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FA-31846 / Keyboard interactions / Open access

Keyboard usage snapshot delta decoder: Invalid report count uses slot count or overwrites prior errors · case 01

The event trace violates the reject counter rule and produces incorrect keyboard state or command output.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Invalid report count uses slot count or overwrites prior errors.

VERIFIED REPAIR

Use the contract transition `rejected+=1` at the reject counter fault site; preserve the other state transitions.

Unsuccessful approach: The partial repair changes this transition to rejected+=len(slots), which still violates the model contract on the explicit regression traces.

Case contract

Each report is [modifier_mask,usage_slots]. Usages are integers >=0; 0 is padding, 1 is an error sentinel that invalidates the whole report. Other usages are unique logical keys even when slots duplicate. Modifier bits 0..7 identify M0..M7. Emit sorted key releases, sorted modifier releases, sorted modifier presses, then sorted key presses per valid report. Return emitted [phase,kind,identity] and final usage/modifier sets. 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):
        old_keys=set(); old_mods=set(); out=[]; rejected=0
        for mask,slots in c:
            if 1 in slots:
                rejected=1
                continue
            keys=set(slots)-{0}
            mods={bit for bit in range(8) if mask & (1<<bit)}
            for key in sorted(old_keys-keys): out.append(['up','key',key])
            for mod in sorted(old_mods-mods): out.append(['up','mod',mod])
            for mod in sorted(mods-old_mods): out.append(['down','mod',mod])
            for key in sorted(keys-old_keys): out.append(['down','key',key])
            old_keys=keys
            old_mods=mods
        return [out,sorted(old_keys),sorted(old_mods),rejected]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hid-report-delta scenario 0', solve([[]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 1', solve([[[0, [0, 0]]]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 2', solve([[[1, [2, 3, 3, 0]], [1, [2, 3, 0]]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]] * N)
check('hid-report-delta scenario 3', solve([[[1, [2, 3]], [2, [3, 4]], [0, []]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]] * N)
check('hid-report-delta scenario 4', solve([[[4, [5]], [0, [1, 0, 0]], [4, [5]]]] * N), [[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]] * N)
check('hid-report-delta scenario 5', solve([[[0, [1, 0]], [0, [1, 2]]]] * N), [[[], [], [], 2]] * N)
check('hid-report-delta scenario 6', solve([[[128, [2]], [0, []], [128, [2]]]] * N), [[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]] * N)
check('hid-report-delta scenario 7', solve([[[0, [2]], [0, []], [0, [2]]]] * N), [[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 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
hid-report-delta scenario 0[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 1[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 2[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]]Passed
hid-report-delta scenario 3[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]]Passed
hid-report-delta scenario 4[[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]][[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]]Passed
hid-report-delta scenario 5[[[], [], [], 1]][[[], [], [], 2]]Failed
hid-report-delta scenario 6[[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]][[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]]Passed
hid-report-delta scenario 7[[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]][[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]]Passed

SHA-256 / cb9afc9b60952911a96d327bdbeb8ce13981d63ef81b50e65fed7f269a02f438

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):
        old_keys=set(); old_mods=set(); out=[]; rejected=0
        for mask,slots in c:
            if 1 in slots:
                rejected+=len(slots)
                continue
            keys=set(slots)-{0}
            mods={bit for bit in range(8) if mask & (1<<bit)}
            for key in sorted(old_keys-keys): out.append(['up','key',key])
            for mod in sorted(old_mods-mods): out.append(['up','mod',mod])
            for mod in sorted(mods-old_mods): out.append(['down','mod',mod])
            for key in sorted(keys-old_keys): out.append(['down','key',key])
            old_keys=keys
            old_mods=mods
        return [out,sorted(old_keys),sorted(old_mods),rejected]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hid-report-delta scenario 0', solve([[]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 1', solve([[[0, [0, 0]]]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 2', solve([[[1, [2, 3, 3, 0]], [1, [2, 3, 0]]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]] * N)
check('hid-report-delta scenario 3', solve([[[1, [2, 3]], [2, [3, 4]], [0, []]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]] * N)
check('hid-report-delta scenario 4', solve([[[4, [5]], [0, [1, 0, 0]], [4, [5]]]] * N), [[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]] * N)
check('hid-report-delta scenario 5', solve([[[0, [1, 0]], [0, [1, 2]]]] * N), [[[], [], [], 2]] * N)
check('hid-report-delta scenario 6', solve([[[128, [2]], [0, []], [128, [2]]]] * N), [[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]] * N)
check('hid-report-delta scenario 7', solve([[[0, [2]], [0, []], [0, [2]]]] * N), [[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 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
hid-report-delta scenario 0[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 1[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 2[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]]Passed
hid-report-delta scenario 3[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]]Passed
hid-report-delta scenario 4[[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 3]][[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]]Failed
hid-report-delta scenario 5[[[], [], [], 4]][[[], [], [], 2]]Failed
hid-report-delta scenario 6[[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]][[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]]Passed
hid-report-delta scenario 7[[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]][[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]]Passed

