FA-29596 / HTTP retries / Open access

Retry reconciliation with a server receipt: Reusing an idempotency key for changed content replays an unrelated result · case 01

Reusing an idempotency key for changed content replays an unrelated result

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ROOT CAUSE

Reusing an idempotency key for changed content replays an unrelated result

VERIFIED REPAIR

Restore the specified transition elif receipts[key][0]!=body:.

Unsuccessful approach: The attempted repair changes the faulty site to elif receipts[key][0]!=body and receipts[key][1]=="pending": but still violates a regression oracle.

Case contract

submit(key,body) returns new for absent key, pending for matching in-flight key, conflict for a changed body, and cached(value) for a completed matching key. commit(key,value) commits only existing pending entries. forget removes a receipt. Return decisions and receipt table.

Why this case matters

Offline deterministic model of HTTP request retries.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(events):
    receipts={}; out=[]
    for e in events:
        if e[0]=='submit':
            key,body=e[1],e[2]
            if key not in receipts:
                receipts[key]=[body,'pending',None]
                out.append('new')
            elif False:
                out.append('conflict')
            elif receipts[key][1]=='pending':
                out.append('pending')
            else:
                out.append(['cached',receipts[key][2]])
        elif e[0]=='commit':
            if e[1] in receipts and receipts[e[1]][1]=='pending':
                receipts[e[1]][1]='done'
                receipts[e[1]][2]=e[2]
        elif e[0]=='forget':
            receipts.pop(e[1],None)
    return [out,receipts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],{}])
check('1', solve([('submit','a',N),('submit','a',N)]), [['new','pending'],{'a':[N,'pending',None]}])
check('2', solve([('submit','a',N),('submit','b',N),('submit','a',N+1)]), [['new','new','conflict'],{'a':[N,'pending',None],'b':[N,'pending',None]}])
check('3', solve([('submit','a',N),('commit','a',N+5),('commit','a',99),('submit','a',N),('submit','a',N+1)]), [['new',['cached',N+5],'conflict'],{'a':[N,'done',N+5]}])
check('4', solve([('commit','absent',N),('forget','absent')]), [[],{}])
check('5', solve([('submit','a',N),('submit','b',N+1),('forget','a'),('submit','a',N+2)]), [['new','new','new'],{'b':[N+1,'pending',None],'a':[N+2,'pending',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 fixture	Actual	Expected	Outcome
0	`[[], {}]`	`[[], {}]`	Passed
1	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	Passed
2	`[['new', 'new', 'pending'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	`[['new', 'new', 'conflict'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	Failed
3	`[['new', ['cached', 6], ['cached', 6]], {'a': [1, 'done', 6]}]`	`[['new', ['cached', 6], 'conflict'], {'a': [1, 'done', 6]}]`	Failed
4	`[[], {}]`	`[[], {}]`	Passed
5	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	Passed

