R12.2: Timer lifecycle cleanup

Short answer: SetTimeout and setInterval handle IDs cleaned on component unmount. A timer that outlives its component updates state that no longer exists.

Group: Memory and resource leaks. Status: stable. Generated from the rule definitions; do not edit by hand.

Playground: https://brevio.pro/tools/agent-guard-playground?rule=R12.2

What it catches

Timer lifecycle cleanup: setTimeout and setInterval handle IDs cleaned on component unmount.

Why

A timer that outlives its component updates state that no longer exists.

A bad example

useEffect(() => { setTimeout(f, 5000); }, []);

A good example

useEffect(() => { const t = setTimeout(f, 5000); return () => clearTimeout(t); }, []);

How it is checked

Nothing yet. No scanner and no slice card checks it: it is a standing rule for authors and reviewers.

How to silence it

A person can silence one finding with brevio-core: ignore R12.2 -- reason on the line or the line above. Without the reason it does not count. An agent cannot silence it: the agent hook and the MCP tools never honour the comment, and a pull request that adds one is reported until a reviewer allows it. Fixing the code is still the better answer.

To change what the rule flags, edit its definition in dev_rules.py or code_rules/__init__.py. That is a code change and is reviewed like one.

R12.3 Stream disposal hygiene
R12.4 WebSocket cleanup
R12.5 Database connection pool hygiene
R12.6 Worker thread termination
Every rule