Debug Runtime

Root-cause fast: evidence → origin → hypothesis → confirm → fix or escalate.

Workflow

1. Evidence

Stack trace/error (file:line), what happened, environment, recent changes. If unavailable, tail the logs:

tail -100 logs/app.log | grep -i "error\|fatal\|exception"
journalctl -u <service> -n 100 --no-pager
docker logs <container> --tail 100

2. Origin

Deepest frame in YOUR code (skip framework frames — Express/Rails/Django/Next.js). Read it and its caller. Sparse? grep -rn "error text" src/

3. Hypothesis

"This occurs because [condition] when [state is X]." Check error type, call path, recent changes.