FA-11141 / Streaming segment lifecycle / Open access

Segment cache key includes rendition · case 01

Two quality renditions share a sequence number and collide in the segment cache.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Two quality renditions share a sequence number and collide in the segment cache.

VERIFIED REPAIR

Preserve the media contract: Return the complete local download identity [rendition ID,absolute sequence,optional partial-segment index].

Unsuccessful approach: Adding rendition but omitting part identity collapses distinct partial segments.

Case contract

Return the complete local download identity [rendition ID,absolute sequence,optional partial-segment index].

Why this case matters

A deterministic local media controller stage; metadata and downloaded data are supplied explicitly. No external player, service or codec is required.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(rendition, sequence, part):
    return [sequence,part]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*('low', 7, 0)),['low', 7, 0])
check('fixture 2',solve(*('high', 7, 0)),['high', 7, 0])
check('fixture 3',solve(*('low', 7, 1)),['low', 7, 1])
check('fixture 4',solve(*('low', 0, None)),['low', 0, 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
fixture 1	`[7, 0]`	`['low', 7, 0]`	Failed
fixture 2	`[7, 0]`	`['high', 7, 0]`	Failed
fixture 3	`[7, 1]`	`['low', 7, 1]`	Failed
fixture 4	`[0, None]`	`['low', 0, None]`	Failed

SHA-256 / 8630be1fb8888467ced251e1b94e5edacf5103106c70a58a2057d4e6cc33a7e4

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(rendition, sequence, part):
    return [rendition,sequence]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*('low', 7, 0)),['low', 7, 0])
check('fixture 2',solve(*('high', 7, 0)),['high', 7, 0])
check('fixture 3',solve(*('low', 7, 1)),['low', 7, 1])
check('fixture 4',solve(*('low', 0, None)),['low', 0, 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
fixture 1	`['low', 7]`	`['low', 7, 0]`	Failed
fixture 2	`['high', 7]`	`['high', 7, 0]`	Failed
fixture 3	`['low', 7]`	`['low', 7, 1]`	Failed
fixture 4	`['low', 0]`	`['low', 0, None]`	Failed

SHA-256 / 4deae4f90f202b8331a905bebb7251920e8c50163998662dcc5f70fe0882672d

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(rendition, sequence, part):
    return [rendition,sequence,part]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('fixture 1',solve(*('low', 7, 0)),['low', 7, 0])
check('fixture 2',solve(*('high', 7, 0)),['high', 7, 0])
check('fixture 3',solve(*('low', 7, 1)),['low', 7, 1])
check('fixture 4',solve(*('low', 0, None)),['low', 0, 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
fixture 1	`['low', 7, 0]`	`['low', 7, 0]`	Passed
fixture 2	`['high', 7, 0]`	`['high', 7, 0]`	Passed
fixture 3	`['low', 7, 1]`	`['low', 7, 1]`	Passed
fixture 4	`['low', 0, None]`	`['low', 0, None]`	Passed

SHA-256 / 175269b0fb0045c5784640c98ff0046d38707c536d99bd7ec6093f1077b99e70

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 2026-09-29T14:38:45.355901+00:00.

Case digest / e20fbb01a12b11b54d1a25ecd4b3b86468403190ea1ed6b3aebba02a918a7b85