Add HIIT watch runner, rest-time setting, and HealthKit watch auto-launch

- Redesign the watch app into an active-workout runner: a root gate shows the
  in-progress workout's exercises or prompts to start one on iPhone, and each
  exercise runs as a horizontally-paged HIIT cycle (count-up work, count-down
  rest with final-three-second haptics + auto-advance, One More / Done on the
  last set). Replaces the old history list.
- Add a configurable rest-between-sets duration in iPhone Settings (default 45s),
  synced to the watch over WatchConnectivity.
- Launch the watch app into the session when a workout starts on the phone via
  HealthKit (startWatchApp); the watch runs an HKWorkoutSession for foreground
  runtime and ends it when the workout finishes. Adds the HealthKit entitlement +
  Health usage strings on both targets and WKBackgroundModes on the watch.

Claude-Session: https://claude.ai/code/session_018gg69MaUetDNzWzBXisfMV

Workouts/AppServices.swift

@@ -11,6 +11,7 @@ final class AppServices {
     let container: ModelContainer
     let syncEngine: SyncEngine
     let watchBridge: PhoneConnectivityBridge
+    let workoutLauncher = WorkoutLauncher()
 
     private var bootstrapTask: Task<Void, Never>?
 

Workouts/Connectivity/PhoneConnectivityBridge.swift

@@ -42,9 +42,11 @@ final class PhoneConnectivityBridge: NSObject {
         wDesc.fetchLimit = 25
         let workouts = (try? context.fetch(wDesc)) ?? []
 
+        let restSeconds = UserDefaults.standard.object(forKey: WCPayload.restSecondsKey) as? Int ?? 45
         let payload = WCPayload.encodeState(
             splits: splits.map(SplitDocument.init(from:)),
-            workouts: workouts.map(WorkoutDocument.init(from:))
+            workouts: workouts.map(WorkoutDocument.init(from:)),
+            restSeconds: restSeconds
         )
         try? session.updateApplicationContext(payload)
     }

Workouts/HealthKit/WorkoutLauncher.swift

@@ -0,0 +1,40 @@
+//
+// WorkoutLauncher.swift
+// Workouts
+//
+// Copyright 2025 Rouslan Zenetl. All Rights Reserved.
+//
+
+import Foundation
+import HealthKit
+
+/// Launches the companion Watch app into a workout when a session starts on the phone.
+///
+/// An iPhone app can't foreground its Watch app on its own — the only sanctioned path
+/// is HealthKit's `startWatchApp(toHandle:)`, which hands watchOS a workout
+/// configuration and brings the Watch app up to run a matching `HKWorkoutSession`.
+/// Calling it requires authorization to *share* workouts first.
+@MainActor
+final class WorkoutLauncher {
+    private let healthStore = HKHealthStore()
+
+    /// Strength/HIIT configuration handed to watchOS; the watch starts a session with
+    /// the same shape (see `WorkoutSessionManager`).
+    static func makeConfiguration() -> HKWorkoutConfiguration {
+        let configuration = HKWorkoutConfiguration()
+        configuration.activityType = .traditionalStrengthTraining
+        configuration.locationType = .indoor
+        return configuration
+    }
+
+    /// Ask watchOS to launch the Watch app into the workout. Best-effort: no-ops where
+    /// HealthKit is unavailable (e.g. iPad without it) and silently tolerates a missing
+    /// or unreachable paired watch.
+    func launchWatchWorkout() {
+        guard HKHealthStore.isHealthDataAvailable() else { return }
+        Task {
+            try? await healthStore.requestAuthorization(toShare: [.workoutType()], read: [])
+            try? await healthStore.startWatchApp(toHandle: Self.makeConfiguration())
+        }
+    }
+}

Workouts/Resources/Info-iOS.plist

@@ -24,6 +24,10 @@
 	<false/>
 	<key>LSRequiresIPhoneOS</key>
 	<true/>
+	<key>NSHealthShareUsageDescription</key>
+	<string>Workouts uses Health so it can launch your Apple Watch into the session when you start a workout on your iPhone.</string>
+	<key>NSHealthUpdateUsageDescription</key>
+	<string>Workouts uses Health so it can launch your Apple Watch into the session when you start a workout on your iPhone.</string>
 	<key>UILaunchScreen</key>
 	<dict/>
 	<key>UISupportedInterfaceOrientations</key>

Workouts/Resources/Workouts-iOS.entitlements

@@ -2,6 +2,10 @@
 <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
 <plist version="1.0">
 <dict>
+	<key>com.apple.developer.healthkit</key>
+	<true/>
+	<key>com.apple.developer.healthkit.access</key>
+	<array/>
 	<key>com.apple.developer.icloud-container-identifiers</key>
 	<array>
 		<string>iCloud.dev.rzen.indie.Workouts</string>

Workouts/Views/Settings/SettingsView.swift

@@ -12,14 +12,27 @@ import IndieAbout
 struct SettingsView: View {
     @Environment(SyncEngine.self) private var sync
     @Environment(\.modelContext) private var modelContext
+    @Environment(AppServices.self) private var services
 
     @Query(sort: \Split.order) private var splits: [Split]
 
+    @AppStorage("restSeconds") private var restSeconds: Int = 45
     @State private var showingAddSplitSheet = false
 
     var body: some View {
         NavigationStack {
             Form {
+                // MARK: - Workout Section
+                Section(header: Text("Workout")) {
+                    Stepper(value: $restSeconds, in: 10...180, step: 5) {
+                        HStack {
+                            Text("Rest Between Sets")
+                            Spacer()
+                            Text("\(restSeconds)s").foregroundColor(.secondary)
+                        }
+                    }
+                }
+
                 // MARK: - Splits Section
                 Section(header: Text("Splits")) {
                     if splits.isEmpty {
@@ -94,6 +107,7 @@ struct SettingsView: View {
             .sheet(isPresented: $showingAddSplitSheet) {
                 SplitAddEditView(split: nil)
             }
+            .onChange(of: restSeconds) { _, _ in services.watchBridge.pushAll() }
         }
     }
 }

Workouts/Views/WorkoutLogs/WorkoutLogsView.swift

@@ -108,6 +108,7 @@ struct WorkoutLogsView: View {
 
 struct SplitPickerSheet: View {
     @Environment(SyncEngine.self) private var sync
+    @Environment(AppServices.self) private var services
     @Environment(\.dismiss) private var dismiss
 
     @Query(sort: [SortDescriptor(\Split.order), SortDescriptor(\Split.name)])
@@ -178,6 +179,8 @@ struct SplitPickerSheet: View {
         )
 
         Task { await sync.save(workout: doc) }
+        // Bring the Apple Watch up into the session so the user can run it from the wrist.
+        services.workoutLauncher.launchWatchWorkout()
         dismiss()
     }
 }