Fix: declare trust_probe capability to unbreak Inngest Cloud sync (v1.4.5)

Inngest.Tests/SyncRegistrationTests.cs

@@ -276,6 +276,63 @@ public async Task HandleSync_InBandMode_IncludesInspection()
         Assert.True(inspection.GetProperty("has_event_key").GetBoolean());
         Assert.True(inspection.GetProperty("has_signing_key").GetBoolean());
         Assert.Equal("dev", inspection.GetProperty("mode").GetString());
+
+        // capabilities.trust_probe must be advertised — without it Inngest Cloud
+        // rejects registrations with 400 "Invalid response returned".
+        Assert.True(inspection.TryGetProperty("capabilities", out var capabilities));
+        Assert.Equal("v1", capabilities.GetProperty("trust_probe").GetString());
+        Assert.Equal("v1", capabilities.GetProperty("in_band_sync").GetString());
+    }
+
+    [Fact]
+    public async Task HandleSync_OutOfBand_RegisterPayloadIncludesTrustProbeCapability()
+    {
+        // Arrange — out-of-band sync POSTs to {apiOrigin}/fn/register. Inngest
+        // Cloud rejects this with 400 "Invalid response returned" when the
+        // payload omits capabilities.trust_probe. Capture the outbound POST
+        // body and assert capabilities are present.
+        var options = new InngestOptions
+        {
+            AppId = "test-app",
+            IsDev = false,
+            EventKey = "test-event-key",
+            SigningKey = "signkey-prod-abc123"
+        };
+        options.ApplyEnvironmentFallbacks();
+
+        var registry = new InngestFunctionRegistry(options.AppId!);
+        registry.RegisterFunction(typeof(SyncTestFunction));
+
+        var services = new ServiceCollection();
+        services.AddSingleton<SyncTestFunction>();
+        var serviceProvider = services.BuildServiceProvider();
+
+        var handler = new MockHttpMessageHandler();
+        handler.QueueResponse(HttpStatusCode.OK, "{\"modified\":true}");
+
+        var client = new InngestClient(
+            options,
+            registry,
+            serviceProvider,
+            new HttpClient(handler),
+            NullLogger<InngestClient>.Instance);
+
+        var context = CreateHttpContext("PUT");
+        // No X-Inngest-Sync-Kind header => out-of-band path.
+
+        // Act
+        await client.HandleRequestAsync(context);
+
+        // Assert
+        var registerRequest = handler.Requests.Single(r =>
+            r.RequestUri != null && r.RequestUri.AbsolutePath.EndsWith("/fn/register"));
+        var sentBody = await registerRequest.Content!.ReadAsStringAsync();
+        var payload = JsonSerializer.Deserialize<JsonElement>(sentBody);
+
+        Assert.True(payload.TryGetProperty("capabilities", out var capabilities),
+            $"register payload missing 'capabilities' field: {sentBody}");
+        Assert.Equal("v1", capabilities.GetProperty("trust_probe").GetString());
+        Assert.Equal("v1", capabilities.GetProperty("in_band_sync").GetString());
     }
 
     [Fact]

Inngest/Inngest.csproj

@@ -19,7 +19,7 @@
         <PackageReleaseNotes>https://github.com/jmarbutt/InngestDotNet/releases</PackageReleaseNotes>
 
         <!-- Version is set by CI, default for local builds -->
-        <Version>1.4.4</Version>
+        <Version>1.4.5</Version>
 
         <!-- Build settings -->
         <GenerateDocumentationFile>true</GenerateDocumentationFile>

Inngest/InngestClient.cs

@@ -30,7 +30,7 @@ public class InngestClient : IInngestClient
     private readonly string _environment;
     private readonly bool _isDev;
     private readonly bool _disableCronTriggersInDev;
-    private readonly string _sdkVersion = "1.4.4";
+    private readonly string _sdkVersion = "1.4.5";
     private readonly string _appId;
     private readonly ILogger _logger;
     private readonly IInngestFunctionRegistry? _registry;
@@ -1058,10 +1058,14 @@ private async Task HandleSyncRequest(HttpContext context)
         {
             _logger.LogInformation("In-band sync: returning {FunctionCount} functions with URL: {Url}", fnArray.Count, url);
 
-            // Build capabilities
+            // Build capabilities. trust_probe is required by Inngest Cloud as of the
+            // 2026-05 cloud rollout; without it /fn/register returns 400 "Invalid
+            // response returned". in_band_sync advertises that we can satisfy a
+            // signed in-band PUT.
             var capabilities = new Dictionary<string, string>
             {
-                ["in_band_sync"] = "v1"
+                ["in_band_sync"] = "v1",
+                ["trust_probe"] = "v1"
             };
 
             // Build inspection data
@@ -1163,7 +1167,9 @@ private async Task HandleSyncRequest(HttpContext context)
         }
 
         // Out-of-band sync - POST to Inngest API
-        // Create register payload according to the SDK specification
+        // Create register payload according to the SDK specification.
+        // capabilities.trust_probe must be declared; Inngest Cloud rejects
+        // registrations without it with 400 "Invalid response returned".
         var registerPayload = new
         {
             url = url,
@@ -1172,7 +1178,12 @@ private async Task HandleSyncRequest(HttpContext context)
             sdk = $"cs:v{_sdkVersion}",
             v = "0.1",
             framework = "aspnetcore",
-            functions = fnArray
+            functions = fnArray,
+            capabilities = new Dictionary<string, string>
+            {
+                ["trust_probe"] = "v1",
+                ["in_band_sync"] = "v1"
+            }
         };
 
         // Log information about registration for debugging
@@ -1617,6 +1628,11 @@ private async Task HandleIntrospectionRequest(HttpContext context)
             responseObj["api_origin"] = _apiOrigin;
             responseObj["event_api_origin"] = _eventApiOrigin;
             responseObj["app_id"] = _appId;
+            responseObj["capabilities"] = new Dictionary<string, string>
+            {
+                ["trust_probe"] = "v1",
+                ["in_band_sync"] = "v1"
+            };
             responseObj["env"] = _environment;
             responseObj["event_key_hash"] = eventKeyHash;
             responseObj["framework"] = "aspnetcore";