Preview server blocks text output on macOS - CLI becomes unresponsive

Bug Report

Environment:

• macOS Darwin 25.3.0 (Tahoe)
• Claude Code CLI with Claude in Chrome MCP + Claude Preview MCP
• Model: claude-opus-4-6[1m]

Issue:
When a preview server is running (via preview_start / launch.json), the text output in the CLI terminal becomes blocked or goes to background. The user cannot see Claude's text responses while the preview is active. The CLI appears to freeze or become unresponsive for text output, though tool calls continue working.

Steps to reproduce:

1. Start Claude Code CLI session
2. Start a preview server via preview_start (Vite dev server)
3. Make code edits and interact with preview tools (screenshot, eval, etc.)
4. Observe that text responses become delayed or blocked in the terminal

Expected behavior:
Text output should remain in foreground and responsive regardless of preview server activity.

Actual behavior:
The terminal/CLI text output gets blocked or deprioritized when preview tools are active. The user has to wait for preview operations to complete before seeing any text output.

Workaround:
None found. Restarting the CLI session temporarily resolves the issue.

Additional context:
This occurs on macOS with the standard Terminal.app and iTerm2. The issue seems related to the MCP tool execution blocking the main output stream.