[mcollina]

Problem

taskMaxRetainedPerPrincipal (default 100) counted every caller without an identity as a single owner: MemoryTaskStore matched undefined === undefined, and RedisTaskStore put every anonymous task in the fleet into one index, mcp:tasks:anonymous. On a deployment without authorization, any client could therefore evict another client's finished task before that client collected it, or block all new anonymous tasks by keeping 100 running.

Fix

• Tasks with no subject and no issuer (new isAnonymousOwner() helper) are no longer held to the per-principal cap. A per-principal quota for callers who can't be told apart is one allowance that any of them can use up for everyone else.
• All anonymous tasks together are capped by a new option, taskMaxRetainedAnonymous (default 1000, the same as the memory store's total capacity). Eviction works as before: at the cap, the oldest finished anonymous task is evicted (orphaned leases are failed first). If every task is still running, the call fails with -32029 "Task limit reached".
• Memory: the existing per-owner check now uses the anonymous cap for anonymous owners. The store-wide maxTasks (1000) still applies on top.
• Redis: the existing atomic CREATE_SCRIPT runs against mcp:tasks:anonymous with the anonymous cap as its limit. The cap therefore holds across instances with no new keys and no extra round trips.
• Identified principals (issuer + subject, see fix(tasks): bind tasks to token issuer as well as subject #296) work exactly as before, each with its own quota.
• README and the JSDoc for taskMaxRetainedPerPrincipal / taskMaxRetainedAnonymous are updated. The old advice to raise the per-principal quota for anonymous workloads now points to taskMaxRetainedAnonymous.

Tests

• Memory store: anonymous tasks above the per-principal cap are kept, and a completed task is not evicted (the repro from the issue). The anonymous cap refuses or evicts the oldest finished task. The store-wide cap still applies. Identified quota is unchanged. Bad option values are rejected.
• Redis store: the same scenarios, including the anonymous cap being enforced across two store instances.
• Plugin level: the repro from the issue over tools/call / tasks/get, plus validation of taskMaxRetainedAnonymous. The two existing anonymous over-the-wire quota tests now use taskMaxRetainedAnonymous.
• npm run lint, npm run typecheck and npm run test pass (775/775).

Fixes #320

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https://claude.ai/code/session_01LmhsFjk8W96X2PvmShmDm9