Settings: preference tab button shows focus on first tab regardless of selection

[schuyler]

Summary

The preference window's tab toolbar does not indicate which tab is currently selected — the focus highlight is fixed on the first tab regardless of which pane is active.

Reported by

@massimo-cassandro in #397 (rc.2 validation, Italian locale):

In italian, all tabs seems to display correctly. But I noticed the selected button doesn't display the focus: it is fixed to the first one

Screenshots were provided showing the General, Editor, and Terminal tabs with the focus indicator stuck on the first tab in each case.

Steps to reproduce

1. Open Settings (⌘,)
2. Click any tab other than General (Editor, Rendering, Markdown, Terminal)
3. Observe: the selected/active tab button does not appear highlighted

Expected behavior

The active tab button should be visually highlighted to indicate which pane is currently shown.

Notes

This may be related to the dynamic pane sizing rework in #481 or the checkbox height constraint changes in #498. It was not present before those changes were introduced.

Related to #397

[schuyler]

Requirements (confirmed)

Symptom: The Preferences window's toolbar tab highlight (the selected-pane indicator) stays fixed on the first tab (General). Switching tabs correctly changes the displayed pane and resizes the window, but the toolbar's selected-tab background never moves off the first item. This is a rendering-only bug — MASPreferencesWindowController.selectedViewController and the actual displayed pane are correct; only the toolbar's visual highlight is stale.

Suspected cause: A regression introduced by MPPreferencesViewController.m's -loadView rework in #481 (two-pass dynamic sizing) and/or #498 (checkbox height constraints), which changed how/when self.view is (re)assigned relative to the Auto Layout passes that resolve the wrapper view's final frame. MASPreferencesWindowController itself (vendored via CocoaPods, unmodified) already correctly calls [[self.window toolbar] setSelectedItemIdentifier:controller.viewIdentifier] on every pane switch, so the fix will need to be in our -loadView wrapping logic, not the vendor pod.

Scope:

• Primary fix: restore correct toolbar tab highlighting when switching preference panes.
• Broader review: also check the Dynamic preferences pane sizing for localized strings #481/Fix checkbox label clipping in localized preference panes #498 two-pass -loadView sizing logic more generally for other side effects on the Preferences window (e.g. resize/animation glitches), while keeping changes minimal and focused on what's actually broken.

Verification: This repo's CI only runs on macOS runners; this session runs in a Linux sandbox with no Xcode, so the fix will be validated via CI (existing + new automated tests) rather than manual visual confirmation from this session. Manual visual verification is deferred to the user/reviewer.

Related to #397

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