FA-79321 / Image orientation metadata / Open access

Invalid sidecar orientation blocks the embedded fallback · case 01

A sidecar with orientation 0 or text garbage overrides a valid embedded tag.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The sidecar value is used raw, without the validity check applied to the embedded value.

VERIFIED REPAIR

Validate and normalise the sidecar value with the same rule as the embedded one.

Unsuccessful approach: A truthiness test drops only 0 and still returns invalid values such as 9 or unparsed text.

Case contract

A photo manager reconciles the embedded orientation with an XMP sidecar. Values are valid if they are integers 1..8 or strings that are exactly one digit 1..8 after trimming. Policy "sidecar" prefers the sidecar, "embedded" prefers the file, and "newest" (also used for unknown policies) prefers the sidecar when both are valid and sidecar_mtime >= file_mtime; the other valid value is the fallback, then 1.

Why this case matters

Camera, phone and scanner images carry an orientation hint separately from the stored pixels; galleries, thumbnailers, editors and upload pipelines must interpret it consistently or photos appear sideways, mirrored or doubly rotated.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(d):
    def ok(v):
        if isinstance(v, str) and v.strip() in ('1', '2', '3', '4', '5', '6', '7', '8'):
            return int(v.strip())
        if isinstance(v, int) and not isinstance(v, bool) and 1 <= v <= 8:
            return v
        return None
    e = ok(d.get('embedded'))
    s = d.get('sidecar')
    pol = d.get('policy')
    if pol not in ('newest', 'sidecar', 'embedded'):
        pol = 'newest'
    if pol == 'sidecar':
        order = [s, e]
    elif pol == 'embedded':
        order = [e, s]
    elif s is not None and e is not None:
        order = [s, e] if d['sidecar_mtime'] >= d['file_mtime'] else [e, s]
    else:
        order = [s, e]
    for v in order:
        if v is not None:
            return v
    return 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[{'embedded': 5, 'sidecar': '+3', 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'newest'}, 5], [{'embedded': 'x', 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': None}, 1], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 8], [{'embedded': ' 8', 'sidecar': 5, 'file_mtime': 105, 'sidecar_mtime': 105, 'policy': 'newest'}, 5], [{'embedded': '06', 'sidecar': None, 'file_mtime': 101, 'sidecar_mtime': 100, 'policy': 'embedded'}, 1], [{'embedded': 9, 'sidecar': 6, 'file_mtime': 100, 'sidecar_mtime': 101, 'policy': None}, 6], [{'embedded': 3, 'sidecar': None, 'file_mtime': 100, 'sidecar_mtime': 99, 'policy': 'embedded'}, 3], [{'embedded': 'x', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 1]], [[{'embedded': 1, 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'sidecar'}, 1], [{'embedded': 3, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'newest'}, 3], [{'embedded': None, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 1], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 107, 'sidecar_mtime': 112, 'policy': 'embedded'}, 8], [{'embedded': 3, 'sidecar': 6, 'file_mtime': 101, 'sidecar_mtime': 96, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 5, 'file_mtime': 107, 'sidecar_mtime': 102, 'policy': None}, 5], [{'embedded': 5, 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 109, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 106, 'sidecar_mtime': 107, 'policy': None}, 8]], [[{'embedded': 3, 'sidecar': '+3', 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': None}, 3], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 1, 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': None}, 1], [{'embedded': 3, 'sidecar': '6', 'file_mtime': 109, 'sidecar_mtime': 104, 'policy': 'latest'}, 3], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 105, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 8], [{'embedded': None, 'sidecar': None, 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'latest'}, 1], [{'embedded': 8, 'sidecar': 6, 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 8], [{'embedded': None, 'sidecar': '06', 'file_mtime': 110, 'sidecar_mtime': 115, 'policy': 'newest'}, 1]], [[{'embedded': None, 'sidecar': '6', 'file_mtime': 104, 'sidecar_mtime': 104, 'policy': 'latest'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 109, 'policy': 'sidecar'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 103, 'sidecar_mtime': 102, 'policy': None}, 8], [{'embedded': ' 8', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 108, 'policy': None}, 8], [{'embedded': '6', 'sidecar': 5, 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': 'sidecar'}, 5], [{'embedded': None, 'sidecar': 6, 'file_mtime': 103, 'sidecar_mtime': 98, 'policy': 'embedded'}, 6], [{'embedded': '+3', 'sidecar': 'x', 'file_mtime': 101, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]], [[{'embedded': 8, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'sidecar'}, 8], [{'embedded': 5, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 6], [{'embedded': '6', 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': 'newest'}, 6], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'embedded'}, 8], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'embedded'}, 5], [{'embedded': 9, 'sidecar': 3, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 3], [{'embedded': 8, 'sidecar': 0, 'file_mtime': 107, 'sidecar_mtime': 106, 'policy': None}, 8], [{'embedded': 0, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]]]
labels = ["regression: sidecar value validation", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
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
regression: sidecar value validation 0	`+3`	`5`	Failed
repair trap 1	`06`	`1`	Failed
combined fault 2	`8`	`8`	Passed
control 3	`5`	`5`	Passed
control 4	`1`	`1`	Passed
boundary 5	`6`	`6`	Passed
boundary 6	`3`	`3`	Passed
control 7	`x`	`1`	Failed

