enqueue_unbounded bypasses the semaphore so control messages
(poison pills, thread removal tasks) can never block on a full
queue. But wait_dequeue always signals a slot after consuming,
so each unbounded item that gets dequeued inflated the semaphore
by +1, permanently raising the effective max queue depth.
Fix by calling tryWait() in enqueue_unbounded before enqueueing.
When the queue has room (common case), this consumes a slot and
the dequeue-side signal restores balance perfectly. When the queue
is genuinely full (tryWait fails), the item still enqueues but
temporarily exceeds max_depth by one until consumed - a transient
overshoot bounded by control messages in flight.
A CAS-based approach that absorbed extra signals on the dequeue
side was also considered but rejected: it can starve blocked
bounded producers by swallowing the signal they are waiting for.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
