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FA-26956 / HTTP ranges / Open access

Partial cache admission publishes complete requested fragments atomically: a contradicting duplicate fragment invalidates admission · case 01

Partial cache admission publishes complete requested fragments atomically: a contradicting duplicate fragment invalidates admission.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The partial-admission-transaction-duplicate-conflict decision uses visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None].

THE FAILURE

The partial-admission-transaction-duplicate-conflict decision uses visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None].

Unsuccessful approach: The partial repair uses visible=dict(x[0]) pending=None reads=[] for event in x[1]: op=event[0] if op=='begin': if pending is not None: continue pending=[event[1],set(event[2]),{}] elif op=='put': if pending is None or event[1]!=pending[0]: continue at,char=event[2:] if at not in pending[1]: continue if at in pending[2] and pending[2][at]!=char: pending[2][at]=char continue pending[2][at]=char elif op=='commit': if pending is None or event[1]!=pending[0]: continue if set(pending[2])!=pending[1]: continue visible=dict(pending[2]) pending=None elif op=='abort': if pending is not None and event[1]==pending[0]: pending=None elif op=='read': reads.append(sorted(visible.items())) return [reads,sorted(visible.items()),pending[0] if pending is not None else None], which still violates the stated contract.

Case contract

x is [old-visible-cells,events]. Events begin(id,expected-offsets), put(id,offset,char), commit(id), abort(id), read. One transaction at a time; unknown or mismatching ids ignored. A conflicting duplicate byte invalidates the active transaction. Commit succeeds only when every expected cell is present and replaces the old generation. Readers see committed cells sorted by offset. Return [read-snapshots,final-cells,pending-id].

Why this case matters

Range responses combine representation identity, conditional requests, framing, and partial-object state.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    visible=dict(x[0])
    pending=None
    reads=[]
    for event in x[1]:
        op=event[0]
        if op=='begin':
            if pending is not None: continue
            pending=[event[1],set(event[2]),{}]
        elif op=='put':
            if pending is None or event[1]!=pending[0]: continue
            at,char=event[2:]
            if at not in pending[1]: continue
            if at in pending[2] and pending[2][at]!=char:
                continue
            pending[2][at]=char
        elif op=='commit':
            if pending is None or event[1]!=pending[0]: continue
            if set(pending[2])!=pending[1]: continue
            visible=dict(pending[2])
            pending=None
        elif op=='abort':
            if pending is not None and event[1]==pending[0]: pending=None
        elif op=='read':
            reads.append(sorted(visible.items()))
    return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('duplicate-conflict fixture 0', json.loads(json.dumps(solve([[[0,'o'],[9,'z']],[['begin','a',[0,1]],['put','a',1,'b'],['read'],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[[0,'o'],[9,'z']],[[0,'a'],[1,'b']]],[[0,'a'],[1,'b']],None])))
check('duplicate-conflict fixture 1', json.loads(json.dumps(solve([[],[['begin','a',[0,1]],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('duplicate-conflict fixture 2', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','wrong',0,'x'],['put','a',1,'y'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('duplicate-conflict fixture 3', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',1,'b'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('duplicate-conflict fixture 4', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'b'],['commit','a']]]))), json.loads(json.dumps([[],[],None])))
check('duplicate-conflict fixture 5', json.loads(json.dumps(solve([[],[['begin','a',[0]],['begin','b',[]],['abort','b'],['put','a',0,'a'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('duplicate-conflict fixture 6', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'a'],['commit','wrong'],['read'],['commit','a']]]))), json.loads(json.dumps([[[]],[[0,'a']],None])))
check('duplicate-conflict fixture 7', json.loads(json.dumps(solve([[],[['begin','a',[]],['commit','a'],['begin','b',[N]],['put','b',N,'p'],['commit','b']]]))), json.loads(json.dumps([[],[[N,'p']],None])))
check('duplicate-conflict fixture 8', json.loads(json.dumps(solve([[[0,'o']],[['begin','a',[0]],['put','a',0,'a'],['abort','a'],['read']]]))), json.loads(json.dumps([[[[0,'o']]],[[0,'o']],None])))
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
duplicate-conflict fixture 0[[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None][[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None]Passed
duplicate-conflict fixture 1[[[]], [], 'a'][[[]], [], 'a']Passed
duplicate-conflict fixture 2[[[]], [], 'a'][[[]], [], 'a']Passed
duplicate-conflict fixture 3[[], [[0, 'a']], None][[], [[0, 'a']], None]Passed
duplicate-conflict fixture 4[[], [[0, 'a']], None][[], [], None]Failed
duplicate-conflict fixture 5[[], [[0, 'a']], None][[], [[0, 'a']], None]Passed
duplicate-conflict fixture 6[[[]], [[0, 'a']], None][[[]], [[0, 'a']], None]Passed
duplicate-conflict fixture 7[[], [[1, 'p']], None][[], [[1, 'p']], None]Passed
duplicate-conflict fixture 8[[[[0, 'o']]], [[0, 'o']], None][[[[0, 'o']]], [[0, 'o']], None]Passed

