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FA-32291 / Keyboard interactions / Open access

Bounded keyboard queue with lossless release backpressure: Keyboard pump admits over-capacity presses or wastes its final available slot · case 01

The event trace violates the capacity boundary rule and produces incorrect keyboard state or command output.

Verified by executionVariant 1 · 10 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Keyboard pump admits over-capacity presses or wastes its final available slot.

THE FAILURE

Keyboard pump admits over-capacity presses or wastes its final available slot.

Unsuccessful approach: The partial repair changes this transition to if len(queue)>=capacity-1: dropped+=1, which still violates the model contract on the explicit regression traces.

Case contract

Case [capacity,events], positive capacity; events [kind,key]. Down admitted only once per physical key and only when queue has capacity; overflow drops down. Up for an admitted key must be retained: dispatch oldest queued events until a slot exists, then queue the up. Tick dispatches one queued event; flush dispatches all. Reset discards pending queue and emits sorted synthetic ups for actually dispatched held keys. Return emitted edges,queue,admitted keys,delivered-held keys,dropped downs. 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):
        capacity,events=c
        queue=[]; admitted=set(); held=set(); out=[]; dropped=0
        def dispatch(event):
            phase,key=event
            out.append([phase,key])
            if phase=='down': held.add(key)
            else: held.discard(key)
        for kind,key in events:
            if kind=='down' and key not in admitted:
                if len(queue)>capacity: dropped+=1
                else:
                    admitted.add(key)
                    queue.append(['down',key])
            elif kind=='up' and key in admitted:
                admitted.discard(key)
                while len(queue)>=capacity: dispatch(queue.pop(0))
                queue.append(['up',key])
            elif kind=='tick' and queue: dispatch(queue.pop(0))
            elif kind=='flush':
                while queue: dispatch(queue.pop(0))
            elif kind=='reset':
                queue.clear(); admitted.clear()
                for k in sorted(held): out.append(['up',k])
                held.clear()
        return [out,queue,sorted(admitted),sorted(held),dropped]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('bounded-keyboard-pump scenario 0', solve([[2, []]] * N), [[[], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 1', solve([[2, [['down', 'A'], ['down', 'B'], ['down', 'C']]]] * N), [[[], [['down', 'A'], ['down', 'B']], ['A', 'B'], [], 1]] * N)
check('bounded-keyboard-pump scenario 2', solve([[2, [['down', 'A'], ['down', 'B'], ['up', 'A']]]] * N), [[[['down', 'A']], [['down', 'B'], ['up', 'A']], ['B'], ['A'], 0]] * N)
check('bounded-keyboard-pump scenario 3', solve([[2, [['down', 'A'], ['down', 'B'], ['tick', '']]]] * N), [[[['down', 'A']], [['down', 'B']], ['A', 'B'], ['A'], 0]] * N)
check('bounded-keyboard-pump scenario 4', solve([[2, [['down', 'A'], ['down', 'B'], ['flush', '']]]] * N), [[[['down', 'A'], ['down', 'B']], [], ['A', 'B'], ['A', 'B'], 0]] * N)
check('bounded-keyboard-pump scenario 5', solve([[2, [['down', 'A'], ['down', 'B'], ['reset', '']]]] * N), [[[], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 6', solve([[2, [['down', 'A'], ['tick', ''], ['down', 'B'], ['reset', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 7', solve([[1, [['down', 'A'], ['up', 'A'], ['flush', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 8', solve([[2, [['down', 'A'], ['down', 'A'], ['up', 'A'], ['flush', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 9', solve([[2, [['up', 'A']]]] * N), [[[], [], [], [], 0]] * 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
bounded-keyboard-pump scenario 0[[[], [], [], [], 0]][[[], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 1[[[], [['down', 'A'], ['down', 'B'], ['down', 'C']], ['A', 'B', 'C'], [], 0]][[[], [['down', 'A'], ['down', 'B']], ['A', 'B'], [], 1]]Failed
bounded-keyboard-pump scenario 2[[[['down', 'A']], [['down', 'B'], ['up', 'A']], ['B'], ['A'], 0]][[[['down', 'A']], [['down', 'B'], ['up', 'A']], ['B'], ['A'], 0]]Passed
bounded-keyboard-pump scenario 3[[[['down', 'A']], [['down', 'B']], ['A', 'B'], ['A'], 0]][[[['down', 'A']], [['down', 'B']], ['A', 'B'], ['A'], 0]]Passed
bounded-keyboard-pump scenario 4[[[['down', 'A'], ['down', 'B']], [], ['A', 'B'], ['A', 'B'], 0]][[[['down', 'A'], ['down', 'B']], [], ['A', 'B'], ['A', 'B'], 0]]Passed
bounded-keyboard-pump scenario 5[[[], [], [], [], 0]][[[], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 6[[[['down', 'A'], ['up', 'A']], [], [], [], 0]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 7[[[['down', 'A'], ['up', 'A']], [], [], [], 0]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 8[[[['down', 'A'], ['up', 'A']], [], [], [], 0]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 9[[[], [], [], [], 0]][[[], [], [], [], 0]]Passed

