[BUG] Browser pane blocks 127.0.0.1 with "only supports localhost URLs" — 127.0.0.1 IS localhost

Summary

Following a link to http://127.0.0.1:<port> inside the in-app Browser pane (mcp__Claude_Browser__* tools, not the Claude in Chrome extension) is blocked with:

Link to 127.0.0.1 was blocked. The Browser pane only supports localhost URLs. Right-click the link to open it in your browser.

This is self-contradictory: 127.0.0.1 is localhost (the loopback address). The block message claims the pane "only supports localhost URLs" while refusing a literal localhost address.

Likely root cause

The Browser pane's allowed-URL check almost certainly does a literal hostname string match against localhost and does not treat 127.0.0.1 (or ::1) as equivalent, even though they resolve to the same loopback interface.

Expected behavior

The Browser pane should treat 127.0.0.1, ::1, and localhost as equivalent for its localhost-only allowance.

Not a duplicate of

• #82626 ("Claude in Chrome MCP bridge refuses localhost/127.0.0.1 navigation") — that is the Claude in Chrome browser-extension remote-control bridge (mcp__claude-in-chrome__*), a different code path from the in-app Browser pane.
• #75289 ("Allow whitelisting localhost/127.0.0.1 in the Claude in Chrome extension") — same extension surface, not the Browser pane.

Repro

1. In a Claude Code session, open the Browser pane (preview_start or navigate).
2. Follow a link to http://127.0.0.1:<some-port> for a running local server.
3. Observe the block message above instead of the page loading.

Environment

• Claude Code session with in-app Browser pane (mcp__Claude_Browser__* tools)
• macOS

Filed via Claude Code on behalf of the account owner.