fix(mcp): Notifications/tools/list_changed support not working

[jacob314]

Summary

This change was done with TDD with tests that were verified to fail before implementing the code.

• Improved MCP Context Refresh Mechanism: The MCP context refresh logic has been enhanced to handle rapid, consecutive refresh requests more robustly. It now includes mechanisms for debouncing, queuing trailing executions, and ensuring that all pending refreshes are processed, preventing potential missed updates.
• Enhanced Robustness for List Changed Notifications: The client now registers notification handlers for 'list_changed' events (for tools, resources, and prompts) even if the server's capabilities do not explicitly declare support for listChanged. This improves resilience against servers that might send notifications without fully adhering to capability declarations.
• Tool Discovery Verification Retry: A verification retry mechanism has been added to the tool refresh process. If an initial tool discovery yields no tools or no changes, the client will wait briefly and attempt discovery again, addressing potential race conditions where a server might notify of changes before its tool list is fully updated.
• Updated Unit Tests: Unit tests for mcp-client have been updated to reflect the new robustness logic, including a new test case to verify notification handler setup when listChanged is false, and improvements to how notification callbacks are identified in mocks.

Fixes #19509

[gemini-code-assist]

Code Review

This pull request improves the robustness of handling MCP list_changed notifications. The changes to always register notification handlers and to add a retry mechanism for tool discovery are good enhancements to deal with non-compliant or racy MCP servers. I've found a potential issue in the new refresh scheduling logic in mcp-client-manager.ts where a pending refresh request could be lost if the current refresh operation fails.

[github-actions]

Size Change: +5.27 kB (+0.02%)

Total Size: 25.9 MB

Filename	Size	Change
./bundle/gemini.js	25.5 MB	+5.27 kB (+0.02%)

ℹ️ View Unchanged

Filename	Size
./bundle/node_modules/@google/gemini-cli-devtools/dist/client/main.js	221 kB
./bundle/node_modules/@google/gemini-cli-devtools/dist/src/_client-assets.js	227 kB
./bundle/node_modules/@google/gemini-cli-devtools/dist/src/index.js	11.5 kB
./bundle/node_modules/@google/gemini-cli-devtools/dist/src/types.js	132 B
./bundle/sandbox-macos-permissive-open.sb	890 B
./bundle/sandbox-macos-permissive-proxied.sb	1.31 kB
./bundle/sandbox-macos-restrictive-open.sb	3.36 kB
./bundle/sandbox-macos-restrictive-proxied.sb	3.56 kB
./bundle/sandbox-macos-strict-open.sb	4.82 kB
./bundle/sandbox-macos-strict-proxied.sb	5.02 kB

_{compressed-size-action}