feat: bind Host interfaces to scope Object lifetimes

Register explicit scope/name coordinates independently of Definition type. Require provider-attested current scope snapshots for fetch and dispatch, compare optional scope_ref at membership precedence, and retain the same Descriptor through result validation.

Migrate FS pinned-root boundaries and public self-scope example; document provider atomicity/lifecycle and root-only FS support. Add lifecycle, ref, replacement-race, root-lineage and compile-time exposure regressions.

Validation: cargo fmt --all --check; git diff --check; cargo check --workspace --all-targets; cargo test --workspace --all-targets and --doc (232 passing test-harness cases including doctests); nix develop --command cargo clippy --workspace --all-targets -- -D warnings; RUSTDOCFLAGS=-Dwarnings cargo doc --workspace --no-deps. Narrow wip-host suite also passed.

crates/wip-fs-server/README.md

@@ -26,9 +26,13 @@ For an external backend/composition:
    protected state. Implement `FilesystemBackend` to resolve one connected
    `ResolvedEntry<Entry>` (root-to-parent ancestry plus pinned target), enumerate
    bounded children, and execute against that already-resolved lineage.
-2. Register generated `#[wip_interface::interface]` definitions using the existing
-   `wip_host::InterfaceRegistry`. `DefaultInterfaces::register` optionally supplies
-   reusable built-in tokens; using those tokens does not force their publication.
+2. Create `wip_host::Scope::new("/")` for the deployment-pinned root, then
+   register generated definitions with `registry.register(&scope, name,
+   Definition, validator)`. `DefaultInterfaces::register(&mut registry, &scope)`
+   optionally supplies reusable built-in tokens named `file.read`,
+   `symlink.inspect`, and `file.write`; tokens do not force publication. The
+   current engine binds only the root scope and fails closed for non-root
+   registrations; broader FS scope semantics remain follow-up work.
 3. Implement `Composition<Entry>` on a local type. Its local Object wraps the entry
    and implements both `WipObject` and the chosen generated traits, avoiding orphan
    rules. `PublishedObject::expose` proves each implementation at compile time.
@@ -61,7 +65,26 @@ from one connected backend traversal/snapshot, not independent path-prefix
 resolutions. A root target has no ancestors; other targets retain the root first,
 then intermediate parent containers. This is backend-private context, never wire
 metadata. Backend `resolve` and `execute` signatures both carry this type;
-compositions still receive only the exact scoped target `Entry`.
+compositions receive exact retained entries, including publication of the root
+scope Object while another target is executing, never independent raw-path
+lookups. Root publication must be deterministic and side-effect-free.
+
+Every lineage must retain the same deployment-pinned root Object. Replacing that
+Object requires a new projection and fresh `Scope`, not reuse of registrations
+at the same path. The engine constructs `ScopeObservation` from the published
+root Object's metadata using the refreshed retained root capability **inside**
+`FilesystemBackend::execute`, then attaches it with `PublishedObject::bind_scope`.
+It never independently looks up the raw configured root path. Root Objects need
+not expose any interfaces. Calls check both the private lifetime and optional
+`scope_ref`; normal root state updates do not retire the lifetime.
+
+`with_object` (including fetch) and individual tree Object publications also
+enter this backend boundary. Generic read callbacks use a `NotStarted` attempt
+as an adapter to the existing execution API; no typed operation runs and no
+commit is implied. Tree observations are bounded traversals, not one global tree
+transaction. Fetch resolves the visible scope Object through the provider and
+returns its ref, Descriptor and Interface validator together; retained registry
+artifacts alone never establish publication.
 
 `FilesystemBackend::execute` must validate ancestor membership/identity and
 refresh **all** lineage state/validators inside its transaction or lock before
@@ -196,14 +219,16 @@ curl -sS -X POST http://127.0.0.1:8080/wip/v1/observe \
 ```
 
 A regular-file observation returns a structured read interface reference and an
-object validator. Built-in legacy registrations use scope `/` and copy the opaque
-registration string verbatim into `name`; they do not emit `scope_ref`. Copy the
-complete reference from the observation to retrieve that descriptor:
+object validator. Built-ins explicitly use scope `/` and the local names
+`file.read`, `symlink.inspect`, and `file.write`. The Linux root does not issue an
+Object ref, so fetch omits `scope_ref`; its private publication lifetime still
+binds fetch and call to the pinned deployment root. Copy the complete reference
+from the observation to retrieve that descriptor:
 
 ```console
 curl -sS -X POST http://127.0.0.1:8080/wip/v1/fetch_interface \
   -H 'Content-Type: application/json' -H 'Accept: application/json' \
-  --data '{"interface":{"scope":"/","name":"<read-interface-name-from-observation>"}}'
+  --data '{"interface":{"scope":"/","name":"file.read"}}'
 ```
 
 Then call a bounded range read:
@@ -213,7 +238,7 @@ curl -sS -X POST http://127.0.0.1:8080/wip/v1/call_operation \
   -H 'Content-Type: application/json' -H 'Accept: application/json' \
   --data '{
     "target":{"path":"/notes.txt","validator":"<base64-validator>"},
-    "interface":{"reference":{"scope":"/","name":"<read-interface-name>"}},
+    "interface":{"reference":{"scope":"/","name":"file.read"}},
     "operation":"read",
     "arguments":{"offset":0,"length":4096}
   }'
@@ -227,7 +252,7 @@ curl -sS -X POST http://127.0.0.1:8080/wip/v1/call_operation \
   -H 'Content-Type: application/json' -H 'Accept: application/json' \
   --data '{
     "target":{"path":"/notes.txt","validator":"<base64-validator>"},
-    "interface":{"reference":{"scope":"/","name":"<write-interface-name>"}},
+    "interface":{"reference":{"scope":"/","name":"file.write"}},
     "operation":"replace",
     "arguments":{"contents":"dXBkYXRlZA=="}
   }'