Expose IncludeSubAgentStreamingEvents in all four SDKs (#1108)

* Expose IncludeSubAgentStreamingEvents in all four SDKs

Add the includeSubAgentStreamingEvents property to session config types
and wire payloads across Node/TS, Python, Go, and .NET. The property
controls whether streaming delta events from sub-agents (e.g.,
assistant.message_delta, assistant.reasoning_delta, assistant.streaming_delta
with agentId set) are forwarded to the connection. When false, only
non-streaming sub-agent events and subagent.* lifecycle events are forwarded.

The SDK defaults the property to true when not specified, so existing
consumers automatically receive sub-agent streaming events without any
code changes.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix gofmt alignment in types.go

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add unit tests for IncludeSubAgentStreamingEvents across all SDKs

- .NET: Clone test assertions for SessionConfig and ResumeSessionConfig
- Node.js: Wire payload tests for session.create and session.resume
- Python: Payload capture tests for create_session and resume_session
- Go: JSON marshal tests for createSessionRequest and resumeSessionRequest

Each language tests both the default (true) and explicit false paths.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

dotnet/src/Client.cs

@@ -497,6 +497,7 @@ public async Task<CopilotSession> CreateSessionAsync(SessionConfig config, Cance
                 hasHooks ? true : null,
                 config.WorkingDirectory,
                 config.Streaming is true ? true : null,
+                config.IncludeSubAgentStreamingEvents,
                 config.McpServers,
                 "direct",
                 config.CustomAgents,
@@ -622,6 +623,7 @@ public async Task<CopilotSession> ResumeSessionAsync(string sessionId, ResumeSes
                 config.EnableConfigDiscovery,
                 config.DisableResume is true ? true : null,
                 config.Streaming is true ? true : null,
+                config.IncludeSubAgentStreamingEvents,
                 config.McpServers,
                 "direct",
                 config.CustomAgents,
@@ -1636,6 +1638,7 @@ internal record CreateSessionRequest(
         bool? Hooks,
         string? WorkingDirectory,
         bool? Streaming,
+        bool? IncludeSubAgentStreamingEvents,
         IDictionary<string, McpServerConfig>? McpServers,
         string? EnvValueMode,
         IList<CustomAgentConfig>? CustomAgents,
@@ -1691,6 +1694,7 @@ internal record ResumeSessionRequest(
         bool? EnableConfigDiscovery,
         bool? DisableResume,
         bool? Streaming,
+        bool? IncludeSubAgentStreamingEvents,
         IDictionary<string, McpServerConfig>? McpServers,
         string? EnvValueMode,
         IList<CustomAgentConfig>? CustomAgents,

dotnet/src/Types.cs

@@ -1732,6 +1732,7 @@ protected SessionConfig(SessionConfig? other)
         SessionId = other.SessionId;
         SkillDirectories = other.SkillDirectories is not null ? [.. other.SkillDirectories] : null;
         Streaming = other.Streaming;
+        IncludeSubAgentStreamingEvents = other.IncludeSubAgentStreamingEvents;
         SystemMessage = other.SystemMessage;
         Tools = other.Tools is not null ? [.. other.Tools] : null;
         WorkingDirectory = other.WorkingDirectory;
@@ -1848,6 +1849,17 @@ protected SessionConfig(SessionConfig? other)
     /// </summary>
     public bool Streaming { get; set; }
 
