SessionStart hook shows 'startup hook error' despite successful execution

Description

SessionStart hooks display 'SessionStart:startup hook error' in the CLI output even when the hook executes successfully (exit code 0, valid JSON output).

Steps to Reproduce

1. Create a SessionStart hook in ~/.claude/settings.json:

{
  "hooks": {
    "SessionStart": [
      {
        "matcher": "",
        "hooks": [
          {
            "type": "command",
            "command": "node \"path/to/my-hook.mjs\""
          }
        ]
      }
    ]
  }
}

1. The hook outputs valid JSON:

{"hookSpecificOutput":{"hookEventName":"SessionStart","additionalContext":"..."}}

1. Start Claude Code CLI in any directory

Expected Behavior

• Hook executes successfully
• No error message shown (or shows "startup hook success")

Actual Behavior

• Hook executes successfully (verified by log files)
• CLI displays: SessionStart:startup hook error
• Despite the error message, the hook output IS correctly injected into Claude's context

Environment

• Claude Code v2.1.23
• Windows 11
• Node.js v22.x

Additional Context

• This appears to be a UI bug where the status message shows "error" regardless of actual hook execution status
• The hook functionality works correctly - only the status display is wrong
• Issue occurs consistently across multiple sessions and restarts
• Related to #12671 (if that issue exists)

Workaround

The hook output is correctly processed despite the error message, so functionality is not affected. The error message can be safely ignored.