[Bug] SessionStart hook receives parent session ID in forked sessions

Bug Description
Bug Report: SessionStart Hook Receives Stale Session ID in Forked Sessions

Summary: When forking a session, the SessionStart hook receives the parent session's ID instead of the newly created session's ID.

Steps to Reproduce:

1. Start a Claude Code session (Session A)
2. Fork the session (creating Session B)
3. Observe the session ID passed to the SessionStart hook

Expected Behavior:
SessionStart hook receives the new session's ID (Session B)

Actual Behavior:
SessionStart hook receives the parent session's ID (Session A)

Evidence:

• /status reports actual session ID: a4abdd71-edbd-46df-80d3-3d1000a7a2d6
• SessionStart hook received: b588daa2-c3b2-459a-a972-6d32ac29cb18 (parent session)

Impact:
Any hook logic that depends on the session ID (logging, state management, file operations keyed by session) will operate on incorrect data in forked sessions.

Environment Info

• Platform: linux
• Terminal: kitty
• Version: 2.0.76
• Feedback ID: c13f0d4c-9fb5-4c2d-8027-cff8b6963505

Errors

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