context-canary

Install a context canary: a standing instruction like starting every reply with your name and a turn counter. Because compliance costs almost nothing, its disappearance is strong evidence that early instructions fell out of effective context.

A context canary is a trivially checkable per-turn signal, such as a name prefix plus turn counter, whose only job is to fail visibly. When it goes missing or the counter breaks, it indicates instruction drift, compaction, or continuity loss.

Watch the canary's turn counter. Summaries rarely preserve exact counts, so a reset, skip, or vague counter after a compaction event reveals the discontinuity within a turn or two, even if the name instruction survives.

No. The test is one-sided: a missing canary is strong evidence of degradation, but a present canary is only weak evidence of health. Cheap stylistic habits can survive while harder constraints quietly rot, so stay suspicious past roughly half the context window.

Stop trusting drifted state, checkpoint durable state (goal, decisions, files touched, next step) into a file, re-read project instructions, restate the task for user confirmation, then start a fresh session seeded with the checkpoint and reinstall the canary.

Only if you want a cross-session habit, and know it measures something different. A file-based canary survives compaction by design, so it tests file-instruction attention rather than conversation context survival. The session canary is the one that detects degradation.