agent-drift-and-re-anchoring

Agent Drift and Re-Anchoring

A long-running agent doesn't fail by crashing — it fails by quietly stopping being the agent that started the task. This skill names the distinct ways that happens ("drift" is the general term; there is no single fix) and the specific, mechanism-matched mitigation for each, because a bigger context window delays when drift becomes visible but does not prevent any of it.

The six drift mechanisms

Treat these as distinct failure modes needing distinct fixes, not one generic "agent got confused" bucket:

1. Goal drift — the agent starts pursuing a plausible-sounding side quest instead of the original ask (asked to fix a flaky test, ends up refactoring the whole test harness). Mitigation: periodic re-anchoring — explicitly restate the original objective and check the current action against it, especially before a costly or hard-to-reverse step.
2. Context drift — reasoning quality on unchanged information degrades as the context window fills; content near the middle/start becomes functionally less influential even though it's still technically present. Mitigation: active compression/pruning of stale detail, not just relying on a larger window to "fit everything."
3. Stale context — the agent reasons over an old snapshot of something that has since changed (a file edited by another process, a decision the user has since revised) without re-checking it's still current. Mitigation: externalize state that can change into a durable, re-readable store, and re-read it at decision points rather than trusting a cached mental model of it.
4. Role drift — a system prompt or initial framing loses influence over a long conversation as more recent content dominates. Mitigation: periodically re-inject the system prompt (or a condensed form of it) near the end of a long context, not just at the start.
5. Tool-use drift — the agent over-relies on one tool whose output is immediately visible and self-reinforcing (e.g., calling search repeatedly) while under-using a tool whose output is easy to lose track of once buried in history. Mitigation: explicit per-tool call budgets, and summarizing a tool's output before continuing rather than letting raw output pile up unprocessed.
6. Plan decay — the agent keeps executing steps of a plan that an earlier step has already made obsolete, because the plan was treated as a fixed script rather than a living hypothesis. Mitigation: treat the plan as mutable state re-evaluated at checkpoints, not as an execution log to be marched through regardless of what's been learned since.