[AI] Sample: Detail page, semantic search, streaming, and UI polish (#34576)

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## Summary

Major improvements to the Essentials AI sample app: new Landmark Detail
page with AI features, semantic search, streaming response handler
improvements, and comprehensive UI polish across all pages for a modern,
edge-to-edge experience on iOS and MacCatalyst.

### New Features

- **Landmark Detail Page** — New intermediate page between browsing and
trip planning with AI-generated travel tips, similar destinations via
semantic search, animated hashtag tags, language picker, full-bleed hero
image with scrolling gradient overlay, and Plan Trip navigation
- **Semantic Search** — Search bar on Landmarks page filters continent
groups using semantic similarity with `Timer`-based debounce (300ms) and
tracks recent searches for contextual AI descriptions
- **ISemanticSearchService abstraction** — Clean interface backed by
`EmbeddingSearchService` (Apple NL embeddings + cosine similarity +
hybrid keyword boost + sentence chunking)
- **StreamingResponseHandler passthrough mode** — Supports streaming
without buffering, with new device tests
(`DeliversMultipleIncrementalUpdates`, `ConcatenatedText`)
- **PromptBasedSchemaClient** — Prompt-based JSON schema middleware for
Phi Silica compatibility

### UI Polish

- **Edge-to-edge layout** — All pages use `SafeAreaEdges="None"` on root
Grid with back buttons wrapped in `SafeAreaEdges="Container"`
- **Scrolling gradient pattern** — Fixed gradient overlay + scrolling
gradient that transitions to solid background
- **Custom search entry** — Replaced `SearchBar` with borderless `Entry`
in rounded `Border` with native border/focus ring removed on
iOS/MacCatalyst
- **Edge-to-edge horizontal scrollers** — Scroll to screen edges, align
with page content padding at rest
- **Removed broken BoxView global style** — Was breaking gradient
overlays
- **Added missing Gray700 color** — Prevented silent navigation crash
- **Background → Background property migration** — Replaced
`BackgroundColor` with `Background` across all pages

### Code Quality

- **IDispatcher injection** instead of
`MainThread.BeginInvokeOnMainThread`
- **Only-once AI initialization** — Guard against re-entry in
`LandmarkDetailViewModel`
- **Null safety** — Fixed CS8602 warnings in DataService search methods
- **Removed debug logging**

### Navigation Flow

`LandmarksPage` (browse + search) → `LandmarkDetailPage` (details + AI
tips) → `TripPlanningPage` (itinerary generation)

### Deleted Files

- `LandmarkDescriptionView`, `LandmarkTripView` — Replaced by new pages
- `LanguagePreferenceService` — Refactored into inline language array

### New Test Coverage

- `StreamingResponseHandlerTests/Passthrough.cs` — Unit tests for
passthrough streaming mode
- `ChatClientStreamingTestsBase` — Updated device tests for streaming
scenarios

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mattleibow

src/AI/samples/Essentials.AI.Sample/AI/ItineraryWorkflowExtensions.cs

@@ -43,23 +43,19 @@ public static IHostApplicationBuilder AddItineraryWorkflow(this IHostApplication
 		builder.AddAIAgent(
 			name: "travel-planner-agent",
 			instructions: """
-				You are a simple text parser. 
-				
-				Extract ONLY these 3 values from the user's request:
-				1. destinationName: The place/location name mentioned (extract it exactly as written)
-				2. dayCount: The number of days mentioned (default: 3 if not specified)
-				3. language: The language mentioned for the output (default: English if not specified)
-				
+				You are a simple text parser. Extract 3 values from the user request.
+
 				Rules:
-				1. ALWAYS extract the raw values.
-				2. NEVER make up values or interpret the user's intent.
-				
+				- place: The destination name, exactly as written.
+				- days: Number of days (default: 3).
+				- language: Output language (default: English).
+
 				Examples:
-				- "5-day trip to Maui in French" → destinationName: "Maui", dayCount: 5, language: "French"
-				- "Visit the Great Wall" → destinationName: "Great Wall", dayCount: 3, language: "English"
-				- "Itinerary for Tokyo" → destinationName: "Tokyo", dayCount: 3, language: "English"
-				- "Give me a Maui itinerary" → destinationName: "Maui", dayCount: 3, language: "English"
-				- "Plan a 7 day Japan trip in Spanish" → destinationName: "Japan", dayCount: 7, language: "Spanish"
+				- "5-day trip to Maui in French" produces {"place": "Maui", "days": 5, "language": "French"}
+				- "Visit the Great Wall" produces {"place": "Great Wall", "days": 3, "language": "English"}
+				- "Plan a 7 day Japan trip in Spanish" produces {"place": "Japan", "days": 7, "language": "Spanish"}
+				- "Give me a Cape Town itinerary" produces {"place": "Cape Town", "days": 3, "language": "English"}
+				- "Itinerary for Tokyo" produces {"place": "Tokyo", "days": 3, "language": "English"}
 				""",
 			chatClientServiceKey: "local-model");
 
