[currentbits]

Problem

The Browser pane binds its guest on did-attach, while the guest's initial about:blank is still loading. A loadURL issued in that window resolves on the initial load's did-finish-load, not ours. So preview.navigate (the pane's Go button, the suggested-URL auto-load and the MCP preview navigate tool) returned about:blank, and an immediate screenshot captured an empty page. The real page committed about 1 ms later.

Event trace from a real Electron 35.7.5 guest:

0   before loadURL isLoading=true url=""
1   did-start-navigation http://127.0.0.1:…/
35  did-navigate about:blank
41  did-finish-load            <- loadURL resolves here
41  loadURL resolved url=about:blank
42  did-navigate http://127.0.0.1:…/

Fix

In navigate, if the guest is still on its initial load (isLoading() with an empty or about:blank URL), wait for did-stop-loading (bounded to 2 s) before calling loadURL. It's one guard in the shared path.

Verification

• New unit test navigate waits for the guest's initial about:blank load to stop: fails without the fix (6/7), passes with it (7/7).
• Isolated Electron probe using the real electron/preview.js and a real <webview> bound on did-attach (same as BrowserPane). It runs bind → info → navigate → click → type → screenshot, refuses an external URL, and returns PANE_CLOSED after the pane is removed. Before: immediate navigate reported about:blank 3/3 times. After: 11/11 checks pass on 3/3 runs.

Found while finishing the Browser→MCP verification for #1369.

🤖 Generated with Claude Code

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