A post-compaction hook runs shell commands after an agent's context has been shortened, either manually or automatically. It can restore active preferences and record the lifecycle event in Open Second Brain.

Use it to re-inject active preferences after compaction and capture that post-compaction event.

Context compaction can remove details from the agent's working context. This hook helps reintroduce active preferences and preserve a record of what happened.

PostCompact — Hook by itechmeat

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods

npx agentmods add hooks/itechmeat/open-second-brain/post-compact

Clone the repo

git clone --depth 1 https://github.com/itechmeat/open-second-brain

Per session not measured What this adds to a session before it is invoked.

When invoked not measured Not applicable: nothing here is loaded into a session.

Security scan A 0 findings. Scan, not verified.

Origin 86% copy Near-identical to another mod in the catalogue.

Security

Grade A, and why

PostCompact scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the commands this hook runs, not an audit. A hook is shell that executes on your machine at the event it names, which is why every command in it is printed with what was found.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

Origin

This is a copy

86% identical to SessionStart — 14 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

hooks/hooks.json · 21 lines

What it actually says

{
  "PostCompact": [
    {
      "matcher": "manual|auto",
      "hooks": [
        {
          "type": "command",
          "command": "r=\"$CLAUDE_PLUGIN_ROOT\"; if [ -n \"$r\" ] && [ -x \"$r/scripts/o2b-hook\" ]; then exec \"$r/scripts/o2b-hook\" active-inject; fi; command -v o2b-hook >/dev/null 2>&1 && exec o2b-hook active-inject; exit 0",
          "timeout": 10,
          "statusMessage": "OSB: re-injecting active preferences after compact"
        },
        {
          "type": "command",
          "command": "r=\"$CLAUDE_PLUGIN_ROOT\"; if [ -n \"$r\" ] && [ -x \"$r/scripts/o2b-hook\" ]; then exec \"$r/scripts/o2b-hook\" session-capture; fi; command -v o2b-hook >/dev/null 2>&1 && exec o2b-hook session-capture; exit 0",
          "timeout": 10,
          "statusMessage": "OSB: capturing post-compact lifecycle event"
        }
      ]
    }
  ]
}

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2d ago First seen · 21 lines scan A 18f3fff9fe99

Subscribe to this mod's changes

PostCompact is a hook published in the GitHub repository itechmeat/open-second-brain (378 stars, last pushed 5d ago), licensed MIT. Its token cost is not measured: a hook is shell that never enters the context. A static security scan graded it A with 0 findings. It is 86% identical to SessionStart, differing in 14 lines, and is treated as a copy.

PostCompact

Getting it into your agent

Grade A, and why

Nothing flagged

This is a copy

What it actually says

What this file has done since we first saw it

Other hooks, from other repositories

PostToolUse

SessionStart

SessionStart

PreToolUse

SessionStart

SessionStart