UIKit & Bridging

You MUST use this skill for ANY UIKit bridging, Auto Layout, Combine, TextKit, or UIKit animation work.

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Auditors are skills here. Where this router says "Launch some-auditor agent", invoke the matching Codex skill instead — same procedure, no Claude Code agent required.

Available: axiom-audit-resize.

The ones that shell out — builds, tests, simulators, crash symbolication — need shell access to run.

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Quick Reference

Symptom / Task	Reference
UIViewRepresentable, UIViewControllerRepresentable	See skills/uikit-bridging.md
Embedding SwiftUI in UIKit (UIHostingController)	See skills/uikit-bridging.md
Coordinator pattern, updateUIView lifecycle	See skills/uikit-bridging.md
Building adaptive UIKit layout: guides, width-conditional constraints, compositional layout, self-sizing cells	See skills/adaptive-layout.md
"Unable to simultaneously satisfy constraints"	See skills/auto-layout-debugging.md
Constraint conflicts, ambiguous layout	See skills/auto-layout-debugging.md
Views not appearing, positioned incorrectly	See skills/auto-layout-debugging.md
CAAnimation completion handler not firing	See skills/uikit-animation-debugging.md
Spring physics wrong on device, duration mismatch	See skills/uikit-animation-debugging.md
Animation jank, CATransaction timing	See skills/uikit-animation-debugging.md
Combine publishers, AnyCancellable lifecycle	See skills/combine-patterns.md
@Published properties, Combine ↔ async/await	See skills/combine-patterns.md
When to use Combine vs async/await	See skills/combine-patterns.md
UIScene lifecycle required, resizable apps, size classes, tab sidebar OS27	See skills/uikit-modernization.md
iPhone Mirroring compat: indirect input, companion Face ID, portrait trap	See skills/uikit-modernization.md
Scene edges: teardown, activation requests, per-scene restoration, external display, activeAppearance	See skills/uikit-modernization.md
Nav bar title and subtitle: UINavigationItem.subtitle, largeSubtitleView, attributedTitle/attributedSubtitle, subtitle text attributes (iOS 26)	See skills/uikit-modernization.md
Automated resize-readiness scan (scene lifecycle, UIScreen.main, fixed-canvas, Mirroring input, iPhone Duo)	axiom-audit-resize
iPhone Duo in UIKit: vertical bars, the fold, window requests on the outer display	See axiom-swiftui (skills/iphone-duo.md) — UIKit equivalents sit beside each SwiftUI API
TextKit 2 architecture, NSTextLayoutManager	See skills/textkit-ref.md
Writing Tools integration (iOS 26)	See skills/textkit-ref.md
Viewport rendering surfaces, attachment reuse, collapsible text OS27	See skills/textkit-ref.md
SwiftUI TextEditor, TextKit 1 migration	See skills/textkit-ref.md
Grammar checking (UITextChecker), per-edge text-block borders OS27	See skills/textkit-ref.md
PencilKit canvas, PKToolPicker, drawing persistence	See skills/pencilkit-paperkit.md
Apple Pencil Pro (squeeze, barrel roll, hover, haptics)	See skills/pencilkit-paperkit.md
Handwriting recognition (PKStrokeRecognizer), stroke identity/slicing OS27	See skills/pencilkit-paperkit-ref.md
PaperKit markup canvas (shapes, images, text + drawing)	See skills/pencilkit-paperkit-ref.md
PaperKit programmatic markup model (subelements, adornments) OS27	See skills/pencilkit-paperkit-ref.md

Decision Tree

digraph uikit {
    start [label="UIKit task" shape=ellipse];
    what [label="What do you need?" shape=diamond];

    start -> what;
    what -> "skills/uikit-bridging.md" [label="wrap UIKit in SwiftUI\nor SwiftUI in UIKit"];
    what -> "skills/adaptive-layout.md" [label="build adaptive layout\n(guides, constraint sets,\ncompositional)"];
    what -> "skills/auto-layout-debugging.md" [label="constraint errors,\nlayout issues"];
    what -> "skills/uikit-animation-debugging.md" [label="CAAnimation bugs,\nspring physics,\ncompletion handlers"];
    what -> "skills/combine-patterns.md" [label="publishers, sinks,\n@Published,\nasync/await bridge"];
    what -> "skills/textkit-ref.md" [label="text layout,\nWriting Tools,\nTextKit migration"];
    what -> "skills/pencilkit-paperkit.md" [label="drawing canvas,\nApple Pencil,\nPaperKit markup"];
    what -> "skills/uikit-modernization.md" [label="scene lifecycle (required 27),\nresizable apps,\nsize classes"];
}

