Input blocked for several minutes when starting a new session

Bug description

When starting a new Claude Code session, keyboard input appears completely blocked for several minutes. Characters typed do not appear on screen at all. After a few minutes, all the buffered text suddenly appears at once, as if the input queue was blocked by something and then flushed.

This happens consistently when launching a fresh session (claude from terminal). It feels like there's a background initialization task (context loading, MCP server startup, etc.) that is blocking the input rendering pipeline.

Expected behavior

Typed characters should appear immediately on screen, even if the backend is still initializing. Input rendering should never be blocked by background tasks.

Actual behavior

1. Run claude to start a new session
2. Start typing immediately
3. Nothing appears on screen — no characters, no cursor movement
4. After ~2-5 minutes, all typed text appears at once
5. Session then works normally

Environment

• Claude Code version: 2.1.62
• OS: macOS 26.3 (Tahoe), arm64 (Apple Silicon)
• Node: v25.6.1
• Shell: fish
• Terminal: default macOS Terminal / Ghostty (reproducible in both)

Additional context

• No error messages in the terminal during the blocked period
• The process is running (not hung) — it eventually accepts all input
• Feels like the event loop or stdin reader is blocked by a synchronous operation during startup
• MCP servers are configured (may be relevant if their initialization is blocking)