[ROOT CAUSE] Session Resume Bug Caused By Summarizer Activity During Startup

Bug Description

Observed Behavior:
Claude Code session resume sometimes creates a new session ID + copies old content instead of continuing with the existing session ID.

Pattern Identified:

• When no messages are added during session startup → resumes correctly with same session ID
• When messages are added during session startup → creates new session ID + copies content

Hypothesis:
The async(!) conversation summarization process may be adding messages during session startup, triggering the inconsistent behavior.

Evidence:
After disabling the summarizer, the bug has not been encountered again. Bug appears to correlate with summarizer activity during session startup.

Environment Info

• Platform: linux
• Terminal: kitty
• Version: 1.0.120
• Feedback ID: 71407332-fe30-417c-a8be-4c86b1caff0a