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🧪 chore: MCP Reconnect Storm Follow-Up Fixes and Integration Tests (#12172)

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* 🧪 test: Add reconnection storm regression tests for MCPConnection

Introduced a comprehensive test suite for reconnection storm scenarios, validating circuit breaker, throttling, cooldown, and timeout fixes. The tests utilize real MCP SDK transports and a StreamableHTTP server to ensure accurate behavior under rapid connect/disconnect cycles and error handling for SSE 400/405 responses. This enhances the reliability of the MCPConnection by ensuring proper handling of reconnection logic and circuit breaker functionality.

* 🔧 fix: Update createUnavailableToolStub to return structured response

Modified the `createUnavailableToolStub` function to return an array containing the unavailable message and a null value, enhancing the response structure. Additionally, added a debug log to skip tool creation when the result is null, improving the handling of reconnection scenarios in the MCP service.

* 🧪 test: Enhance MCP tool creation tests for cache and throttle interactions

Added new test cases for the `createMCPTool` function to validate the caching behavior when tools are unavailable or throttled. The tests ensure that tools are correctly cached as missing and prevent unnecessary reconnects across different users, improving the reliability of the MCP service under concurrent usage scenarios. Additionally, introduced a test for the `createMCPTools` function to verify that it returns an empty array when reconnect is throttled, ensuring proper handling of throttling logic.

* 📝 docs: Update AGENTS.md with testing philosophy and guidelines

Expanded the testing section in AGENTS.md to emphasize the importance of using real logic over mocks, advocating for the use of spies and real dependencies in tests. Added specific recommendations for testing with MongoDB and MCP SDK, highlighting the need to mock only uncontrollable external services. This update aims to improve testing practices and encourage more robust test implementations.

* 🧪 test: Enhance reconnection storm tests with socket tracking and SSE handling

Updated the reconnection storm test suite to include a new socket tracking mechanism for better resource management during tests. Improved the handling of SSE 400/405 responses by ensuring they are processed in the same branch as 404 errors, preventing unhandled cases. This enhances the reliability of the MCPConnection under rapid reconnect scenarios and ensures proper error handling.

* 🔧 fix: Implement cache eviction for stale reconnect attempts and missing tools

Added an `evictStale` function to manage the size of the `lastReconnectAttempts` and `missingToolCache` maps, ensuring they do not exceed a maximum cache size. This enhancement improves resource management by removing outdated entries based on a specified time-to-live (TTL), thereby optimizing the MCP service's performance during reconnection scenarios.
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Danny Avila 2026-03-10 17:44:13 -04:00 • committed by GitHub
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AGENTS.md
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@ -149,7 +149,15 @@ Multi-line imports count total character length across all lines. Consolidate va
- Run tests from their workspace directory: `cd api && npx jest <pattern>`, `cd packages/api && npx jest <pattern>`, etc.
- Frontend tests: `__tests__` directories alongside components; use `test/layout-test-utils` for rendering.
- Cover loading, success, and error states for UI/data flows.
- Mock data-provider hooks and external dependencies.
### Philosophy
- **Real logic over mocks.** Exercise actual code paths with real dependencies. Mocking is a last resort.
- **Spies over mocks.** Assert that real functions are called with expected arguments and frequency without replacing underlying logic.
- **MongoDB**: use `mongodb-memory-server` for a real in-memory MongoDB instance. Test actual queries and schema validation, not mocked DB calls.
- **MCP**: use real `@modelcontextprotocol/sdk` exports for servers, transports, and tool definitions. Mirror real scenarios, don't stub SDK internals.
- Only mock what you cannot control: external HTTP APIs, rate-limited services, non-deterministic system calls.
- Heavy mocking is a code smell, not a testing strategy.
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