SessionEnd hooks are killed before completion when running async work #41577

Description

SessionEnd hooks that perform any non-trivial async work (e.g., an API call) are killed before they can complete. Claude Code appears to exit the process without waiting for the hook to finish, even when a generous timeout is configured (tested up to 90s).

Reproduction

1. Configure a SessionEnd hook in settings.json:

{
  "hooks": {
    "SessionEnd": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "/path/to/session-log.sh",
            "timeout": 90
          }
        ]
      }
    ]
  }
}

2. The hook script calls claude -p --model haiku to summarize the session transcript (takes ~5s):

#!/bin/bash
set -euo pipefail
INPUT=$(cat)
TRANSCRIPT_PATH=$(echo "$INPUT" | jq -r '.transcript_path // empty')
# ... extract condensed transcript with jq ...
SUMMARY=$(echo "$CONDENSED" | claude -p --bare --model haiku "Summarize this session" 2>/dev/null)
# ... write to log file ...

3. Exit a Claude Code session normally

Expected: The hook runs to completion within the configured 90s timeout, then Claude Code exits.

Actual: Claude Code exits almost immediately. The claude -p subprocess is killed before it can return. Debug logging confirms the script reaches the claude -p call but never reaches the line after it.

Workaround

Detach the heavy work into a background process so it survives parent exit:

nohup bash -c '
  # ... summarization work here ...
' _ "$TRANSCRIPT_PATH" "$SESSION_ID" "$CWD" >/dev/null 2>&1 &
disown
exit 0

This works reliably but means the hook has no way to report errors back to Claude Code, and users need to manage their own timeout (e.g., wrapping the API call in timeout 60).

Suggestion

Either:

• Wait for SessionEnd hooks to complete (up to the configured timeout) before exiting the process, consistent with how other hook events appear to work
• Document the limitation that SessionEnd hooks must not rely on completing before the parent exits, and recommend the nohup/disown pattern for async work

Environment

• Claude Code: latest (CLI)
• macOS 15 (Darwin 24.6.0)
• Shell: zsh