fix(dotnet): forward CustomAgentsLocalOnly in session.create and session.resume

CustomAgentsLocalOnly was only sent via the post-create
session.options.update call, which arrives after agent discovery
has already completed. Mirror the Go SDK by including
customAgentsLocalOnly in CreateSessionRequest and
ResumeSessionRequest wire payloads.

Fixes #1888

Author: syf2211

dotnet/src/Client.cs

@@ -1158,6 +1158,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
                 config.Agent,
                 config.ConfigDirectory,
                 config.EnableConfigDiscovery,
+                config.CustomAgentsLocalOnly,
                 config.SkipEmbeddingRetrieval,
                 config.EmbeddingCacheStorage,
                 config.OrganizationCustomInstructions,
@@ -1361,6 +1362,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
                 config.WorkingDirectory,
                 config.ConfigDirectory,
                 config.EnableConfigDiscovery,
+                config.CustomAgentsLocalOnly,
                 config.SkipEmbeddingRetrieval,
                 config.EmbeddingCacheStorage,
                 config.OrganizationCustomInstructions,
@@ -2722,6 +2724,7 @@ internal record CreateSessionRequest(
         string? Agent,
         [property: JsonPropertyName("configDir")] string? ConfigDirectory,
         bool? EnableConfigDiscovery,
+        [property: JsonPropertyName("customAgentsLocalOnly")] bool? CustomAgentsLocalOnly,
         bool? SkipEmbeddingRetrieval,
         EmbeddingCacheStorageMode? EmbeddingCacheStorage,
         string? OrganizationCustomInstructions,
@@ -2818,6 +2821,7 @@ internal record ResumeSessionRequest(
         string? WorkingDirectory,
         [property: JsonPropertyName("configDir")] string? ConfigDirectory,
         bool? EnableConfigDiscovery,
+        [property: JsonPropertyName("customAgentsLocalOnly")] bool? CustomAgentsLocalOnly,
         bool? SkipEmbeddingRetrieval,
         EmbeddingCacheStorageMode? EmbeddingCacheStorage,
         string? OrganizationCustomInstructions,

dotnet/test/E2E/ClientOptionsE2ETests.cs

@@ -178,6 +178,65 @@ public async Task Should_Omit_EnableSessionTelemetry_When_Not_Set()
         await session.DisposeAsync();
     }
 
+    [Fact]
+    public async Task Should_Forward_CustomAgentsLocalOnly_In_Create_Wire_Request()
+    {
+        var (cliPath, capturePath) = await CreateFakeCliCaptureAsync();
+
+        await using var client = Ctx.CreateClient(options: new CopilotClientOptions
+        {
+            Connection = RuntimeConnection.ForStdio(path: cliPath, args: ["--capture-file", capturePath]),
+            UseLoggedInUser = false,
+        });
+
+        await client.StartAsync();
+
+        var session = await client.CreateSessionAsync(new SessionConfig
+        {
+            CustomAgentsLocalOnly = true,
+            OnPermissionRequest = PermissionHandler.ApproveAll,
+        });
+
+        using var capture = JsonDocument.Parse(await File.ReadAllTextAsync(capturePath));
+        var createRequest = GetCapturedRequestParams(capture.RootElement, "session.create");
+        Assert.True(createRequest.GetProperty("customAgentsLocalOnly").GetBoolean());
+
+        await session.DisposeAsync();
+    }
+
+    [Fact]
+    public async Task Should_Forward_CustomAgentsLocalOnly_In_Resume_Wire_Request()
+    {
+        var (cliPath, capturePath) = await CreateFakeCliCaptureAsync();
+
+        await using var client = Ctx.CreateClient(options: new CopilotClientOptions
+        {
+            Connection = RuntimeConnection.ForStdio(path: cliPath, args: ["--capture-file", capturePath]),
+            UseLoggedInUser = false,
+        });
+
+        await client.StartAsync();
+
+        var createSession = await client.CreateSessionAsync(new SessionConfig
+        {
+            OnPermissionRequest = PermissionHandler.ApproveAll,
+        });
+        var sessionId = createSession.SessionId;
+        await createSession.DisposeAsync();
+
+        var resumeSession = await client.ResumeSessionAsync(sessionId, new ResumeSessionConfig
+        {
+            CustomAgentsLocalOnly = true,
+            OnPermissionRequest = PermissionHandler.ApproveAll,
+        });
+
+        using var capture = JsonDocument.Parse(await File.ReadAllTextAsync(capturePath));
+        var resumeRequest = GetCapturedRequestParams(capture.RootElement, "session.resume");
+        Assert.True(resumeRequest.GetProperty("customAgentsLocalOnly").GetBoolean());
+
+        await resumeSession.DisposeAsync();
+    }
+
     [Fact]
     public async Task Should_Forward_Granular_Multitenancy_Fields_In_Create_Wire_Request()
     {

