Behavioral Patterns: Mistake Clinic

Module-Specific Mistake Radar

Symptom	Likely missing contract	Repair witness
Two disposals remove two registrations	Registration identity	Same callback twice, one handle twice
A nested publish hangs or silently interleaves	Reentrancy/order	Finite outer/inner trace
One bad listener prevents all views	Error policy unspecified	Failure followed by successful callback
Failed edit destroys redo	Validation/history ordering	Undo, invalid edit, redo
Undo changes another user's work	Snapshot boundary	Outside edit between capture and restore
Retry sends twice	Uncertain effect/deduplication	Success before lost acknowledgement
State refactor changes errors	Public observation boundary	Exact invalid-transition message
Empty page ends traversal	Pagination termination	Empty page with more=True
Next page fetched too soon	Laziness	Stop exactly at page boundary
Authentication bypasses remaining checks	Terminal policy	Allow followed by mandatory denial
New AST node gets silently ignored	Exhaustive operation coverage	Add Neg to every operation
UI updates cycle forever	Coordination ownership	Programmatic render feeds a user event

Practice Mistake Checks

Reproduce duplicate disposal (P06), failed-edit history (P11), stale approval (P14) and early page fetching (P16). Predict each trace before running it and repeat with a changed input after repair.

Keep real failures, their smallest witnesses, repairs and later transfer results. One well-explained counterexample is worth more than a fabricated error count. Use practice feedback after your attempt and return to the appropriate competency gate.