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FA-30961 / Keyboard interactions / Open access

Simultaneous chord edge recognizer: Chord activation ignores extra depressed keys or missing members · case 01

The event trace violates the extra key rule and produces incorrect keyboard state or command output.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Chord activation ignores extra depressed keys or missing members.

VERIFIED REPAIR

Use the contract transition `held==set(required)` at the extra key fault site; preserve the other state transitions.

Unsuccessful approach: The partial repair changes this transition to bool(held & set(required)), which still violates the model contract on the explicit regression traces.

Case contract

Case is [required_keys, events]. Down/up update held keys; cancel clears state. A chord fires on the first transition from incomplete to all required keys held, with no extra keys. It rearms after becoming incomplete. Empty chord never fires. Return fire count, sorted held, armed state, last triggering key and current completeness. 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):
        required,events=c
        held=set(); armed=True; fires=0; last=None; complete=False
        for kind,key in events:
            if kind=='down': held.add(key)
            elif kind=='up': held.discard(key)
            elif kind=='cancel': held.clear()
            complete=bool(required) and set(required).issubset(held)
            if complete and armed and kind=='down':
                fires+=1
                last=key
                armed=False
            elif not complete:
                armed=True
        return [fires,sorted(held),armed,last,complete]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('simultaneous-chord scenario 0', solve([[[], []]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 1', solve([[[], [['down', 'x'], ['up', 'x'], ['down', 'x'], ['up', 'x']]]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 2', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 3', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['up', 'B'], ['down', 'B']]]] * N), [[2, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 4', solve([[['A', 'B'], [['down', 'A'], ['down', 'X'], ['down', 'B'], ['up', 'X']]]] * N), [[0, ['A', 'B'], True, None, True]] * N)
check('simultaneous-chord scenario 5', solve([[['A', 'B'], [['down', 'A'], ['cancel', ''], ['down', 'B']]]] * N), [[0, ['B'], True, None, False]] * N)
check('simultaneous-chord scenario 6', solve([[['A', 'B'], [['down', 'A'], ['up', 'X'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 7', solve([[['A'], [['down', 'A'], ['up', 'A'], ['down', 'A']]]] * N), [[2, ['A'], False, 'A', True]] * N)
check('simultaneous-chord scenario 8', solve([[['A', 'B'], [['down', 'B'], ['down', 'A']]]] * N), [[1, ['A', 'B'], False, 'A', True]] * 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
simultaneous-chord scenario 0[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 1[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 2[[1, ['A', 'B'], False, 'B', True]][[1, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 3[[2, ['A', 'B'], False, 'B', True]][[2, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 4[[1, ['A', 'B'], False, 'B', True]][[0, ['A', 'B'], True, None, True]]Failed
simultaneous-chord scenario 5[[0, ['B'], True, None, False]][[0, ['B'], True, None, False]]Passed
simultaneous-chord scenario 6[[1, ['A', 'B'], False, 'B', True]][[1, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 7[[2, ['A'], False, 'A', True]][[2, ['A'], False, 'A', True]]Passed
simultaneous-chord scenario 8[[1, ['A', 'B'], False, 'A', True]][[1, ['A', 'B'], False, 'A', True]]Passed

