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FA-50796 / Raster clipping / Open access

Run length clip stream: negative run advance · case 01

An invalid negative run silently rewinds the cursor instead of consuming zero samples.

Verified by executionVariant 1 · 13 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

An invalid negative run silently rewinds the cursor instead of consuming zero samples.

THE FAILURE

An invalid negative run silently rewinds the cursor instead of consuming zero samples.

Unsuccessful approach: Turning negative runs positive creates coverage instead of treating malformed runs as empty.

Case contract

A scanline clip stream carries signed cursor moves, covered and uncovered runs, an explicit covered/uncovered mode and row reset. Only covered samples in the finite target are emitted. Repeat reruns the previous run with its original mode. Draw observes unique sorted coverage; clear removes coverage without resetting cursor or mode.

Why this case matters

Raster clip state can leak coverage across draws even when every individual region is valid.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(commands, size):
    covered=set()
    cursor=0
    mode=True
    previous=None
    out=[]
    for cmd in commands:
        op=cmd[0]
        if op=='seek': cursor=cmd[1]
        elif op=='move': cursor+=cmd[1]
        elif op=='mode': mode=cmd[1]
        elif op=='row': cursor=0; previous=None
        elif op=='clear': covered.clear()
        elif op=='run':
            length=cmd[1]
            if mode: covered.update(i for i in range(cursor,cursor+length) if 0<=i<size)
            cursor+=length
            previous=(length,mode)
        elif op=='repeat' and previous is not None:
            length,saved=previous
            for _ in range(max(0,cmd[1])):
                if saved: covered.update(i for i in range(cursor,cursor+length) if 0<=i<size)
                cursor+=length
        elif op=='draw': out.append(sorted(covered))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 4), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 4), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 4), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 4), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 4), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 4), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 4), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 4), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 4), [[2, 3]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 4), [[0, 1, 2, 3]])
if N == 2:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 5), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 5), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 5), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 5), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 5), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 5), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 5), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 5), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 5), [[2, 3, 4]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 5), [[0, 1, 2, 3]])
if N == 3:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 6), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 6), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 6), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 6), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 6), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 6), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 6), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 6), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 6), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 6), [[0, 1, 2, 3]])
if N == 4:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 7), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 7), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 7), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 7), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 7), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 7), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 7), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 7), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 7), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 7), [[0, 1, 2, 3]])
if N == 5:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 8), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 8), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 8), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 8), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 8), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 8), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 8), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 8), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 8), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 8), [[0, 1, 2, 3]])
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 fixtureActualExpectedOutcome
explicit sequence 0[[0, 1]][[0, 1]]Passed
explicit sequence 1[[0]][[0]]Passed
explicit sequence 2[[2]][[2]]Passed
explicit sequence 3[[0, 1]][[0, 1, 2]]Failed
explicit sequence 4[[0, 1, 2]][[0, 1, 2]]Passed
explicit sequence 5[[0, 1]][[0, 1]]Passed
explicit sequence 6[[]][[]]Passed
explicit sequence 7[[2]][[2]]Passed
explicit sequence 8[[]][[]]Passed
explicit sequence 9[[0, 1, 2]][[0, 1, 2]]Passed
explicit sequence 10[[0]][[0]]Passed
explicit sequence 11[[2, 3]][[2, 3]]Passed
explicit sequence 12[[0, 1, 2, 3]][[0, 1, 2, 3]]Passed

