runtime: a State panic in the deferred prelude leaks the queue turn record and admission slot #135

runtime: under DispatchDeferred, a panicking State.AcquireLock in the prelude leaks the queue turn record and the admission slot.

What happens

1. Under DispatchDeferred, the prelude's AcquireLock runs on the net/http handler goroutine.
2. If that call panics, net/http recovers the panic, but dispatchDeferred (runtime.go#L711-L718) never calls release.
3. The scope's turn record and the admission slot both stay taken. Shutdown then waits for the slot and returns context deadline exceeded.

The independent verifier of #134 reproduced this with a real httptest.Server. It got the same result on e93bdb8, before #134, so #134 did not cause it. There is no committed test for it yet.

Scope

#129 and #134 cover the DispatchSync path: a State panic while a queue waiter polls. This issue is the deferred-dispatch path, which #129 did not list.

Possible fix

Release the admission and leave the queue scope on every exit from the deferred prelude, a panic included (for example a defer that runs the idempotent release when the tail never started). First commit: a failing test that panics AcquireLock once under DispatchDeferred, then asserts Shutdown returns promptly and QueueTurnCount is 0.

Owner and trigger

The coder/chat maintainer triages this. Fix it with the next change to deferred dispatch, or before the queue strategy is called production-grade, whichever comes first.

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