FA-4531 / Listener lifecycle / Open access

Listener callback registration · case 01

The operation returns a result or retained state that violates this contract: Listeners have identity, event name, once flag, and registration order. Dispatch uses a snapshot; listener actions remove another listener or add a new one. Return callback identities in invocation order. A listener installed by a callback starts participating on the next dispatch and uses the action-specified event name.

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ROOT CAUSE

A listener installed by a callback starts participating on the next dispatch and uses the action-specified event name. The broken transition violates that invariant.

VERIFIED REPAIR

Listeners have identity, event name, once flag, and registration order. Dispatch uses a snapshot; listener actions remove another listener or add a new one. Return callback identities in invocation order. A listener installed by a callback starts participating on the next dispatch and uses the action-specified event name.

Unsuccessful approach: The attempted transition changes the behavior but still violates the same invariant in at least one independent regression fixture.

Case contract

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x, y=None):
    listeners={}; out=[]
    for event in x:
        op=event[0]
        if op=='on':
            _,k,name,once,action=event
            if True: listeners[k]=[name,once,action]
        elif op=='off':
            listeners.pop(event[1],None)
        elif op=='emit':
            name=event[1]
            batch=list(listeners.items())
            for k,entry in batch:
                if entry[0]==name:
                    if entry[1]:
                        listeners.pop(k,None)
                    out.append(k)
                    action=entry[2]
                    if action and action[0]=='off':
                        listeners.pop(action[1],None)
                    elif action and action[0]=='on':
                        listeners[action[1]]=[name,False,None]
        elif op=='names': out.append(list(listeners))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('replacement changes event but preserves order', solve([['on', 'a', 'old', False, None], ['on', 'b', 'new', False, None], ['on', 'a', 'new', False, None], ['emit', 'new'], ['names']]), ['a', 'b', ['a', 'b']])
check('snapshot removal and once lifetime', solve([['on', 'a', 'e', True, ['off', 'b']], ['on', 'b', 'e', False, None], ['on', 'c', 'e', False, None], ['emit', 'e'], ['emit', 'e'], ['names']]), ['a', 'b', 'c', 'c', ['c']])
check('explicit identity removal and event filtering', solve([['on', 'a', 'e', False, None], ['on', 'b', '*', False, None], ['on', 'c', 'e', False, None], ['off', 'a'], ['emit', 'e'], ['names']]), ['c', ['b', 'c']])
check('callback replaces existing target event', solve([['on', 'a', 'e', True, ['on', 'b', 'later']], ['on', 'b', 'old', False, None], ['emit', 'e'], ['emit', 'later'], ['emit', 'old'], ['names']]), ['a', 'b', ['b']])
check('callback replaces metadata rather than setdefault', solve([['on','a','e',True,['on','b','later']],['on','b','old',False,None],['emit','e'],['emit','later'],['emit','later'],['emit','old']]), ['a','b','b'])
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 fixture	Actual	Expected	Outcome
replacement changes event but preserves order	`['a', 'b', ['a', 'b']]`	`['a', 'b', ['a', 'b']]`	Passed
snapshot removal and once lifetime	`['a', 'b', 'c', 'c', ['c']]`	`['a', 'b', 'c', 'c', ['c']]`	Passed
explicit identity removal and event filtering	`['c', ['b', 'c']]`	`['c', ['b', 'c']]`	Passed
callback replaces existing target event	`['a', ['b']]`	`['a', 'b', ['b']]`	Failed
callback replaces metadata rather than setdefault	`['a']`	`['a', 'b', 'b']`	Failed

