[Bug] v2.1.30 regression: CLI freezes when SessionStart hook errors (Windows)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Claude Code v2.1.30 freezes completely on startup when a SessionStart hook returns an error. The CLI displays SessionStart:startup hook error then becomes permanently unresponsive — no input accepted, no timeout, requires force-kill.

This is a regression. In earlier versions, hook errors were displayed as warnings but the CLI continued functioning normally.

The freeze is triggered by the known Windows hook execution failure (see #21468), but the freeze itself is a separate bug — hook errors should never render the CLI unresponsive.

What Should Happen?

When a SessionStart hook errors, Claude Code should:

1. Log the error
2. Display a warning to the user
3. Continue startup normally

Error Messages/Logs

SessionStart:startup hook error

After this message, the CLI is completely frozen. No prompt appears, no input is accepted.

Steps to Reproduce

1. Install Claude Code v2.1.30 on Windows 11
2. Enable the superpowers plugin (superpowers@claude-plugins-official: true)
3. Launch claude from any project directory
4. Observe: SessionStart:startup hook error appears, CLI freezes indefinitely

Note: Any SessionStart hook that errors should reproduce the freeze — superpowers is just the most common trigger on Windows due to #21468.

Claude Model

None

Is this a regression?

Yes — earlier versions displayed the error but continued to a working prompt.

Last Working Version

~v2.1.27 (hook error was displayed but CLI remained functional)

Claude Code Version

2.1.30

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Git Bash 5.2.37 (MSYS2)

Additional Information

Compounding factor

Large accumulated session .jsonl files in ~/.claude/projects/ (370MB+) appear to exacerbate the hang duration. Cleaning these files (see #22041) helps but does not fix the root cause.

Why this is NOT a duplicate of #21468 / #22337

Those issues track the hook execution failure on Windows (.sh scripts not executing, path handling). This issue tracks a separate bug: Claude Code's error handling when any hook fails — the CLI should not freeze regardless of why the hook errored.

| Issue | Bug | Status |
|-------|-----|--------|
| #21468 | Hook script never executes on Windows | OPEN |
| #22337 | Path handling strips backslashes | OPEN (duplicate) |
| This issue | CLI freezes when hook errors | NEW |

Workaround

Disable the plugin to prevent the hook from running:

{
  "enabledPlugins": {
    "superpowers@claude-plugins-official": false
  }
}

Also clean up large session files to reduce hang severity:

find ~/.claude/projects -name "*.jsonl" -size +10M -delete

Suggested Fix

The hook runner in Claude Code should have:

1. A timeout for hook execution (e.g., 30s)
2. Graceful error recovery — catch hook failures and continue startup
3. Never block the main event loop waiting on a failed hook

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "startup",
        "hooks": [
          {
            "type": "command",
            "command": "powershell.exe -NoProfile -NonInteractive -Command \"Write-Error 'intentional SessionStart failure'; exit 42\"",
            "timeout": 5
          }
        ]
      }
    ]
  }
}

Hook SessionStart:startup (SessionStart) error:
intentional SessionStart failure