feat: externalize AI configuration, implement resilience policies, and update extraction prompt formatting

src/NexusReader.Infrastructure/DependencyInjection.cs

@@ -7,6 +7,9 @@ using GeminiDotnet.Extensions.AI;
 using NexusReader.Infrastructure.Persistence;
 using NexusReader.Application.Abstractions.Services;
 using NexusReader.Infrastructure.Services;
+using NexusReader.Infrastructure.Configuration;
+using Polly;
+using Polly.Retry;
 
 namespace NexusReader.Infrastructure;
 
@@ -18,17 +21,31 @@ public static class DependencyInjection
         services.AddDbContext<AppDbContext>(options =>
             options.UseSqlite(connectionString));
 
-        var apiKey = configuration["Ai:Google:ApiKey"];
-        if (string.IsNullOrWhiteSpace(apiKey))
-        {
-            throw new InvalidOperationException("AI Studio ApiKey is missing in configuration (Ai:Google:ApiKey).");
-        }
-        var modelId = configuration["Ai:Google:Model"] ?? "gemini-1.5-flash";
+        services.Configure<AiSettings>(configuration.GetSection(AiSettings.SectionName));
+        var aiSettings = configuration.GetSection(AiSettings.SectionName).Get<AiSettings>() ?? new AiSettings();
 
-        services.AddSingleton<IChatClient>(new GeminiChatClient(new GeminiClientOptions 
+        if (string.IsNullOrWhiteSpace(aiSettings.ApiKey) || aiSettings.ApiKey == "PLACEHOLDER")
+        {
+            // We don't throw here to allow the app to start, but services using AI will fail gracefully
+        }
+
+        services.AddResiliencePipeline("ai-retry", builder =>
+        {
+            builder.AddRetry(new RetryStrategyOptions
+            {
+                ShouldHandle = new PredicateBuilder().Handle<Exception>(ex => 
+                    ex.Message.Contains("429") || ex.Message.Contains("Too Many Requests") || ex.Message.Contains("quota")),
+                BackoffType = DelayBackoffType.Exponential,
+                UseJitter = true,
+                MaxRetryAttempts = aiSettings.RetryAttempts,
+                Delay = TimeSpan.FromSeconds(2)
+            });
+        });
+
+        services.AddChatClient(new GeminiChatClient(new GeminiClientOptions 
         { 
-            ApiKey = apiKey, 
-            ModelId = modelId 
+            ApiKey = aiSettings.ApiKey, 
+            ModelId = aiSettings.Model 
         }));
 
         services.AddScoped<IKnowledgeService, KnowledgeService>();