FA-26616 / HTTP ranges / Open access

Queued partial payloads preserve FIFO order under backpressure · case 01

Queued partial payloads preserve FIFO order under backpressure.

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

ROOT CAUSE

The stream-buffer-retains-order decision uses return ([new] if new else [])+queued.

VERIFIED REPAIR

Apply the bounded decision exactly: return queued+([new] if new else [])

Unsuccessful approach: The partial repair uses return queued+[new], which still violates the stated contract.

Case contract

Append new complete byte chunk to FIFO queue; empty chunks carry no payload and are not added.

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(queued, new):
    return ([new] if new else [])+queued
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-buffer-retains-order fixture 0', solve( ["a"*N],"b"*N), ["a"*N,"b"*N])
check('stream-buffer-retains-order fixture 1', solve(["a"],""), ["a"])
check('stream-buffer-retains-order fixture 2', solve([],"x"), ["x"])
check('stream-buffer-retains-order fixture 3', solve([],""), [])
check('stream-buffer-retains-order fixture 4', solve(["a","b"],"c"), ["a","b","c"])
check('stream-buffer-retains-order fixture 5', solve([""],"x"), ["","x"])
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
stream-buffer-retains-order fixture 0	`['b', 'a']`	`['a', 'b']`	Failed
stream-buffer-retains-order fixture 1	`['a']`	`['a']`	Passed
stream-buffer-retains-order fixture 2	`['x']`	`['x']`	Passed
stream-buffer-retains-order fixture 3	`[]`	`[]`	Passed
stream-buffer-retains-order fixture 4	`['c', 'a', 'b']`	`['a', 'b', 'c']`	Failed
stream-buffer-retains-order fixture 5	`['x', '']`	`['', 'x']`	Failed

SHA-256 / 0c819cdb6518552859bcceac71c30e5764ec8c1f694f1d495c8c37ed0ba3e027

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(queued, new):
    return queued+[new]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-buffer-retains-order fixture 0', solve( ["a"*N],"b"*N), ["a"*N,"b"*N])
check('stream-buffer-retains-order fixture 1', solve(["a"],""), ["a"])
check('stream-buffer-retains-order fixture 2', solve([],"x"), ["x"])
check('stream-buffer-retains-order fixture 3', solve([],""), [])
check('stream-buffer-retains-order fixture 4', solve(["a","b"],"c"), ["a","b","c"])
check('stream-buffer-retains-order fixture 5', solve([""],"x"), ["","x"])
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
stream-buffer-retains-order fixture 0	`['a', 'b']`	`['a', 'b']`	Passed
stream-buffer-retains-order fixture 1	`['a', '']`	`['a']`	Failed
stream-buffer-retains-order fixture 2	`['x']`	`['x']`	Passed
stream-buffer-retains-order fixture 3	`['']`	`[]`	Failed
stream-buffer-retains-order fixture 4	`['a', 'b', 'c']`	`['a', 'b', 'c']`	Passed
stream-buffer-retains-order fixture 5	`['', 'x']`	`['', 'x']`	Passed

SHA-256 / 5bdb8b0f8801dc676e01f06ace8562194eb2e4f699f17c93aad60948fbad46c9

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(queued, new):
    return queued+([new] if new else [])
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('stream-buffer-retains-order fixture 0', solve( ["a"*N],"b"*N), ["a"*N,"b"*N])
check('stream-buffer-retains-order fixture 1', solve(["a"],""), ["a"])
check('stream-buffer-retains-order fixture 2', solve([],"x"), ["x"])
check('stream-buffer-retains-order fixture 3', solve([],""), [])
check('stream-buffer-retains-order fixture 4', solve(["a","b"],"c"), ["a","b","c"])
check('stream-buffer-retains-order fixture 5', solve([""],"x"), ["","x"])
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
stream-buffer-retains-order fixture 0	`['a', 'b']`	`['a', 'b']`	Passed
stream-buffer-retains-order fixture 1	`['a']`	`['a']`	Passed
stream-buffer-retains-order fixture 2	`['x']`	`['x']`	Passed
stream-buffer-retains-order fixture 3	`[]`	`[]`	Passed
stream-buffer-retains-order fixture 4	`['a', 'b', 'c']`	`['a', 'b', 'c']`	Passed
stream-buffer-retains-order fixture 5	`['', 'x']`	`['', 'x']`	Passed

SHA-256 / c59e892744922b3270b62e1bcf93e183c48dc735b5e2c2787113f32528ab85cb

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 2026-09-29T14:41:17.580372+00:00.

Case digest / 52837cb6cf10ff049726ae215e0c1921590e640d605ee83419efc85dc8f2ed77