
-    pub ty: TypeExpr,
+    pub r#type: TypeExpr,
 }
 
-/// A logical protocol value.
+/// A schema-neutral logical protocol value.
 ///
-/// There is no general `Null` variant: optional record fields and operation
-/// parameters are omitted. JSON null remains available inside [`Value::Json`].
+/// Enum cases, union cases, entries, and JSON are interpretations imposed by a
+/// descriptor. They are deliberately not variants of this enum. Record key
+/// ordering is not protocol-significant.
 #[derive(Debug, Clone, PartialEq)]
 pub enum Value {
-    /// A UTF-8 string.
-    String(String),
+    /// A value carrying no data; it also represents JSON null under `Json`.
+    Unit,
     /// A boolean.
     Boolean(bool),
-    /// An integer, validated against the JavaScript safe integer range.
+    /// A JavaScript-lossless integer.
     Integer(i64),
-    /// A number, validated to be finite.
+    /// A finite IEEE-754 binary64 number.
     Number(f64),
+    /// A Unicode string.
+    String(String),
     /// An opaque byte sequence.
     Bytes(Vec<u8>),
+    /// String-keyed fields with order-insensitive semantics.
+    Record(BTreeMap<String, Value>),
     /// An ordered sequence.
     List(Vec<Value>),
-    /// A key/value entry.
-    Entry {
-        /// Entry key.
-        key: Box<Value>,
-        /// Entry value.
-        value: Box<Value>,
-    },
-    /// Record fields. Duplicate names are invalid.
-    Record(Vec<NamedValue>),
-    /// An enum variant name.
-    Enum(String),
-    /// A tagged-union value.
-    Union {
-        /// Selected variant tag.
-        variant: String,
-        /// Variant payload.
-        value: Box<Value>,
-    },
-    /// A logical JSON value.
-    Json(JsonValue),
 }
 
 impl Value {
@@ -252,132 +206,219 @@ impl Value {
     #[must_use]
     pub fn kind(&self) -> crate::ValueKind {
         match self {
-            Self::String(_) => crate::ValueKind::String,
+            Self::Unit => crate::ValueKind::Unit,
             Self::Boolean(_) => crate::ValueKind::Boolean,
             Self::Integer(_) => crate::ValueKind::Integer,
             Self::Number(_) => crate::ValueKind::Number,
+            Self::String(_) => crate::ValueKind::String,
             Self::Bytes(_) => crate::ValueKind::Bytes,
-            Self::List(_) => crate::ValueKind::List,
-            Self::Entry { .. } => crate::ValueKind::Entry,
             Self::Record(_) => crate::ValueKind::Record,
-            Self::Enum(_) => crate::ValueKind::Enum,
-            Self::Union { .. } => crate::ValueKind::Union,
-            Self::Json(_) => crate::ValueKind::Json,
+            Self::List(_) => crate::ValueKind::List,
         }
     }
 }
 
