fix(ios): honor fixed-height boxes

ios/MobRootView.swift

@@ -767,6 +767,10 @@
                     height: node.fixedHeight > 0 ? CGFloat(node.fixedHeight) : nil,
                     alignment: alignment
                 )
+            } else if node.fixedHeight > 0 {
+                stack
+                    .frame(height: CGFloat(node.fixedHeight), alignment: alignment)
+                    .frame(maxWidth: .infinity, alignment: alignment)
             } else if node.fillHeight {
                 // fill_height: true is what lets a wrapping box stretch to the
                 // viewport so center alignment lands on the visible midpoint
@@ -1200,7 +1204,7 @@
 // no manual frame management required.
 private class CameraPreviewUIView: UIView {
     override class var layerClass: AnyClass { AVCaptureVideoPreviewLayer.self }
     var cameraLayer: AVCaptureVideoPreviewLayer { layer as! AVCaptureVideoPreviewLayer }
 }
 
 private struct MobCameraPreviewView: UIViewRepresentable {
@@ -2020,4 +2024,4 @@
                 }
             }
     }
 }

test/mob/native_box_layout_test.exs

@@ -0,0 +1,19 @@
+# These source-contract tests guard native SwiftUI behavior that Elixir cannot execute.
+# credo:disable-for-this-file Jump.CredoChecks.VacuousTest
+defmodule Mob.NativeBoxLayoutTest do
+  use ExUnit.Case, async: true
+
+  @root Path.expand("../..", __DIR__)
+
+  test "iOS box applies a fixed height without a fixed width" do
+    source = File.read!(Path.join(@root, "ios/MobRootView.swift"))
+
+    assert source =~
+             "            } else if node.fixedHeight > 0 {\n" <>
+               "                stack\n" <>
+               "                    .frame(height: CGFloat(node.fixedHeight), " <>
+               "alignment: alignment)\n" <>
+               "                    .frame(maxWidth: .infinity, alignment: alignment)\n" <>
+               "            } else if node.fillHeight {\n"
+  end
+end