feat: Add Bounded Queues With Backpressure Signaling - #10
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Finite ready-queue capacity with reject-on-full, plus high/low watermark hysteresis so producers can pause and resume without dropping work the queue already accepted.
Sync ack still sits inside deliver's handler try/catch. Flow notifications from that path were swallowed after the entry settled. Defer applyFlow until pumping is false, and cover the consume-drain listener throw.
ThomasHartDev
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The work queue used to grow its ready list without a limit. Slow or missing consumers could pile up forever and the producer had no way to find out.
This adds a finite ready-queue capacity. enqueue throws QueueFullError when the backlog is full, and tryEnqueue returns { accepted: false } so a caller can wait. A WatermarkGate watches ready depth: pause at or above high, resume at or below low, hold the last state in the open band. Occupancy bouncing between high and high-1 only stays paused when low is at most high-2. Default bounds for capacity 2 are high=2 and low=1, so 2 vs 1 does flip. Redelivery of a message that already got in is still allowed to sit above capacity. Prefetch still caps in-flight.
Flow notifications run after the pump is idle so a listener throw on consume/ack is not swallowed by deliver's handler try/catch. enqueue can still throw a listener error after the payload is already on ready: treat that as notify-after-accept, not reject-and-retry.
Closes #9