OcaWritablePropertyView: handle property errors instead of staying stuck on ProgressView

Previously, OcaWritablePropertyView only handled .success results from the
property async stream, silently ignoring .failure. This caused the view to
remain stuck on ProgressView indefinitely when a property returned an error.
Align error handling with OcaPropertyView by using Result<Value, Error> for
currentValue and displaying an error message on failure.

Author: lhoward

Sources/SwiftOCAUI/Views/PropertyView.swift

@@ -75,7 +75,7 @@ public struct OcaWritablePropertyView<Value: Sendable, Resolved: View>: View {
   let content: (Binding<Value>) -> Resolved
 
   @State
-  private var currentValue: Value?
+  private var currentValue: Result<Value, Error>?
 
   public init(
     _ object: OcaRoot,
@@ -89,9 +89,14 @@ public struct OcaWritablePropertyView<Value: Sendable, Resolved: View>: View {
 
   private var binding: Binding<Value> {
     Binding<Value>(
-      get: { currentValue! },
+      get: {
+        if case let .success(value) = currentValue {
+          return value
+        }
+        preconditionFailure()
+      },
       set: { newValue in
-        currentValue = newValue
+        currentValue = .success(newValue)
         Task {
           try? await property._setValue(object, newValue)
         }
@@ -101,8 +106,13 @@ public struct OcaWritablePropertyView<Value: Sendable, Resolved: View>: View {
 
   public var body: some View {
     Group {
-      if currentValue != nil {
-        content(binding)
+      if let currentValue {
+        switch currentValue {
+        case .success:
+          content(binding)
+        case let .failure(error):
+          Text("Error: \(error.localizedDescription)").foregroundStyle(.tertiary)
+        }
       } else {
         ProgressView()
       }
@@ -111,8 +121,15 @@ public struct OcaWritablePropertyView<Value: Sendable, Resolved: View>: View {
       await property.subscribe(object)
       do {
         for try await result in property.async {
-          if case let .success(value) = result, let typed = value as? Value {
-            currentValue = typed
+          switch result {
+          case let .success(value):
+            if let typed = value as? Value {
+              currentValue = .success(typed)
+            } else {
+              currentValue = .failure(Ocp1Error.status(.badFormat))
+            }
+          case let .failure(error):
+            currentValue = .failure(error)
           }
         }
       } catch {}