SHA-256 / a3aba56241464d586edd3ba444953c65254e1ca81dc1f2a2ccd392f918eb08e1

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(d):
    def ok(v):
        if isinstance(v, str) and v.strip() in ('1', '2', '3', '4', '5', '6', '7', '8'):
            return int(v.strip())
        if isinstance(v, int) and not isinstance(v, bool) and 1 <= v <= 8:
            return v
        return None
    e = ok(d.get('embedded'))
    s = d.get('sidecar') or None
    pol = d.get('policy')
    if pol not in ('newest', 'sidecar', 'embedded'):
        pol = 'newest'
    if pol == 'sidecar':
        order = [s, e]
    elif pol == 'embedded':
        order = [e, s]
    elif s is not None and e is not None:
        order = [s, e] if d['sidecar_mtime'] >= d['file_mtime'] else [e, s]
    else:
        order = [s, e]
    for v in order:
        if v is not None:
            return v
    return 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[{'embedded': 5, 'sidecar': '+3', 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'newest'}, 5], [{'embedded': 'x', 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': None}, 1], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 8], [{'embedded': ' 8', 'sidecar': 5, 'file_mtime': 105, 'sidecar_mtime': 105, 'policy': 'newest'}, 5], [{'embedded': '06', 'sidecar': None, 'file_mtime': 101, 'sidecar_mtime': 100, 'policy': 'embedded'}, 1], [{'embedded': 9, 'sidecar': 6, 'file_mtime': 100, 'sidecar_mtime': 101, 'policy': None}, 6], [{'embedded': 3, 'sidecar': None, 'file_mtime': 100, 'sidecar_mtime': 99, 'policy': 'embedded'}, 3], [{'embedded': 'x', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 1]], [[{'embedded': 1, 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'sidecar'}, 1], [{'embedded': 3, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'newest'}, 3], [{'embedded': None, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 1], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 107, 'sidecar_mtime': 112, 'policy': 'embedded'}, 8], [{'embedded': 3, 'sidecar': 6, 'file_mtime': 101, 'sidecar_mtime': 96, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 5, 'file_mtime': 107, 'sidecar_mtime': 102, 'policy': None}, 5], [{'embedded': 5, 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 109, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 106, 'sidecar_mtime': 107, 'policy': None}, 8]], [[{'embedded': 3, 'sidecar': '+3', 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': None}, 3], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 1, 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': None}, 1], [{'embedded': 3, 'sidecar': '6', 'file_mtime': 109, 'sidecar_mtime': 104, 'policy': 'latest'}, 3], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 105, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 8], [{'embedded': None, 'sidecar': None, 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'latest'}, 1], [{'embedded': 8, 'sidecar': 6, 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 8], [{'embedded': None, 'sidecar': '06', 'file_mtime': 110, 'sidecar_mtime': 115, 'policy': 'newest'}, 1]], [[{'embedded': None, 'sidecar': '6', 'file_mtime': 104, 'sidecar_mtime': 104, 'policy': 'latest'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 109, 'policy': 'sidecar'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 103, 'sidecar_mtime': 102, 'policy': None}, 8], [{'embedded': ' 8', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 108, 'policy': None}, 8], [{'embedded': '6', 'sidecar': 5, 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': 'sidecar'}, 5], [{'embedded': None, 'sidecar': 6, 'file_mtime': 103, 'sidecar_mtime': 98, 'policy': 'embedded'}, 6], [{'embedded': '+3', 'sidecar': 'x', 'file_mtime': 101, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]], [[{'embedded': 8, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'sidecar'}, 8], [{'embedded': 5, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 6], [{'embedded': '6', 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': 'newest'}, 6], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'embedded'}, 8], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'embedded'}, 5], [{'embedded': 9, 'sidecar': 3, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 3], [{'embedded': 8, 'sidecar': 0, 'file_mtime': 107, 'sidecar_mtime': 106, 'policy': None}, 8], [{'embedded': 0, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]]]
labels = ["regression: sidecar value validation", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
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
regression: sidecar value validation 0	`+3`	`5`	Failed
repair trap 1	`06`	`1`	Failed
combined fault 2	`8`	`8`	Passed
control 3	`5`	`5`	Passed
control 4	`1`	`1`	Passed
boundary 5	`6`	`6`	Passed
boundary 6	`3`	`3`	Passed
control 7	`x`	`1`	Failed

