fix: local AI chat backend wiring and fallback handling

[BenjaminMichaelis]

Summary

• replace environment-gated chat registration with config-driven backend selection
• add IChatCompletionService abstraction with Azure, Local, and Unavailable implementations
• wire local Ollama-compatible chat path with endpoint/model config and safe fallback behavior
• return explicit 503 + chat_unavailable contracts when chat backend is unavailable
• add tests covering unavailable chat contracts for /api/chat/message and /api/chat/stream

Validation

• pwsh .github/hooks/scripts/validate-repos.ps1 -Projects web (pass)

[Copilot]

Pull request overview

This PR moves chat backend registration to configuration-driven selection and introduces local/unavailable chat service abstractions so the web app can continue running when chat is not configured.

Changes:

• Replaces direct Azure chat registration with AddConfiguredChatServices.
• Adds IChatCompletionService implementations for Azure, local OpenAI-compatible backends, and unavailable fallback.
• Adds controller/test coverage for 503 chat_unavailable responses, plus unrelated development CAPTCHA/login bypass changes.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
EssentialCSharp.Web/Program.cs	Wires chat registration through the new configuration-driven extension.
EssentialCSharp.Web/Controllers/ChatController.cs	Uses IChatCompletionService and returns unavailable/error contracts.
EssentialCSharp.Web/Areas/Identity/Pages/Account/Register.cshtml.cs	Adds development-only CAPTCHA test-token bypass.
EssentialCSharp.Web/Areas/Identity/Pages/Account/Login.cshtml.cs	Adds development-only CAPTCHA and email-confirmation bypass behavior.
EssentialCSharp.Web.Tests/ChatAvailabilityTests.cs	Adds tests for unavailable chat responses.
EssentialCSharp.Chat.Shared/Services/UnavailableChatService.cs	Adds fallback unavailable chat implementation.
EssentialCSharp.Chat.Shared/Services/LocalChatService.cs	Adds local OpenAI-compatible chat backend implementation.
EssentialCSharp.Chat.Shared/Services/IChatCompletionService.cs	Defines the chat completion abstraction.
EssentialCSharp.Chat.Shared/Services/ChatBackendUnavailableException.cs	Adds domain exception for unavailable backends.
EssentialCSharp.Chat.Shared/Services/AIChatService.cs	Implements the new abstraction for Azure chat.
EssentialCSharp.Chat.Shared/Models/AIOptions.cs	Adds local AI configuration options.
EssentialCSharp.Chat.Shared/Extensions/ServiceCollectionExtensions.cs	Adds backend selection and local/unavailable service registration.

Comments suppressed due to low confidence (3)

EssentialCSharp.Web.Tests/ChatAvailabilityTests.cs:39

• This test also depends on ambient app configuration leaving chat unavailable. Because the factory does not clear AIOptions/user secrets/environment settings, machines with a configured Azure or local backend will not return 503 here. Use a test-specific factory/service override so the unavailable path is guaranteed.

        HttpClient client = factory.CreateClient(new WebApplicationFactoryClientOptions { AllowAutoRedirect = false });

        string userId = await McpTestHelper.CreateUserAsync(factory, "chat-stream-unavailable");
        (string cookieName, string cookieValue) = await McpTestHelper.CreateIdentityApplicationCookieAsync(factory, userId);

EssentialCSharp.Web/Areas/Identity/Pages/Account/Login.cshtml.cs:110

• This change adds an authentication bypass for unconfirmed accounts when a hard-coded test CAPTCHA token is submitted in Development. That is a significant auth behavior change unrelated to the chat-backend PR scope and can grant access to any unconfirmed local/development account that knows the token; keep this in the test host or a dedicated test-only service override instead of production code paths.

                // For test tokens, bypass email confirmation requirement
                if (isTestToken && !foundUser.EmailConfirmed)
                {
                    // Temporarily set email as confirmed for this sign-in when using test token
                    var tempConfirmed = foundUser.EmailConfirmed;
                    foundUser.EmailConfirmed = true;
                    result = await signInManager.PasswordSignInAsync(foundUser, Input.Password, Input.RememberMe, lockoutOnFailure: true);
                    foundUser.EmailConfirmed = tempConfirmed;

EssentialCSharp.Web/Controllers/ChatController.cs:208

• The streaming path has the same gap as SendMessage: backend failures from the Azure/OpenAI client that are not already wrapped as ChatBackendUnavailableException fall into the generic 500/error event path, so the new chat_unavailable/503 contract is only used for the unavailable stub/local wrapper. Convert known backend/network exceptions to ChatBackendUnavailableException before this generic handler.

        catch (Exception ex) when (!Response.HasStarted)
        {
            LogChatStreamErrorBeforeResponseStarted(_Logger, ex, User.Identity?.Name);
            Response.StatusCode = 500;
            Response.ContentType = "application/json";
            await Response.WriteAsJsonAsync(new { error = "Chat service unavailable" }, CancellationToken.None);
        }

[BenjaminMichaelis]

Memory leak fix pushed in 1b89b5b: replaced unbounded \ConcurrentDictionary\ with a private \MemoryCache\ (SizeLimit=500, 30-min sliding TTL). Also implemented \IDisposable\ with \GC.SuppressFinalize\ for correct singleton cleanup.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

[BenjaminMichaelis]

Security cleanup pushed in 413e352: removed the hard-coded development hCaptcha bypass and the temporary email-confirmation mutation from the Identity login/register flows. Local/E2E testing should rely on the configured official hCaptcha test keys or test-host service overrides instead of bypass logic in production page handlers.

[Copilot]

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (2)

EssentialCSharp.Chat.Shared/Extensions/ServiceCollectionExtensions.cs:122

• The Azure path now calls the overload that only validates EmbeddingRetryOptions defaults, so AIOptions:EmbeddingRetry values from appsettings or environment variables are no longer bound. This regresses the previous AddAzureOpenAIServices(configuration) behavior and makes customized embedding retry/backoff settings silently ignored whenever Azure is selected.

                services.AddAzureOpenAIServices(aiOptions, postgresConnectionString!);

EssentialCSharp.Chat.Shared/Extensions/ServiceCollectionExtensions.cs:142

• This 120-second timeout is still subject to the app-wide ConfigureHttpClientDefaults(http => http.AddStandardResilienceHandler()) in Program.cs, whose standard timeout policy can cancel requests earlier than HttpClient.Timeout. Local models often take longer on first token/model load, so the new local backend may report chat_unavailable before the configured 120 seconds unless this named client overrides the resilience timeouts or opts out.

                client.Timeout = TimeSpan.FromSeconds(120);

[Copilot]

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 4 comments.

Comments suppressed due to low confidence (1)

EssentialCSharp.Chat.Shared/Services/UnavailableChatService.cs:41

• The streaming unavailable path also yields normal SSE content plus a response ID. If a caller forgets the IsAvailable pre-check, the fallback backend will appear to produce a valid stream rather than raising ChatBackendUnavailableException and letting the API return the unavailable contract.

        yield return ("Chat service is unavailable in this environment.", responseId: null);
        yield return (string.Empty, Guid.NewGuid().ToString("N"));

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

EssentialCSharp.Web.Tests/ChatAvailabilityTests.cs:45

• This test can be affected by real hCaptcha configuration from user secrets/environment variables. With HCaptcha:SecretKey configured, the stream action validates this hard-coded token before checking chat availability, so the test may fail before exercising the intended chat_unavailable contract. Override ICaptchaService or clear HCaptcha options in the test factory.

            Content = JsonContent.Create(new { message = "Hello", enableContextualSearch = false, captchaResponse = HCaptchaTestToken })