Propagate request handler agent metadata

Thread agentId, parentAgentId, and interactionType from llmInference request-start frames into the public request handler contexts across SDK languages.

Extend CAPI/BYOK and subagent request-handler tests to prove the metadata is observable, and fix .NET forwarding so GET/HEAD requests do not get an empty content body when forwarding headers.

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

Author: stephentoub

dotnet/src/CopilotRequestHandler.cs

@@ -49,6 +49,9 @@ public CopilotRequestContext(CopilotRequestContext original)
         : this(original.RequestId, original.Url, original.Headers)
     {
         SessionId = original.SessionId;
+        AgentId = original.AgentId;
+        ParentAgentId = original.ParentAgentId;
+        InteractionType = original.InteractionType;
         Transport = original.Transport;
         CancellationToken = original.CancellationToken;
         WebSocketResponse = original.WebSocketResponse;
@@ -67,6 +70,15 @@ internal CopilotRequestContext(string requestId, string url, IReadOnlyDictionary
     /// <summary>Runtime session id that triggered the request, if any.</summary>
     public string? SessionId { get; init; }
 
+    /// <summary>Stable per-agent-instance id for the agent trajectory that issued this request.</summary>
+    public string? AgentId { get; init; }
+
+    /// <summary>Id of the parent agent when this request was issued by a subagent.</summary>
+    public string? ParentAgentId { get; init; }
+
+    /// <summary>Runtime classification for the interaction that produced this request.</summary>
+    public string? InteractionType { get; init; }
+
     /// <summary>Transport the runtime would otherwise use.</summary>
     public CopilotRequestTransport Transport { get; init; }
 
@@ -524,7 +536,7 @@ private static async Task<HttpRequestMessage> BuildHttpRequestAsync(LlmInference
                 continue;
             }
 
-            if (!message.Headers.TryAddWithoutValidation(name, values))
+            if (!message.Headers.TryAddWithoutValidation(name, values) && hasBody)
             {
                 message.Content ??= new ByteArrayContent([]);
                 message.Content.Headers.TryAddWithoutValidation(name, values);
@@ -870,6 +882,9 @@ public Task<LlmInferenceHttpRequestStartResult> HttpRequestStartAsync(LlmInferen
         exchange.Context = new CopilotRequestContext(request.RequestId, request.Url, ToReadOnlyHeaders(request.Headers))
         {
             SessionId = request.SessionId,
+            AgentId = request.AgentId,
+            ParentAgentId = request.ParentAgentId,
+            InteractionType = request.InteractionType,
             Transport = transport,
             CancellationToken = exchange.Abort.Token,
         };

dotnet/test/E2E/CopilotRequestE2EProvider.cs

@@ -56,7 +56,13 @@ protected override async Task<HttpResponseMessage> SendRequestAsync(HttpRequestM
 #else
             : await request.Content.ReadAsStringAsync().ConfigureAwait(false);
 #endif
-        _records.Enqueue(new InterceptedRequest(url, ctx.SessionId, bodyText));
+        _records.Enqueue(new InterceptedRequest(
+            url,
+            ctx.SessionId,
+            ctx.AgentId,
+            ctx.ParentAgentId,
+            ctx.InteractionType,
+            bodyText));
 
         return IsInferenceUrl(url)
             ? BuildInferenceResponse(url, bodyText)
@@ -188,4 +194,10 @@ internal static HttpResponseMessage BuildNonInferenceResponse(string url)
 }
 
 /// <summary>A single request the callback intercepted.</summary>
-internal sealed record InterceptedRequest(string Url, string? SessionId, string Body);
+internal sealed record InterceptedRequest(
+    string Url,
+    string? SessionId,
+    string? AgentId,
+    string? ParentAgentId,
+    string? InteractionType,
+    string Body);

dotnet/test/E2E/CopilotRequestSessionIdE2ETests.cs

@@ -53,7 +53,11 @@ public async Task Threads_The_Session_Id_Into_A_Capi_Session_Inference_Request()
 
         var inference = provider.InferenceRequests;
         Assert.NotEmpty(inference);
-        Assert.All(inference, r => Assert.Equal(capiSessionId, r.SessionId));
+        Assert.All(inference, r =>
+        {
+            Assert.Equal(capiSessionId, r.SessionId);
+            AssertAgentMetadata(r);
+        });
 
         // Validate the final assistant response arrived (guards against truncated captures)
         Assert.Contains("OK from the synthetic", content);
@@ -96,9 +100,19 @@ public async Task Threads_The_Session_Id_Into_A_Byok_Session_Inference_Request()
 
         var inference = provider.InferenceRequests;
         Assert.NotEmpty(inference);
-        Assert.All(inference, r => Assert.Equal(byokSessionId, r.SessionId));
+        Assert.All(inference, r =>
+        {
+            Assert.Equal(byokSessionId, r.SessionId);
+            AssertAgentMetadata(r);
+        });
 