SHA-256 / 4d3397717a88cbbe98bc80e4a38c3e5f09879c99fb9bb9a3aace1821e0a307bf

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x):
    visible=dict(x[0])
    pending=None
    reads=[]
    for event in x[1]:
        op=event[0]
        if op=='begin':
            if pending is not None: continue
            pending=[event[1],set(event[2]),{}]
        elif op=='put':
            if pending is None or event[1]!=pending[0]: continue
            at,char=event[2:]
            if at not in pending[1]: continue
            if at in pending[2] and pending[2][at]!=char:
                pending[2][at]=char
                continue
            pending[2][at]=char
        elif op=='commit':
            if pending is None or event[1]!=pending[0]: continue
            if set(pending[2])!=pending[1]: continue
            visible=dict(pending[2])
            pending=None
        elif op=='abort':
            if pending is not None and event[1]==pending[0]: pending=None
        elif op=='read':
            reads.append(sorted(visible.items()))
    return [reads,sorted(visible.items()),pending[0] if pending is not None else None]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('duplicate-conflict fixture 0', json.loads(json.dumps(solve([[[0,'o'],[9,'z']],[['begin','a',[0,1]],['put','a',1,'b'],['read'],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[[0,'o'],[9,'z']],[[0,'a'],[1,'b']]],[[0,'a'],[1,'b']],None])))
check('duplicate-conflict fixture 1', json.loads(json.dumps(solve([[],[['begin','a',[0,1]],['put','a',0,'a'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('duplicate-conflict fixture 2', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','wrong',0,'x'],['put','a',1,'y'],['commit','a'],['read']]]))), json.loads(json.dumps([[[]],[],'a'])))
check('duplicate-conflict fixture 3', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',1,'b'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('duplicate-conflict fixture 4', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'b'],['commit','a']]]))), json.loads(json.dumps([[],[],None])))
check('duplicate-conflict fixture 5', json.loads(json.dumps(solve([[],[['begin','a',[0]],['begin','b',[]],['abort','b'],['put','a',0,'a'],['commit','a']]]))), json.loads(json.dumps([[],[[0,'a']],None])))
check('duplicate-conflict fixture 6', json.loads(json.dumps(solve([[],[['begin','a',[0]],['put','a',0,'a'],['put','a',0,'a'],['commit','wrong'],['read'],['commit','a']]]))), json.loads(json.dumps([[[]],[[0,'a']],None])))
check('duplicate-conflict fixture 7', json.loads(json.dumps(solve([[],[['begin','a',[]],['commit','a'],['begin','b',[N]],['put','b',N,'p'],['commit','b']]]))), json.loads(json.dumps([[],[[N,'p']],None])))
check('duplicate-conflict fixture 8', json.loads(json.dumps(solve([[[0,'o']],[['begin','a',[0]],['put','a',0,'a'],['abort','a'],['read']]]))), json.loads(json.dumps([[[[0,'o']]],[[0,'o']],None])))
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
duplicate-conflict fixture 0[[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None][[[[0, 'o'], [9, 'z']], [[0, 'a'], [1, 'b']]], [[0, 'a'], [1, 'b']], None]Passed
duplicate-conflict fixture 1[[[]], [], 'a'][[[]], [], 'a']Passed
duplicate-conflict fixture 2[[[]], [], 'a'][[[]], [], 'a']Passed
duplicate-conflict fixture 3[[], [[0, 'a']], None][[], [[0, 'a']], None]Passed
duplicate-conflict fixture 4[[], [[0, 'b']], None][[], [], None]Failed
duplicate-conflict fixture 5[[], [[0, 'a']], None][[], [[0, 'a']], None]Passed
duplicate-conflict fixture 6[[[]], [[0, 'a']], None][[[]], [[0, 'a']], None]Passed
duplicate-conflict fixture 7[[], [[1, 'p']], None][[], [[1, 'p']], None]Passed
duplicate-conflict fixture 8[[[[0, 'o']]], [[0, 'o']], None][[[[0, 'o']]], [[0, 'o']], None]Passed

SHA-256 / 9653faa2d4205f4435a04d84571ec4bb03c05cc43e8e439cbacab2e56971da94

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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Verification & scope

Deterministic simplified range service, with stipulated local policies and already parsed trusted inputs; not a complete HTTP implementation. 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.

Observations recorded using Python 3.12.14 at 2026-09-29T14:41:20.639618+00:00.

Case digest / c6893763ac9429c7efd2965865fabb2e15ee1169a9a273c0d9a7e870eb30c7e1