SHA-256 / 92397ce2dee402ee9ee6327de083f54abb8f00f99b34eab1a3c1e3a9b2185e60

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x, y=None):
    listeners={}; out=[]
    for event in x:
        op=event[0]
        if op=='on':
            _,k,name,once,action=event
            if True: listeners[k]=[name,once,action]
        elif op=='off':
            listeners.pop(event[1],None)
        elif op=='emit':
            name=event[1]
            batch=list(listeners.items())
            for k,entry in batch:
                if entry[0]==name:
                    if entry[1]:
                        listeners.pop(k,None)
                    out.append(k)
                    action=entry[2]
                    if action and action[0]=='off':
                        listeners.pop(action[1],None)
                    elif action and action[0]=='on':
                        listeners.setdefault(action[1],[action[2],False,None])
        elif op=='names': out.append(list(listeners))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('replacement changes event but preserves order', solve([['on', 'a', 'old', False, None], ['on', 'b', 'new', False, None], ['on', 'a', 'new', False, None], ['emit', 'new'], ['names']]), ['a', 'b', ['a', 'b']])
check('snapshot removal and once lifetime', solve([['on', 'a', 'e', True, ['off', 'b']], ['on', 'b', 'e', False, None], ['on', 'c', 'e', False, None], ['emit', 'e'], ['emit', 'e'], ['names']]), ['a', 'b', 'c', 'c', ['c']])
check('explicit identity removal and event filtering', solve([['on', 'a', 'e', False, None], ['on', 'b', '*', False, None], ['on', 'c', 'e', False, None], ['off', 'a'], ['emit', 'e'], ['names']]), ['c', ['b', 'c']])
check('callback replaces existing target event', solve([['on', 'a', 'e', True, ['on', 'b', 'later']], ['on', 'b', 'old', False, None], ['emit', 'e'], ['emit', 'later'], ['emit', 'old'], ['names']]), ['a', 'b', ['b']])
check('callback replaces metadata rather than setdefault', solve([['on','a','e',True,['on','b','later']],['on','b','old',False,None],['emit','e'],['emit','later'],['emit','later'],['emit','old']]), ['a','b','b'])
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 fixture	Actual	Expected	Outcome
replacement changes event but preserves order	`['a', 'b', ['a', 'b']]`	`['a', 'b', ['a', 'b']]`	Passed
snapshot removal and once lifetime	`['a', 'b', 'c', 'c', ['c']]`	`['a', 'b', 'c', 'c', ['c']]`	Passed
explicit identity removal and event filtering	`['c', ['b', 'c']]`	`['c', ['b', 'c']]`	Passed
callback replaces existing target event	`['a', 'b', ['b']]`	`['a', 'b', ['b']]`	Passed
callback replaces metadata rather than setdefault	`['a', 'b']`	`['a', 'b', 'b']`	Failed

SHA-256 / e1b1a9615df98f68648c362df2db481853551ad1cbc2222df32864fcaf330593

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(x, y=None):
    listeners={}; out=[]
    for event in x:
        op=event[0]
        if op=='on':
            _,k,name,once,action=event
            if True: listeners[k]=[name,once,action]
        elif op=='off':
            listeners.pop(event[1],None)
        elif op=='emit':
            name=event[1]
            batch=list(listeners.items())
            for k,entry in batch:
                if entry[0]==name:
                    if entry[1]:
                        listeners.pop(k,None)
                    out.append(k)
                    action=entry[2]
                    if action and action[0]=='off':
                        listeners.pop(action[1],None)
                    elif action and action[0]=='on':
                        listeners[action[1]]=[action[2],False,None]
        elif op=='names': out.append(list(listeners))
    return out
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('replacement changes event but preserves order', solve([['on', 'a', 'old', False, None], ['on', 'b', 'new', False, None], ['on', 'a', 'new', False, None], ['emit', 'new'], ['names']]), ['a', 'b', ['a', 'b']])
check('snapshot removal and once lifetime', solve([['on', 'a', 'e', True, ['off', 'b']], ['on', 'b', 'e', False, None], ['on', 'c', 'e', False, None], ['emit', 'e'], ['emit', 'e'], ['names']]), ['a', 'b', 'c', 'c', ['c']])
check('explicit identity removal and event filtering', solve([['on', 'a', 'e', False, None], ['on', 'b', '*', False, None], ['on', 'c', 'e', False, None], ['off', 'a'], ['emit', 'e'], ['names']]), ['c', ['b', 'c']])
check('callback replaces existing target event', solve([['on', 'a', 'e', True, ['on', 'b', 'later']], ['on', 'b', 'old', False, None], ['emit', 'e'], ['emit', 'later'], ['emit', 'old'], ['names']]), ['a', 'b', ['b']])
check('callback replaces metadata rather than setdefault', solve([['on','a','e',True,['on','b','later']],['on','b','old',False,None],['emit','e'],['emit','later'],['emit','later'],['emit','old']]), ['a','b','b'])
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 fixture	Actual	Expected	Outcome
replacement changes event but preserves order	`['a', 'b', ['a', 'b']]`	`['a', 'b', ['a', 'b']]`	Passed
snapshot removal and once lifetime	`['a', 'b', 'c', 'c', ['c']]`	`['a', 'b', 'c', 'c', ['c']]`	Passed
explicit identity removal and event filtering	`['c', ['b', 'c']]`	`['c', ['b', 'c']]`	Passed
callback replaces existing target event	`['a', 'b', ['b']]`	`['a', 'b', ['b']]`	Passed
callback replaces metadata rather than setdefault	`['a', 'b', 'b']`	`['a', 'b', 'b']`	Passed

SHA-256 / 0935085c19d93738649b6d9ccffd7369a704e5b24acd1f60e71a44e5d457e3d4

Verification & scope

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 2026-09-29T14:37:40.080052+00:00.

Case digest / 7d17e5568e376ecbc12a3912e3527912af5034cce2a6767bca6378c8b45a1e97