Context Canary

A context canary is a trivially checkable standing instruction whose only job is to fail visibly. The classic form: "start every response with my name." The agent costs almost nothing to comply — so when the name disappears, that absence is data. The instruction didn't get harder; the agent's hold on its early-context instructions got weaker. Like the coal-mine canary, it dies first, before the failures you actually care about (forgotten constraints, ignored conventions, re-litigated decisions) start landing in your code.

This works because context degradation is silent and gradual. Models don't announce that they've stopped attending to instructions from 80k tokens ago, and compaction summaries quietly drop standing instructions. The canary converts an invisible failure into a binary, per-turn, zero-effort check. The research behind why this happens — context rot, lost-in-the-middle, instruction drift, compaction loss — is in references/research.md.

When to use this skill

• Installing a canary at the start of a long or high-stakes session.
• The user notices the canary stopped appearing and asks what happened.
• The agent itself realizes it can no longer find its canary contract in context.
• The user asks how trustworthy the current context still is.

The canary contract

When invoked, install the canary by stating the contract explicitly in one short message, then follow it. Default format — first line of every response from then on: