{"abstract":"A message whose prerequisites arrive later is dropped or never revisited after another pending message becomes ready.","category":"Distributed coordination","checks":7,"contract":"Initial IDs are already applied. Deliveries are [ID,dependency IDs], with duplicate IDs denoting the same operation. Apply an ID only after all dependencies are applied. Return sorted applied and pending IDs after exhausting all currently satisfiable dependencies; missing dependencies and cycles remain pending. Payload conflict resolution is outside this model.","evaluation_group":"model-808b45b3bf1025ca","failed_approach":"A single buffer sweep can leave a chain pending because its earlier entries become ready only after the sweep passes them.","family":"dist-causal-delivery-buffer","id":"FA-106","implementations":{"attempt":{"sha256":"b016456cf64a3816d21039cc269d1fe0256eaef8f2d9a82067ec9afb82c8ad11","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(initial, deliveries):\n    applied = set(initial)\n    pending = {identity: set(dependencies) for identity, dependencies in deliveries if identity not in applied}\n    for identity, dependencies in list(pending.items()):\n        if dependencies <= applied:\n            applied.add(identity)\n            del pending[identity]\n    return [sorted(applied), sorted(pending)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nids = ['op-'+str(i) for i in range(N+3)]\nchain = [[identity, [ids[i-1]] if i else []] for i, identity in enumerate(ids)]\ncheck('reverse dependency chain', solve([], list(reversed(chain))), [sorted(ids), []])\ncheck('already causal arrival', solve([], chain), [sorted(ids), []])\ncheck('missing prerequisite retained', solve([], [['waiting', ['absent']]]), [[], ['waiting']])\ncheck('initial context unlocks delivery', solve(['root'], [['child', ['root']]]), [['child', 'root'], []])\ncheck('dependency cycle stays pending', solve([], [['a', ['b']], ['b', ['a']]]), [[], ['a', 'b']])\ncheck('replayed delivery', solve([], chain+chain), [sorted(ids), []])\ncheck('empty delivery', solve(['root'], []), [['root'], []])\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":"7033e4e40fd7fdca3444e83f724c8de313a01b28cbeffa0509be3e8ae16e170c","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(initial, deliveries):\n    applied = set(initial)\n    for identity, dependencies in deliveries:\n        if set(dependencies) <= applied:\n            applied.add(identity)\n    return [sorted(applied), []]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nids = ['op-'+str(i) for i in range(N+3)]\nchain = [[identity, [ids[i-1]] if i else []] for i, identity in enumerate(ids)]\ncheck('reverse dependency chain', solve([], list(reversed(chain))), [sorted(ids), []])\ncheck('already causal arrival', solve([], chain), [sorted(ids), []])\ncheck('missing prerequisite retained', solve([], [['waiting', ['absent']]]), [[], ['waiting']])\ncheck('initial context unlocks delivery', solve(['root'], [['child', ['root']]]), [['child', 'root'], []])\ncheck('dependency cycle stays pending', solve([], [['a', ['b']], ['b', ['a']]]), [[], ['a', 'b']])\ncheck('replayed delivery', solve([], chain+chain), [sorted(ids), []])\ncheck('empty delivery', solve(['root'], []), [['root'], []])\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"},"fixed":{"sha256":"645feb364e4b9fc3e15c19d361ff2e1560e929bde1c7d418be1d96fccb8a7d52","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(initial, deliveries):\n    applied = set(initial)\n    pending = {identity: set(dependencies) for identity, dependencies in deliveries if identity not in applied}\n    while pending:\n        ready = [identity for identity, dependencies in pending.items() if dependencies <= applied]\n        if not ready:\n            break\n        for identity in ready:\n            applied.add(identity)\n            del pending[identity]\n    return [sorted(applied), sorted(pending)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\nids = ['op-'+str(i) for i in range(N+3)]\nchain = [[identity, [ids[i-1]] if i else []] for i, identity in enumerate(ids)]\ncheck('reverse dependency chain', solve([], list(reversed(chain))), [sorted(ids), []])\ncheck('already causal arrival', solve([], chain), [sorted(ids), []])\ncheck('missing prerequisite retained', solve([], [['waiting', ['absent']]]), [[], ['waiting']])\ncheck('initial context unlocks delivery', solve(['root'], [['child', ['root']]]), [['child', 'root'], []])\ncheck('dependency cycle stays pending', solve([], [['a', ['b']], ['b', ['a']]]), [[], ['a', 'b']])\ncheck('replayed delivery', solve([], chain+chain), [sorted(ids), []])\ncheck('empty delivery', solve(['root'], []), [['root'], []])\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-causal-delivery-buffer","generated_at":"2026-09-29T14:36:50.462840+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Models causal message admission over reordered delivery, including transitive unlocks, replayed deliveries and permanently unavailable prerequisites.","repair":"Keep unresolved messages and repeatedly apply ready entries until no further progress is possible.","root_cause":"Readiness is evaluated only at arrival or in one pass, instead of draining the dependency buffer to a fixed point.","sha256":"ea20422576fc10e0fa4156bc505735d5477886e4c2985f33c4fa6ad29759fbd5","title":"Out-of-order delivery permanently loses a dependent update · case 01","variant":1,"variant_policy":"Five numbered records share a model and may reuse boundary fixtures.","verification":{"attempt":{"elapsed_ms":34.809,"exit_code":1,"observations":[{"actual":[["op-0"],["op-1","op-2","op-3"]],"check":"reverse dependency chain","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":false},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"already causal arrival","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[[],["waiting"]],"check":"missing prerequisite retained","expected":[[],["waiting"]],"passed":true},{"actual":[["child","root"],[]],"check":"initial context unlocks delivery","expected":[["child","root"],[]],"passed":true},{"actual":[[],["a","b"]],"check":"dependency cycle stays pending","expected":[[],["a","b"]],"passed":true},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"replayed delivery","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[["root"],[]],"check":"empty delivery","expected":[["root"],[]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"reverse dependency chain\", \"actual\": [[\"op-0\"], [\"op-1\", \"op-2\", \"op-3\"]], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": false}, {\"check\": \"already causal arrival\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"missing prerequisite retained\", \"actual\": [[], [\"waiting\"]], \"expected\": [[], [\"waiting\"]], \"passed\": true}, {\"check\": \"initial context unlocks delivery\", \"actual\": [[\"child\", \"root\"], []], \"expected\": [[\"child\", \"root\"], []], \"passed\": true}, {\"check\": \"dependency cycle stays pending\", \"actual\": [[], [\"a\", \"b\"]], \"expected\": [[], [\"a\", \"b\"]], \"passed\": true}, {\"check\": \"replayed delivery\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"empty delivery\", \"actual\": [[\"root\"], []], \"expected\": [[\"root\"], []], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":35.579,"exit_code":1,"observations":[{"actual":[["op-0"],[]],"check":"reverse dependency chain","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":false},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"already causal arrival","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[[],[]],"check":"missing prerequisite retained","expected":[[],["waiting"]],"passed":false},{"actual":[["child","root"],[]],"check":"initial context unlocks delivery","expected":[["child","root"],[]],"passed":true},{"actual":[[],[]],"check":"dependency cycle stays pending","expected":[[],["a","b"]],"passed":false},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"replayed delivery","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[["root"],[]],"check":"empty delivery","expected":[["root"],[]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"reverse dependency chain\", \"actual\": [[\"op-0\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": false}, {\"check\": \"already causal arrival\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"missing prerequisite retained\", \"actual\": [[], []], \"expected\": [[], [\"waiting\"]], \"passed\": false}, {\"check\": \"initial context unlocks delivery\", \"actual\": [[\"child\", \"root\"], []], \"expected\": [[\"child\", \"root\"], []], \"passed\": true}, {\"check\": \"dependency cycle stays pending\", \"actual\": [[], []], \"expected\": [[], [\"a\", \"b\"]], \"passed\": false}, {\"check\": \"replayed delivery\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"empty delivery\", \"actual\": [[\"root\"], []], \"expected\": [[\"root\"], []], \"passed\": true}], \"passed\": false}\n"},"fixed":{"elapsed_ms":50.146,"exit_code":0,"observations":[{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"reverse dependency chain","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"already causal arrival","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[[],["waiting"]],"check":"missing prerequisite retained","expected":[[],["waiting"]],"passed":true},{"actual":[["child","root"],[]],"check":"initial context unlocks delivery","expected":[["child","root"],[]],"passed":true},{"actual":[[],["a","b"]],"check":"dependency cycle stays pending","expected":[[],["a","b"]],"passed":true},{"actual":[["op-0","op-1","op-2","op-3"],[]],"check":"replayed delivery","expected":[["op-0","op-1","op-2","op-3"],[]],"passed":true},{"actual":[["root"],[]],"check":"empty delivery","expected":[["root"],[]],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"reverse dependency chain\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"already causal arrival\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"missing prerequisite retained\", \"actual\": [[], [\"waiting\"]], \"expected\": [[], [\"waiting\"]], \"passed\": true}, {\"check\": \"initial context unlocks delivery\", \"actual\": [[\"child\", \"root\"], []], \"expected\": [[\"child\", \"root\"], []], \"passed\": true}, {\"check\": \"dependency cycle stays pending\", \"actual\": [[], [\"a\", \"b\"]], \"expected\": [[], [\"a\", \"b\"]], \"passed\": true}, {\"check\": \"replayed delivery\", \"actual\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"expected\": [[\"op-0\", \"op-1\", \"op-2\", \"op-3\"], []], \"passed\": true}, {\"check\": \"empty delivery\", \"actual\": [[\"root\"], []], \"expected\": [[\"root\"], []], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}