SHA-256 / daa8787ccd70a0476f80d62d54aa30c2386bca82da5b5a60f6a154b5d17d9815

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(commands, size):
    covered=set()
    cursor=0
    mode=True
    previous=None
    out=[]
    for cmd in commands:
        op=cmd[0]
        if op=='seek': cursor=cmd[1]
        elif op=='move': cursor+=cmd[1]
        elif op=='mode': mode=cmd[1]
        elif op=='row': cursor=0; previous=None
        elif op=='clear': covered.clear()
        elif op=='run':
            length=abs(cmd[1])
            if mode: covered.update(i for i in range(cursor,cursor+length) if 0<=i<size)
            cursor+=length
            previous=(length,mode)
        elif op=='repeat' and previous is not None:
            length,saved=previous
            for _ in range(max(0,cmd[1])):
                if saved: covered.update(i for i in range(cursor,cursor+length) if 0<=i<size)
                cursor+=length
        elif op=='draw': out.append(sorted(covered))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
if N == 1:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 4), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 4), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 4), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 4), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 4), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 4), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 4), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 4), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 4), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 4), [[2, 3]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 4), [[0, 1, 2, 3]])
if N == 2:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 5), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 5), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 5), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 5), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 5), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 5), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 5), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 5), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 5), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 5), [[2, 3, 4]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 5), [[0, 1, 2, 3]])
if N == 3:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 6), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 6), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 6), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 6), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 6), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 6), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 6), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 6), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 6), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 6), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 6), [[0, 1, 2, 3]])
if N == 4:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 7), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 7), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 7), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 7), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 7), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 7), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 7), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 7), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 7), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 7), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 7), [[0, 1, 2, 3]])
if N == 5:
    check('explicit sequence 0', solve([['run', 2], ['seek', 1], ['run', 1], ['draw']], 8), [[0, 1]])
    check('explicit sequence 1', solve([['move', -2], ['run', 3], ['draw']], 8), [[0]])
    check('explicit sequence 2', solve([['mode', False], ['run', 2], ['mode', True], ['run', 1], ['draw']], 8), [[2]])
    check('explicit sequence 3', solve([['run', 2], ['run', -1], ['run', 1], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 4', solve([['run', 1], ['mode', False], ['repeat', 2], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 5', solve([['run', 2], ['row'], ['run', 1], ['draw']], 8), [[0, 1]])
    check('explicit sequence 6', solve([['run', 1], ['clear'], ['row'], ['repeat', 1], ['draw']], 8), [[]])
    check('explicit sequence 7', solve([['run', 2], ['clear'], ['run', 1], ['draw']], 8), [[2]])
    check('explicit sequence 8', solve([['seek', 99], ['run', 2], ['draw']], 8), [[]])
    check('explicit sequence 9', solve([['run', 1], ['repeat', 2], ['draw']], 8), [[0, 1, 2]])
    check('explicit sequence 10', solve([['run', 1], ['repeat', 0], ['draw']], 8), [[0]])
    check('explicit sequence 11', solve([['run', 2], ['clear'], ['repeat', 2], ['draw']], 8), [[2, 3, 4, 5]])
    check('explicit sequence 12', solve([['run', 2], ['clear'], ['seek', 0], ['repeat', 2], ['draw']], 8), [[0, 1, 2, 3]])
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 fixtureActualExpectedOutcome
explicit sequence 0[[0, 1]][[0, 1]]Passed
explicit sequence 1[[0]][[0]]Passed
explicit sequence 2[[2]][[2]]Passed
explicit sequence 3[[0, 1, 2, 3]][[0, 1, 2]]Failed
explicit sequence 4[[0, 1, 2]][[0, 1, 2]]Passed
explicit sequence 5[[0, 1]][[0, 1]]Passed
explicit sequence 6[[]][[]]Passed
explicit sequence 7[[2]][[2]]Passed
explicit sequence 8[[]][[]]Passed
explicit sequence 9[[0, 1, 2]][[0, 1, 2]]Passed
explicit sequence 10[[0]][[0]]Passed
explicit sequence 11[[2, 3]][[2, 3]]Passed
explicit sequence 12[[0, 1, 2, 3]][[0, 1, 2, 3]]Passed

SHA-256 / 38d5e7496723836a5c6d26e9fc8868f9b83b0530e29037dba78ddad615e2b718

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 13 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.

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Verification & scope

Finite one-dimensional integer sample sets model coverage state only; no geometric intersection, memory layout, GPU or graphics-standard conformance is claimed. 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 2026-09-29T14:45:12.873542+00:00.

Case digest / 1371de8c5754865732a4981ba0a6ea66b26e9c4735acd150514ade0cc18f5a71