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Fixes modelcontextprotocol#4710. The subscriptions Map retained sessionIds after disconnect because cleanup() only cleared intervals and task store. Export removeSubscriber(sessionId) that iterates the map, deletes the session from each Set and drops empty entries, and call it from server factory cleanup() (used by streamableHttp and sse onclose). The reference server is the example clients copy; this prevents unbounded growth from clients that subscribe then disconnect without unsubscribing.
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Sep 26, 2026
syncRoots caches one Root[] per session in the module-level map at server/roots.ts:8, and that cache is the only thing deciding whether a session's roots get fetched again. cleanup(sessionId) at server/index.ts:109 stops the simulated logging and resource-update intervals and clears the task store, but never removes the session's entry, so on an SSE or streamable-HTTP server the map grows by one entry per past connection for the life of the process. The sibling map in resources/subscriptions.ts has the same gap, and five open pull requests fix it: modelcontextprotocol#4798, modelcontextprotocol#4718, modelcontextprotocol#4716, modelcontextprotocol#4715 and modelcontextprotocol#4712. Not one of them touches roots.ts, so fixing subscriptions leaves this identical leak alive next to it. Tests: 108 passed. One new case sets an entry, calls cleanup, and asserts the entry is gone. Reverting roots.ts and index.ts and keeping the test gives 1 failed, 5 passed in server.test.ts. npm run build is clean.
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Fixes #4710 — resources/subscribeadded tosubscriptionsmap butcleanup()never removed session on disconnect, leaking sessionIds. AddremoveSubscriber(sessionId)iterating map and deleting empty entries, called fromserver/index.ts:cleanup(). Verified with npm test (107 passed).