fix: preserve handoff agent attribution

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

BACKEND_UI_CHANGES.md

@@ -61,7 +61,7 @@ The .NET sidecar emits `agent-activity` events when the workflow stream exposes
 
 In practice, `thinking` and `completed` are driven by executor lifecycle events, while `tool-calling` and `handoff` are emitted when request-info payloads expose recognizable tool-call or handoff targets.
 
-One important runtime nuance is that MAF / Copilot executor identifiers are not always the raw configured agent IDs. Real streams can emit composite values such as `Architect_agent_concurrent_architect` or generic names such as `assistant`. The sidecar therefore normalizes these runtime identifiers back to the configured pattern agents before emitting `agent-activity` events or choosing the visible author name.
+One important runtime nuance is that MAF / Copilot executor identifiers are not always the raw configured agent IDs. Real streams can emit composite values such as `Architect_agent_concurrent_architect` or generic names such as `assistant`. The sidecar therefore normalizes these runtime identifiers back to the configured pattern agents before emitting `agent-activity` events or choosing the visible author name. This is especially important in handoff flows, where the target agent can continue emitting generic `assistant` updates after control transfer; the sidecar now carries the handed-off identity forward so those updates and final messages still belong to the real target agent.
 
 ### .NET sidecar changes
 

sidecar/src/Kopaya.AgentHost/Services/AgentIdentityResolver.cs

@@ -35,6 +35,27 @@ internal static class AgentIdentityResolver
         return true;
     }
 
+    public static bool TryResolveObservedAgentIdentity(
+        PatternDefinitionDto pattern,
+        string? agentIdentifier,
+        AgentIdentity? fallbackAgent,
+        out AgentIdentity agent)
+    {
+        if (TryResolveKnownAgentIdentity(pattern, agentIdentifier, out agent))
+        {
+            return true;
+        }
+
+        if (fallbackAgent.HasValue && IsGenericAssistantIdentifier(agentIdentifier))
+        {
+            agent = fallbackAgent.Value;
+            return true;
+        }
+
+        agent = default;
+        return false;
+    }
+
     public static AgentIdentity ResolveAgentIdentity(
         PatternDefinitionDto pattern,
         string? agentId,
@@ -147,7 +168,7 @@ internal static class AgentIdentityResolver
             && normalizedCandidate.Contains(normalizedName, StringComparison.Ordinal);
     }
 
-    private static bool IsGenericAssistantIdentifier(string? candidate)
+    internal static bool IsGenericAssistantIdentifier(string? candidate)
     {
         return string.Equals(
             NormalizeComparisonKey(candidate),

sidecar/src/Kopaya.AgentHost/Services/CopilotWorkflowRunner.cs

@@ -77,6 +77,13 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
 
                 if (activity is not null)
                 {
+                    if (string.Equals(activity.ActivityType, "handoff", StringComparison.Ordinal)
+                        && !string.IsNullOrWhiteSpace(activity.AgentId)
+                        && !string.IsNullOrWhiteSpace(activity.AgentName))
+                    {
+                        activeAgent = new AgentIdentity(activity.AgentId, activity.AgentName);
+                    }
+
                     await onActivity(activity).ConfigureAwait(false);
                 }
             }
@@ -84,9 +91,10 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
             {
                 AgentIdentity? updateAgent = null;
                 string authorName = update.ExecutorId;
-                if (AgentIdentityResolver.TryResolveKnownAgentIdentity(
+                if (AgentIdentityResolver.TryResolveObservedAgentIdentity(
                     command.Pattern,
                     update.ExecutorId,
+                    activeAgent,
                     out AgentIdentity resolvedUpdateAgent))
                 {
                     updateAgent = resolvedUpdateAgent;
@@ -123,9 +131,10 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                 }).ConfigureAwait(false);
             }
             else if (evt is ExecutorCompletedEvent completed
-                && AgentIdentityResolver.TryResolveKnownAgentIdentity(
+                && AgentIdentityResolver.TryResolveObservedAgentIdentity(
                     command.Pattern,
                     completed.ExecutorId,
+                    activeAgent,
                     out AgentIdentity completedAgent))
             {
                 if (activeAgent.HasValue
@@ -141,7 +150,8 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                 completedMessages = ProjectCompletedMessages(
                     command,
                     newMessages,
-                    segments.Select(segment => (segment.MessageId, segment.AuthorName, segment.Content.ToString())).ToList());
+                    segments.Select(segment => (segment.MessageId, segment.AuthorName, segment.Content.ToString())).ToList(),
+                    activeAgent);
             }
         }
 
