{"abstract":"Concurrent callers start separate fetches, or a completed fetch incorrectly absorbs a later request.","category":"Distributed coordination","checks":6,"contract":"Events are ['start',key,waiter] or ['complete',key,value]. Distinct waiters share an active job. Completion emits [waiter,value] in registration order and removes that flight. Later starts create new jobs. Return [jobs started,deliveries]; unsolicited completions are ignored.","contract_signature":"events","evaluation_group":"model-af07ce79b3756c56","failed_approach":"Retaining completed keys suppresses fresh remote work and delivers a stale result to later callers.","family":"dist-inflight-coalescing","id":"FA-086","implementations":{"attempt":{"sha256":"c4e02eefbeafe043065b0d6e8a55e0981f6fce2be18b26edc6e2ba715db27da9","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(events):\n    active, completed, deliveries, started = {}, {}, [], 0\n    for kind, key, value in events:\n        if kind == 'start':\n            if key in completed:\n                deliveries.append([value, completed[key]])\n            else:\n                if key not in active:\n                    started += 1\n                active.setdefault(key, []).append(value)\n        elif key in active:\n            deliveries.extend([[waiter, value] for waiter in active.pop(key)])\n            completed[key] = value\n    return [started, deliveries]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nstarts = [['start', 'k', 'w'+str(i)] for i in range(N+1)]\ncheck('overlapping callers share work', solve(starts+[['complete', 'k', N]]), [1, [['w'+str(i), N] for i in range(N+1)]])\ncheck('later request starts fresh', solve([['start', 'k', 'a'], ['complete', 'k', N], ['start', 'k', 'b'], ['complete', 'k', N+1]]), [2, [['a', N], ['b', N+1]]])\ncheck('separate keys remain separate', solve([['start', 'x', 'a'], ['start', 'y', 'b'], ['complete', 'y', N], ['complete', 'x', N+1]]), [2, [['b', N], ['a', N+1]]])\ncheck('unsolicited completion', solve([['complete', 'unknown', N]]), [0, []])\ncheck('empty arrival stream', solve([]), [0, []])\ncheck('unfinished flight is pending', solve(starts), [1, []])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"d20810d824ebe15634f61251bc8913dcb8f667425aa5a9ad8c1e13f7514f69c2","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(events):\n    active, deliveries, started = {}, [], 0\n    for kind, key, value in events:\n        if kind == 'start':\n            started += 1\n            active.setdefault(key, []).append(value)\n        else:\n            deliveries.extend([[waiter, value] for waiter in active.pop(key, [])])\n    return [started, deliveries]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nstarts = [['start', 'k', 'w'+str(i)] for i in range(N+1)]\ncheck('overlapping callers share work', solve(starts+[['complete', 'k', N]]), [1, [['w'+str(i), N] for i in range(N+1)]])\ncheck('later request starts fresh', solve([['start', 'k', 'a'], ['complete', 'k', N], ['start', 'k', 'b'], ['complete', 'k', N+1]]), [2, [['a', N], ['b', N+1]]])\ncheck('separate keys remain separate', solve([['start', 'x', 'a'], ['start', 'y', 'b'], ['complete', 'y', N], ['complete', 'x', N+1]]), [2, [['b', N], ['a', N+1]]])\ncheck('unsolicited completion', solve([['complete', 'unknown', N]]), [0, []])\ncheck('empty arrival stream', solve([]), [0, []])\ncheck('unfinished flight is pending', solve(starts), [1, []])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"dist-inflight-coalescing","generated_at":"2026-09-29T14:36:50.441720+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Models request coalescing for distributed reads. This is not durable event deduplication: completed requests deliberately do not establish a cache or permanent idempotency record.","root_cause":"The request registry does not distinguish active shared work from a permanent result cache.","sha256":"aa7e1b868a6a66e02c191d58e98cff08156a3f808231e024711a6ce8b1f55ea6","title":"Overlapping identical reads start duplicate remote jobs · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":35.536,"exit_code":1,"observations":[{"actual":[1,[["w0",1],["w1",1]]],"check":"overlapping callers share work","expected":[1,[["w0",1],["w1",1]]],"passed":true},{"actual":[1,[["a",1],["b",1]]],"check":"later request starts fresh","expected":[2,[["a",1],["b",2]]],"passed":false},{"actual":[2,[["b",1],["a",2]]],"check":"separate keys remain separate","expected":[2,[["b",1],["a",2]]],"passed":true},{"actual":[0,[]],"check":"unsolicited completion","expected":[0,[]],"passed":true},{"actual":[0,[]],"check":"empty arrival stream","expected":[0,[]],"passed":true},{"actual":[1,[]],"check":"unfinished flight is pending","expected":[1,[]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overlapping callers share work\", \"actual\": [1, [[\"w0\", 1], [\"w1\", 1]]], \"expected\": [1, [[\"w0\", 1], [\"w1\", 1]]], \"passed\": true}, {\"check\": \"later request starts fresh\", \"actual\": [1, [[\"a\", 1], [\"b\", 1]]], \"expected\": [2, [[\"a\", 1], [\"b\", 2]]], \"passed\": false}, {\"check\": \"separate keys remain separate\", \"actual\": [2, [[\"b\", 1], [\"a\", 2]]], \"expected\": [2, [[\"b\", 1], [\"a\", 2]]], \"passed\": true}, {\"check\": \"unsolicited completion\", \"actual\": [0, []], \"expected\": [0, []], \"passed\": true}, {\"check\": \"empty arrival stream\", \"actual\": [0, []], \"expected\": [0, []], \"passed\": true}, {\"check\": \"unfinished flight is pending\", \"actual\": [1, []], \"expected\": [1, []], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":34.578,"exit_code":1,"observations":[{"actual":[2,[["w0",1],["w1",1]]],"check":"overlapping callers share work","expected":[1,[["w0",1],["w1",1]]],"passed":false},{"actual":[2,[["a",1],["b",2]]],"check":"later request starts fresh","expected":[2,[["a",1],["b",2]]],"passed":true},{"actual":[2,[["b",1],["a",2]]],"check":"separate keys remain separate","expected":[2,[["b",1],["a",2]]],"passed":true},{"actual":[0,[]],"check":"unsolicited completion","expected":[0,[]],"passed":true},{"actual":[0,[]],"check":"empty arrival stream","expected":[0,[]],"passed":true},{"actual":[2,[]],"check":"unfinished flight is pending","expected":[1,[]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"overlapping callers share work\", \"actual\": [2, [[\"w0\", 1], [\"w1\", 1]]], \"expected\": [1, [[\"w0\", 1], [\"w1\", 1]]], \"passed\": false}, {\"check\": \"later request starts fresh\", \"actual\": [2, [[\"a\", 1], [\"b\", 2]]], \"expected\": [2, [[\"a\", 1], [\"b\", 2]]], \"passed\": true}, {\"check\": \"separate keys remain separate\", \"actual\": [2, [[\"b\", 1], [\"a\", 2]]], \"expected\": [2, [[\"b\", 1], [\"a\", 2]]], \"passed\": true}, {\"check\": \"unsolicited completion\", \"actual\": [0, []], \"expected\": [0, []], \"passed\": true}, {\"check\": \"empty arrival stream\", \"actual\": [0, []], \"expected\": [0, []], \"passed\": true}, {\"check\": \"unfinished flight is pending\", \"actual\": [2, []], \"expected\": [1, []], \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}