A hook that runs a shell command before the coding agent's conversation context is shortened to fit its limits.

Running the AgentCairn session-end script before context compaction. The hook itself does not describe other actions.

It provides a defined point to run a session-end script before earlier context is compacted.

PreCompact — Hook by ccf

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/ccf/agentcairn/pre-compact

Clone the repo

git clone --depth 1 https://github.com/ccf/agentcairn

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 88% 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 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

88% identical to SessionEnd — 4 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.

plugin/hooks/hooks.json · 17 lines

What it actually says

{
  "PreCompact": [
    {
      "matcher": "*",
      "hooks": [
        {
          "type": "command",
          "command": "sh",
          "args": [
            "${CLAUDE_PLUGIN_ROOT}/scripts/session-end.sh"
          ],
          "timeout": 30
        }
      ]
    }
  ]
}

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 · 17 lines scan A 34a5e3db1612

Subscribe to this mod's changes

PreCompact is a hook published in the GitHub repository ccf/agentcairn (46 stars, last pushed 5d ago), licensed Apache-2.0. 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 88% identical to SessionEnd, differing in 4 lines, and is treated as a copy.

agentmemory ai ai-agents claude claude-code codex

PreCompact

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

PreToolUse

SessionStart

UserPromptSubmit

PostToolUse

PostToolUseFailure

SubagentStart