[pyramation]

Summary

Bug. In createAdmissionControlMiddleware, the res.on('close') / res.on('finish') listeners that release a concurrency slot were attached only after await concurrency.acquire(...) resolved. acquire can wait up to maxQueueWaitMs in the queue, so a client that hung up while queued emitted close before any listener existed. When its turn came the dead request was handed the slot, next() ran it against a closed socket, and nothing ever called lease.release() — the per-database budget shrank by one for the life of the process. Reachable anonymously: a few hundred connect-queue-abort cycles starve the endpoint.

Fix.

// packages/express-context/src/admission.ts
interface AdmissionRequest { …; signal?: AbortSignal }          // new
type AdmissionRefusal = 'queue_full' | 'queue_timeout' | 'aborted' // new member
// acquire(): an aborted waiter leaves the queue immediately and resolves
// REFUSED('aborted'); already-aborted callers are refused without queueing.

// graphql/server/src/middleware/admission-control.ts
const gone = new AbortController();
res.once('close', () => gone.abort());            // watched from BEFORE the wait
lease = await concurrency.acquire(databaseId, { …, signal: gone.signal });
res.off('close', …);
if (gone.signal.aborted) { lease.release(); return; }  // grant that raced the hang-up

The existing post-grant close/finish release listeners are unchanged; release stays idempotent.

Tests

• admission-control.test.ts — does not leak the slot when the client hangs up while queued: slot held, second request queued, queued response emits close, holder finishes; the queued request must not start and a third caller (maxQueueWaitMs: 0) must be admitted immediately.
• admission.test.ts (ConcurrencyLimiter) — an aborted waiter leaves the queue with refusal 'aborted' and the next arrival gets the slot; a pre-aborted signal is refused without queueing.

Before (main + these tests):

✕ does not leak the slot when the client hangs up while queued
    Expected number of calls: 0   // queued.next — the dead request was run
    Received number of calls: 1
Tests: 1 failed
packages/express-context admission.test.ts: does not compile (`signal` is not an AdmissionRequest field)

After: admission-control.test.ts 18 passed, admission.test.ts 28 passed; eslint clean on the four touched files.

Link to Devin session: https://app.devin.ai/sessions/959661f0d69640789bd6b38550d379b7
Open in Devin Desktop: https://app.devin.ai/desktop/session/959661f0d69640789bd6b38550d379b7?variant=devin
Requested by: @pyramation

[devin-ai-integration]

I'll fix CI failures and address comments from users with write access. I'll skip comments containing "(aside)".

• Disable automatic comment, CI, and merge conflict monitoring

[tenki-reviewer]

Review complete. No issues found — approved ✅.

---

This PR wires request abort signals into the admission control path: the middleware listens for connection close and aborts queued waiters, and the shared ConcurrencyLimiter learns to settle aborted waiters and evict idle tenant state. Tests cover pre-abort, mid-queue abort, and granted-then-aborted paths.

Files	Change
packages/express-context/src/admission.ts	Limiter support for abort-driven settling, waiter removal, and idle-state eviction.
graphql/server/src/middleware/admission-control.ts	Middleware attaches close/abort handling around acquire/release with listener cleanup.
packages/express-context/__tests__/admission.test.ts	Limiter unit tests for abort and eviction semantics.
graphql/server/src/middleware/__tests__/admission-control.test.ts	Middleware tests for hang-up during queue wait and after grant.

_{Reviewed commit: 9648a44}