Open Assist from the watch complication via SwiftUI App lifecycle

The Assist complication's `homeassistant://assist` widget URL was never received:
the watch app ran on the legacy WatchKit lifecycle (@main on ExtensionDelegate +
WKHostingController), where SwiftUI's .onOpenURL / .onContinueUserActivity are inert
(runtime warned "Cannot use Scene methods for URL … without SwiftUI Lifecycle").

- Adopt the SwiftUI App lifecycle: @main HomeAssistantWatchApp with
  WKApplicationDelegateAdaptor(ExtensionDelegate.self) and WindowGroup { WatchHomeView() }
- WatchHomeView now handles the assist deep link via .onOpenURL / .onContinueUserActivity,
  plus a cold-launch pending flag consumed on appear
- Replace the Assist fullScreenCover fatalError with a "configure Assist" message

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: bgoncal

Sources/WatchApp/Complication/Assist/AssistDefaultComplication.swift

@@ -4,4 +4,9 @@ enum AssistDefaultComplication {
     static let title = "Assist"
     static let launchNotification: Notification.Name = .init("assist-detault-complication-launch")
     static let defaultComplicationId = "default-assist"
+
+    /// Set when the app is launched from the Assist complication before the UI is ready to present it.
+    /// `WatchHomeView` consumes this on appear so a cold launch still opens Assist (the launch
+    /// notification would otherwise fire before the view subscribes to it).
+    static var pendingLaunch = false
 }

Sources/WatchApp/ExtensionDelegate.swift

@@ -6,7 +6,6 @@ import WatchKit
 import WidgetKit
 import XCGLogger
 
-@main
 class ExtensionDelegate: NSObject, WKApplicationDelegate {
     // MARK: Fileprivate
 
@@ -124,6 +123,9 @@ class ExtensionDelegate: NSObject, WKApplicationDelegate {
     }
 
     private func launchAssist() {
+        // Record the intent so a cold launch still opens Assist once the UI appears, and post the
+        // notification for the case where the view is already on screen (warm launch).
+        AssistDefaultComplication.pendingLaunch = true
         NotificationCenter.default.post(name: AssistDefaultComplication.launchNotification, object: nil)
     }
 

Sources/WatchApp/Home/WatchHomeView.swift

@@ -57,6 +57,14 @@ struct WatchHomeView: View {
         .onReceive(NotificationCenter.default.publisher(for: AssistDefaultComplication.launchNotification)) { _ in
             showAssist = true
         }
+        // The Assist complication opens the app via a `homeassistant://assist` widget URL. Depending on
+        // launch state watchOS delivers this either as an opened URL or as a browsing-web user activity.
+        .onOpenURL { url in
+            if isAssistDeepLink(url) { showAssist = true }
+        }
+        .onContinueUserActivity(NSUserActivityTypeBrowsingWeb) { activity in
+            if isAssistDeepLink(activity.webpageURL) { showAssist = true }
+        }
         .onReceive(NotificationCenter.default.publisher(for: .watchConfigDidChange)) { _ in
             viewModel.loadCache()
         }
@@ -68,7 +76,13 @@ struct WatchHomeView: View {
                     pipelineId: pipelineId
                 )
             } else {
-                fatalError("Assist launched without serverId or pipelineId")
+                // Assist isn't configured yet (e.g. cold launch before the config synced). Surface a
+                // message instead of crashing; the user can retry once configuration is available.
+                Text(verbatim: L10n.Watch.Assist.LackConfig.Error.title)
+                    .font(.footnote)
+                    .foregroundStyle(.secondary)
+                    .multilineTextAlignment(.center)
+                    .padding()
             }
         })
         .sheet(isPresented: $showSettings) {
@@ -96,6 +110,11 @@ struct WatchHomeView: View {
             Text(verbatim: L10n.Watch.Config.Conflict.message)
         }
         .onAppear {
+            // Consume a launch requested from the complication before this view existed (cold launch).
+            if AssistDefaultComplication.pendingLaunch {
+                AssistDefaultComplication.pendingLaunch = false
+                showAssist = true
+            }
             guard autoLoad else { return }
             viewModel.startNetworkMonitoring()
             Task {
@@ -289,6 +308,11 @@ struct WatchHomeView: View {
         }
     }
 
+    private func isAssistDeepLink(_ url: URL?) -> Bool {
+        guard let url else { return false }
+        return ["homeassistant", "homeassistant-dev"].contains(url.scheme) && url.host == "assist"
+    }
+
     private func enterEditMode() {
         withAnimation { isEditing = true }
     }

Sources/WatchApp/HostingController.swift

@@ -2,12 +2,27 @@ import Foundation
 import Shared
 import SwiftUI
 
-final class HostingController: WKHostingController<WatchHomeView> {
-    override init() {
-        super.init()
+// The watch app uses the SwiftUI App lifecycle so SwiftUI can deliver external events (URLs /
+// NSUserActivity) — notably the `homeassistant://assist` widget URL from the Assist complication.
+// The legacy WatchKit lifecycle (WKApplicationDelegate + WKHostingController) cannot receive those,
+// hence the "Cannot use Scene methods for URL … without using SwiftUI Lifecycle" runtime warning.
+@main
+struct HomeAssistantWatchApp: App {
+    @WKApplicationDelegateAdaptor(ExtensionDelegate.self) private var delegate
+
+    init() {
         MaterialDesignIcons.register()
     }
 
+    var body: some Scene {
+        WindowGroup {
+            WatchHomeView()
+        }
+    }
+}
+
+// Retained so the legacy `Interface.storyboard` reference resolves; unused under the SwiftUI lifecycle.
+final class HostingController: WKHostingController<WatchHomeView> {
     override var body: WatchHomeView {
         WatchHomeView()
     }