SHA-256 / 754a25b7fd881147161a3f96c10d4f0589817959742b13d9f24df9364e270068

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(events):
    receipts={}; out=[]
    for e in events:
        if e[0]=='submit':
            key,body=e[1],e[2]
            if key not in receipts:
                receipts[key]=[body,'pending',None]
                out.append('new')
            elif receipts[key][0]!=body and receipts[key][1]=="pending":
                out.append('conflict')
            elif receipts[key][1]=='pending':
                out.append('pending')
            else:
                out.append(['cached',receipts[key][2]])
        elif e[0]=='commit':
            if e[1] in receipts and receipts[e[1]][1]=='pending':
                receipts[e[1]][1]='done'
                receipts[e[1]][2]=e[2]
        elif e[0]=='forget':
            receipts.pop(e[1],None)
    return [out,receipts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],{}])
check('1', solve([('submit','a',N),('submit','a',N)]), [['new','pending'],{'a':[N,'pending',None]}])
check('2', solve([('submit','a',N),('submit','b',N),('submit','a',N+1)]), [['new','new','conflict'],{'a':[N,'pending',None],'b':[N,'pending',None]}])
check('3', solve([('submit','a',N),('commit','a',N+5),('commit','a',99),('submit','a',N),('submit','a',N+1)]), [['new',['cached',N+5],'conflict'],{'a':[N,'done',N+5]}])
check('4', solve([('commit','absent',N),('forget','absent')]), [[],{}])
check('5', solve([('submit','a',N),('submit','b',N+1),('forget','a'),('submit','a',N+2)]), [['new','new','new'],{'b':[N+1,'pending',None],'a':[N+2,'pending',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 fixture	Actual	Expected	Outcome
0	`[[], {}]`	`[[], {}]`	Passed
1	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	Passed
2	`[['new', 'new', 'conflict'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	`[['new', 'new', 'conflict'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	Passed
3	`[['new', ['cached', 6], ['cached', 6]], {'a': [1, 'done', 6]}]`	`[['new', ['cached', 6], 'conflict'], {'a': [1, 'done', 6]}]`	Failed
4	`[[], {}]`	`[[], {}]`	Passed
5	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	Passed

SHA-256 / 48abc3b86e4a73688c3a2d667851dd465ef691d9adf4439c51f4b89f2da48bf6

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(events):
    receipts={}; out=[]
    for e in events:
        if e[0]=='submit':
            key,body=e[1],e[2]
            if key not in receipts:
                receipts[key]=[body,'pending',None]
                out.append('new')
            elif receipts[key][0]!=body:
                out.append('conflict')
            elif receipts[key][1]=='pending':
                out.append('pending')
            else:
                out.append(['cached',receipts[key][2]])
        elif e[0]=='commit':
            if e[1] in receipts and receipts[e[1]][1]=='pending':
                receipts[e[1]][1]='done'
                receipts[e[1]][2]=e[2]
        elif e[0]=='forget':
            receipts.pop(e[1],None)
    return [out,receipts]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [[],{}])
check('1', solve([('submit','a',N),('submit','a',N)]), [['new','pending'],{'a':[N,'pending',None]}])
check('2', solve([('submit','a',N),('submit','b',N),('submit','a',N+1)]), [['new','new','conflict'],{'a':[N,'pending',None],'b':[N,'pending',None]}])
check('3', solve([('submit','a',N),('commit','a',N+5),('commit','a',99),('submit','a',N),('submit','a',N+1)]), [['new',['cached',N+5],'conflict'],{'a':[N,'done',N+5]}])
check('4', solve([('commit','absent',N),('forget','absent')]), [[],{}])
check('5', solve([('submit','a',N),('submit','b',N+1),('forget','a'),('submit','a',N+2)]), [['new','new','new'],{'b':[N+1,'pending',None],'a':[N+2,'pending',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 fixture	Actual	Expected	Outcome
0	`[[], {}]`	`[[], {}]`	Passed
1	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	`[['new', 'pending'], {'a': [1, 'pending', None]}]`	Passed
2	`[['new', 'new', 'conflict'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	`[['new', 'new', 'conflict'], {'a': [1, 'pending', None], 'b': [1, 'pending', None]}]`	Passed
3	`[['new', ['cached', 6], 'conflict'], {'a': [1, 'done', 6]}]`	`[['new', ['cached', 6], 'conflict'], {'a': [1, 'done', 6]}]`	Passed
4	`[[], {}]`	`[[], {}]`	Passed
5	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	`[['new', 'new', 'new'], {'a': [3, 'pending', None], 'b': [2, 'pending', None]}]`	Passed

SHA-256 / d954eef688bc7ddbed441b3968ffe7e8f2aca46edfd6335bbe8676104a62e2cb

Verification & scope

Stipulated bounded simulator, not a complete HTTP implementation or a standards conformance claim. 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 2026-09-29T14:41:44.786360+00:00.

Case digest / 2bdb7f13272ca9c69a6ca3745cb707498aeab2818fa135b18c54db7381f4bf09