@@ -108,6 +104,7 @@ Return the exact name of the best matching destination from the candidates.
 					Name = name,
 					ChatOptions = new ChatOptions
 					{
+						Temperature = 0.6f,
 						Instructions = $"""
 							You create detailed travel itineraries.
 							

src/AI/samples/Essentials.AI.Sample/AI/WorkflowModels.cs

@@ -1,30 +1,31 @@
 using System.ComponentModel;
+using System.Text.Json.Serialization;
 
 namespace Maui.Controls.Sample.AI;
 
 /// <summary>
 /// Result from the Travel Planner Agent - raw extraction of user intent.
-/// These values should be extracted exactly as the user stated them, with no interpretation or expansion.
+/// Short JSON names (place/days/language) reduce misspelling by small language models.
 /// </summary>
 public record TravelPlanResult(
-	[property: DisplayName("destinationName")]
-	[property: Description("The exact place/location name as written in the user's request. Extract the raw text only - do NOT interpret, expand, or look up actual landmarks. Example: 'Maui' not 'Maui, Hawaii' or 'Haleakala National Park'.")]
+	[property: JsonPropertyName("place")]
+	[property: Description("The destination name mentioned by the user.")]
 	string DestinationName,
-	[property: DisplayName("dayCount")]
-	[property: Description("The exact number of days mentioned by the user. Use 3 as default only if no number is specified.")]
+	[property: JsonPropertyName("days")]
+	[property: Description("Number of days for the trip. Default is 3.")]
 	int DayCount,
-	[property: DisplayName("language")]
-	[property: Description("The exact output language mentioned by the user. Use 'English' as default only if no language is specified.")]
+	[property: JsonPropertyName("language")]
+	[property: Description("Output language for the itinerary. Default is English.")]
 	string Language);
 
 /// <summary>
 /// Result from the Researcher Agent - the best matching destination (for JSON schema).
 /// </summary>
 internal record DestinationMatchResult(
-	[property: DisplayName("matchedDestinationName")]
+	[property: JsonPropertyName("dest")]
 	[property: Description("The exact name of the best matching destination from the available list.")]
 	string MatchedDestinationName,
-	[property: DisplayName("matchedDestinationDescription")]
+	[property: JsonPropertyName("desc")]
 	[property: Description("A brief description of the matched destination, based on the information provided in the additional context.")]
 	string MatchedDestinationDescription);
 

src/AI/samples/Essentials.AI.Sample/App.xaml

@@ -15,6 +15,7 @@
             <converters:IsNotNullConverter x:Key="IsNotNullConverter" />
             <converters:InvertedBoolConverter x:Key="InvertedBoolConverter" />
             <converters:IsNotNullOrEmptyConverter x:Key="IsNotNullOrEmptyConverter" />
+            <converters:IsPositiveConverter x:Key="IsPositiveConverter" />
         </ResourceDictionary>
     </Application.Resources>
 </Application>

src/AI/samples/Essentials.AI.Sample/AppShell.xaml.cs

@@ -8,8 +8,7 @@ public AppShell()
 	{
 		InitializeComponent();
 
-		// Register routes for navigation
-		// Only TripPlanningPage is navigable - LandmarkTripView is a child component
+		Routing.RegisterRoute(nameof(LandmarkDetailPage), typeof(LandmarkDetailPage));
 		Routing.RegisterRoute(nameof(TripPlanningPage), typeof(TripPlanningPage));
 	}
 }

src/AI/samples/Essentials.AI.Sample/Converters/IsPositiveConverter.cs

@@ -0,0 +1,16 @@
+using System.Globalization;
+
+namespace Maui.Controls.Sample.Converters;
+
+public class IsPositiveConverter : IValueConverter
+{
+	public object Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+	{
+		return value is int i && i > 0;
+	}
+
+	public object ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+	{
+		throw new NotImplementedException();
+	}
+}