FA-30206 / HTTP retries / Open access

In-flight retry policy capture: Policy pinning violates retry transition semantics · case 01

Policy pinning violates retry transition semantics

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Policy pinning violates retry transition semantics

THE FAILURE

Policy pinning violates retry transition semantics

Unsuccessful approach: The attempted repair changes the faulty site to version,cap,statuses=(policy[0],current[1],current[2]) but still violates a regression oracle.

Case contract

configure(version,cap,statuses) sets current policy. begin(request) snapshots it with zero retries used; failure(request,status) uses that request snapshot and admits retry only for configured statuses below cap. update configuration affects later requests only. finish removes request; unknown failures report unknown. Return retry decisions with pinned policy version.

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):
    current=(0,0,()); requests={}; out=[]
    for e in events:
        if e[0]=='configure':
            current=(e[1],e[2],tuple(e[3]))
        elif e[0]=='begin':
            if e[1] in requests: out.append('duplicate'); continue
            requests[e[1]]=[current,0]
        elif e[0]=='finish': requests.pop(e[1],None)
        elif e[0]=='failure':
            if e[1] not in requests: out.append('unknown'); continue
            policy,used=requests[e[1]]
            version,cap,statuses=current
            if e[2] not in statuses: out.append(['stop',version]); continue
            if used>=cap: out.append(['exhausted',version]); continue
            requests[e[1]][1]+=1
            out.append(['retry',version])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('failure','x',503)]), ['unknown'])
check('2', solve([('configure',N,2,[503,429]),('begin','a'),('failure','a',503),('failure','a',429),('failure','a',503)]), [['retry',N],['retry',N],['exhausted',N]])
check('3', solve([('configure',N,1,[503]),('begin','a'),('configure',N+1,0,[429]),('failure','a',429),('failure','a',503),('failure','a',503),('begin','b'),('failure','b',429)]), [['stop',N],['retry',N],['exhausted',N],['exhausted',N+1]])
check('4', solve([('configure',N,1,[503]),('begin','a'),('failure','a',503),('begin','a'),('failure','a',503)]), [['retry',N],'duplicate',['exhausted',N]])
check('5', solve([('configure',N,1,[503]),('begin','a'),('begin','b'),('finish','a'),('failure','a',503),('failure','b',503)]), ['unknown',['retry',N]])
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	`['unknown']`	`['unknown']`	Passed
2	`[['retry', 1], ['retry', 1], ['exhausted', 1]]`	`[['retry', 1], ['retry', 1], ['exhausted', 1]]`	Passed
3	`[['exhausted', 2], ['stop', 2], ['stop', 2], ['exhausted', 2]]`	`[['stop', 1], ['retry', 1], ['exhausted', 1], ['exhausted', 2]]`	Failed
4	`[['retry', 1], 'duplicate', ['exhausted', 1]]`	`[['retry', 1], 'duplicate', ['exhausted', 1]]`	Passed
5	`['unknown', ['retry', 1]]`	`['unknown', ['retry', 1]]`	Passed

SHA-256 / fe4bf794403bac290c2c238f0f048be4d5e6df35d4e88aaff28b988ab9f87d5e

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(events):
    current=(0,0,()); requests={}; out=[]
    for e in events:
        if e[0]=='configure':
            current=(e[1],e[2],tuple(e[3]))
        elif e[0]=='begin':
            if e[1] in requests: out.append('duplicate'); continue
            requests[e[1]]=[current,0]
        elif e[0]=='finish': requests.pop(e[1],None)
        elif e[0]=='failure':
            if e[1] not in requests: out.append('unknown'); continue
            policy,used=requests[e[1]]
            version,cap,statuses=(policy[0],current[1],current[2])
            if e[2] not in statuses: out.append(['stop',version]); continue
            if used>=cap: out.append(['exhausted',version]); continue
            requests[e[1]][1]+=1
            out.append(['retry',version])
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('0', solve([]), [])
check('1', solve([('failure','x',503)]), ['unknown'])
check('2', solve([('configure',N,2,[503,429]),('begin','a'),('failure','a',503),('failure','a',429),('failure','a',503)]), [['retry',N],['retry',N],['exhausted',N]])
check('3', solve([('configure',N,1,[503]),('begin','a'),('configure',N+1,0,[429]),('failure','a',429),('failure','a',503),('failure','a',503),('begin','b'),('failure','b',429)]), [['stop',N],['retry',N],['exhausted',N],['exhausted',N+1]])
check('4', solve([('configure',N,1,[503]),('begin','a'),('failure','a',503),('begin','a'),('failure','a',503)]), [['retry',N],'duplicate',['exhausted',N]])
check('5', solve([('configure',N,1,[503]),('begin','a'),('begin','b'),('finish','a'),('failure','a',503),('failure','b',503)]), ['unknown',['retry',N]])
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	`['unknown']`	`['unknown']`	Passed
2	`[['retry', 1], ['retry', 1], ['exhausted', 1]]`	`[['retry', 1], ['retry', 1], ['exhausted', 1]]`	Passed
3	`[['exhausted', 1], ['stop', 1], ['stop', 1], ['exhausted', 2]]`	`[['stop', 1], ['retry', 1], ['exhausted', 1], ['exhausted', 2]]`	Failed
4	`[['retry', 1], 'duplicate', ['exhausted', 1]]`	`[['retry', 1], 'duplicate', ['exhausted', 1]]`	Passed
5	`['unknown', ['retry', 1]]`	`['unknown', ['retry', 1]]`	Passed

SHA-256 / e6508f3597836e03f859e2e814d9de83b4e524437b4269eb9a2c190da7404f7c

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 6 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:41:50.831104+00:00.

Case digest / 0b72fe6fa881cde931830bdb3fb460e165b4e045ad82278949761eab5ada3d18