fix(desktop): account for main-window zoom in preview_resize

[macodev00]

What

• Set preview guest webview zoom to tab.zoomFactor × mainWindow zoom so preview_resize matches CSS size when the main window is zoomed.

Why

Fixes #12319

The guest was reset to preview-only zoom while Chromium multiplies layout by main-window zoom, so a 1280×800 request reported ~2019×1262 and the wait always timed out (evicting the automation host).

UI

N/A for product chrome — preview automation resize succeeds while View → Zoom is above 100%.

Checklist

• I read CONTRIBUTING.md and kept this small / bug-only
• What + why explained above
• Followed AGENTS.md documentation rules (no new docs)
• No unrelated changes
• CLA / AI-reviewed standing override for macodev00 auto-contrib

Summary by CodeRabbit

• Bug Fixes

  • Preview content now correctly combines its configured zoom with the desktop window’s zoom, keeping embedded previews visually consistent when the app zoom changes.
  • Zoom handling remains stable when the window is unavailable, invalid, or has an unusual zoom value.

• Tests

  • Added coverage for default zoom, zoom updates, zoom reapplication, and custom preview and window zoom combinations.

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 7445aa7 and bdd04f6.

📒 Files selected for processing (3)

• apps/desktop/src/preview/Manager.test.ts
• apps/desktop/src/preview/Manager.ts
• apps/desktop/src/window/DesktopWindow.ts

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📝 Walkthrough

Walkthrough

Preview guests now use the product of their preview zoom and the main window zoom. Invalid or unavailable window zoom values fall back to 1.0. Tests cover default, updated, reapplied, and custom zoom values.

Changes

Preview guest zoom alignment

Layer / File(s)	Summary
Apply combined guest zoom apps/desktop/src/preview/Manager.ts, apps/desktop/src/window/DesktopWindow.ts	PreviewManager validates and reads the main window zoom, then applies tabZoom × windowZoom during registration, assertion, reapplication, and updates. Comments describe the combined behavior.
Validate combined zoom behavior apps/desktop/src/preview/Manager.test.ts	Tests cover default zoom, zoom-in updates, reapplyZoom, and a custom preview zoom of 1.25 with a main window zoom of 1.2 ** 2.5.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: juliusmarminge

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #12319 requires preview resize to succeed when the main window is zoomed and the guest to report the requested CSS viewport. Manager.ts now reads the main window zoom and applies `tab.zoomFact…
Out of Scope Changes check	✅ Passed	The changes stay within issue #12319. They update preview guest zoom handling, add focused automated tests, and update related comments. No product chrome UI changes or unrelated behavior changes are …
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
Title check	✅ Passed	The title clearly identifies the desktop fix: applying main-window zoom to preview resizing.
Description check	✅ Passed	The description explains what changed, why it changed, the UI impact, and the focused scope. It provides checklist information and appropriately marks UI screenshots as not applicable.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create a new PR

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[macodev00]

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