+    /// <summary>
+    /// Include sub-agent streaming events in the event stream. When true, streaming
+    /// delta events from sub-agents (e.g., <c>assistant.message_delta</c>,
+    /// <c>assistant.reasoning_delta</c>, <c>assistant.streaming_delta</c> with
+    /// <c>agentId</c> set) are forwarded to this connection. When false, only
+    /// non-streaming sub-agent events and <c>subagent.*</c> lifecycle events are
+    /// forwarded; streaming deltas from sub-agents are suppressed.
+    /// Default: true.
+    /// </summary>
+    public bool IncludeSubAgentStreamingEvents { get; set; } = true;
+
     /// <summary>
     /// MCP server configurations for the session.
     /// Keys are server names, values are server configurations (<see cref="McpStdioServerConfig"/> or <see cref="McpHttpServerConfig"/>).
@@ -1961,6 +1973,7 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
         CreateSessionFsHandler = other.CreateSessionFsHandler;
         SkillDirectories = other.SkillDirectories is not null ? [.. other.SkillDirectories] : null;
         Streaming = other.Streaming;
+        IncludeSubAgentStreamingEvents = other.IncludeSubAgentStreamingEvents;
         SystemMessage = other.SystemMessage;
         Tools = other.Tools is not null ? [.. other.Tools] : null;
         WorkingDirectory = other.WorkingDirectory;
@@ -2082,6 +2095,17 @@ protected ResumeSessionConfig(ResumeSessionConfig? other)
     /// </summary>
     public bool Streaming { get; set; }
 
+    /// <summary>
+    /// Include sub-agent streaming events in the event stream. When true, streaming
+    /// delta events from sub-agents (e.g., <c>assistant.message_delta</c>,
+    /// <c>assistant.reasoning_delta</c>, <c>assistant.streaming_delta</c> with
+    /// <c>agentId</c> set) are forwarded to this connection. When false, only
+    /// non-streaming sub-agent events and <c>subagent.*</c> lifecycle events are
+    /// forwarded; streaming deltas from sub-agents are suppressed.
+    /// Default: true.
+    /// </summary>
+    public bool IncludeSubAgentStreamingEvents { get; set; } = true;
+
     /// <summary>
     /// MCP server configurations for the session.
     /// Keys are server names, values are server configurations (<see cref="McpStdioServerConfig"/> or <see cref="McpHttpServerConfig"/>).

dotnet/test/CloneTests.cs

@@ -86,6 +86,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
             ExcludedTools = ["tool3"],
             WorkingDirectory = "/workspace",
             Streaming = true,
+            IncludeSubAgentStreamingEvents = false,
             McpServers = new Dictionary<string, McpServerConfig> { ["server1"] = new McpStdioServerConfig { Command = "echo" } },
             CustomAgents = [new CustomAgentConfig { Name = "agent1" }],
             Agent = "agent1",
@@ -104,6 +105,7 @@ public void SessionConfig_Clone_CopiesAllProperties()
         Assert.Equal(original.ExcludedTools, clone.ExcludedTools);
         Assert.Equal(original.WorkingDirectory, clone.WorkingDirectory);
         Assert.Equal(original.Streaming, clone.Streaming);
+        Assert.Equal(original.IncludeSubAgentStreamingEvents, clone.IncludeSubAgentStreamingEvents);
         Assert.Equal(original.McpServers.Count, clone.McpServers!.Count);
         Assert.Equal(original.CustomAgents.Count, clone.CustomAgents!.Count);
         Assert.Equal(original.Agent, clone.Agent);
@@ -243,6 +245,7 @@ public void Clone_WithNullCollections_ReturnsNullCollections()
         Assert.Null(clone.SkillDirectories);
         Assert.Null(clone.DisabledSkills);
         Assert.Null(clone.Tools);
+        Assert.True(clone.IncludeSubAgentStreamingEvents);
     }
 
     [Fact]
@@ -272,4 +275,27 @@ public void ResumeSessionConfig_Clone_CopiesAgentProperty()
 
