fix: align protocol model with canonical WIP

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>,
+    /// 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.
-    pub fields: Vec<FieldDeclaration>,
+        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)
     }
+
+    /// 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)
     }
 
-impl InterfaceObservation {
-    /// Validates the object, descriptor structure, and their correspondence.
-    pub fn validate(&self) -> Result<(), ValidationError> {
-        crate::validation::validate_observation(self)
+    /// 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)
     }
 }