dotnet/test/Unit/SerializationTests.cs

@@ -590,6 +590,58 @@ public void CreateSessionRequest_CanSerializeEnableSessionTelemetry_WithSdkOptio
         Assert.False(root.GetProperty("enableSessionTelemetry").GetBoolean());
     }
 
+    [Fact]
+    public void CreateSessionRequest_CanSerializeCustomAgentsLocalOnly_WithSdkOptions()
+    {
+        var options = GetSerializerOptions();
+        var requestType = GetNestedType(typeof(CopilotClient), "CreateSessionRequest");
+        var request = CreateInternalRequest(
+            requestType,
+            ("SessionId", "session-id"),
+            ("CustomAgentsLocalOnly", true));
+
+        var json = JsonSerializer.Serialize(request, requestType, options);
+        using var document = JsonDocument.Parse(json);
+        Assert.True(document.RootElement.GetProperty("customAgentsLocalOnly").GetBoolean());
+    }
+
+    [Fact]
+    public void ResumeSessionRequest_CanSerializeCustomAgentsLocalOnly_WithSdkOptions()
+    {
+        var options = GetSerializerOptions();
+        var requestType = GetNestedType(typeof(CopilotClient), "ResumeSessionRequest");
+        var request = CreateInternalRequest(
+            requestType,
+            ("SessionId", "session-id"),
+            ("CustomAgentsLocalOnly", true));
+
+        var json = JsonSerializer.Serialize(request, requestType, options);
+        using var document = JsonDocument.Parse(json);
+        Assert.True(document.RootElement.GetProperty("customAgentsLocalOnly").GetBoolean());
+    }
+
+    [Fact]
+    public void SessionRequests_OmitCustomAgentsLocalOnly_WhenUnset()
+    {
+        var options = GetSerializerOptions();
+
+        var createRequestType = GetNestedType(typeof(CopilotClient), "CreateSessionRequest");
+        var createRequest = CreateInternalRequest(
+            createRequestType,
+            ("SessionId", "session-id"));
+        var createJson = JsonSerializer.Serialize(createRequest, createRequestType, options);
+        using var createDocument = JsonDocument.Parse(createJson);
+        Assert.False(createDocument.RootElement.TryGetProperty("customAgentsLocalOnly", out _));
+
+        var resumeRequestType = GetNestedType(typeof(CopilotClient), "ResumeSessionRequest");
+        var resumeRequest = CreateInternalRequest(
+            resumeRequestType,
+            ("SessionId", "session-id"));
+        var resumeJson = JsonSerializer.Serialize(resumeRequest, resumeRequestType, options);
+        using var resumeDocument = JsonDocument.Parse(resumeJson);
+        Assert.False(resumeDocument.RootElement.TryGetProperty("customAgentsLocalOnly", out _));
+    }
+
     [Fact]
     public void ResumeSessionRequest_CanSerializeEnableSessionTelemetry_WithSdkOptions()
     {