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FA-30951 / Keyboard interactions / Open access

Simultaneous chord edge recognizer: Cancellation retains a partial chord across input ownership loss · case 01

The event trace violates the cancel reset rule and produces incorrect keyboard state or command output.

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

ROOT CAUSE

Cancellation retains a partial chord across input ownership loss.

THE FAILURE

Cancellation retains a partial chord across input ownership loss.

Unsuccessful approach: The partial repair changes this transition to elif kind=='cancel': held.discard(key), 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': pass
            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[[1, ['A', 'B'], False, 'B', True]][[0, ['B'], True, None, False]]Failed
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 / 155ee27e2a84350e103f3ce5ca58b2742d1b4e03f081d7da654c974b98c04631

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.discard(key)
            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[[1, ['A', 'B'], False, 'B', True]][[0, ['B'], True, None, False]]Failed
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 / eccc88bf8c0a2b8a44adea73fb576b2e1c1794baf71b7b84b59f21e3213ac385

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 9 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

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 2026-09-29T14:41:57.956607+00:00.

Case digest / 999d1c7acbb160310b5dedf49b57245a3f761e2a14f851dd974953f1e2ee8d11