Preview server opens twice — Browser pane + external browser window

When starting a dev server via the Browser pane / preview_start in the Claude Code desktop app, the app opens in two places at once: inside the Claude window's Browser pane, and simultaneously in a separate external browser window.

Verified it is not the project's doing:

• "dev": "next dev" with no --open
• no BROWSER env var set
• no open option in next.config.ts
• .claude/launch.json has no openBrowser/suppressBrowser property
• no hook fires on preview start, so there is no way to intercept it

Request: a launch.json option (or a setting) to suppress the external window while keeping the Browser pane. The existing Settings → Claude Code toggle disables the Browser entirely, which is not the desired behavior.

Platform: macOS (Darwin 25.5.0), Claude Code desktop.