Claude Code freezes on startup with large session history (~468 sessions)

Description

Claude Code completely freezes on the first prompt when a project has accumulated a large number of sessions. The UI shows the thinking indicator ("Thundering...") but never responds. The process must be killed manually.

Reproduction

• Project: TypeScript monorepo (~1.9GB including node_modules)
• Session count: 468 sessions (~264MB in ~/.claude/projects/<project-path>/)
• Claude Code version: v2.1.27
• OS: macOS (Darwin 25.2.0)
• Affects: Both VS Code extension and TUI

Steps to reproduce

1. Use Claude Code extensively in a single project over time (accumulating hundreds of sessions)
2. Launch Claude Code in that project directory
3. Type any prompt (e.g., "hi") and press enter
4. Observe: thinking indicator appears but response never arrives

Workaround

Moving the session history directory unblocks the issue:

mv ~/.claude/projects/<project-path> ~/.claude/projects/<project-path>.bak

After this, Claude Code starts and responds normally.

Debugging performed

Systematically ruled out:

• Model: Freezes with both Opus 4.5 and Haiku
• Project config: Same .claude/settings.json, hooks, commands, and CLAUDE.md work fine on a VM with fewer sessions
• Plugins: Freezes with all plugins disabled
• Global hooks: Freezes with all hooks removed
• MCP servers: None configured
• Git repo: node_modules is gitignored, repo itself is ~77MB

The only difference between the working environment (VM) and the frozen one (local) was the number of accumulated sessions in ~/.claude/projects/.

Expected behavior

Claude Code should handle hundreds of sessions without freezing. Session scanning at startup should be async/paginated or capped.