feat(ai): enforce local-first routing

Keep external providers behind server consent, task, and prompt-cost gates while persisting actual provider provenance.

JobTrackerApi.Tests/SummarizerServiceTests.cs

@@ -57,6 +57,46 @@ public sealed class SummarizerServiceTests
         Assert.Contains("\"min_length\":180", handler.LastBody);
     }
 
+    [Fact]
+    public async Task Generate_section_returns_actual_provider_model_and_fallback_metadata()
+    {
+        var handler = new CapturingHandler();
+        var httpClient = new HttpClient(handler) { BaseAddress = new Uri("http://localhost:8001") };
+        var httpFactory = new Mock<IHttpClientFactory>();
+        httpFactory.Setup(x => x.CreateClient("ai-service")).Returns(httpClient);
+        using var memoryCache = new MemoryCache(new MemoryCacheOptions());
+        var service = new SummarizerService(httpFactory.Object, memoryCache);
+
+        var result = await service.GenerateSectionWithMetadataAsync("Rewrite", "Synthetic CV", cancellationToken: default);
+
+        Assert.NotNull(result);
+        Assert.Equal("rewritten cv", result!.Text);
+        Assert.Equal("gemini", result.Provider);
+        Assert.Equal("gemini-test", result.Model);
+        Assert.Equal("local_provider_unavailable", result.FallbackReason);
+        Assert.Equal("external_fallback", result.RouteReason);
+    }
+
+    [Fact]
+    public async Task Metadata_path_returns_a_typed_sanitized_provider_failure_while_legacy_path_returns_null()
+    {
+        var httpClient = new HttpClient(new FailureHandler()) { BaseAddress = new Uri("http://localhost:8001") };
+        var httpFactory = new Mock<IHttpClientFactory>();
+        httpFactory.Setup(x => x.CreateClient("ai-service")).Returns(httpClient);
+        using var memoryCache = new MemoryCache(new MemoryCacheOptions());
+        var service = new SummarizerService(httpFactory.Object, memoryCache);
+
+        var failure = await Assert.ThrowsAsync<AiGenerationException>(() =>
+            service.GenerateSectionWithMetadataAsync("Rewrite", "Synthetic CV", cancellationToken: default));
+
+        Assert.Equal("provider_unavailable", failure.Category);
+        Assert.True(failure.Retryable);
+        Assert.Equal("gemini", failure.Provider);
+        Assert.Equal("external_fallback", failure.RouteReason);
+        Assert.DoesNotContain("synthetic upstream detail", failure.Message, StringComparison.OrdinalIgnoreCase);
+        Assert.Null(await service.SummarizeSectionAsync("Rewrite again", "Synthetic CV"));
+    }
+
     private sealed class CapturingHandler : HttpMessageHandler
     {
         public string? LastBody { get; private set; }
@@ -69,10 +109,33 @@ public sealed class SummarizerServiceTests
             var responseBody = LastPath == "/cv/rewrite"
                 ? "{\"rewritten_text\":\"rewritten cv\"}"
                 : "{\"summary\":\"ok\"}";
-            return new HttpResponseMessage(HttpStatusCode.OK)
+            var response = new HttpResponseMessage(HttpStatusCode.OK)
             {
                 Content = new StringContent(responseBody, Encoding.UTF8, "application/json")
             };
+            if (LastPath == "/cv/rewrite")
+            {
+                response.Headers.Add("X-Ai-Provider", "gemini");
+                response.Headers.Add("X-Ai-Model", "gemini-test");
+                response.Headers.Add("X-Ai-Fallback-Reason", "local_provider_unavailable");
+                response.Headers.Add("X-Ai-Route-Reason", "external_fallback");
+            }
+            return response;
+        }
+    }
+
+    private sealed class FailureHandler : HttpMessageHandler
+    {
+        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
+        {
+            var response = new HttpResponseMessage(HttpStatusCode.ServiceUnavailable)
+            {
+                Content = new StringContent("{\"detail\":\"synthetic upstream detail\"}", Encoding.UTF8, "application/json"),
+            };
+            response.Headers.Add("X-Ai-Provider", "gemini");
+            response.Headers.Add("X-Ai-Model", "gemini-test");
+            response.Headers.Add("X-Ai-Route-Reason", "external_fallback");
+            return Task.FromResult(response);
         }
     }
 }