[BUG] SessionStart hook not invoked when prompt contains @ folder/file references

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?

When the opening prompt includes @folder or @file context references, the SessionStart hook does not fire. Without @ references, the hook works correctly. Suspected cause: @ reference resolution runs in a preprocessing path that doesn't raise the session-start event.

What Should Happen?

session start hook should still be invoked irrespective of what character user prompt has

Error Messages/Logs

Steps to Reproduce

1. Add a SessionStart hook to .claude/settings.json:

{
"hooks": {
"SessionStart": [
{
"hooks": [
{ "type": "command", "command": "echo 'hook fired' >> /tmp/hook-test.log" }
]
}
]
}
}

1. Start a new Claude Code session with an opening prompt that includes an @ reference:

@src/components can you help me onboard my library
→ Check /tmp/hook-test.log — hook does not fire

1. Start another new session with the same prompt but without the @ reference:

can you help me onboard my library
→ Check /tmp/hook-test.log — hook fires

Expected: Hook fires in both cases.
Actual: Hook is skipped when @ references are present.

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.233

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_