fix(gateway): fail-closed publish_schema compile + compile-once cache (GW-01 follow-up)

- new gateway::schema_cache — PublishSchemaCache: compile the op's
  publish_schema once per registration (value-keyed invalidation for
  hot reload), cache compile failures (logged once at error level,
  never retried per request)
- /publish compile failure is now fail-closed: the chunk stream
  terminates with INTERNAL (500), the error text stays in the log
  (no schema internals on the wire) — the per-request warn-and-skip
  unvalidated ingest path is removed
- schema resolution is lazy (first chunk poll, after invoke_sink's
  404/403/422 pre-checks — GW-11 order preserved) and keyed by schema
  value, so re-registration/hot reload is picked up (test)
- NdjsonChunkStream: first Err item is terminal (done + stream end),
  mirroring the wire pump's send(Err) + break — Ok chunks can never
  follow an error on the HTTP path either (found by spy-handler test)

Verified: cargo test (308), cargo test --all-features, clippy
--all-targets -D warnings (default + all-features), fmt --check.

Tasks: review-001-publish-schema-validation-robust

src/server/state.rs

@@ -42,6 +42,10 @@ pub(crate) struct RouterState {
     pub(crate) ws_session_slots: Arc<tokio::sync::Semaphore>,
     /// Idle-read timeout for the WS pumps (WS-01); `None` disables.
     pub(crate) ws_idle_timeout: Option<std::time::Duration>,
+    /// Compile-once `publish_schema` validator cache for the `/publish`
+    /// route (GW-01 follow-up); built empty at adapter construction and
+    /// populated lazily per operation.
+    pub(crate) publish_schemas: crate::gateway::schema_cache::PublishSchemaCache,
 }
 
 impl axum::extract::FromRef<RouterState> for crate::websocket::SessionState {
@@ -102,6 +106,7 @@ mod tests {
                 crate::websocket::DEFAULT_WS_MAX_SESSIONS,
             )),
             ws_idle_timeout: Some(crate::websocket::DEFAULT_WS_IDLE_TIMEOUT),
+            publish_schemas: crate::gateway::schema_cache::PublishSchemaCache::new(),
         };
         let extracted: DecoyConfig = axum::extract::FromRef::from_ref(&state);
         assert!(matches!(extracted, DecoyConfig::Redirect { .. }));