Fix external monitor geometry conversion

[Jam-Cai]

Summary

• convert Accessibility/CoreGraphics rectangles by matching the owning display before flipping into AppKit coordinates
• preserve Retina text-range fallback behavior while scaling relative to the display origin instead of the main screen
• choose overlay visible frames by caret midpoint before falling back to intersection order
• add pure display-coordinate tests for above-primary, negative-X, and Retina-origin monitor layouts

Validation

• xcodebuild -project tabby.xcodeproj -scheme tabby -destination 'platform=macOS' -only-testing:tabbyTests/DisplayCoordinateConverterTests test CODE_SIGNING_ALLOWED=NO
• xcodebuild -project tabby.xcodeproj -scheme tabby -destination 'platform=macOS' build CODE_SIGNING_ALLOWED=NO
• xcodebuild -project tabby.xcodeproj -scheme tabby -destination 'platform=macOS' build-for-testing CODE_SIGNING_ALLOWED=NO

Greptile Summary

This PR fixes AX/CG rectangle conversion for multi-monitor setups by replacing a single desktop-union Y-flip with per-display geometry. A new DisplayCoordinateConverter enum handles all coordinate math against injected DisplayGeometry snapshots, keeping it fully testable without NSScreen.

• Adds DisplayCoordinateConverter and DisplayGeometry to tabby/Support/, correctly flipping CG rects within their owning display and handling Retina pixel-to-point scaling anchored at each display's own origin rather than the global origin.
• Updates AXHelper.cocoaRect and validatedCocoaTextRect to use the new per-display converter with legacyDesktopUnionFlip as a last-resort fallback, and refactors OverlayController.targetScreenVisibleFrame to prefer caret-midpoint containment in visibleFrame before the frame-intersection fallback.
• Adds DisplayCoordinateConverterTests with three pure-geometry tests covering above-primary, negative-X boundary-crossing, and Retina-origin display layouts.

Confidence Score: 5/5

Safe to merge; the per-display Y-flip math is correct for primary, side-by-side, above-primary, and Retina configurations, and the legacy fallback is preserved for virtual/mirrored displays without an NSScreenNumber.

The coordinate arithmetic has been verified against all three test scenarios and the fallback paths (legacyDesktopUnionFlip, displays.isEmpty early-return) correctly mirror the pre-existing behavior. No new crash paths, data loss, or security concerns were introduced.

No files require special attention.

Important Files Changed

Filename	Overview
tabby/Support/DisplayCoordinateConverter.swift	New pure-math type for CG→AppKit rect conversion; bestDisplay uses midpoint containment then intersection-area fallback; appKitRectsFromPixelRect correctly anchors pixel-to-point scaling at each display's own CG origin.
tabby/Support/AXHelper.swift	Replaces desktop-union Y-flip in cocoaRect and validatedCocoaTextRect with per-display converter calls; legacyDesktopUnionFlip kept as fallback for displays without an NSScreenNumber; logic is clean and symmetric between both methods.
tabby/Services/UI/OverlayController.swift	Adds midpoint-in-visibleFrame priority check before the existing frame-intersection fallback, correctly routing the overlay to the screen that owns the caret rather than any intersecting screen.
tabbyTests/DisplayCoordinateConverterTests.swift	Three new deterministic geometry tests; expected values are arithmetically verified for above-primary, negative-X boundary crossing, and Retina pixel scaling on a right-side 2x display.
tabby.xcodeproj/project.pbxproj	Registers DisplayCoordinateConverterTests.swift in the test target; mechanical Xcode project file change.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[AX/CG rect from Accessibility API] --> B{cocoaRect or validatedCocoaTextRect?}
    B -->|cocoaRect| C[displayGeometries]
    B -->|validatedCocoaTextRect| D[displayGeometries]
    C --> E{displays empty?}
    E -->|no| F[DisplayCoordinateConverter.appKitRect]
    E -->|yes| G[legacyDesktopUnionFlip]
    F -->|nil| G
    F -->|converted| H[Return AppKit rect]
    G --> H
    D --> I{displays empty?}
    I -->|yes| J[Return raw textRect no Y-flip]
    I -->|no| K[Candidate A: appKitRect ?? legacyDesktopUnionFlip]
    K --> L{anchor available?}
    L -->|no| M[Return Candidate A]
    L -->|yes| N{Candidate A midpoint inside expandedAnchor?}
    N -->|yes| M
    N -->|no| O[Candidate B: appKitRectsFromPixelRect]
    O --> P{Any Candidate B inside expandedAnchor?}
    P -->|yes| Q[Return first matching Candidate B]
    P -->|no| R[Return Candidate A best-effort]

Loading

_{Reviews (2): Last reviewed commit: "Fix external monitor geometry conversion" | Re-trigger Greptile}