SHA-256 / b2d8e3aea644d7a64485d294280efe201aa0ff6c298205205f7381910025060e

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):
        old_keys=set(); old_mods=set(); out=[]; rejected=0
        for mask,slots in c:
            if 1 in slots:
                rejected+=1
                continue
            keys=set(slots)-{0}
            mods={bit for bit in range(8) if mask & (1<<bit)}
            for key in sorted(old_keys-keys): out.append(['up','key',key])
            for mod in sorted(old_mods-mods): out.append(['up','mod',mod])
            for mod in sorted(mods-old_mods): out.append(['down','mod',mod])
            for key in sorted(keys-old_keys): out.append(['down','key',key])
            old_keys=keys
            old_mods=mods
        return [out,sorted(old_keys),sorted(old_mods),rejected]
    return [run(c) for c in cases]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('hid-report-delta scenario 0', solve([[]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 1', solve([[[0, [0, 0]]]] * N), [[[], [], [], 0]] * N)
check('hid-report-delta scenario 2', solve([[[1, [2, 3, 3, 0]], [1, [2, 3, 0]]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]] * N)
check('hid-report-delta scenario 3', solve([[[1, [2, 3]], [2, [3, 4]], [0, []]]] * N), [[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]] * N)
check('hid-report-delta scenario 4', solve([[[4, [5]], [0, [1, 0, 0]], [4, [5]]]] * N), [[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]] * N)
check('hid-report-delta scenario 5', solve([[[0, [1, 0]], [0, [1, 2]]]] * N), [[[], [], [], 2]] * N)
check('hid-report-delta scenario 6', solve([[[128, [2]], [0, []], [128, [2]]]] * N), [[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]] * N)
check('hid-report-delta scenario 7', solve([[[0, [2]], [0, []], [0, [2]]]] * N), [[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 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
hid-report-delta scenario 0[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 1[[[], [], [], 0]][[[], [], [], 0]]Passed
hid-report-delta scenario 2[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3]], [2, 3], [0], 0]]Passed
hid-report-delta scenario 3[[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]][[[['down', 'mod', 0], ['down', 'key', 2], ['down', 'key', 3], ['up', 'key', 2], ['up', 'mod', 0], ['down', 'mod', 1], ['down', 'key', 4], ['up', 'key', 3], ['up', 'key', 4], ['up', 'mod', 1]], [], [], 0]]Passed
hid-report-delta scenario 4[[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]][[[['down', 'mod', 2], ['down', 'key', 5]], [5], [2], 1]]Passed
hid-report-delta scenario 5[[[], [], [], 2]][[[], [], [], 2]]Passed
hid-report-delta scenario 6[[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]][[[['down', 'mod', 7], ['down', 'key', 2], ['up', 'key', 2], ['up', 'mod', 7], ['down', 'mod', 7], ['down', 'key', 2]], [2], [7], 0]]Passed
hid-report-delta scenario 7[[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]][[[['down', 'key', 2], ['up', 'key', 2], ['down', 'key', 2]], [2], [], 0]]Passed

SHA-256 / 3fa9febfbb463c08e459fe498b09838f18150df53e3cee5648703597a622ee6f

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 2026-09-29T14:42:06.121434+00:00.

Case digest / 1eb8b73e6a05a0a9d9ab1de3417654ca1346b88ca3967cc1419b7c220e1de415