[Bug]: Device-toolbar viewport size does not match the CSS viewport the page receives (~1.44× larger)

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

1. Open any local page in the Preview panel (I used a Vite dev server on http://localhost:5243).

2. Open the device toolbar and set the viewport to 375 × 667 (freeform), or pick the iPhone SE preset.

3. In the page, read the CSS viewport:

   ({ innerWidth, innerHeight, devicePixelRatio, scale: visualViewport.scale })
   

4. Repeat with 390 × 844 and 271 × 586.

Expected behavior

The CSS viewport the page lays out in matches the size the device toolbar displays: 375 × 667 gives innerWidth === 375, so mobile breakpoints and wrapping behave as they would on the named device.

Actual behavior

The page receives a viewport about 1.44× larger than the displayed size, at every size:

devicePixelRatio is 2 and visualViewport.scale is 1, so the page itself is not zoomed; the panel is supplying a larger viewport than it reports. preview_status sometimes reports the displayed size (viewport: {width: 390, height: 844}) while the DOM reports 562 for the same tab.

The practical effect is that a "375 wide" preview renders layouts a real 375px device would not: a header that wraps to two rows on an iPhone SE stays on one row here, and a day strip shows eight days where the device shows five. To see the true 375px layout you have to type 260 × 463.

This may be tied to the preview zoom level (the kebab-menu zoom from #8900). In Chrome's device toolbar, zoom scales the rendered frame without changing the CSS viewport; here the CSS viewport seems to scale with it. The preview_resize timeouts are already covered by #3712 and are not part of this report.

Version

T3 Code (Nightly) 0.0.38-nightly.20260901.1250, macOS 26.6.2, external display reporting screen.width 2560 at 2×. MCP client: Claude Code.

Reproduce the issue in apps/desktop using the device toolbar at the reported viewport sizes, then compare the toolbar dimensions with innerWidth, innerHeight, devicePixelRatio, visualViewport.scale, and preview_status. Trace the preview sizing and zoom behavior, including the preview_resize path mentioned in the report. Done means the page receives the displayed CSS viewport at each size without changing the reported device pixel ratio or zoom.