Lower deployment target from iOS 26 to iOS 18, gate Foundation Models behind @available

Broadens installable audience to iOS 18+ while keeping AI insights available on iOS 26.
Foundation Models types and service wrapped in @available(iOS 26, *), InsightsViewModel
conditionally instantiates the service with fallback UI on older versions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Shared/Models/AIInsight.swift

@@ -9,6 +9,7 @@ import Foundation
 import FoundationModels
 
 /// Represents a single AI-generated insight using @Generable for structured LLM output
+@available(iOS 26, *)
 @Generable
 struct AIInsight: Equatable {
     @Guide(description: "A brief, engaging title for the insight (3-6 words)")
@@ -31,6 +32,7 @@ struct AIInsight: Equatable {
 }
 
 /// Container for period-specific insights - the LLM generates this structure
+@available(iOS 26, *)
 @Generable
 struct AIInsightsResponse: Equatable {
     @Guide(description: "Array of exactly 5 diverse insights covering patterns, advice, and predictions")
@@ -39,6 +41,7 @@ struct AIInsightsResponse: Equatable {
 
 // MARK: - Conversion to App's Insight Model
 
+@available(iOS 26, *)
 extension AIInsight {
     /// Converts AI-generated insight to the app's existing Insight model
     func toInsight() -> Insight {
@@ -60,6 +63,7 @@ extension AIInsight {
     }
 }
 
+@available(iOS 26, *)
 extension AIInsightsResponse {
     /// Converts all AI insights to app's Insight models
     func toInsights() -> [Insight] {

Shared/Models/UserDefaultsStore.swift

@@ -127,7 +127,7 @@ enum DayViewStyle: Int, CaseIterable {
     case wave = 13        // Horizontal gradient river bands
     case pattern = 14     // Mood icons as repeating background pattern
     case leather = 15     // Skeuomorphic leather with stitching
-    case glass = 16       // iOS 26 liquid glass with variable blur
+    case glass = 16       // Liquid glass with variable blur
     case motion = 17      // Accelerometer-driven parallax effect
     case micro = 18       // Ultra compact single-line entries
     case orbit = 19       // Celestial circular orbital arrangement

Shared/Services/FoundationModelsInsightService.swift

@@ -30,6 +30,7 @@ enum InsightGenerationError: Error, LocalizedError {
 }
 
 /// Service responsible for generating AI-powered mood insights using Apple's Foundation Models
+@available(iOS 26, *)
 @MainActor
 class FoundationModelsInsightService: ObservableObject {
 

Shared/Views/InsightsView/InsightsViewModel.swift

@@ -43,7 +43,8 @@ class InsightsViewModel: ObservableObject {
 
     // MARK: - Dependencies
 
-    private let insightService = FoundationModelsInsightService()
+    /// Stored as Any? to avoid referencing @available(iOS 26, *) type at the property level
+    private var insightService: Any?
     private let healthService = HealthService.shared
     private let calendar = Calendar.current
 
@@ -52,7 +53,14 @@ class InsightsViewModel: ObservableObject {
     private var dataListenerToken: DataController.DataListenerToken?
 
     init() {
-        isAIAvailable = insightService.isAvailable
+        if #available(iOS 26, *) {
+            let service = FoundationModelsInsightService()
+            insightService = service
+            isAIAvailable = service.isAvailable
+        } else {
+            insightService = nil
+            isAIAvailable = false
+        }
 
         dataListenerToken = DataController.shared.addNewDataListener { [weak self] in
             self?.onDataChanged()
@@ -70,7 +78,9 @@ class InsightsViewModel: ObservableObject {
     /// Called when mood data changes in another tab. Invalidates cached insights
     /// so they are regenerated with fresh data on next view appearance.
     private func onDataChanged() {
-        insightService.invalidateCache()
+        if #available(iOS 26, *), let service = insightService as? FoundationModelsInsightService {
+            service.invalidateCache()
+        }
         monthLoadingState = .idle
         yearLoadingState = .idle
         allTimeLoadingState = .idle
@@ -87,7 +97,9 @@ class InsightsViewModel: ObservableObject {
 
     /// Force refresh all insights (invalidates cache)
     func refreshInsights() {
-        insightService.invalidateCache()
+        if #available(iOS 26, *), let service = insightService as? FoundationModelsInsightService {
+            service.invalidateCache()
+        }
         generateInsights()
     }
 
@@ -179,24 +191,34 @@ class InsightsViewModel: ObservableObject {
             healthAverages = healthService.computeHealthAverages(entries: validEntries, healthData: healthData)
         }
 
-        do {
-            let insights = try await insightService.generateInsights(
-                for: validEntries,
-                periodName: periodName,
-                count: 5,
-                healthAverages: healthAverages
-            )
-            updateInsights(insights)
-            updateState(.loaded)
-        } catch {
-            // On error, provide a helpful message
+        if #available(iOS 26, *), let service = insightService as? FoundationModelsInsightService {
+            do {
+                let insights = try await service.generateInsights(
+                    for: validEntries,
+                    periodName: periodName,
+                    count: 5,
+                    healthAverages: healthAverages
+                )
+                updateInsights(insights)
+                updateState(.loaded)
+            } catch {
+                // On error, provide a helpful message
+                updateInsights([Insight(
+                    icon: "exclamationmark.triangle",
+                    title: "Insights Unavailable",
+                    description: "Unable to generate AI insights right now. Please try again later.",
+                    mood: nil
+                )])
+                updateState(.error(error.localizedDescription))
+            }
+        } else {
             updateInsights([Insight(
-                icon: "exclamationmark.triangle",
-                title: "Insights Unavailable",
-                description: "Unable to generate AI insights right now. Please try again later.",
+                icon: "brain.head.profile",
+                title: "AI Unavailable",
+                description: "Apple Intelligence is required for personalized insights. Please enable it in Settings.",
                 mood: nil
             )])
-            updateState(.error(error.localizedDescription))
+            updateState(.error("AI not available"))
         }
     }
 }