SHA-256 / 0aab747c7f9592869c0abfe4ed5cd264d70a82ca54a461cc6d294815058a59bf

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(d):
    def ok(v):
        if isinstance(v, str) and v.strip() in ('1', '2', '3', '4', '5', '6', '7', '8'):
            return int(v.strip())
        if isinstance(v, int) and not isinstance(v, bool) and 1 <= v <= 8:
            return v
        return None
    e = ok(d.get('embedded'))
    s = ok(d.get('sidecar'))
    pol = d.get('policy')
    if pol not in ('newest', 'sidecar', 'embedded'):
        pol = 'newest'
    if pol == 'sidecar':
        order = [s, e]
    elif pol == 'embedded':
        order = [e, s]
    elif s is not None and e is not None:
        order = [s, e] if d['sidecar_mtime'] >= d['file_mtime'] else [e, s]
    else:
        order = [s, e]
    for v in order:
        if v is not None:
            return v
    return 1
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[[{'embedded': 5, 'sidecar': '+3', 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'newest'}, 5], [{'embedded': 'x', 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': None}, 1], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 8], [{'embedded': ' 8', 'sidecar': 5, 'file_mtime': 105, 'sidecar_mtime': 105, 'policy': 'newest'}, 5], [{'embedded': '06', 'sidecar': None, 'file_mtime': 101, 'sidecar_mtime': 100, 'policy': 'embedded'}, 1], [{'embedded': 9, 'sidecar': 6, 'file_mtime': 100, 'sidecar_mtime': 101, 'policy': None}, 6], [{'embedded': 3, 'sidecar': None, 'file_mtime': 100, 'sidecar_mtime': 99, 'policy': 'embedded'}, 3], [{'embedded': 'x', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 1]], [[{'embedded': 1, 'sidecar': '06', 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'sidecar'}, 1], [{'embedded': 3, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'newest'}, 3], [{'embedded': None, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 1], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 107, 'sidecar_mtime': 112, 'policy': 'embedded'}, 8], [{'embedded': 3, 'sidecar': 6, 'file_mtime': 101, 'sidecar_mtime': 96, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 5, 'file_mtime': 107, 'sidecar_mtime': 102, 'policy': None}, 5], [{'embedded': 5, 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 109, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 'x', 'file_mtime': 106, 'sidecar_mtime': 107, 'policy': None}, 8]], [[{'embedded': 3, 'sidecar': '+3', 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': None}, 3], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'newest'}, 5], [{'embedded': 8, 'sidecar': 1, 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': None}, 1], [{'embedded': 3, 'sidecar': '6', 'file_mtime': 109, 'sidecar_mtime': 104, 'policy': 'latest'}, 3], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 105, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 