Deduplicate markerOverlay/shouldShowActivationPoint and guard against non-finite shape geometry

- Extract shared markerOverlayView() and shouldShowActivationPoint() free
  functions, eliminating identical copies in AccessibilitySnapshotView and
  PreParsedAccessibilitySnapshotView.

- Add AccessibilityShape.isFinite to the portable model layer so all
  consumers (rendering, Codable round-trips, external callers of the
  public init) are protected from degenerate coordinates.

- ElementOverlay.body bails to an empty view when shape.isFinite is
  false, preventing Int(_:) traps on NaN/infinity in BadgePlacement.

Author: RoyalPineapple

Sources/AccessibilitySnapshot/AccessibilitySnapshotPreviews/ElementView.swift

@@ -51,10 +51,12 @@ public struct ElementOverlay: View {
     private var strokeColor: Color { palette.strokeColor(at: index) }
 
     public var body: some View {
-        ZStack(alignment: .topLeading) {
-            shapeView
-            NumberBadge(index: index, palette: palette)
-                .position(badgeCenter)
+        if shape.isFinite {
+            ZStack(alignment: .topLeading) {
+                shapeView
+                NumberBadge(index: index, palette: palette)
+                    .position(badgeCenter)
+            }
         }
     }
 

Sources/AccessibilitySnapshot/AccessibilitySnapshotPreviews/SwiftUIAccessibilitySnapshotView.swift

@@ -70,30 +70,18 @@ public struct AccessibilitySnapshotView<Content: View>: View {
                 .frame(width: renderSize.width, height: renderSize.height)
 
             ForEach(markers.indices, id: \.self) { index in
-                markerOverlay(at: index)
+                markerOverlayView(
+                    marker: markers[index],
+                    index: index,
+                    palette: palette,
+                    activationPointDisplayMode: configuration.activationPointDisplayMode
+                )
             }
         }
         .frame(width: renderSize.width, height: renderSize.height)
         .clipped()
     }
 
-    @ViewBuilder
-    private func markerOverlay(at index: Int) -> some View {
-        let marker = markers[index]
-        ElementOverlay(
-            index: index,
-            shape: marker.shape,
-            palette: palette
-        )
-
-        if shouldShowActivationPoint(for: marker) {
-            ActivationPointView(
-                position: marker.activationPoint.cgPoint,
-                color: palette.strokeColor(at: index)
-            )
-        }
-    }
-
     @ViewBuilder
     private func errorView(error: Error) -> some View {
         VStack {
@@ -145,17 +133,6 @@ public struct AccessibilitySnapshotView<Content: View>: View {
             parseError = error
         }
     }
-
-    private func shouldShowActivationPoint(for marker: AccessibilityMarker) -> Bool {
-        switch configuration.activationPointDisplayMode {
-        case .always:
-            return true
-        case .whenOverridden:
-            return !marker.usesDefaultActivationPoint
-        case .never:
-            return false
-        }
-    }
 }
 
 /// Backwards compatibility alias.
@@ -285,39 +262,54 @@ public struct PreParsedAccessibilitySnapshotView: View {
                 .frame(width: renderSize.width, height: renderSize.height)
 
             ForEach(markers.indices, id: \.self) { index in
-                markerOverlay(at: index)
+                markerOverlayView(
+                    marker: markers[index],
+                    index: index,
+                    palette: palette,
+                    activationPointDisplayMode: configuration.activationPointDisplayMode
+                )
             }
         }
         .frame(width: renderSize.width, height: renderSize.height)
         .clipped()
     }
+}
 
-    @ViewBuilder
-    private func markerOverlay(at index: Int) -> some View {
-        let marker = markers[index]
-        ElementOverlay(
-            index: index,
-            shape: marker.shape,
-            palette: palette
-        )
+// MARK: - Shared Overlay Helpers
 
-        if shouldShowActivationPoint(for: marker) {
-            ActivationPointView(
-                position: marker.activationPoint.cgPoint,
-                color: palette.strokeColor(at: index)
-            )
-        }
+@available(iOS 16.0, *)
+@ViewBuilder
+func markerOverlayView(
+    marker: AccessibilityMarker,
+    index: Int,
+    palette: ColorPalette,
+    activationPointDisplayMode: AccessibilityContentDisplayMode
+) -> some View {
+    ElementOverlay(
+        index: index,
+        shape: marker.shape,
+        palette: palette
+    )
+
+    if shouldShowActivationPoint(for: marker, displayMode: activationPointDisplayMode) {
+        ActivationPointView(
+            position: marker.activationPoint.cgPoint,
+            color: palette.strokeColor(at: index)
+        )
     }
+}
 
-    private func shouldShowActivationPoint(for marker: AccessibilityMarker) -> Bool {
-        switch configuration.activationPointDisplayMode {
-        case .always:
-            return true
-        case .whenOverridden:
-            return !marker.usesDefaultActivationPoint
-        case .never:
-            return false
-        }
+private func shouldShowActivationPoint(
+    for marker: AccessibilityMarker,
+    displayMode: AccessibilityContentDisplayMode
+) -> Bool {
+    switch displayMode {
+    case .always:
+        return true
+    case .whenOverridden:
+        return !marker.usesDefaultActivationPoint
+    case .never:
+        return false
     }
 }
 

Sources/AccessibilitySnapshot/Model/AccessibilityPrimitives.swift

@@ -79,6 +79,23 @@ public enum AccessibilityPathElement: Hashable, Codable, Sendable {
 public enum AccessibilityShape: Hashable, Codable, Sendable {
     case frame(AccessibilityRect)
     case path([AccessibilityPathElement])
+
+    public var isFinite: Bool {
+        switch self {
+        case let .frame(rect):
+            return rect.isFinite
+        case let .path(elements):
+            return elements.allSatisfy { element in
+                switch element {
+                case let .move(to): return to.isFinite
+                case let .line(to): return to.isFinite
+                case let .quadCurve(to, control): return to.isFinite && control.isFinite
+                case let .curve(to, control1, control2): return to.isFinite && control1.isFinite && control2.isFinite
+                case .closeSubpath: return true
+                }
+            }
+        }
+    }
 }
 
 // MARK: - Wire-Compatible Codable