Context Engineering: Guards, Hygiene, Compaction, Recovery

The goal: prevent long sessions from degrading into overflow, provider 400s, or half-compacted states.

Entry points:

• Context
• Compaction
• Session pruning

A practical formula

Stability ≈ preflight window guard + hygiene + tool pairing repair + compaction retry + timeout snapshot + overflow recovery.

Acceptance checks

1. Long sessions stay bounded and keep replying.
2. No orphan tool_result messages after trimming.
3. Compaction retries don’t return early “done”.
4. Timeout during compaction still returns a usable snapshot.