8], [{'embedded': None, 'sidecar': None, 'file_mtime': 103, 'sidecar_mtime': 108, 'policy': 'latest'}, 1], [{'embedded': 8, 'sidecar': 6, 'file_mtime': 109, 'sidecar_mtime': 109, 'policy': 'embedded'}, 8], [{'embedded': None, 'sidecar': '06', 'file_mtime': 110, 'sidecar_mtime': 115, 'policy': 'newest'}, 1]], [[{'embedded': None, 'sidecar': '6', 'file_mtime': 104, 'sidecar_mtime': 104, 'policy': 'latest'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 109, 'policy': 'sidecar'}, 6], [{'embedded': 6, 'sidecar': '6', 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'sidecar'}, 6], [{'embedded': 'x', 'sidecar': 8, 'file_mtime': 103, 'sidecar_mtime': 102, 'policy': None}, 8], [{'embedded': ' 8', 'sidecar': 'x', 'file_mtime': 109, 'sidecar_mtime': 108, 'policy': None}, 8], [{'embedded': '6', 'sidecar': 5, 'file_mtime': 109, 'sidecar_mtime': 114, 'policy': 'sidecar'}, 5], [{'embedded': None, 'sidecar': 6, 'file_mtime': 103, 'sidecar_mtime': 98, 'policy': 'embedded'}, 6], [{'embedded': '+3', 'sidecar': 'x', 'file_mtime': 101, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]], [[{'embedded': 8, 'sidecar': 9, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'sidecar'}, 8], [{'embedded': 5, 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 103, 'policy': 'sidecar'}, 6], [{'embedded': '6', 'sidecar': '6', 'file_mtime': 108, 'sidecar_mtime': 108, 'policy': 'newest'}, 6], [{'embedded': ' 8', 'sidecar': 8, 'file_mtime': 110, 'sidecar_mtime': 110, 'policy': 'embedded'}, 8], [{'embedded': 5, 'sidecar': 9, 'file_mtime': 104, 'sidecar_mtime': 105, 'policy': 'embedded'}, 5], [{'embedded': 9, 'sidecar': 3, 'file_mtime': 102, 'sidecar_mtime': 101, 'policy': 'newest'}, 3], [{'embedded': 8, 'sidecar': 0, 'file_mtime': 107, 'sidecar_mtime': 106, 'policy': None}, 8], [{'embedded': 0, 'sidecar': 'x', 'file_mtime': 102, 'sidecar_mtime': 102, 'policy': 'embedded'}, 1]]]
labels = ["regression: sidecar value validation", "repair trap", "combined fault", "control", "control", "boundary", "boundary", "control"]
for i, (args, expected) in enumerate(fixtures[N-1]):
    check("%s %d" % (labels[i % len(labels)], i), solve(args), expected)
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
regression: sidecar value validation 0	`5`	`5`	Passed
repair trap 1	`1`	`1`	Passed
combined fault 2	`8`	`8`	Passed
control 3	`5`	`5`	Passed
control 4	`1`	`1`	Passed
boundary 5	`6`	`6`	Passed
boundary 6	`3`	`3`	Passed
control 7	`1`	`1`	Passed

SHA-256 / 5079b3ce3d72d5dc20093590fa91b414619d621acb1d1d167a70b6b6007a0375

Verification & scope

A deterministic bounded teaching model with a stipulated contract; it makes no claim of conformance to any published specification. 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 2026-09-29T14:49:43.476231+00:00.

Case digest / ceb541a7c137461bc49154ce3bc392268a181e0658cc2116d4baee8b95e759e5