FA-29381 / HTTP retries / Open access

Replay source snapshot: Retry preserves an already consumed cursor · case 01

Retry preserves an already consumed cursor

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Retry preserves an already consumed cursor

VERIFIED REPAIR

Reset the cursor to the captured origin on each retry.

Unsuccessful approach: The attempted repair changes the faulty site to pos = max(origin,pos) out.append but still violates a regression oracle.

Case contract

Events open(list of integer bytes, starting index), mutate(index,byte), read(count), retry, close. Opening freezes bytes and origin. Reads advance within the frozen representation. Retry rewinds to origin. Reads after close return closed; retry after close returns closed. Output read chunks or status markers.

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):
    body = (); live = []; origin = 0; pos = 0; closed = True; out = []
    for e in events:
        if e[0] == 'open':
            live = list(e[1])
            body = tuple(live)
            origin = e[2]
            pos = origin
            closed = False
        elif e[0] == 'mutate':
            live[e[1]] = e[2]
        elif e[0] == 'close':
            closed = True
        elif e[0] == 'read':
            if closed:
                out.append('closed')
                continue
            chunk = list(body[pos:pos+e[1]])
            pos += len(chunk)
            out.append(chunk)
        elif e[0] == 'retry':
            if closed:
                out.append('closed')
                continue
            pos = 0
            out.append('rewound')
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('open',[N,N+1,N+2],1),('read',1),('retry',),('read',2)]), [[N+1],'rewound',[N+1,N+2]])
check('2', solve([('open',[N,N+1,N+2],0),('read',2),('read',1),('read',1)]), [[N,N+1],[N+2],[]])
check('3', solve([('open',[N,N+1],0),('mutate',0,99),('retry',),('read',2)]), ['rewound',[N,N+1]])
check('4', solve([('open',[],0),('read',0),('retry',),('read',1)]), [[],'rewound',[]])
check('5', solve([('open',[N,N+1],0),('close',),('read',1),('retry',)]), ['closed','closed'])
check('6', solve([('open',[N],0),('read',1),('close',),('read',1),('retry',),('open',[N+2],0),('read',1)]), [[N],'closed','closed',[N+2]])
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	`[[2], 'rewound', [1, 2]]`	`[[2], 'rewound', [2, 3]]`	Failed
2	`[[1, 2], [3], []]`	`[[1, 2], [3], []]`	Passed
3	`['rewound', [1, 2]]`	`['rewound', [1, 2]]`	Passed
4	`[[], 'rewound', []]`	`[[], 'rewound', []]`	Passed
5	`['closed', 'closed']`	`['closed', 'closed']`	Passed
6	`[[1], 'closed', 'closed', [3]]`	`[[1], 'closed', 'closed', [3]]`	Passed

SHA-256 / d1914b5e4b51fd7f3e259e6d01db2364f6dc577c05ea89510d0aeba5b38b258a

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(events):
    body = (); live = []; origin = 0; pos = 0; closed = True; out = []
    for e in events:
        if e[0] == 'open':
            live = list(e[1])
            body = tuple(live)
            origin = e[2]
            pos = origin
            closed = False
        elif e[0] == 'mutate':
            live[e[1]] = e[2]
        elif e[0] == 'close':
            closed = True
        elif e[0] == 'read':
            if closed:
                out.append('closed')
                continue
            chunk = list(body[pos:pos+e[1]])
            pos += len(chunk)
            out.append(chunk)
        elif e[0] == 'retry':
            if closed:
                out.append('closed')
                continue
            pos = max(origin,pos)
            out.append('rewound')
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('open',[N,N+1,N+2],1),('read',1),('retry',),('read',2)]), [[N+1],'rewound',[N+1,N+2]])
check('2', solve([('open',[N,N+1,N+2],0),('read',2),('read',1),('read',1)]), [[N,N+1],[N+2],[]])
check('3', solve([('open',[N,N+1],0),('mutate',0,99),('retry',),('read',2)]), ['rewound',[N,N+1]])
check('4', solve([('open',[],0),('read',0),('retry',),('read',1)]), [[],'rewound',[]])
check('5', solve([('open',[N,N+1],0),('close',),('read',1),('retry',)]), ['closed','closed'])
check('6', solve([('open',[N],0),('read',1),('close',),('read',1),('retry',),('open',[N+2],0),('read',1)]), [[N],'closed','closed',[N+2]])
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	`[[2], 'rewound', [3]]`	`[[2], 'rewound', [2, 3]]`	Failed
2	`[[1, 2], [3], []]`	`[[1, 2], [3], []]`	Passed
3	`['rewound', [1, 2]]`	`['rewound', [1, 2]]`	Passed
4	`[[], 'rewound', []]`	`[[], 'rewound', []]`	Passed
5	`['closed', 'closed']`	`['closed', 'closed']`	Passed
6	`[[1], 'closed', 'closed', [3]]`	`[[1], 'closed', 'closed', [3]]`	Passed

SHA-256 / ed7a062931cf1f1b3149ab5ee5cc9695c2ef13ff07f0e2ba10fad7af73216f48

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(events):
    body = (); live = []; origin = 0; pos = 0; closed = True; out = []
    for e in events:
        if e[0] == 'open':
            live = list(e[1])
            body = tuple(live)
            origin = e[2]
            pos = origin
            closed = False
        elif e[0] == 'mutate':
            live[e[1]] = e[2]
        elif e[0] == 'close':
            closed = True
        elif e[0] == 'read':
            if closed:
                out.append('closed')
                continue
            chunk = list(body[pos:pos+e[1]])
            pos += len(chunk)
            out.append(chunk)
        elif e[0] == 'retry':
            if closed:
                out.append('closed')
                continue
            pos = origin
            out.append('rewound')
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('open',[N,N+1,N+2],1),('read',1),('retry',),('read',2)]), [[N+1],'rewound',[N+1,N+2]])
check('2', solve([('open',[N,N+1,N+2],0),('read',2),('read',1),('read',1)]), [[N,N+1],[N+2],[]])
check('3', solve([('open',[N,N+1],0),('mutate',0,99),('retry',),('read',2)]), ['rewound',[N,N+1]])
check('4', solve([('open',[],0),('read',0),('retry',),('read',1)]), [[],'rewound',[]])
check('5', solve([('open',[N,N+1],0),('close',),('read',1),('retry',)]), ['closed','closed'])
check('6', solve([('open',[N],0),('read',1),('close',),('read',1),('retry',),('open',[N+2],0),('read',1)]), [[N],'closed','closed',[N+2]])
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	`[[2], 'rewound', [2, 3]]`	`[[2], 'rewound', [2, 3]]`	Passed
2	`[[1, 2], [3], []]`	`[[1, 2], [3], []]`	Passed
3	`['rewound', [1, 2]]`	`['rewound', [1, 2]]`	Passed
4	`[[], 'rewound', []]`	`[[], 'rewound', []]`	Passed
5	`['closed', 'closed']`	`['closed', 'closed']`	Passed
6	`[[1], 'closed', 'closed', [3]]`	`[[1], 'closed', 'closed', [3]]`	Passed

SHA-256 / 5f84087f10982bdd62ce744fb9e49abe266682dab8d7e0790a9253cf04d033cb

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 2026-09-29T14:41:42.679062+00:00.

Case digest / e2712e24982941dd2098400745b6ec551b89c82f5c84fb5d02176ee119a6b60c