fix: replace GeometryReader height cap with HeightCapLayout to eliminate flicker

clients/shared/Features/Chat/MediaEmbeds/InlineImageEmbedView.swift

@@ -15,10 +15,34 @@ import AppKit
 /// image at once.
 ///
 /// Tapping the image opens the URL in the user's default browser.
-private struct ImageHeightKey: PreferenceKey {
-    static var defaultValue: CGFloat = 0
-    static func reduce(value: inout CGFloat, nextValue: () -> CGFloat) {
-        value = nextValue()
+
+/// Caps content height at a maximum using the Layout protocol (O(1)).
+/// Unlike `.frame(maxHeight:)` which creates `_FlexFrameLayout` with its
+/// O(n × depth) alignment cascade, this measures the child, caps the
+/// reported height, and re-measures with the capped height so the child
+/// can adjust its width (e.g. to preserve aspect ratio).
+/// Unlike GeometryReader + PreferenceKey, this resolves in a single layout
+/// pass — no @State round-trip, so no first-render flicker.
+private struct HeightCapLayout: Layout {
+    let cap: CGFloat
+
+    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
+        guard let child = subviews.first else { return .zero }
+        let childSize = child.sizeThatFits(proposal)
+        guard childSize.height > cap else { return childSize }
+        // Re-measure with capped height so the child can adjust its width
+        // (e.g. a resizable image with .fit will narrow to preserve aspect ratio).
+        let cappedSize = child.sizeThatFits(ProposedViewSize(width: proposal.width, height: cap))
+        return CGSize(width: cappedSize.width, height: min(cap, cappedSize.height))
+    }
+
+    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
+        guard let child = subviews.first else { return }
+        child.place(
+            at: bounds.origin,
+            anchor: .topLeading,
+            proposal: ProposedViewSize(width: bounds.width, height: bounds.height)
+        )
     }
 }
 
@@ -32,38 +56,31 @@ public struct InlineImageEmbedView: View {
     /// Flipped to `true` by `onAppear`; prevents eager network fetches
     /// for images that are off-screen in long chat histories.
     @State private var isVisible = false
-    /// Tracks intrinsic image height for capping without `_FlexFrameLayout`.
-    @State private var imageIntrinsicHeight: CGFloat = 0
 
     public var body: some View {
-        Group {
-            if isVisible {
-                AsyncImage(url: url) { phase in
-                    switch phase {
-                    case .empty:
-                        placeholderSkeleton
-                            .overlay(ProgressView())
-                    case .success(let image):
-                        image
-                            .resizable()
-                            .aspectRatio(contentMode: .fit)
-                    case .failure:
-                        EmptyView()
-                    @unknown default:
-                        EmptyView()
+        HeightCapLayout(cap: 300) {
+            Group {
+                if isVisible {
+                    AsyncImage(url: url) { phase in
+                        switch phase {
+                        case .empty:
+                            placeholderSkeleton
+                                .overlay(ProgressView())
+                        case .success(let image):
+                            image
+                                .resizable()
+                                .aspectRatio(contentMode: .fit)
+                        case .failure:
+                            EmptyView()
+                        @unknown default:
+                            EmptyView()
+                        }
                     }
+                } else {
+                    placeholderSkeleton
                 }
-            } else {
-                placeholderSkeleton
             }
         }
-        .background(
-            GeometryReader { geo in
-                Color.clear.preference(key: ImageHeightKey.self, value: geo.size.height)
-            }
-        )
-        .onPreferenceChange(ImageHeightKey.self) { imageIntrinsicHeight = $0 }
-        .frame(height: imageIntrinsicHeight > 300 ? 300 : nil)
         .clipped()
         .clipShape(RoundedRectangle(cornerRadius: 8))
         .onAppear { isVisible = true }