feat: migrate protocol and HTTP to structured interface references

T-20: identify interfaces by exact scope/name pairs; add optional opaque scope_ref metadata and separate shape validation from path-dependent scope compatibility. Preserve call error precedence, strict JSON, validators and transport boundaries. Mechanically migrate consumers and document API/wire compatibility and deferred lifecycle semantics.

Validation: cargo fmt --all --check; git diff --check; cargo check --workspace --all-targets; cargo test -p wip-protocol -p wip-http; cargo test --workspace (221 passing tests including doctests); cargo test --workspace --all-targets; nix develop --command cargo clippy --workspace --all-targets -- -D warnings; RUSTDOCFLAGS="-D warnings" cargo doc --workspace --no-deps. All pass. cargo/rustc 1.95.0; development-shell Clippy/rustc 1.97.1.

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

@@ -576,7 +576,7 @@ fn observation_and_fetch_policy_panics_remain_sanitized_read_failures() {
         let mut registry = InterfaceRegistry::new();
         let defaults = DefaultInterfaces::register(&mut registry).unwrap();
         let custom = registry.register(MemoryOperationsDefinition, None).unwrap();
-        let reference = custom.reference().as_str().to_owned();
+        let reference = custom.reference().protocol_reference();
         let engine = Projection::new(
             MemoryBackend(fixture.shared.clone()),
             registry,
@@ -616,8 +616,8 @@ type Engine = Projection<MemoryBackend, MemoryComposition, Policy>;
 struct Fixture {
     engine: Engine,
     shared: Arc<Shared>,
-    custom: String,
-    read: String,
+    custom: wip_protocol::InterfaceReference,
+    read: wip_protocol::InterfaceReference,
     limits: ResourceLimits,
 }
 impl Fixture {
@@ -696,8 +696,8 @@ impl Fixture {
                 limits,
             ),
             shared,
-            custom: custom_ref.as_str().into(),
-            read: read_ref.as_str().into(),
+            custom: custom_ref.protocol_reference(),
+            read: read_ref.protocol_reference(),
             limits,
         }
     }
@@ -707,7 +707,11 @@ impl Fixture {
             .observe(&ExecutionContext::new(), &observe_request(path, depth))
             .unwrap()
     }
-    fn descriptor(&self, principal: &Principal, reference: &str) -> InterfaceDescriptor {
+    fn descriptor(
+        &self,
+        principal: &Principal,
+        reference: &wip_protocol::InterfaceReference,
+    ) -> InterfaceDescriptor {
         self.engine
             .view(principal)
             .fetch_interface(&fetch_request(reference))
@@ -717,7 +721,7 @@ impl Fixture {
     fn request(
         &self,
         path: &str,
-        reference: &str,
+        reference: &wip_protocol::InterfaceReference,
         operation: &str,
         validator: Option<Vec<u8>>,
     ) -> CallOperationRequest {
@@ -727,7 +731,8 @@ impl Fixture {
                 validator,
             },
             interface: InterfaceTarget {
-                reference: reference.into(),
+                scope_ref: None,
+                reference: reference.clone(),
                 validator: None,
             },
             operation: operation.into(),
@@ -866,9 +871,9 @@ fn observe_request(path: &str, depth: u32) -> ObserveRequest {
         depth,
     }
 }
-fn fetch_request(reference: &str) -> FetchInterfaceRequest {
+fn fetch_request(reference: &wip_protocol::InterfaceReference) -> FetchInterfaceRequest {
     FetchInterfaceRequest {
-        interface: reference.into(),
+        interface: reference.clone(),
     }
 }
 fn success<T: std::fmt::Debug>(response: DecodedResponse<T>) -> T {
@@ -1804,8 +1809,8 @@ fn policy_panics_and_guessed_operation_diagnostics_do_not_leak_to_http() {
     // This valid metadata names a nonexistent operation; bypass client-side
     // descriptor validation to exercise server diagnostics for untrusted names.
     let body = format!(
-        r#"{{"target":{{"path":"/added"}},"interface":{{"reference":"{}"}},"operation":"{}","arguments":{{}}}}"#,
-        fixture.custom, POLICY_SECRET
+        r#"{{"target":{{"path":"/added"}},"interface":{{"reference":{{"scope":"{}","name":"{}"}}}},"operation":"{}","arguments":{{}}}}"#,
+        fixture.custom.scope, fixture.custom.name, POLICY_SECRET
     );
     let request = http::Request::builder()
         .method(http::Method::POST)