         // Validate the final assistant response arrived (guards against truncated captures)
         Assert.Contains("OK from the synthetic", content);
     }
+
+    private static void AssertAgentMetadata(InterceptedRequest request)
+    {
+        Assert.False(string.IsNullOrEmpty(request.AgentId));
+        Assert.False(string.IsNullOrEmpty(request.InteractionType));
+    }
 }

dotnet/test/E2E/SubagentHooksE2ETests.cs

@@ -3,24 +3,31 @@
  *--------------------------------------------------------------------------------------------*/
 
 using System.Collections.Concurrent;
+using System.Net.Http;
 using GitHub.Copilot.Test.Harness;
 using Xunit;
 using Xunit.Abstractions;
 
 namespace GitHub.Copilot.Test.E2E;
 
+#pragma warning disable GHCP001 // The LLM inference surface is intentionally experimental.
+
 public class SubagentHooksE2ETests(E2ETestFixture fixture, ITestOutputHelper output)
     : E2ETestBase(fixture, "subagent_hooks", output)
 {
     [Fact]
     public async Task Should_Invoke_PreToolUse_And_PostToolUse_Hooks_For_Sub_Agent_Tool_Calls()
     {
         var hookLog = new ConcurrentBag<(string Kind, string ToolName, string SessionId)>();
+        var requestHandler = new RecordingForwardingRequestHandler();
 
         // Create a client with the session-based subagents feature flag
         var env = new Dictionary<string, string>(Ctx.GetEnvironment());
         env["COPILOT_EXP_COPILOT_CLI_SESSION_BASED_SUBAGENTS"] = "true";
-        var client = Ctx.CreateClient(environment: env);
+        var client = Ctx.CreateClient(new CopilotClientOptions
+        {
+            RequestHandler = requestHandler
+        }, environment: env);
 
         var session = await client.CreateSessionAsync(new SessionConfig
         {
@@ -69,5 +76,42 @@ await session.SendAndWaitAsync(
 
         // input.SessionId distinguishes parent from sub-agent
         Assert.NotEqual(viewPre[0].SessionId, taskPre[0].SessionId);
+        AssertSubagentRequestMetadata(requestHandler.InferenceRequests);
+    }
+
+    private static void AssertSubagentRequestMetadata(IReadOnlyCollection<RequestRecord> records)
+    {
+        Assert.NotEmpty(records);
+        var subagentRequest = records.FirstOrDefault(r => !string.IsNullOrEmpty(r.ParentAgentId));
+        Assert.NotNull(subagentRequest);
+        Assert.False(string.IsNullOrEmpty(subagentRequest.AgentId),
+            "Sub-agent inference request should carry an agent id");
+        Assert.False(string.IsNullOrEmpty(subagentRequest.InteractionType),
+            "Sub-agent inference request should carry an interaction type");
+        Assert.NotEqual(subagentRequest.ParentAgentId, subagentRequest.AgentId);
+    }
+
+    private sealed class RecordingForwardingRequestHandler : CopilotRequestHandler
+    {
+        private readonly ConcurrentBag<RequestRecord> _records = [];
+
+        public IReadOnlyCollection<RequestRecord> InferenceRequests =>
+            [.. _records.Where(r => RecordingRequestHandler.IsInferenceUrl(r.Url))];
+
+        protected override Task<HttpResponseMessage> SendRequestAsync(HttpRequestMessage request, CopilotRequestContext ctx)
+        {
+            _records.Add(new RequestRecord(
+                request.RequestUri!.ToString(),
+                ctx.AgentId,
+                ctx.ParentAgentId,
+                ctx.InteractionType));
+            return base.SendRequestAsync(request, ctx);
+        }
     }
+
+    private sealed record RequestRecord(
+        string Url,
+        string? AgentId,
+        string? ParentAgentId,
+        string? InteractionType);
 }

go/copilot_request_handler.go

@@ -50,8 +50,11 @@ var sharedHTTPTransport = func() http.RoundTripper {
 // CopilotRequestContext is the per-request context handed to every
 // [CopilotRequestHandler] seam.
 type CopilotRequestContext struct {
-	RequestID string
-	SessionID string
+	RequestID       string
+	SessionID       string
+	AgentID         string
+	ParentAgentID   string
+	InteractionType string
 	// Transport is "http" (covering plain HTTP and SSE) or "websocket".
 	Transport string
 	Method    string
@@ -144,12 +147,12 @@ type CopilotWebSocketHandler interface {
 
 // copilotContextKey is used to attach [CopilotRequestContext] to an
 // [http.Request] so custom [http.RoundTripper] implementations can access
-// metadata (e.g. SessionID) without additional parameters.
+// metadata (e.g. SessionID and AgentID) without additional parameters.
 type copilotContextKey struct{}
 
