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Drop-oldest listener buffering preserves stale callback payloads · case 03

Drop-oldest listener buffering preserves stale callback payloads; the returned lifecycle plan violates the stated transition contract.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Plan a local subscription callback buffer. Input queue is arrival ordered. Drop-oldest keeps the newest capacity records; drop-newest keeps the oldest. Capacity zero retains nothing. Delivery removes at most one item, cancellation clears all items, completion waits for a nonempty buffer, and overflow errors are signaled only under error policy. Notification storage may contain stale records after termination. Deliver values only before the first complete or error marker. 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: oldest = s['queue'][-s['capacity']:] if s['capacity'] else []; newest = s['queue'][:s['capacity']]; append = list(s['queue'])+([s['incoming']] if s['incoming'] is not None else []); next = s['queue'][0] if s['queue'] and s['deliver'] and not s['cancel'] else None; after_delivery = s['queue'][1:] if s['deliver'] and s['queue'] else list(s['queue']); cancelled_queue = [] if s['cancel'] else list(s['queue']); overflow_error = len(s['queue'])>s['capacity'] and s['policy']=='error'; complete_now = [r[1] for r in s['notifications'][:next((i for i,r in enumerate(s['notifications']) if r[0] in ('complete','error')),len(s['notifications']))] if r[0]=='value']; dropped = max(0,len(s['queue'])-s['capacity']); errors = s['errors']+int(len(s['queue'])>s['capacity'] and s['policy']=='error')

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	`{"after_delivery": ["b", "c"], "append": ["a", "b", "c"], "cancelled_queue": [], "complete_now": ["a"], "dropped": 2, "errors": 6, "newest": ["a"], "next": null, "oldest": ["a"], "overflow_error": false}`	`{"after_delivery": ["b", "c"], "append": ["a", "b", "c"], "cancelled_queue": [], "complete_now": ["a"], "dropped": 2, "errors": 6, "newest": ["a"], "next": null, "oldest": ["c"], "overflow_error": false}`	Failed

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