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FA-31371 / Keyboard interactions / Open access

Sticky modifier latch lifecycle: Emitted chord modifier representation is noncanonical or omits latches · case 01

The event trace violates the modifier order rule and produces incorrect keyboard state or command output.

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

ROOT CAUSE

Emitted chord modifier representation is noncanonical or omits latches.

THE FAILURE

Emitted chord modifier representation is noncanonical or omits latches.

Unsuccessful approach: The partial repair changes this transition to sorted(physical), which still violates the model contract on the explicit regression traces.

Case contract

Events [kind,key]. Tap of modifier cycles absent -> once -> locked -> absent. Modifier down/up sets physical state independently. Character emits [key,sorted effective modifiers] then consumes all once latches but preserves locked and physical modifiers. Cancel clears latches only; blur clears both. Return emitted events, latches and physical state. 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):
        latches={}; physical=set(); out=[]
        for kind,key in c:
            if kind=='tap':
                state=latches.get(key,0)
                next_state=(state+1)%3
                if next_state: latches[key]=next_state
                else: latches.pop(key,None)
            elif kind=='down': physical.add(key)
            elif kind=='up': physical.discard(key)
            elif kind=='char':
                effective=physical | set(latches)
                out.append([key,list(reversed(sorted(effective)))])
                latches={k:v for k,v in latches.items() if v==2}
            elif kind=='cancel': latches.clear()
            elif kind=='blur':
                latches.clear(); physical.clear()
        return [out,sorted([[k,v] for k,v in latches.items()]),sorted(physical)]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('sticky-modifiers scenario 0', solve([[]] * N), [[[], [], []]] * N)
check('sticky-modifiers scenario 1', solve([[['tap', 'Shift'], ['char', 'A'], ['char', 'B']]] * N), [[[['A', ['Shift']], ['B', []]], [], []]] * N)
check('sticky-modifiers scenario 2', solve([[['tap', 'Shift'], ['tap', 'Shift'], ['char', 'A'], ['char', 'B']]] * N), [[[['A', ['Shift']], ['B', ['Shift']]], [['Shift', 2]], []]] * N)
check('sticky-modifiers scenario 3', solve([[['tap', 'Shift'], ['tap', 'Shift'], ['tap', 'Alt'], ['tap', 'Shift'], ['char', 'A']]] * N), [[[['A', ['Alt']]], [], []]] * N)
check('sticky-modifiers scenario 4', solve([[['down', 'Control'], ['down', 'Alt'], ['down', 'Alt'], ['char', 'A']]] * N), [[[['A', ['Alt', 'Control']]], [], ['Alt', 'Control']]] * N)
check('sticky-modifiers scenario 5', solve([[['down', 'Control'], ['down', 'Alt'], ['up', 'Alt'], ['char', 'A']]] * N), [[[['A', ['Control']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 6', solve([[['down', 'Control'], ['tap', 'Shift'], ['char', 'A']]] * N), [[[['A', ['Control', 'Shift']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 7', solve([[['down', 'Control'], ['tap', 'Shift'], ['cancel', ''], ['char', 'A']]] * N), [[[['A', ['Control']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 8', solve([[['down', 'Control'], ['tap', 'Shift'], ['blur', '']]] * N), [[[], [], []]] * 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
sticky-modifiers scenario 0[[[], [], []]][[[], [], []]]Passed
sticky-modifiers scenario 1[[[['A', ['Shift']], ['B', []]], [], []]][[[['A', ['Shift']], ['B', []]], [], []]]Passed
sticky-modifiers scenario 2[[[['A', ['Shift']], ['B', ['Shift']]], [['Shift', 2]], []]][[[['A', ['Shift']], ['B', ['Shift']]], [['Shift', 2]], []]]Passed
sticky-modifiers scenario 3[[[['A', ['Alt']]], [], []]][[[['A', ['Alt']]], [], []]]Passed
sticky-modifiers scenario 4[[[['A', ['Control', 'Alt']]], [], ['Alt', 'Control']]][[[['A', ['Alt', 'Control']]], [], ['Alt', 'Control']]]Failed
sticky-modifiers scenario 5[[[['A', ['Control']]], [], ['Control']]][[[['A', ['Control']]], [], ['Control']]]Passed
sticky-modifiers scenario 6[[[['A', ['Shift', 'Control']]], [], ['Control']]][[[['A', ['Control', 'Shift']]], [], ['Control']]]Failed
sticky-modifiers scenario 7[[[['A', ['Control']]], [], ['Control']]][[[['A', ['Control']]], [], ['Control']]]Passed
sticky-modifiers scenario 8[[[], [], []]][[[], [], []]]Passed

