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FA-31391 / Keyboard interactions / Open access

Keyboard default edit cancellation pipeline: Keyboard default mutation is suppressed despite a noncancelable keydown · case 01

The event trace violates the keydown cancelable rule and produces incorrect keyboard state or command output.

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

ROOT CAUSE

Keyboard default mutation is suppressed despite a noncancelable keydown.

VERIFIED REPAIR

Use the contract transition `if prevent_down and cancelable:` at the keydown cancelable fault site; preserve the other state transitions.

Unsuccessful approach: The partial repair changes this transition to if prevent_down and not cancelable:, which still violates the model contract on the explicit regression traces.

Case contract

Case [text,lo,hi,key,prevent_down,prevent_before,cancelable,readonly]. Selection is a valid half-open code-point interval. Printable single characters replace selection, Backspace deletes previous point and Delete deletes next point for collapsed selections. Other keys do not edit. A cancelable prevented keydown stops editing; readonly suppresses beforeinput. A changed candidate fires beforeinput, cancellation suppresses mutation; successful edit fires input. Always log keydown and keyup. Return text, selection endpoints and event log. Inputs are finite ordered event traces; return the stated deterministic state. Batch entries are independent. N varies the number of independent input transactions.

Why this case matters

Controlled keyboard event processing model for debugging application event logic.

1 / The failure

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

N = 1
observations = []
def solve(cases):
    def run(c):
        text,lo,hi,key,prevent_down,prevent_before,cancelable,readonly=c
        log=['keydown']; original=[text,lo,hi]
        if prevent_down:
            return original+[log+['keyup']]
        if readonly or not (len(key)==1 or key in ('Backspace','Delete')):
            return original+[log+['keyup']]
        insert=key if len(key)==1 else ''
        if key=='Backspace' and lo==hi: lo=max(0,lo-1)
        elif key=='Delete' and lo==hi: hi=min(len(text),hi+1)
        changed=text[:lo]+insert+text[hi:]
        if changed==text:
            return original+[log+['keyup']]
        log.append('beforeinput')
        if prevent_before:
            return original+[log+['keyup']]
        text=changed
        hi=lo+len(insert); lo=hi
        log.append('input')
        return [text,lo,hi,log+['keyup']]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('key-default-edit scenario 0', solve([['abc', 1, 1, 'X', False, False, True, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 1', solve([['abc', 1, 2, 'XY', False, False, True, False]] * N), [['abc', 1, 2, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 2', solve([['abcd', 1, 3, 'Z', False, False, True, False]] * N), [['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 3', solve([['abcd', 1, 3, 'Backspace', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 4', solve([['abcd', 1, 3, 'Delete', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 5', solve([['abcd', 2, 2, 'Backspace', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 6', solve([['abcd', 1, 1, 'Delete', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 7', solve([['abc', 0, 0, 'Backspace', False, False, True, False]] * N), [['abc', 0, 0, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 8', solve([['abc', 0, 3, 'Delete', False, False, True, False]] * N), [['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 9', solve([['abc', 1, 1, 'X', True, False, False, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 10', solve([['abc', 1, 1, 'X', True, False, True, False]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 11', solve([['abc', 1, 1, 'X', False, True, False, False]] * N), [['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]] * N)
check('key-default-edit scenario 12', solve([['abc', 1, 1, 'X', False, False, True, True]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
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
key-default-edit scenario 0[['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 1[['abc', 1, 2, ['keydown', 'keyup']]][['abc', 1, 2, ['keydown', 'keyup']]]Passed
key-default-edit scenario 2[['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 3[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 4[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 5[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 6[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 7[['abc', 0, 0, ['keydown', 'keyup']]][['abc', 0, 0, ['keydown', 'keyup']]]Passed
key-default-edit scenario 8[['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]][['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 9[['abc', 1, 1, ['keydown', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Failed
key-default-edit scenario 10[['abc', 1, 1, ['keydown', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Passed
key-default-edit scenario 11[['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]][['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]]Passed
key-default-edit scenario 12[['abc', 1, 1, ['keydown', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Passed

