Resume shows only partial conversation history due to stale sessions-index.json

Description

When using --resume to resume a conversation, only a few recent messages appear instead of the full conversation history. The conversation data file contains the complete history, but sessions-index.json has incorrect/stale metadata.

Steps to Reproduce

1. Have a long conversation with many messages
2. Exit the session
3. Resume with claude --resume and select the conversation
4. Only the last few messages appear, earlier conversation history is missing

Investigation Findings

Examined the conversation files in ~/.claude/projects/<project>/:

• Conversation file (*.jsonl): Contains 1480 lines with 678 user messages and 741 assistant messages
• sessions-index.json: Shows messageCount: 3 and has incorrect firstPrompt

Example discrepancy:

Actual first message: "i want to run a detailed security review on this code base..."
sessions-index.json firstPrompt: "i want you to create a html file that look like a ppt..."

The firstPrompt in the index corresponds to a message from much later in the conversation, and messageCount is drastically underreported.

Expected Behaviour

• sessions-index.json should accurately reflect the conversation's message count and first prompt
• Resume should restore the full conversation history as stored in the .jsonl file

Actual Behaviour

• sessions-index.json metadata becomes stale/out of sync with actual conversation file
• Resume uses the incorrect index metadata, showing only partial history
• Full conversation data IS preserved in the .jsonl file but not loaded

Environment

• macOS (Darwin 24.6.0)
• Issue occurred on multiple separate conversations

Workaround

The conversation data is intact. Deleting sessions-index.json may force a rebuild, though this hasn't been tested.