@@ -150,7 +160,8 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
             completedMessages = ProjectCompletedMessages(
                 command,
                 [],
-                segments.Select(segment => (segment.MessageId, segment.AuthorName, segment.Content.ToString())).ToList());
+                segments.Select(segment => (segment.MessageId, segment.AuthorName, segment.Content.ToString())).ToList(),
+                activeAgent);
         }
 
         return completedMessages;
@@ -305,26 +316,40 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
     internal static List<ChatMessageDto> ProjectCompletedMessages(
         RunTurnCommandDto command,
         IReadOnlyList<ChatMessage> newMessages,
-        IReadOnlyList<(string MessageId, string AuthorName, string Content)> segments)
+        IReadOnlyList<(string MessageId, string AuthorName, string Content)> segments,
+        AgentIdentity? fallbackAgent = null)
     {
         List<ChatMessageDto> mapped = [];
         int segmentIndex = 0;
+        int fallbackOutputIndex = 0;
 
         foreach (ChatMessage message in newMessages.Where(message => message.Role != ChatRole.User))
         {
             (string MessageId, string AuthorName, string Content)? segment =
                 segmentIndex < segments.Count ? segments[segmentIndex] : null;
-            segmentIndex++;
+            string content = message.Text ?? segment?.Content ?? string.Empty;
+            if (string.IsNullOrWhiteSpace(content))
+            {
+                continue;
+            }
+
+            if (segment.HasValue)
+            {
+                segmentIndex++;
+            }
+
+            fallbackOutputIndex++;
 
             mapped.Add(new ChatMessageDto
             {
-                Id = segment?.MessageId ?? $"{command.RequestId}-final-{segmentIndex}",
+                Id = segment?.MessageId ?? $"{command.RequestId}-final-{fallbackOutputIndex}",
                 Role = message.Role == ChatRole.System ? "system" : "assistant",
-                AuthorName = AgentIdentityResolver.ResolveDisplayAuthorName(
+                AuthorName = ResolveProjectedAuthorName(
                     command.Pattern,
                     message.AuthorName,
-                    segment?.AuthorName),
+                    segment?.AuthorName,
-                Content = message.Text ?? segment?.Content ?? string.Empty,
+                    fallbackAgent),
+                Content = content,
                 CreatedAt = DateTimeOffset.UtcNow.ToString("O"),
             });
         }
@@ -344,6 +369,23 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
         return mapped;
     }
 
+    private static string ResolveProjectedAuthorName(
+        PatternDefinitionDto pattern,
+        string? primaryIdentifier,
+        string? fallbackIdentifier,
+        AgentIdentity? fallbackAgent)
+    {
+        if (fallbackAgent.HasValue && AgentIdentityResolver.IsGenericAssistantIdentifier(primaryIdentifier))
+        {
+            return fallbackAgent.Value.AgentName;
+        }
+
+        return AgentIdentityResolver.ResolveDisplayAuthorName(
+            pattern,
+            primaryIdentifier,
+            fallbackIdentifier);
+    }
+
     private static ChatMessage ToChatMessage(ChatMessageDto message)
     {
         ChatMessage mapped = new(message.Role switch

sidecar/tests/Kopaya.AgentHost.Tests/AgentIdentityResolverTests.cs

@@ -95,6 +95,26 @@ public sealed class AgentIdentityResolverTests
         Assert.Equal("Implementer", authorName);
     }
 
