fix(client): serialize response cache invalidation

[tandede]

Summary

• serialize response-cache mutations per logical key so a delayed asynchronous ResponseCacheStore.set() cannot restore stale data after invalidation
• preserve invocation order so writes started after list_changed or resources/updated invalidation remain cached
• add deterministic regressions for both stale-write removal and fresh-write preservation
• add a patch changeset for @modelcontextprotocol/client

Why

ResponseCacheStore permits asynchronous implementations. The existing generation check prevents a response that was already stale before write() from being stored, but it cannot stop an invalidation that arrives while store.set() is already pending:

1. write() passes the generation check and enters an asynchronous set().
2. An invalidation increments the generation and finishes delete() before that set has applied anything.
3. The delayed set then commits the old response after the invalidation.

Serializing mutations for each logical cache key makes the earlier set finish before its invalidation delete. A fresh write invoked after that invalidation queues behind the delete, so it is not removed.

Test plan

• pnpm --filter @modelcontextprotocol/client test (806 passed)
• pnpm typecheck:all
• pnpm lint:all
• pnpm build:all

[changeset-bot]

🦋 Changeset detected

Latest commit: 8ec0121

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 6 packages

Name	Type
@modelcontextprotocol/client	Patch
@modelcontextprotocol/core	Patch
@modelcontextprotocol/server	Patch
@modelcontextprotocol/server-legacy	Patch
@modelcontextprotocol/codemod	Patch
@modelcontextprotocol/core-internal	Patch

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commit: 8ec0121