FA-11306 / Media playlist lifecycle / Open access

Play next queue: Fails to advance the playlist cursor on ordinary fallback · case 01

Fails to advance the playlist cursor on ordinary fallback and produces an incorrect media-control or presentation result.

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

ROOT CAUSE

Fails to advance the playlist cursor on ordinary fallback. The fixture suite isolates this decision from network delivery and codec details.

VERIFIED REPAIR

Consume the first enabled play-next queue occurrence before advancing the playlist. Queue plays do not move the playlist cursor; disabled queued occurrences are discarded. Return [selected ID or None,remaining queue,new playlist cursor]. Queue duplicates are independent requests.

Unsuccessful approach: The alternative still fails because it consumes play-next requests in reverse insertion order.

Case contract

Why this case matters

A deterministic in-memory media application model with explicit playlist, timeline or synchronization semantics. Does not implement codecs, transport protocols, rendering hardware or concurrent playback.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(playlist, cursor, queue, disabled):
    pending=list(queue)
    while pending:
        candidate=pending.pop(0)
        if candidate in disabled: continue
        return [candidate,pending,cursor]
    start=playlist.index(cursor) if cursor in playlist else -1
    for candidate in playlist[start+1:]:
        if candidate not in disabled:
            return [candidate,pending,cursor]
    return [None,pending,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('queue has priority', solve(['a', 'b'], 'a', ['x', 'y'], []), ['x', ['y'], 'a'])
check('same track queued twice', solve(['a', 'b'], 'a', ['x', 'x', 'y'], []), ['x', ['x', 'y'], 'a'])
check('disabled queue discarded', solve(['a', 'b'], 'a', ['x', 'y'], ['x']), ['y', [], 'a'])
check('fallback advances cursor', solve(['a', 'b'], 'a', [], []), ['b', [], 'b'])
check('all queued disabled falls back', solve(['a', 'b'], 'a', ['x'], ['x']), ['b', [], 'b'])
check('end has no track', solve(['a'], 'a', [], []), [None, [], 'a'])
check('queue works without playlist', solve([], None, ['x'], []), ['x', [], 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
queue has priority	`['x', ['y'], 'a']`	`['x', ['y'], 'a']`	Passed
same track queued twice	`['x', ['x', 'y'], 'a']`	`['x', ['x', 'y'], 'a']`	Passed
disabled queue discarded	`['y', [], 'a']`	`['y', [], 'a']`	Passed
fallback advances cursor	`['b', [], 'a']`	`['b', [], 'b']`	Failed
all queued disabled falls back	`['b', [], 'a']`	`['b', [], 'b']`	Failed
end has no track	`[None, [], 'a']`	`[None, [], 'a']`	Passed
queue works without playlist	`['x', [], None]`	`['x', [], None]`	Passed

SHA-256 / 5975f79860516f865c42cca4de40fa2102dff978e6a6d50ffb43d826df97156c

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(playlist, cursor, queue, disabled):
    pending=list(queue)
    while pending:
        candidate=pending.pop()
        if candidate in disabled: continue
        return [candidate,pending,cursor]
    start=playlist.index(cursor) if cursor in playlist else -1
    for candidate in playlist[start+1:]:
        if candidate not in disabled:
            return [candidate,pending,candidate]
    return [None,pending,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('queue has priority', solve(['a', 'b'], 'a', ['x', 'y'], []), ['x', ['y'], 'a'])
check('same track queued twice', solve(['a', 'b'], 'a', ['x', 'x', 'y'], []), ['x', ['x', 'y'], 'a'])
check('disabled queue discarded', solve(['a', 'b'], 'a', ['x', 'y'], ['x']), ['y', [], 'a'])
check('fallback advances cursor', solve(['a', 'b'], 'a', [], []), ['b', [], 'b'])
check('all queued disabled falls back', solve(['a', 'b'], 'a', ['x'], ['x']), ['b', [], 'b'])
check('end has no track', solve(['a'], 'a', [], []), [None, [], 'a'])
check('queue works without playlist', solve([], None, ['x'], []), ['x', [], 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
queue has priority	`['y', ['x'], 'a']`	`['x', ['y'], 'a']`	Failed
same track queued twice	`['y', ['x', 'x'], 'a']`	`['x', ['x', 'y'], 'a']`	Failed
disabled queue discarded	`['y', ['x'], 'a']`	`['y', [], 'a']`	Failed
fallback advances cursor	`['b', [], 'b']`	`['b', [], 'b']`	Passed
all queued disabled falls back	`['b', [], 'b']`	`['b', [], 'b']`	Passed
end has no track	`[None, [], 'a']`	`[None, [], 'a']`	Passed
queue works without playlist	`['x', [], None]`	`['x', [], None]`	Passed

SHA-256 / f1df0f68e351204cdf5e2b388b6891ca706aa5127653f84e1486c446be72805f

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(playlist, cursor, queue, disabled):
    pending=list(queue)
    while pending:
        candidate=pending.pop(0)
        if candidate in disabled: continue
        return [candidate,pending,cursor]
    start=playlist.index(cursor) if cursor in playlist else -1
    for candidate in playlist[start+1:]:
        if candidate not in disabled:
            return [candidate,pending,candidate]
    return [None,pending,cursor]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('queue has priority', solve(['a', 'b'], 'a', ['x', 'y'], []), ['x', ['y'], 'a'])
check('same track queued twice', solve(['a', 'b'], 'a', ['x', 'x', 'y'], []), ['x', ['x', 'y'], 'a'])
check('disabled queue discarded', solve(['a', 'b'], 'a', ['x', 'y'], ['x']), ['y', [], 'a'])
check('fallback advances cursor', solve(['a', 'b'], 'a', [], []), ['b', [], 'b'])
check('all queued disabled falls back', solve(['a', 'b'], 'a', ['x'], ['x']), ['b', [], 'b'])
check('end has no track', solve(['a'], 'a', [], []), [None, [], 'a'])
check('queue works without playlist', solve([], None, ['x'], []), ['x', [], 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
queue has priority	`['x', ['y'], 'a']`	`['x', ['y'], 'a']`	Passed
same track queued twice	`['x', ['x', 'y'], 'a']`	`['x', ['x', 'y'], 'a']`	Passed
disabled queue discarded	`['y', [], 'a']`	`['y', [], 'a']`	Passed
fallback advances cursor	`['b', [], 'b']`	`['b', [], 'b']`	Passed
all queued disabled falls back	`['b', [], 'b']`	`['b', [], 'b']`	Passed
end has no track	`[None, [], 'a']`	`[None, [], 'a']`	Passed
queue works without playlist	`['x', [], None]`	`['x', [], None]`	Passed

SHA-256 / 56916a6d2ba54f92ccbcfd620cd4015ac7afdeff5ebaea521ce8f88a3c45aaf1

Verification & scope

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 2026-09-29T14:38:46.798677+00:00.

Case digest / e8e07d6bc9d11ab70decba68cee46d9e17788e4b0bcad26dcb0323659aa1cb92