+    [Fact]
+    public void TryResolveObservedAgentIdentity_UsesFallbackAgentForGenericAssistant()
+    {
+        PatternDefinitionDto pattern = CreatePattern(
+        [
+            CreateAgent(id: "agent-handoff-ux", name: "UX Specialist"),
+            CreateAgent(id: "agent-handoff-runtime", name: "Runtime Specialist"),
+        ]);
+
+        bool resolved = AgentIdentityResolver.TryResolveObservedAgentIdentity(
+            pattern,
+            "assistant",
+            new AgentIdentity("agent-handoff-ux", "UX Specialist"),
+            out AgentIdentity agent);
+
+        Assert.True(resolved);
+        Assert.Equal("agent-handoff-ux", agent.AgentId);
+        Assert.Equal("UX Specialist", agent.AgentName);
+    }
+
     private static PatternDefinitionDto CreatePattern(
         IReadOnlyList<PatternAgentDefinitionDto> agents,
         string mode = "concurrent")

sidecar/tests/Kopaya.AgentHost.Tests/CopilotWorkflowRunnerTests.cs

@@ -89,6 +89,84 @@ public sealed class CopilotWorkflowRunnerTests
         Assert.Equal("Hello", message.Content);
     }
 
+    [Fact]
+    public void ProjectCompletedMessages_UsesFallbackAgentForGenericAssistantOutput()
+    {
+        RunTurnCommandDto command = new()
+        {
+            RequestId = "turn-1",
+            SessionId = "session-1",
+            Pattern = new PatternDefinitionDto
+            {
+                Id = "pattern-handoff",
+                Name = "Handoff Support Flow",
+                Mode = "handoff",
+                Availability = "available",
+                Agents =
+                [
+                    CreateAgent(id: "agent-handoff-triage", name: "Triage"),
+                    CreateAgent(id: "agent-handoff-ux", name: "UX Specialist"),
+                ],
+            },
+        };
+
+        IReadOnlyList<ChatMessageDto> messages = CopilotWorkflowRunner.ProjectCompletedMessages(
+            command,
+            [
+                new ChatMessage(ChatRole.Assistant, "The button is in place.")
+                {
+                    AuthorName = "assistant",
+                },
+            ],
+            [],
+            new AgentIdentity("agent-handoff-ux", "UX Specialist"));
+
+        ChatMessageDto message = Assert.Single(messages);
+        Assert.Equal("UX Specialist", message.AuthorName);
+        Assert.Equal("The button is in place.", message.Content);
+    }
+
+    [Fact]
+    public void ProjectCompletedMessages_DropsBlankAssistantOutputMessages()
+    {
+        RunTurnCommandDto command = new()
+        {
+            RequestId = "turn-1",
+            SessionId = "session-1",
+            Pattern = new PatternDefinitionDto
+            {
+                Id = "pattern-handoff",
+                Name = "Handoff Support Flow",
+                Mode = "handoff",
+                Availability = "available",
+                Agents =
+                [
+                    CreateAgent(id: "agent-handoff-triage", name: "Triage"),
+                    CreateAgent(id: "agent-handoff-ux", name: "UX Specialist"),
+                ],
+            },
+        };
+
+        IReadOnlyList<ChatMessageDto> messages = CopilotWorkflowRunner.ProjectCompletedMessages(
+            command,
+            [
+                new ChatMessage(ChatRole.Assistant, string.Empty)
+                {
+                    AuthorName = "assistant",
+                },
+                new ChatMessage(ChatRole.Assistant, "Real content")
+                {
+                    AuthorName = "assistant",
+                },
+            ],
+            [],
+            new AgentIdentity("agent-handoff-ux", "UX Specialist"));
+
+        ChatMessageDto message = Assert.Single(messages);
+        Assert.Equal("UX Specialist", message.AuthorName);
+        Assert.Equal("Real content", message.Content);
+    }
+
     private static PatternAgentDefinitionDto CreateAgent(string id, string name)
     {
         return new PatternAgentDefinitionDto