SHA-256 / 5befcb5988e33ff58dc2cd5fce8fe795c65aa27afec05e0d456be089edd8ec18

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(cases):
    def run(c):
        text,lo,hi,key,prevent_down,prevent_before,cancelable,readonly=c
        log=['keydown']; original=[text,lo,hi]
        if prevent_down and not cancelable:
            return original+[log+['keyup']]
        if readonly or not (len(key)==1 or key in ('Backspace','Delete')):
            return original+[log+['keyup']]
        insert=key if len(key)==1 else ''
        if key=='Backspace' and lo==hi: lo=max(0,lo-1)
        elif key=='Delete' and lo==hi: hi=min(len(text),hi+1)
        changed=text[:lo]+insert+text[hi:]
        if changed==text:
            return original+[log+['keyup']]
        log.append('beforeinput')
        if prevent_before:
            return original+[log+['keyup']]
        text=changed
        hi=lo+len(insert); lo=hi
        log.append('input')
        return [text,lo,hi,log+['keyup']]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('key-default-edit scenario 0', solve([['abc', 1, 1, 'X', False, False, True, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 1', solve([['abc', 1, 2, 'XY', False, False, True, False]] * N), [['abc', 1, 2, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 2', solve([['abcd', 1, 3, 'Z', False, False, True, False]] * N), [['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 3', solve([['abcd', 1, 3, 'Backspace', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 4', solve([['abcd', 1, 3, 'Delete', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 5', solve([['abcd', 2, 2, 'Backspace', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 6', solve([['abcd', 1, 1, 'Delete', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 7', solve([['abc', 0, 0, 'Backspace', False, False, True, False]] * N), [['abc', 0, 0, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 8', solve([['abc', 0, 3, 'Delete', False, False, True, False]] * N), [['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 9', solve([['abc', 1, 1, 'X', True, False, False, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 10', solve([['abc', 1, 1, 'X', True, False, True, False]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 11', solve([['abc', 1, 1, 'X', False, True, False, False]] * N), [['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]] * N)
check('key-default-edit scenario 12', solve([['abc', 1, 1, 'X', False, False, True, True]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
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
key-default-edit scenario 0[['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 1[['abc', 1, 2, ['keydown', 'keyup']]][['abc', 1, 2, ['keydown', 'keyup']]]Passed
key-default-edit scenario 2[['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 3[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 4[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 5[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 6[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 7[['abc', 0, 0, ['keydown', 'keyup']]][['abc', 0, 0, ['keydown', 'keyup']]]Passed
key-default-edit scenario 8[['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]][['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 9[['abc', 1, 1, ['keydown', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Failed
key-default-edit scenario 10[['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Failed
key-default-edit scenario 11[['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]][['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]]Passed
key-default-edit scenario 12[['abc', 1, 1, ['keydown', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Passed

SHA-256 / a60903aedf99c9854a479b545fddf9c8b56412e5f7470110f50473482138bc04

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(cases):
    def run(c):
        text,lo,hi,key,prevent_down,prevent_before,cancelable,readonly=c
        log=['keydown']; original=[text,lo,hi]
        if prevent_down and cancelable:
            return original+[log+['keyup']]
        if readonly or not (len(key)==1 or key in ('Backspace','Delete')):
            return original+[log+['keyup']]
        insert=key if len(key)==1 else ''
        if key=='Backspace' and lo==hi: lo=max(0,lo-1)
        elif key=='Delete' and lo==hi: hi=min(len(text),hi+1)
        changed=text[:lo]+insert+text[hi:]
        if changed==text:
            return original+[log+['keyup']]
        log.append('beforeinput')
        if prevent_before:
            return original+[log+['keyup']]
        text=changed
        hi=lo+len(insert); lo=hi
        log.append('input')
        return [text,lo,hi,log+['keyup']]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('key-default-edit scenario 0', solve([['abc', 1, 1, 'X', False, False, True, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 1', solve([['abc', 1, 2, 'XY', False, False, True, False]] * N), [['abc', 1, 2, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 2', solve([['abcd', 1, 3, 'Z', False, False, True, False]] * N), [['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 3', solve([['abcd', 1, 3, 'Backspace', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 4', solve([['abcd', 1, 3, 'Delete', False, False, True, False]] * N), [['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 5', solve([['abcd', 2, 2, 'Backspace', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 6', solve([['abcd', 1, 1, 'Delete', False, False, True, False]] * N), [['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 7', solve([['abc', 0, 0, 'Backspace', False, False, True, False]] * N), [['abc', 0, 0, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 8', solve([['abc', 0, 3, 'Delete', False, False, True, False]] * N), [['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 9', solve([['abc', 1, 1, 'X', True, False, False, False]] * N), [['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]] * N)
check('key-default-edit scenario 10', solve([['abc', 1, 1, 'X', True, False, True, False]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
check('key-default-edit scenario 11', solve([['abc', 1, 1, 'X', False, True, False, False]] * N), [['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]] * N)
check('key-default-edit scenario 12', solve([['abc', 1, 1, 'X', False, False, True, True]] * N), [['abc', 1, 1, ['keydown', 'keyup']]] * N)
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
key-default-edit scenario 0[['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 1[['abc', 1, 2, ['keydown', 'keyup']]][['abc', 1, 2, ['keydown', 'keyup']]]Passed
key-default-edit scenario 2[['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aZd', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 3[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 4[['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['ad', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 5[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 6[['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]][['acd', 1, 1, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 7[['abc', 0, 0, ['keydown', 'keyup']]][['abc', 0, 0, ['keydown', 'keyup']]]Passed
key-default-edit scenario 8[['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]][['', 0, 0, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 9[['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]][['aXbc', 2, 2, ['keydown', 'beforeinput', 'input', 'keyup']]]Passed
key-default-edit scenario 10[['abc', 1, 1, ['keydown', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Passed
key-default-edit scenario 11[['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]][['abc', 1, 1, ['keydown', 'beforeinput', 'keyup']]]Passed
key-default-edit scenario 12[['abc', 1, 1, ['keydown', 'keyup']]][['abc', 1, 1, ['keydown', 'keyup']]]Passed

SHA-256 / c0c60075f03e76ea4cae283d680c3a204401ac65b5b85df71f07606e58329c53

Verification & scope

Offline stipulated event model, not a browser implementation or web standard conformance claim. 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 2026-09-29T14:42:01.573014+00:00.

Case digest / 93f4d5bf665ae558bf4a4f9017154e2bc8e2595999b140c0f1e8e104490c5507