         Assert.Equal("test-agent", clone.Agent);
     }
+
+    [Fact]
+    public void ResumeSessionConfig_Clone_CopiesIncludeSubAgentStreamingEvents()
+    {
+        var original = new ResumeSessionConfig
+        {
+            IncludeSubAgentStreamingEvents = false,
+        };
+
+        var clone = original.Clone();
+
+        Assert.False(clone.IncludeSubAgentStreamingEvents);
+    }
+
+    [Fact]
+    public void ResumeSessionConfig_Clone_PreservesIncludeSubAgentStreamingEventsDefault()
+    {
+        var original = new ResumeSessionConfig();
+
+        var clone = original.Clone();
+
+        Assert.True(clone.IncludeSubAgentStreamingEvents);
+    }
 }

go/client.go

@@ -611,6 +611,11 @@ func (c *Client) CreateSession(ctx context.Context, config *SessionConfig) (*Ses
 	if config.Streaming {
 		req.Streaming = Bool(true)
 	}
+	if config.IncludeSubAgentStreamingEvents != nil {
+		req.IncludeSubAgentStreamingEvents = config.IncludeSubAgentStreamingEvents
+	} else {
+		req.IncludeSubAgentStreamingEvents = Bool(true)
+	}
 	if config.OnUserInputRequest != nil {
 		req.RequestUserInput = Bool(true)
 	}
@@ -744,6 +749,11 @@ func (c *Client) ResumeSessionWithOptions(ctx context.Context, sessionID string,
 	if config.Streaming {
 		req.Streaming = Bool(true)
 	}
+	if config.IncludeSubAgentStreamingEvents != nil {
+		req.IncludeSubAgentStreamingEvents = config.IncludeSubAgentStreamingEvents
+	} else {
+		req.IncludeSubAgentStreamingEvents = Bool(true)
+	}
 	if config.OnUserInputRequest != nil {
 		req.RequestUserInput = Bool(true)
 	}

go/client_test.go

@@ -861,6 +861,80 @@ func TestResumeSessionRequest_RequestElicitation(t *testing.T) {
 	})
 }
 
+func TestCreateSessionRequest_IncludeSubAgentStreamingEvents(t *testing.T) {
+	t.Run("defaults to true when nil", func(t *testing.T) {
+		req := createSessionRequest{
+			IncludeSubAgentStreamingEvents: Bool(true),
+		}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["includeSubAgentStreamingEvents"] != true {
+			t.Errorf("Expected includeSubAgentStreamingEvents to be true, got %v", m["includeSubAgentStreamingEvents"])
+		}
+	})
+
+	t.Run("preserves explicit false", func(t *testing.T) {
+		req := createSessionRequest{
+			IncludeSubAgentStreamingEvents: Bool(false),
+		}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["includeSubAgentStreamingEvents"] != false {
+			t.Errorf("Expected includeSubAgentStreamingEvents to be false, got %v", m["includeSubAgentStreamingEvents"])
+		}
+	})
+}
+
+func TestResumeSessionRequest_IncludeSubAgentStreamingEvents(t *testing.T) {
+	t.Run("defaults to true when nil", func(t *testing.T) {
+		req := resumeSessionRequest{
+			SessionID:                      "s1",
+			IncludeSubAgentStreamingEvents: Bool(true),
+		}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["includeSubAgentStreamingEvents"] != true {
+			t.Errorf("Expected includeSubAgentStreamingEvents to be true, got %v", m["includeSubAgentStreamingEvents"])
+		}
+	})
+
+	t.Run("preserves explicit false", func(t *testing.T) {
+		req := resumeSessionRequest{
+			SessionID:                      "s1",
+			IncludeSubAgentStreamingEvents: Bool(false),
+		}
+		data, err := json.Marshal(req)
+		if err != nil {
+			t.Fatalf("Failed to marshal: %v", err)
+		}
+		var m map[string]any
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("Failed to unmarshal: %v", err)
+		}
+		if m["includeSubAgentStreamingEvents"] != false {
+			t.Errorf("Expected includeSubAgentStreamingEvents to be false, got %v", m["includeSubAgentStreamingEvents"])
+		}
+	})
+}
+
 func TestCreateSessionResponse_Capabilities(t *testing.T) {
 	t.Run("reads capabilities from session.create response", func(t *testing.T) {
 		responseJSON := `{"sessionId":"s1","workspacePath":"/tmp","capabilities":{"ui":{"elicitation":true}}}`