fix: tighten handoff routing behavior

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

sidecar/src/Eryx.AgentHost/Services/AgentInstructionComposer.cs

@@ -48,7 +48,9 @@ internal static class AgentInstructionComposer
             ? """
               You are the routing gate for this handoff workflow.
               Your job is to classify the request and hand it off to the most appropriate specialist as soon as you know who should own the substantive work.
-              Do not perform the specialist's implementation, design, or execution work yourself once a specialist is appropriate.
+              For any substantive task, your next meaningful action must be the actual handoff rather than a plain-text promise to delegate later.
+              Do not inspect files, call tools, draft the implementation, or produce the final user-facing answer yourself once a specialist is appropriate.
+              Do not claim that you handed work off unless you actually executed the handoff.
               Only answer directly if the user is asking for pure triage or a minimal clarification that must happen before delegation.
               """
             : """

sidecar/src/Eryx.AgentHost/Services/CopilotAgentBundle.cs

@@ -136,10 +136,17 @@ internal sealed class CopilotAgentBundle : IAsyncDisposable
                 continue;
             }
 
+            string handoffReason = string.Equals(
+                route.TargetAgentId,
+                topology.EntryAgentId,
+                StringComparison.Ordinal)
+                ? HandoffWorkflowGuidance.CreateReturnReason(targetDefinition)
+                : HandoffWorkflowGuidance.CreateForwardReason(targetDefinition);
+
             builder = builder.WithHandoff(
                 sourceAgent,
                 targetAgent,
-                HandoffWorkflowGuidance.CreateForwardReason(targetDefinition));
+                handoffReason);
         }
 
         return builder.Build();

sidecar/src/Eryx.AgentHost/Services/HandoffWorkflowGuidance.cs

@@ -11,6 +11,8 @@ internal static class HandoffWorkflowGuidance
                If another agent should do the substantive work, perform an actual handoff instead of answering as though the handoff already happened.
                Do not claim that you delegated unless you actually executed the handoff.
                The triage agent should route to the best specialist promptly once ownership is clear.
+               In a specialist workflow, the triage agent should hand off before inspecting files, calling tools, or drafting the substantive implementation.
+               Do not narrate a handoff in plain text without executing the handoff itself.
                Specialists should complete the substantive work after handoff and only hand control back when the task needs re-routing, broader coordination, or is outside their specialty.
                """;
     }