Compaction checkpoint and steering prompt

[dean0x]

Summary

Two complementary mechanisms to improve context survival across compaction events:

1. Checkpoint: Before compaction, parse session transcript and extract structured state
2. Steering prompt: Inject guidance text during PreCompact to bias what gets preserved

Key Features

Checkpoint

• PreCompact hook extracts structured markdown checkpoint from session state
• SessionStart hook (compact matcher) reinjects checkpoint post-compaction
• Sections: Active Task, Key Decisions, Modified Files, Open Questions, Error Context, Agent State

Steering Prompt

• Zero-LLM-cost echo in PreCompact hook
• Biases compaction: "Preserve code changes, key decisions, and file paths. Discard intermediate attempts."
• Dynamic project-aware compactInstructions generation for settings.json

Competitive Reference

Ref: SIEVE — measure.py:11674-11815 (compact_capture/restore), hooks.json:36-39 (steering echo), measure.py:12026-12071 (generate_compact_instructions).

Implementation Notes

• Extends existing pre-compact-memory hook which already saves git state
• Steering prompt is trivial: add echo line to existing hook
• Checkpoint extraction extends the WORKING-MEMORY.md pattern
• Consider dynamic compactInstructions generation based on active orchestration intent

Milestone

post-v2