PreCompact

A pre-compaction hook that runs a Node.js command before the agent's conversation context is shortened. It invokes a harness script with the pre-compact argument.

In plain words
What is it for?
Use it in Claude Code or a similar setup when the auto-harness needs to execute its pre-compaction script automatically.
Why use it?
It provides a defined point for the harness to run its preparation logic before context compaction occurs.

Hook

Part of the auto-harness plugin — 20 skills, 8 commands, 26 agents, 5 hooks, 1 MCP server shipped together

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/redker56/auto-harness/pre-compact
Clone the repo
git clone --depth 1 https://github.com/redker56/auto-harness

Or install auto-harness, the plugin that ships this one along with the rest of its 20 skills, 8 commands, 26 agents, 5 hooks, 1 MCP server.

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 50% copy Near-identical to another mod in the catalogue.
Security

Grade A, and why

PreCompact 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 3d 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

50% identical to SessionStart — 7 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 · 14 lines

What it actually says

{
  "PreCompact": [
    {
      "matcher": "",
      "hooks": [
        {
          "type": "command",
          "command": "node \"${CLAUDE_PLUGIN_ROOT}/scripts/harness-hook.mjs\" pre-compact",
          "async": false
        }
      ]
    }
  ]
}
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.

  1. 3d ago First seen · 14 lines scan A e6b446f9139b

Subscribe to this mod's changes

PreCompact is a hook published in the GitHub repository redker56/auto-harness (14 stars, last pushed 4mo 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 50% identical to SessionStart, differing in 7 lines, and is treated as a copy.