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Hooks and heartbeat

Lifecycle events trigger hooks on three distinct cadences, SessionStart and SessionEnd form the natural pair for automating the memory protocol, and nightly consolidation remains an operating system scheduled task you build yourself, not a Claude Code mechanism documented under that name.

A hook is an automatic action triggered by the harness on a precise lifecycle event, never a preference the model chooses to follow or not. The table of available events has grown since mid 2026, the figure accompanying this lesson gives the exact count and its measurement date rather than repeating it here.

Three cadences, a natural pair for memory

Hook events do not all fire at the same rate. Some run once per session, SessionStart and SessionEnd. Others run once per turn, such as UserPromptSubmit or Stop. Others still run on every tool call inside the agent loop, PreToolUse and PostToolUse. For the memory protocol described in wiring file based memory to git, SessionStart and SessionEnd form exactly the pair needed: a SessionStart hook triggers the pull before the first read, a SessionEnd hook triggers the commit and the push after the last reply. SessionEnd hooks share a 1.5 second budget between all of them, a push to a remote does not fit in that: it needs an explicit timeout in the hook, which raises the shared budget up to sixty seconds, and a witness file written at the end so the next session checks that the push succeeded rather than assuming it.

{
  "hooks": {
    "SessionStart": [
      { "hooks": [{ "type": "command", "command": "cd ~/memoire && git pull", "timeout": 30 }] }
    ],
    "SessionEnd": [
      { "hooks": [{ "type": "command", "command": "cd ~/memoire && git add notes-du-jour.md && git commit -m sync && git push && date > .dernier-sync-reussi", "timeout": 55 }] }
    ]
  }
}

Two details in this example matter as much as the timeout. First, the git add names the wanted files rather than a git add -A that would sweep the whole folder with no filter, which respects the rule set by the previous lesson of grepping for a secret before any push. Second, the standard output of a SessionStart hook, like that of this git pull, enters the context Claude can read, unlike most other events: a shared folder therefore deserves watching before wiring up this kind of hook. The status line follows the same automatic trigger logic: it can refresh itself at an interval set in seconds, not in milliseconds as an older setting might suggest.

Nightly consolidation stays outside the documented product

An operating system scheduled task, which relaunches Claude in non interactive mode in the middle of the night to consolidate the day's notes, has no documented Anthropic equivalent under this exact name: what the documentation calls scheduled tasks runs inside the desktop application, not through a Windows task or a cron driving the command line tool. The gesture therefore stays to be built yourself, exactly like the previous lesson's protocol, with an explicit anti loop safeguard: the task never relaunches a new session as long as the previous one has not written its end of run witness.