 // RequestContextFrom returns the [CopilotRequestContext] attached to an
 // http.Request by the adapter, or nil if not present. Call this from a custom
-// [http.RoundTripper] to access metadata such as SessionID.
+// [http.RoundTripper] to access metadata such as SessionID and AgentID.
 func RequestContextFrom(r *http.Request) *CopilotRequestContext {
 	v, _ := r.Context().Value(copilotContextKey{}).(*CopilotRequestContext)
 	return v
@@ -194,7 +197,7 @@ func buildHTTPRequest(rctx *CopilotRequestContext) (*http.Request, error) {
 		return nil, err
 	}
 	// Attach rctx so custom RoundTripper implementations can read metadata
-	// (e.g. SessionID) via [RequestContextFrom].
+	// (e.g. SessionID and AgentID) via [RequestContextFrom].
 	httpReq = httpReq.WithContext(context.WithValue(httpReq.Context(), copilotContextKey{}, rctx))
 	for name, values := range rctx.Headers {
 		if isForbiddenRequestHeader(name) {
@@ -615,14 +618,17 @@ func (a *copilotRequestAdapter) HttpRequestStart(params *rpc.LlmInferenceHTTPReq
 	}
 
 	rctx := &CopilotRequestContext{
-		RequestID: params.RequestID,
-		SessionID: sessionID,
-		Method:    params.Method,
-		URL:       params.URL,
-		Headers:   headers,
-		Transport: transport,
-		body:      bodyCh,
-		Context:   ctx,
+		RequestID:       params.RequestID,
+		SessionID:       sessionID,
+		AgentID:         stringOrEmpty(params.AgentID),
+		ParentAgentID:   stringOrEmpty(params.ParentAgentID),
+		InteractionType: stringOrEmpty(params.InteractionType),
+		Method:          params.Method,
+		URL:             params.URL,
+		Headers:         headers,
+		Transport:       transport,
+		body:            bodyCh,
+		Context:         ctx,
 	}
 	sink := &responseSink{requestID: params.RequestID, adapter: a, exchange: exchange}
 	go a.runHandler(rctx, sink, exchange)
@@ -706,6 +712,13 @@ func (a *copilotRequestAdapter) removePending(requestID string) {
 	a.mu.Unlock()
 }
 
+func stringOrEmpty(value *string) string {
+	if value == nil {
+		return ""
+	}
+	return *value
+}
+
 func decodeChunkData(data string, binary bool) ([]byte, error) {
 	if binary {
 		return base64.StdEncoding.DecodeString(data)

go/internal/e2e/copilot_request_session_id_e2e_test.go

@@ -16,9 +16,12 @@ import (
 )
 
 type interceptedRequest struct {
-	url       string
-	sessionID string
-	body      string
+	url             string
+	sessionID       string
+	agentID         string
+	parentAgentID   string
+	interactionType string
+	body            string
 }
 
 // recordingTransport intercepts every model-layer request, records its URL and
@@ -32,8 +35,14 @@ type recordingTransport struct {
 func (rt *recordingTransport) RoundTrip(req *http.Request) (*http.Response, error) {
 	rctx := copilot.RequestContextFrom(req)
 	sessionID := ""
+	agentID := ""
+	parentAgentID := ""
+	interactionType := ""
 	if rctx != nil {
 		sessionID = rctx.SessionID
+		agentID = rctx.AgentID
+		parentAgentID = rctx.ParentAgentID
+		interactionType = rctx.InteractionType
 	}
 	bodyBytes := []byte(nil)
 	if req.Body != nil {
@@ -42,7 +51,14 @@ func (rt *recordingTransport) RoundTrip(req *http.Request) (*http.Response, erro
 	bodyText := string(bodyBytes)
 
 	rt.mu.Lock()
-	rt.records = append(rt.records, interceptedRequest{url: req.URL.String(), sessionID: sessionID, body: bodyText})
+	rt.records = append(rt.records, interceptedRequest{
+		url:             req.URL.String(),
+		sessionID:       sessionID,
+		agentID:         agentID,
+		parentAgentID:   parentAgentID,
+		interactionType: interactionType,
+		body:            bodyText,
+	})
 	rt.mu.Unlock()
 
 	if isInferenceURL(req.URL.String()) {
@@ -63,6 +79,16 @@ func (rt *recordingTransport) inferenceRecords() []interceptedRequest {
 	return out
 }
 
+func assertAgentMetadata(t *testing.T, r interceptedRequest) {
+	t.Helper()
+	if r.agentID == "" {
+		t.Fatal("inference request must carry an agent id")
+	}
+	if r.interactionType == "" {
+		t.Fatal("inference request must carry an interaction type")
+	}
+}
+
 func TestCopilotRequestSessionID(t *testing.T) {
 	ctx := testharness.NewTestContext(t)
 	transport := &recordingTransport{}
@@ -99,6 +125,7 @@ func TestCopilotRequestSessionID(t *testing.T) {
 			if r.sessionID != capiSessionID {
 				t.Fatalf("CAPI inference request must carry session id %q, got %q", capiSessionID, r.sessionID)
 			}
+			assertAgentMetadata(t, r)
 		}
 
 		// Validate the final assistant response arrived (guards against truncated captures)
@@ -140,6 +167,7 @@ func TestCopilotRequestSessionID(t *testing.T) {
 			if r.sessionID != byokSessionID {
 				t.Fatalf("BYOK inference request must carry session id %q, got %q", byokSessionID, r.sessionID)
 			}
+			assertAgentMetadata(t, r)
 		}
 
 		if byokSessionID == capiSessionID {