0. Scene-lifecycle migration, "app won't launch on 27", resizability, size classes, tab sidebar? → skills/uikit-modernization.md 0b. App misbehaves in iPhone Mirroring (gestures dead, Face ID blocked, layout stuck portrait)? → skills/uikit-modernization.md 0c. iPhone Duo / foldable iPhone (vertical bars, the fold, outer-display window requests)? → axiom-swiftui (skills/iphone-duo.md)
1. UIViewRepresentable / UIViewControllerRepresentable / UIHostingController? → skills/uikit-bridging.md
2. "Unable to simultaneously satisfy constraints" / layout bugs? → skills/auto-layout-debugging.md 2b. Building a layout that adapts (layout guides, size-class constraint sets, compositional column math, self-sizing cells)? → skills/adaptive-layout.md
3. CAAnimation completion missing / spring physics wrong / animation jank? → skills/uikit-animation-debugging.md
4. Combine publishers / AnyCancellable / @Published / Combine ↔ async bridge? → skills/combine-patterns.md
5. TextKit 2 / Writing Tools / TextEditor / TextKit 1 migration? → skills/textkit-ref.md
6. PencilKit canvas / Apple Pencil / PaperKit markup? → skills/pencilkit-paperkit.md
7. Pure SwiftUI view question (no UIKit bridging)? → /skill axiom-swiftui
8. Design decisions, HIG, Liquid Glass, SF Symbols, typography? → /skill axiom-design
9. Block retain cycles in UIKit callbacks? → See axiom-performance (skills/objc-block-retain-cycles.md)
10. Memory leaks from Combine subscriptions? → Start with skills/combine-patterns.md, then axiom-performance if leak persists

Conflict Resolution

uikit vs swiftui: When working with UI code:

• Use uikit when wrapping UIKit in SwiftUI or vice versa, or debugging UIKit-specific issues (Auto Layout, CAAnimation)
• Use swiftui for pure SwiftUI views, navigation, layout, animations

uikit vs concurrency: When Combine interacts with async/await:

• Use uikit (skills/combine-patterns.md) for bridging Combine pipelines with async/await
• Use concurrency for pure async/await patterns, actors, Sendable

uikit vs performance: When animations or layout cause performance issues:

1. Try uikit FIRST — Most animation jank is CATransaction timing or layer state, not a profiling issue
2. Only use performance if animation logic is correct but rendering is slow

uikit vs axiom-data: When @Published properties relate to data persistence:

• Use uikit for Combine publisher patterns and @Published lifecycle
• Use axiom-data for SwiftData/Core Data model layer concerns

Anti-Rationalization

Thought	Reality
"I'll just use UIHostingController, it's simple"	Hosting has sizing, lifecycle, and navigation edge cases. skills/uikit-bridging.md covers the gotchas.
"Auto Layout error is just a warning, I'll ignore it"	Unsatisfied constraints cause unpredictable layout at runtime. Fix them now.
"I know how CAAnimation works"	90% of CAAnimation bugs are CATransaction timing, not Core Animation. Check skills/uikit-animation-debugging.md.
"Combine is dead, just rewrite with async/await"	Combine has no deprecation notice. Rewriting working pipelines wastes time. skills/combine-patterns.md covers when to migrate vs maintain.
"TextKit 1 still works fine"	TextKit 1 misses Writing Tools integration and has known layout bugs Apple won't fix. See skills/textkit-ref.md.
"I'll store cancellables in a local variable"	Local AnyCancellable deallocates immediately, killing the subscription.
"I'll archive the PKCanvasView to save the drawing"	Archiving the view loses editability. Persist drawing.dataRepresentation(). See skills/pencilkit-paperkit.md.
"My tool picker won't show, the API must be broken"	The canvas must becomeFirstResponder() after setVisible(_:forFirstResponder:). See skills/pencilkit-paperkit.md.

Example Invocations

User: "How do I wrap a UIKit view in SwiftUI?" → Read: skills/uikit-bridging.md

User: "I'm getting 'Unable to simultaneously satisfy constraints'" → Read: skills/auto-layout-debugging.md

User: "My CAAnimation completion handler never fires" → Read: skills/uikit-animation-debugging.md

User: "Should I use Combine or async/await for this?" → Read: skills/combine-patterns.md

User: "How do I integrate Writing Tools with my text editor?" → Read: skills/textkit-ref.md

User: "How do I add an Apple Pencil drawing canvas with the tool picker?" → Read: skills/pencilkit-paperkit.md

User: "How do I add a PaperKit markup canvas with shapes and text?" → Read: skills/pencilkit-paperkit-ref.md

User: "My SwiftUI view has a memory leak from a Combine subscription" → Read: skills/combine-patterns.md

User: "How do I embed SwiftUI in my UIKit app?" → Read: skills/uikit-bridging.md

User: "Audit my app for screen resizing support" → axiom-audit-resize (or axiom-audit-resize)

User: "My custom pinch gesture stops working when the app runs in iPhone Mirroring" → Read: skills/uikit-modernization.md

User: "How do I vary my collection view's column count with the window width?" → Read: skills/adaptive-layout.md