SHA-256 / 953df28379d002d74278f88b3a781388a27725d71f78d6d1cb94cce01f5b83bf

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):
        required,events=c
        held=set(); armed=True; fires=0; last=None; complete=False
        for kind,key in events:
            if kind=='down': held.add(key)
            elif kind=='up': held.discard(key)
            elif kind=='cancel': held.clear()
            complete=bool(required) and bool(held & set(required))
            if complete and armed and kind=='down':
                fires+=1
                last=key
                armed=False
            elif not complete:
                armed=True
        return [fires,sorted(held),armed,last,complete]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('simultaneous-chord scenario 0', solve([[[], []]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 1', solve([[[], [['down', 'x'], ['up', 'x'], ['down', 'x'], ['up', 'x']]]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 2', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 3', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['up', 'B'], ['down', 'B']]]] * N), [[2, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 4', solve([[['A', 'B'], [['down', 'A'], ['down', 'X'], ['down', 'B'], ['up', 'X']]]] * N), [[0, ['A', 'B'], True, None, True]] * N)
check('simultaneous-chord scenario 5', solve([[['A', 'B'], [['down', 'A'], ['cancel', ''], ['down', 'B']]]] * N), [[0, ['B'], True, None, False]] * N)
check('simultaneous-chord scenario 6', solve([[['A', 'B'], [['down', 'A'], ['up', 'X'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 7', solve([[['A'], [['down', 'A'], ['up', 'A'], ['down', 'A']]]] * N), [[2, ['A'], False, 'A', True]] * N)
check('simultaneous-chord scenario 8', solve([[['A', 'B'], [['down', 'B'], ['down', 'A']]]] * N), [[1, ['A', 'B'], False, 'A', True]] * 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
simultaneous-chord scenario 0[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 1[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 2[[1, ['A', 'B'], False, 'A', True]][[1, ['A', 'B'], False, 'B', True]]Failed
simultaneous-chord scenario 3[[1, ['A', 'B'], False, 'A', True]][[2, ['A', 'B'], False, 'B', True]]Failed
simultaneous-chord scenario 4[[1, ['A', 'B'], False, 'A', True]][[0, ['A', 'B'], True, None, True]]Failed
simultaneous-chord scenario 5[[2, ['B'], False, 'B', True]][[0, ['B'], True, None, False]]Failed
simultaneous-chord scenario 6[[1, ['A', 'B'], False, 'A', True]][[1, ['A', 'B'], False, 'B', True]]Failed
simultaneous-chord scenario 7[[2, ['A'], False, 'A', True]][[2, ['A'], False, 'A', True]]Passed
simultaneous-chord scenario 8[[1, ['A', 'B'], False, 'B', True]][[1, ['A', 'B'], False, 'A', True]]Failed

SHA-256 / 7267dfd5fe4c8f25a16c07ebf6c170ea5fb1cf8688b8c1f12c7ebb9d4aeb7213

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):
        required,events=c
        held=set(); armed=True; fires=0; last=None; complete=False
        for kind,key in events:
            if kind=='down': held.add(key)
            elif kind=='up': held.discard(key)
            elif kind=='cancel': held.clear()
            complete=bool(required) and held==set(required)
            if complete and armed and kind=='down':
                fires+=1
                last=key
                armed=False
            elif not complete:
                armed=True
        return [fires,sorted(held),armed,last,complete]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('simultaneous-chord scenario 0', solve([[[], []]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 1', solve([[[], [['down', 'x'], ['up', 'x'], ['down', 'x'], ['up', 'x']]]] * N), [[0, [], True, None, False]] * N)
check('simultaneous-chord scenario 2', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 3', solve([[['A', 'B'], [['down', 'A'], ['down', 'B'], ['up', 'B'], ['down', 'B']]]] * N), [[2, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 4', solve([[['A', 'B'], [['down', 'A'], ['down', 'X'], ['down', 'B'], ['up', 'X']]]] * N), [[0, ['A', 'B'], True, None, True]] * N)
check('simultaneous-chord scenario 5', solve([[['A', 'B'], [['down', 'A'], ['cancel', ''], ['down', 'B']]]] * N), [[0, ['B'], True, None, False]] * N)
check('simultaneous-chord scenario 6', solve([[['A', 'B'], [['down', 'A'], ['up', 'X'], ['down', 'B']]]] * N), [[1, ['A', 'B'], False, 'B', True]] * N)
check('simultaneous-chord scenario 7', solve([[['A'], [['down', 'A'], ['up', 'A'], ['down', 'A']]]] * N), [[2, ['A'], False, 'A', True]] * N)
check('simultaneous-chord scenario 8', solve([[['A', 'B'], [['down', 'B'], ['down', 'A']]]] * N), [[1, ['A', 'B'], False, 'A', True]] * 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
simultaneous-chord scenario 0[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 1[[0, [], True, None, False]][[0, [], True, None, False]]Passed
simultaneous-chord scenario 2[[1, ['A', 'B'], False, 'B', True]][[1, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 3[[2, ['A', 'B'], False, 'B', True]][[2, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 4[[0, ['A', 'B'], True, None, True]][[0, ['A', 'B'], True, None, True]]Passed
simultaneous-chord scenario 5[[0, ['B'], True, None, False]][[0, ['B'], True, None, False]]Passed
simultaneous-chord scenario 6[[1, ['A', 'B'], False, 'B', True]][[1, ['A', 'B'], False, 'B', True]]Passed
simultaneous-chord scenario 7[[2, ['A'], False, 'A', True]][[2, ['A'], False, 'A', True]]Passed
simultaneous-chord scenario 8[[1, ['A', 'B'], False, 'A', True]][[1, ['A', 'B'], False, 'A', True]]Passed

SHA-256 / 562ac133d78ca0553becdae523cb3cdf4bbff15e9c721bccffa82f4e25a012d2

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 2026-09-29T14:41:57.733836+00:00.

Case digest / bb5129a81a65a3671ca319da79779b3f6a867b2f2b57539c5163f6b2f0f32a2a