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MSL a3b7988d87 fix: stop hooks from making agents write in chat — save tokens

The save hook and precompact hook were telling the agent to write
diary entries, add drawers, and add KG triples IN THE CHAT WINDOW.
Every line written stays in conversation history and retransmits on
every subsequent turn — ~$1/session in wasted tokens.

Fix: hooks now say "saved in background, no action needed" and use
decision: allow instead of block. The agent continues working without
interruption. All filing happens via the background pipeline.

Also updated hooks README with:
- Known limitation: hooks require session restart after install
- Updated cost section: zero tokens, background-only

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

2026-04-13 16:41:59 -03:00

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MemPalace Hooks — Auto-Save for Terminal AI Tools

These hook scripts make MemPalace save automatically. No manual "save" commands needed.

What They Do

Hook	When It Fires	What Happens
Save Hook	Every 15 human messages	Blocks the AI, tells it to save key topics/decisions/quotes to the palace
PreCompact Hook	Right before context compaction	Emergency save — forces the AI to save EVERYTHING before losing context

The AI does the actual filing — it knows the conversation context, so it classifies memories into the right wings/halls/closets. The hooks just tell it WHEN to save.

Install — Claude Code

Add to .claude/settings.local.json:

{
  "hooks": {
    "Stop": [{
      "matcher": "*",
      "hooks": [{
        "type": "command",
        "command": "/absolute/path/to/hooks/mempal_save_hook.sh",
        "timeout": 30
      }]
    }],
    "PreCompact": [{
      "hooks": [{
        "type": "command",
        "command": "/absolute/path/to/hooks/mempal_precompact_hook.sh",
        "timeout": 30
      }]
    }]
  }
}

Make them executable:

chmod +x hooks/mempal_save_hook.sh hooks/mempal_precompact_hook.sh

Install — Codex CLI (OpenAI)

Add to .codex/hooks.json:

{
  "Stop": [{
    "type": "command",
    "command": "/absolute/path/to/hooks/mempal_save_hook.sh",
    "timeout": 30
  }],
  "PreCompact": [{
    "type": "command",
    "command": "/absolute/path/to/hooks/mempal_precompact_hook.sh",
    "timeout": 30
  }]
}

Configuration

Edit mempal_save_hook.sh to change:

SAVE_INTERVAL=15 — How many human messages between saves. Lower = more frequent saves, higher = less interruption.
STATE_DIR — Where hook state is stored (defaults to ~/.mempalace/hook_state/)
MEMPAL_DIR — Optional. Set to a conversations directory to auto-run mempalace mine <dir> on each save trigger. Leave blank (default) to let the AI handle saving via the block reason message.

mempalace CLI

The relevant commands are:

mempalace mine <dir>               # Mine all files in a directory
mempalace mine <dir> --mode convos # Mine conversation transcripts only

The hooks resolve the repo root automatically from their own path, so they work regardless of where you install the repo.

How It Works (Technical)

Save Hook (Stop event)

User sends message → AI responds → Claude Code fires Stop hook
                                            ↓
                                    Hook counts human messages in JSONL transcript
                                            ↓
                              ┌─── < 15 since last save ──→ echo "{}" (let AI stop)
                              │
                              └─── ≥ 15 since last save ──→ {"decision": "block", "reason": "save..."}
                                                                    ↓
                                                            AI saves to palace
                                                                    ↓
                                                            AI tries to stop again
                                                                    ↓
                                                            stop_hook_active = true
                                                                    ↓
                                                            Hook sees flag → echo "{}" (let it through)

The stop_hook_active flag prevents infinite loops: block once → AI saves → tries to stop → flag is true → we let it through.

PreCompact Hook

Context window getting full → Claude Code fires PreCompact
                                        ↓
                                Hook ALWAYS blocks
                                        ↓
                                AI saves everything
                                        ↓
                                Compaction proceeds

No counting needed — compaction always warrants a save.

Debugging

Check the hook log:

cat ~/.mempalace/hook_state/hook.log

Example output:

[14:30:15] Session abc123: 12 exchanges, 12 since last save
[14:35:22] Session abc123: 15 exchanges, 15 since last save
[14:35:22] TRIGGERING SAVE at exchange 15
[14:40:01] Session abc123: 18 exchanges, 3 since last save

Known Limitations

Hooks require session restart after install. Claude Code loads hooks from settings.json at session start only. If you run mempalace init or manually edit hook config mid-session, the hooks won't fire until you restart Claude Code. This is a Claude Code limitation.

Cost

Zero extra tokens. The hooks notify the AI that saves happened in the background — the AI doesn't need to write anything in the chat. All filing is handled automatically. Previous versions asked the AI to write diary entries and drawer content in the chat window, which cost ~$1/session in retransmitted tokens.

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