FA-42298 / Listener lifecycle / Member archive

Async callback rejection is delivered twice on duplicate settlement · case 03

Async callback rejection is delivered twice on duplicate settlement; the returned lifecycle plan violates the stated transition contract.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Plan settlement of one asynchronous observer callback. Only the current generation may publish a result. Cancellation suppresses publication but still releases acquired resources. Settled callback IDs are ignored on duplicate completion. Outstanding count decreases once and never below zero. Rejections route to the error observer, not the value observer; an absent successful value is a legitimate None payload. If the error observer itself fails, report the original rejection followed by its handler failure, preserving both causes; successful handlers consume the original. Rejection diagnostics retain the actual completing generation and error reason even when the current subscription generation has advanced. Inputs are finite state snapshots, including transitional and stale states; output fields are the exact independent actions/metadata defined by the corrected expression table. Numeric fixture capacities and counts vary with N. Field definitions, each independently computed from the input snapshot: publish = s['generation']==s['settled_generation'] and not s['cancel'] and not s['duplicate'] and not s['rejected']; reject = s['rejected'] and not s['duplicate'] and s['generation']==s['settled_generation'] and not s['cancel']; outstanding = max(0,s['outstanding']-int(not s['duplicate'])); release = s['acquired'] and not s['duplicate']; value = [s['value']] if not s['rejected'] else []; error = {'generation':s['settled_generation'],'reason':s['error']} if s['rejected'] else None; unhandled = ([s['error'],s['handler_failure']] if s['handler_failure'] is not None else ([] if s['handler'] else [s['error']])) if s['rejected'] else []; finalize = s['closing'] and max(0,s['outstanding']-int(not s['duplicate']))==0; stale = s['generation']!=s['settled_generation']; consumed = not s['duplicate']

Why this case matters

Observer implementations need to preserve this state while subscriptions enter, execute, and leave their lifecycle.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
transition 0	`{"consumed": true, "error": {"generation": 0, "reason": null}, "finalize": false, "outstanding": 8, "publish": false, "reject": true, "release": true, "stale": true, "unhandled": [null, "handler-failure"], "value": []}`	`{"consumed": true, "error": {"generation": 0, "reason": null}, "finalize": false, "outstanding": 8, "publish": false, "reject": false, "release": true, "stale": true, "unhandled": [null, "handler-failure"], "value": []}`	Failed

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