-/// A named value used by records and operation arguments.
-#[derive(Debug, Clone, PartialEq)]
-pub struct NamedValue {
-    /// Field or parameter name.
-    pub name: String,
-    /// Associated value.
-    pub value: Value,
-}
-
-/// A transport-independent JSON value.
-#[derive(Debug, Clone, PartialEq)]
-pub enum JsonValue {
-    /// JSON null.
-    Null,
-    /// JSON boolean.
-    Boolean(bool),
-    /// JSON integer, validated against the JavaScript safe integer range.
-    Integer(i64),
-    /// JSON number, validated to be finite.
-    Number(f64),
-    /// JSON string.
-    String(String),
-    /// JSON array.
-    Array(Vec<JsonValue>),
-    /// JSON object. Duplicate member names are invalid.
-    Object(Vec<JsonMember>),
-}
-
-/// A member of a logical JSON object.
-#[derive(Debug, Clone, PartialEq)]
-pub struct JsonMember {
-    /// Member name.
-    pub name: String,
-    /// Member value.
-    pub value: JsonValue,
-}
-
-/// Logical destination of an operation call.
+/// Request for the object currently published at one path.
 #[derive(Debug, Clone, PartialEq, Eq)]
-pub struct OperationTarget {
-    /// Target object.
-    pub object: ObjectId,
-    /// Target interface name.
+pub struct FetchRequest {
+    /// Canonical absolute Worldspace path.
+    pub path: String,
+}
+
+/// Successful `fetch` response.
+pub type FetchResponse = Object;
+
+/// Request for a bounded breadth-first object-tree observation.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FetchTreeRequest {
+    /// Canonical absolute path of the tree root.
+    pub path: String,
+    /// Maximum depth, where the requested object has depth zero.
+    pub depth: u32,
+    /// Maximum total node count, including the root. Must be nonzero.
+    pub limit: u32,
+}
+
+/// One node in a tree observation.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ObjectTreeNode {
+    /// Object observed at this tree position.
+    pub object: Object,
+    /// Direct children in host-defined traversal order.
+    pub children: Vec<ObjectTreeNode>,
+}
+
+/// Successful `fetch_tree` response.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FetchTreeResponse {
+    /// Observed tree rooted at the requested path.
+    pub root: ObjectTreeNode,
+    /// Whether public indexable children were omitted by depth or limit.
+    pub truncated: bool,
+}
+
+/// Request for the current descriptor of one opaque interface reference.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FetchInterfaceRequest {
+    /// Opaque interface reference obtained from an object.
     pub interface: String,
-    /// Target operation name.
+}
+
+/// Successful `fetch_interface` response.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct FetchInterfaceResponse {
+    /// Opaque interface reference corresponding to the request.
+    pub interface: String,
+    /// Current validated descriptor.
+    pub descriptor: InterfaceDescriptor,
+    /// Optional opaque validator for this descriptor observation.
+    pub validator: Option<Vec<u8>>,
+}
+
+/// Object portion of an operation target.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Target {
+    /// Canonical absolute path of the target object.
+    pub path: String,
+    /// Optional validator copied from the object observation.
+    pub validator: Option<Vec<u8>>,
+}
+
+/// Interface portion of an operation target.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct InterfaceTarget {
+    /// Opaque interface reference selected from the object's interface set.
+    pub reference: String,
+    /// Optional validator copied from the interface observation.
+    pub validator: Option<Vec<u8>>,
+}
+
+/// Transport-independent request to execute one operation.
+#[derive(Debug, Clone, PartialEq)]
+pub struct CallOperationRequest {
+    /// Path and optional object-state precondition.
+    pub target: Target,
+    /// Interface reference and its independent optional precondition.
+    pub interface: InterfaceTarget,
+    /// Operation name within the selected descriptor.
     pub operation: String,
+    /// Named arguments; map iteration order has no protocol meaning.
+    pub arguments: BTreeMap<String, Value>,
 }
 
-/// A transport-independent operation call.
+/// Successful operation response.
 #[derive(Debug, Clone, PartialEq)]
-pub struct OperationCall {
-    /// Logical call target.
-    pub target: OperationTarget,
-    /// Named arguments. Optional arguments are represented by omission.
-    pub arguments: Vec<NamedValue>,
+pub struct CallOperationResponse {
+    /// Application result validated against the operation return declaration.
+    pub result: Value,
+    /// Optional validator for the object state observed after execution.
+    pub validator: Option<Vec<u8>>,
 }
 
-/// Successful or failed logical outcome of an operation.
-#[derive(Debug, Clone, PartialEq)]
-pub enum OperationOutcome {
-    /// Operation returned. `None` represents a declared no-return operation.
-    Returned(Option<Value>),
-    /// Operation failed with a protocol-level error.
-    Failed(ProtocolError),
-}
-
-/// A transport-independent operation result.
-#[derive(Debug, Clone, PartialEq)]
-pub struct OperationResult {
-    /// Target corresponding to the result.
-    pub target: OperationTarget,
-    /// Logical outcome.
-    pub outcome: OperationOutcome,
+/// Logical outcome of any core interaction.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ProtocolResult<T> {
+    /// The interaction succeeded.
+    Success(T),
+    /// The interaction failed at the protocol boundary.
+    Failure(ProtocolError),
 }
 
 impl Object {
-    /// Validates ordered-set interface semantics.
+    /// Validates the object-independent name and ordered-interface-set rules.
     pub fn validate(&self) -> Result<(), ValidationError> {
         crate::validation::validate_object(self)
     }
-}
 
