sessions-index.json not created for new projects — Recent Activity empty

Bug Description

The "Recent Activity" section on the Claude Code welcome screen shows empty, even though multiple sessions exist and are resumable via claude --resume.

Root Cause

sessions-index.json is not being created/maintained in the project directory (~/.claude/projects/<project-id>/). The session .jsonl files are written correctly, but the index file that powers the Recent Activity UI is missing.

Reproduction

1. Start Claude Code in a new project directory
2. Have multiple conversations (creating multiple sessions)
3. Exit and re-launch Claude Code
4. Observe: "Recent Activity" is empty on the welcome screen
5. However, claude --resume correctly finds and lists all sessions

Evidence

• 5 session .jsonl files exist in ~/.claude/projects/-root-agent-sandbox/
• 40 entries in ~/.claude/history.jsonl
• sessions-index.json exists for older projects but was never created for the new project
• claude --resume works fine (it reads .jsonl files directly)

Environment

• Claude Code version: 2.1.63
• Platform: Linux (Ubuntu)
• Shell: zsh

Workaround

Manually creating sessions-index.json by parsing the existing .jsonl session files restores the Recent Activity display. The format matches the existing index files from other projects (version 1, with entries containing sessionId, fullPath, fileMtime, firstPrompt, messageCount, created, modified, gitBranch, projectPath, isSidechain).