feat(adapters): from_mcp + to_mcp behind the mcp feature (rmcp 1.8)

from_mcp (src/adapters/from_mcp/):
- tools/list discovery over streamable HTTP; per-tool
  HandlerRegistration (Mutation, Once, FromMCP leaf, Internal;
  ADR-015/022)
- structuredContent-preferred output, ContentBlock-union fallback,
  isError -> MCP_TOOL_ERROR with content blocks as details (ADR-023)
- bearer token flows via capabilities key 'mcp' (ADR-014 no-env-vars)
- 19 unit tests + tests/from_mcp_integration.rs (5 tests vs a real
  rmcp streamable-HTTP MCP server)

to_mcp (src/adapters/to_mcp.rs):
- 4 fixed gateway tools (search/schema/call/batch, ADR-041); Sub ops
  excluded from search and uncallable (MCP is request/response)
- identity survives rmcp framing: bearer_auth_middleware stashes
  Option<Identity> in http::request::Parts extensions, call_tool reads
  it back from RequestContext extensions
- StreamableHttpService nested at /mcp in HttpAdapter's router,
  bearer middleware around it (feature-gated)

Streamable HTTP only (ADR-037): rmcp default-features off, no stdio.
Default build compiles without rmcp (cargo tree: 0 hits).

Verified: cargo test (182 lib default / 218 all-features) + 5 MCP
integration + 10 WS, clippy -D warnings (both), fmt.

tasks/adapters/mcp.md

@@ -1,7 +1,7 @@
 ---
 id: adapter-mcp
 name: from_mcp + to_mcp (mcp feature)
-status: pending
+status: completed
 depends_on: [client-http-host, gateway-routes]
 scope: broad
 risk: medium
@@ -24,11 +24,11 @@ middleware. Shared dispatch spine with to_openapi via GatewayDispatch.
 
 ## Acceptance Criteria
 
-- [ ] Both adapters behind `mcp`; default features compile without rmcp
-- [ ] from_mcp round-trip against a mock MCP server (tools/list, tools/call, structured + content-block outputs)
-- [ ] to_mcp: 4 tools listed; call dispatch filtered by ACL; Pub/Sub ops excluded
-- [ ] stdio transport not present anywhere (dependency audit)
-- [ ] `cargo test --all-features` passes
+- [x] Both adapters behind `mcp`; default features compile without rmcp
+- [x] from_mcp round-trip against a mock MCP server (tools/list, tools/call, structured + content-block outputs)
+- [x] to_mcp: 4 tools listed; call dispatch filtered by ACL; Pub/Sub ops excluded
+- [x] stdio transport not present anywhere (dependency audit)
+- [x] `cargo test --all-features` passes
 
 ## References
 
@@ -38,8 +38,38 @@ middleware. Shared dispatch spine with to_openapi via GatewayDispatch.
 
 ## Notes
 
-> Agent fills during implementation.
+Port split internally as from_mcp/ (dir: mod.rs + tests.rs) + to_mcp.rs,
+mirroring the old crate layout. Streamable HTTP only (rmcp 1.8,
+default-features off; client + server + streamable-http transport
+features only — no stdio anywhere in the feature set).
 
 ## Summary
 
-> Agent fills on completion.
+Ported both MCP adapters behind the `mcp` feature (rmcp 1.8):
+
+- `src/adapters/from_mcp/` (mod.rs + tests.rs): tools/list discovery
+  over StreamableHttpClientTransport; per-tool HandlerRegistration
+  (Mutation, HandlerKind::Once, FromMCP leaf, Internal, ADR-015/022);
+  structuredContent-preferred output, ContentBlock-union fallback
+  schema (5 variants), isError -> MCP_TOOL_ERROR CallError with
+  content blocks as details; bearer token via capabilities key "mcp"
+  (ADR-014). 19 unit tests + 5 integration tests vs a real rmcp
+  streamable-HTTP server (tests/from_mcp_integration.rs, gated on the
+  mcp feature): tools round-trip incl. structured + legacy
+  content-block outputs, no-env-vars, unreachable-server error
+  classification.
+- `src/adapters/to_mcp.rs`: ToMcpGateway with exactly 4 gateway tools
+  (search/schema/call/batch — ADR-041), Sub ops excluded from search
+  listings (op_type wire strings "sub"/"subscription"/"Sub"), call
+  dispatch through the shared GatewayDispatch spine with
+  ACL-filtered FORBIDDEN/NOT_FOUND mapping, batch returns per-call
+  result array. Identity survives rmcp framing: bearer_auth_middleware
+  stashes Option<Identity> in http::request::Parts extensions;
+  extract_identity reads it back from RequestContext extensions.
+  StreamableHttpService nested at /mcp in build_router (feature-gated)
+  with bearer middleware around it. 19 tests.
+- `GET|POST /mcp` reserved path unchanged; default build compiles
+  without rmcp (cargo tree -e normal: 0 rmcp occurrences).
+
+218 lib tests (default 182 / all-features 218) + 5 MCP integration +
+10 WS integration green. clippy -D warnings both feature sets, fmt.