-impl InterfaceObservation {
-    /// Validates the object, descriptor structure, and their correspondence.
-    pub fn validate(&self) -> Result<(), ValidationError> {
-        crate::validation::validate_observation(self)
+    /// Validates this object as the response observed at `path`.
+    pub fn validate_at_path(&self, path: &str) -> Result<(), ValidationError> {
+        crate::validation::validate_object_at_path(self, path)
+    }
+
+    /// Validates equal representations for a shared ref and present validator.
+    pub fn validate_consistency_with(&self, other: &Self) -> Result<(), ValidationError> {
+        crate::validation::validate_object_consistency(self, other)
     }
 }
 
 impl InterfaceDescriptor {
-    /// Validates declaration structure, references, and absence of recursion.
+    /// Validates declaration structure, named references, and absence of cycles.
     pub fn validate(&self) -> Result<(), ValidationError> {
         crate::validation::validate_descriptor(self)
     }
 
-    /// Validates a value against a type expression in this descriptor.
-    pub fn validate_value(&self, ty: &TypeExpr, value: &Value) -> Result<(), ValidationError> {
-        crate::validation::validate_root_value(self, ty, value)
+    /// Validates a raw value against a type expression in this descriptor.
+    pub fn validate_value(&self, r#type: &TypeExpr, value: &Value) -> Result<(), ValidationError> {
+        crate::validation::validate_root_value(self, r#type, value)
     }
 
-    /// Validates a call target and arguments against this descriptor.
-    pub fn validate_call(&self, call: &OperationCall) -> Result<(), ValidationError> {
-        crate::validation::validate_call(self, call)
-    }
-
-    /// Validates an operation's returned value against this descriptor.
-    pub fn validate_return(
+    /// Validates named arguments for one declared operation.
+    pub fn validate_arguments(
         &self,
         operation: &str,
-        value: Option<&Value>,
+        arguments: &BTreeMap<String, Value>,
     ) -> Result<(), ValidationError> {
-        crate::validation::validate_return(self, operation, value)
+        crate::validation::validate_arguments(self, operation, arguments)
+    }
+
+    /// Validates one operation result against its return declaration.
+    pub fn validate_result(&self, operation: &str, result: &Value) -> Result<(), ValidationError> {
+        crate::validation::validate_result(self, operation, result)
+    }
+
+    /// Validates the path, operation, and arguments in a call request.
+    pub fn validate_call(&self, request: &CallOperationRequest) -> Result<(), ValidationError> {
+        crate::validation::validate_call(self, request)
+    }
+}
+
+impl FetchRequest {
+    /// Validates the request path.
+    pub fn validate(&self) -> Result<(), ValidationError> {
+        crate::validation::validate_path(&self.path)
+    }
+
+    /// Validates an object returned for this request.
+    pub fn validate_response(&self, response: &FetchResponse) -> Result<(), ValidationError> {
+        response.validate_at_path(&self.path)
+    }
+}
+
+impl FetchTreeRequest {
+    /// Validates the request path and nonzero node limit.
+    pub fn validate(&self) -> Result<(), ValidationError> {
+        crate::validation::validate_fetch_tree_request(self)
+    }
+}
+
+impl FetchTreeResponse {
+    /// Validates tree shape, names, depth, and node limit for `request`.
+    pub fn validate_for(&self, request: &FetchTreeRequest) -> Result<(), ValidationError> {
+        crate::validation::validate_fetch_tree_response(self, request)
+    }
+}
+
+impl FetchInterfaceResponse {
+    /// Validates request correspondence and descriptor semantics.
+    pub fn validate_for(&self, request: &FetchInterfaceRequest) -> Result<(), ValidationError> {
+        crate::validation::validate_fetch_interface_response(self, request)
+    }
+}
+
+impl CallOperationRequest {
+    /// Validates this call against the descriptor selected by `interface`.
+    pub fn validate_with(&self, descriptor: &InterfaceDescriptor) -> Result<(), ValidationError> {
+        descriptor.validate_call(self)
+    }
+}
+
+impl CallOperationResponse {
+    /// Validates this result against the named operation in `descriptor`.
+    pub fn validate_for(
+        &self,
+        descriptor: &InterfaceDescriptor,
+        operation: &str,
+    ) -> Result<(), ValidationError> {
+        descriptor.validate_result(operation, &self.result)
     }
 }