fix(mcp): ignore JSON-RPC notifications without id (so can working with codex)

[wukeying]

Summary

This change makes the MCP server ignore JSON-RPC notifications (requests without id) instead of replying with an
error.

Why

Some MCP clients send notification messages such as notifications/initialized during handshake.
Per JSON-RPC semantics, notifications must not receive responses. Returning an error response can cause client
transport/session startup failures.

Change

• In the MCP request loop, skip response writing when request.id.is_none().
• Keep existing request/response behavior unchanged for normal requests with id.

Validation

• Built and ran the patched server.
• Verified initialize + tools/list still work.
• Verified notification messages no longer generate error responses.
• Tested in codex

[ervinpopescu]

I think this will fix gemini-cli as well:

│ ℹ  Registering notification handlers for server 'rust-analyzer'. Capabilities: { tools: {} }                                                                                               │
│ ℹ  Server 'rust-analyzer' has tools but did not declare 'listChanged' capability. Listening anyway for robustness...                                                                       │
│ ⚠  [STARTUP] Cannot start phase 'load_builtin_commands': phase is already active. Call end() before starting again.                                                                        │
│ ℹ  [MCP error] MCP ERROR (rust-analyzer) Error: Received a response for an unknown message ID: {"jsonrpc":"2.0","error":{"code":-32601,"message":"Method not found:                        │
│    notifications/initialized","data":null}}                                                                                                                                                │
│        at Client._onresponse (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:270841:21)                                       │
│        at _transport.onmessage (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:270653:14)                                     │
│        at StdioClientTransport.processReadBuffer (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:273671:25)                   │
│        at Socket.<anonymous> (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:273633:14)                                       │
│        at Socket.emit (node:events:508:28)                                                                                                                                                 │
│        at addChunk (node:internal/streams/readable:563:12)                                                                                                                                 │
│        at readableAddChunkPushByteMode (node:internal/streams/readable:514:3)                                                                                                              │
│        at Readable.push (node:internal/streams/readable:394:5)                                                                                                                             │
│        at Pipe.onStreamRead (node:internal/stream_base_commons:189:23)                                                                                                                     │
│ ℹ  [MCP error] Error during discovery for MCP server 'rust-analyzer': Client is not connected, must connect before interacting with the server. Current state is disconnected Error:       │
│    Client is not connected, must connect before interacting with the server. Current state is disconnected                                                                                 │
│        at McpClient.assertConnected (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:340721:13)                                │
│        at McpClient.discoverResources (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:340738:10)                              │
│        at McpClient.discoverInto (file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:340657:34)                                   │
│        at process.processTicksAndRejections (node:internal/process/task_queues:104:5)                                                                                                      │
│        at async file:///usr/local/google/home/ervinadrian/node/lib/node_modules/@google/gemini-cli/bundle/chunk-IKYTUXTH.js:342020:15                                                      │
│ ℹ  Scheduling MCP context refresh...                                                                                                                                                       │
│ ℹ  Executing MCP context refresh...                                                                                                                                                        │
│ ⚠  [STARTUP] Cannot start phase 'load_builtin_commands': phase is already active. Call end() before starting again. (x2)                                                                   │
│ ⚠  [STARTUP] Phase 'load_builtin_commands' was started but never ended. Skipping metrics.                                                                                                  │
│ ℹ  MCP context refresh complete.                

Testing it now.

Looks like it does:

 ℹ  MCP context refresh complete.                                                                                                                                                          █│
│ ℹ  Registering notification handlers for server 'rust-analyzer'. Capabilities: { tools: {} }                                                                                              █│
│ ℹ  Server 'rust-analyzer' has tools but did not declare 'listChanged' capability. Listening anyway for robustness...                                                                      █│
│ ℹ  Scheduling MCP context refresh...                                                                                                                                                      █│
│ ℹ  Executing MCP context refresh...                                                                                                                                                       █│
│ ℹ  MCP context refresh complete.