[Bug]: Latest chat session permanently lost from /chat list after using gemini --resume #27368

Description

Using gemini --resume causes the most recent chat session to permanently disappear from the /chat list on the subsequent normal launch. The data appears to be lost or the session index corrupted by the --resume flow.

Steps to Reproduce

1. Open Gemini normally.
2. Run /chat and confirm all existing sessions are visible.
3. Close Gemini.
4. Run gemini --resume in the terminal. The CLI auto-loads into the most recent chat session.
5. Run /chat inside the resumed session and verify all sessions are still visible at this point.
6. Close Gemini.
7. Open Gemini normally (without any flags).
8. Run /chat again.

Actual Behavior

The most recent chat session is permanently gone from the /chat list. The session does not reappear on subsequent launches.

Expected Behavior

All chat sessions should persist regardless of how the CLI was previously closed. Using gemini --resume must not affect the integrity of the session list. The most recent chat session should remain visible and accessible in /chat after any combination of normal and --resume launches.

Client Environment

• CLI Version: 0.43.0
• Git Commit: c0775c38b
• Model: gemini-3.1-pro-preview
• Sandbox: no sandbox
• OS: win32 (Windows)
• Tier: Gemini Code Assist in Google One AI Pro

Authentication & Login

• Method: Signed in with Google Account via standard OAuth flow.

Additional Information

• The bug is consistently reproducible following the exact steps above.
• Sessions created and closed without utilizing the --resume flag do not exhibit this behavior.
• The issue appears isolated to the interaction between the --resume flag and session index management, specifically affecting the serialization or state persistence of the active session during the --resume execution path.