Stop hook intermittently stops firing mid-session

Description

The Stop hook (configured in settings.json under hooks.Stop) intermittently stops being invoked mid-session. The hook works correctly for several assistant turns, then silently stops being called. No error, no crash — it just stops firing.

Steps to reproduce

1. Configure a Stop hook in ~/.claude/settings.json:

{
  "hooks": {
    "Stop": [{
      "matcher": "",
      "hooks": [{
        "type": "command",
        "command": "python C:/Users/User/.claude/hooks/speak.py"
      }]
    }]
  }
}

1. Start a Claude Code session
2. The hook fires correctly for multiple responses (verified via debug log timestamps)
3. After ~10-15 assistant turns, the hook silently stops being invoked
4. Manual invocation via echo '{"session_id":"test",...}' | python speak.py still works perfectly
5. Starting a new session restores hook functionality

Expected behavior

The Stop hook should fire on every assistant turn for the entire session.

Actual behavior

Hook fires correctly for the first ~10-15 turns, then stops being called. No error output. No crash log. The hook process isn't stuck (no orphaned python/ffplay processes).

Environment

• Claude Code version: 2.1.71
• OS: Windows 11
• Hook type: command (python script)
• Hook event: Stop (no matcher filter)