SHA-256 / 9866120bb7ebe3d21736efe79dd6314b8f5105b16ce089c2dbce3be7e1c33ddc

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):
        capacity,events=c
        queue=[]; admitted=set(); held=set(); out=[]; dropped=0
        def dispatch(event):
            phase,key=event
            out.append([phase,key])
            if phase=='down': held.add(key)
            else: held.discard(key)
        for kind,key in events:
            if kind=='down' and key not in admitted:
                if len(queue)>=capacity-1: dropped+=1
                else:
                    admitted.add(key)
                    queue.append(['down',key])
            elif kind=='up' and key in admitted:
                admitted.discard(key)
                while len(queue)>=capacity: dispatch(queue.pop(0))
                queue.append(['up',key])
            elif kind=='tick' and queue: dispatch(queue.pop(0))
            elif kind=='flush':
                while queue: dispatch(queue.pop(0))
            elif kind=='reset':
                queue.clear(); admitted.clear()
                for k in sorted(held): out.append(['up',k])
                held.clear()
        return [out,queue,sorted(admitted),sorted(held),dropped]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('bounded-keyboard-pump scenario 0', solve([[2, []]] * N), [[[], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 1', solve([[2, [['down', 'A'], ['down', 'B'], ['down', 'C']]]] * N), [[[], [['down', 'A'], ['down', 'B']], ['A', 'B'], [], 1]] * N)
check('bounded-keyboard-pump scenario 2', solve([[2, [['down', 'A'], ['down', 'B'], ['up', 'A']]]] * N), [[[['down', 'A']], [['down', 'B'], ['up', 'A']], ['B'], ['A'], 0]] * N)
check('bounded-keyboard-pump scenario 3', solve([[2, [['down', 'A'], ['down', 'B'], ['tick', '']]]] * N), [[[['down', 'A']], [['down', 'B']], ['A', 'B'], ['A'], 0]] * N)
check('bounded-keyboard-pump scenario 4', solve([[2, [['down', 'A'], ['down', 'B'], ['flush', '']]]] * N), [[[['down', 'A'], ['down', 'B']], [], ['A', 'B'], ['A', 'B'], 0]] * N)
check('bounded-keyboard-pump scenario 5', solve([[2, [['down', 'A'], ['down', 'B'], ['reset', '']]]] * N), [[[], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 6', solve([[2, [['down', 'A'], ['tick', ''], ['down', 'B'], ['reset', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 7', solve([[1, [['down', 'A'], ['up', 'A'], ['flush', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 8', solve([[2, [['down', 'A'], ['down', 'A'], ['up', 'A'], ['flush', '']]]] * N), [[[['down', 'A'], ['up', 'A']], [], [], [], 0]] * N)
check('bounded-keyboard-pump scenario 9', solve([[2, [['up', 'A']]]] * N), [[[], [], [], [], 0]] * 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
bounded-keyboard-pump scenario 0[[[], [], [], [], 0]][[[], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 1[[[], [['down', 'A']], ['A'], [], 2]][[[], [['down', 'A'], ['down', 'B']], ['A', 'B'], [], 1]]Failed
bounded-keyboard-pump scenario 2[[[], [['down', 'A'], ['up', 'A']], [], [], 1]][[[['down', 'A']], [['down', 'B'], ['up', 'A']], ['B'], ['A'], 0]]Failed
bounded-keyboard-pump scenario 3[[[['down', 'A']], [], ['A'], ['A'], 1]][[[['down', 'A']], [['down', 'B']], ['A', 'B'], ['A'], 0]]Failed
bounded-keyboard-pump scenario 4[[[['down', 'A']], [], ['A'], ['A'], 1]][[[['down', 'A'], ['down', 'B']], [], ['A', 'B'], ['A', 'B'], 0]]Failed
bounded-keyboard-pump scenario 5[[[], [], [], [], 1]][[[], [], [], [], 0]]Failed
bounded-keyboard-pump scenario 6[[[['down', 'A'], ['up', 'A']], [], [], [], 0]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 7[[[], [], [], [], 1]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Failed
bounded-keyboard-pump scenario 8[[[['down', 'A'], ['up', 'A']], [], [], [], 0]][[[['down', 'A'], ['up', 'A']], [], [], [], 0]]Passed
bounded-keyboard-pump scenario 9[[[], [], [], [], 0]][[[], [], [], [], 0]]Passed

SHA-256 / f26fb531a0a4a3ec58553aae029b7d53662ac6219764e3071f9eee3243691663

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 10 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 2026-09-29T14:42:11.188513+00:00.

Case digest / 64c5016196b20d63af02a1aa64c0d95c2450d8649f376ff668a3255e90a18d90