SHA-256 / f21ce97384bbc265fd499fb80e489d0117301eea1824005eb5d17c9b6950baaa

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):
        latches={}; physical=set(); out=[]
        for kind,key in c:
            if kind=='tap':
                state=latches.get(key,0)
                next_state=(state+1)%3
                if next_state: latches[key]=next_state
                else: latches.pop(key,None)
            elif kind=='down': physical.add(key)
            elif kind=='up': physical.discard(key)
            elif kind=='char':
                effective=physical | set(latches)
                out.append([key,sorted(physical)])
                latches={k:v for k,v in latches.items() if v==2}
            elif kind=='cancel': latches.clear()
            elif kind=='blur':
                latches.clear(); physical.clear()
        return [out,sorted([[k,v] for k,v in latches.items()]),sorted(physical)]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('sticky-modifiers scenario 0', solve([[]] * N), [[[], [], []]] * N)
check('sticky-modifiers scenario 1', solve([[['tap', 'Shift'], ['char', 'A'], ['char', 'B']]] * N), [[[['A', ['Shift']], ['B', []]], [], []]] * N)
check('sticky-modifiers scenario 2', solve([[['tap', 'Shift'], ['tap', 'Shift'], ['char', 'A'], ['char', 'B']]] * N), [[[['A', ['Shift']], ['B', ['Shift']]], [['Shift', 2]], []]] * N)
check('sticky-modifiers scenario 3', solve([[['tap', 'Shift'], ['tap', 'Shift'], ['tap', 'Alt'], ['tap', 'Shift'], ['char', 'A']]] * N), [[[['A', ['Alt']]], [], []]] * N)
check('sticky-modifiers scenario 4', solve([[['down', 'Control'], ['down', 'Alt'], ['down', 'Alt'], ['char', 'A']]] * N), [[[['A', ['Alt', 'Control']]], [], ['Alt', 'Control']]] * N)
check('sticky-modifiers scenario 5', solve([[['down', 'Control'], ['down', 'Alt'], ['up', 'Alt'], ['char', 'A']]] * N), [[[['A', ['Control']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 6', solve([[['down', 'Control'], ['tap', 'Shift'], ['char', 'A']]] * N), [[[['A', ['Control', 'Shift']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 7', solve([[['down', 'Control'], ['tap', 'Shift'], ['cancel', ''], ['char', 'A']]] * N), [[[['A', ['Control']]], [], ['Control']]] * N)
check('sticky-modifiers scenario 8', solve([[['down', 'Control'], ['tap', 'Shift'], ['blur', '']]] * N), [[[], [], []]] * 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
sticky-modifiers scenario 0[[[], [], []]][[[], [], []]]Passed
sticky-modifiers scenario 1[[[['A', []], ['B', []]], [], []]][[[['A', ['Shift']], ['B', []]], [], []]]Failed
sticky-modifiers scenario 2[[[['A', []], ['B', []]], [['Shift', 2]], []]][[[['A', ['Shift']], ['B', ['Shift']]], [['Shift', 2]], []]]Failed
sticky-modifiers scenario 3[[[['A', []]], [], []]][[[['A', ['Alt']]], [], []]]Failed
sticky-modifiers scenario 4[[[['A', ['Alt', 'Control']]], [], ['Alt', 'Control']]][[[['A', ['Alt', 'Control']]], [], ['Alt', 'Control']]]Passed
sticky-modifiers scenario 5[[[['A', ['Control']]], [], ['Control']]][[[['A', ['Control']]], [], ['Control']]]Passed
sticky-modifiers scenario 6[[[['A', ['Control']]], [], ['Control']]][[[['A', ['Control', 'Shift']]], [], ['Control']]]Failed
sticky-modifiers scenario 7[[[['A', ['Control']]], [], ['Control']]][[[['A', ['Control']]], [], ['Control']]]Passed
sticky-modifiers scenario 8[[[], [], []]][[[], [], []]]Passed

SHA-256 / fd87dedeeda1a76f7030d98a85a2b8c52065ed03e97df6c58a0b4d6a65c3dd25

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 2026-09-29T14:42:01.579755+00:00.

Case digest / 92f25cdf1afa13ac54f7386e981d7dabc74c866ccc904f18fbe118796b36e890