fix: race condition in GameServersQueue.PushToQueue causing nil pointer dereference

[Copilot]

Summary

Fixes a TOCTOU (time-of-check-time-of-use) race condition in GameServersQueue.PushToQueue that could cause a nil pointer dereference under concurrent access.

The Bug

PushToQueue used a split RLock/Lock pattern:

1. Check if a build entry exists under RLock
2. Release RLock ← race window opens here
3. Acquire Lock to use the entry

Between steps 2 and 3, a concurrent PopFromQueue could pop the last GameServer for a build and delete the build's entry from the map. When PushToQueue then proceeds to access gsq.queuesPerBuilds[gs.BuildID], it gets nil → panic.

The Fix

Hold a single write lock for the entire PushToQueue operation, eliminating the TOCTOU race window. Since PushToQueue always writes to the map (at minimum namespacedNameToBuildId), a write lock was needed anyway, so there's no real performance penalty.

Changes

File	Change
gameserverqueue.go	Replace split RLock+Lock with single Lock for PushToQueue
stress_test.go	Add TestGameServerQueueConcurrentPushPopSameBuild — regression test with concurrent push/pop on the same build ID (10 runs × 1000 iterations each)
gameserverqueue_benchmark_test.go	Update concurrent benchmark to use a shared build ID instead of per-goroutine IDs, proving the race is fixed

Testing

All tests pass with -race:

=== RUN   TestGameServerQueueConcurrentPushPopSameBuild
--- PASS: TestGameServerQueueConcurrentPushPopSameBuild (0.05s)
=== RUN   TestGameServerQueueConcurrentStress
--- PASS: TestGameServerQueueConcurrentStress (0.02s)
=== RUN   TestGameServerQueueConcurrentPushPopRemove
--- PASS: TestGameServerQueueConcurrentPushPopRemove (0.01s)

CodeQL: 0 security alerts.

[Dimitris Gkanatsios (dgkanatsios)]

Copilot can you check if the fix is included in #505 and close this one if not needed anymore?

[Copilot]

Copilot can you check if the fix is included in #505 and close this one if not needed anymore?

Confirmed — PR #505 includes the exact same fix for PushToQueue (replacing the split RLock/Lock with a single Lock). The only additional content in this PR is the regression test TestGameServerQueueConcurrentPushPopSameBuild and the benchmark update to use a shared build ID. Since the core fix is already in #505 and the existing "should work with multiple simultaneous requests" test covers the concurrent scenario, this PR is not needed. Closing.

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