fix: enforce handoff delegation roles

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

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

@@ -0,0 +1,35 @@
+using Kopaya.AgentHost.Contracts;
+
+namespace Kopaya.AgentHost.Services;
+
+internal static class AgentInstructionComposer
+{
+    public static string Compose(
+        PatternDefinitionDto pattern,
+        PatternAgentDefinitionDto agent,
+        int agentIndex)
+    {
+        string baseInstructions = agent.Instructions.Trim();
+        if (!string.Equals(pattern.Mode, "handoff", StringComparison.OrdinalIgnoreCase))
+        {
+            return baseInstructions;
+        }
+
+        string runtimeGuidance = agentIndex == 0
+            ? """
+              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.
+              Only answer directly if the user is asking for pure triage or a minimal clarification that must happen before delegation.
+              """
+            : """
+              You are a specialist participating in a handoff workflow.
+              Once the triage agent hands work to you, you own the substantive answer within your specialty and should carry it through.
+              Do not push the actual work back to triage unless you are blocked or the request is clearly outside your specialty.
+              """;
+
+        return string.IsNullOrWhiteSpace(baseInstructions)
+            ? runtimeGuidance
+            : $"{baseInstructions}\n\n{runtimeGuidance}";
+    }
+}

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

@@ -438,7 +438,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
             List<AIAgent> agents = [];
             CopilotClientOptions clientOptions = CopilotCliPathResolver.CreateClientOptions();
 
-            foreach (PatternAgentDefinitionDto definition in pattern.Agents)
+            foreach ((PatternAgentDefinitionDto definition, int agentIndex) in pattern.Agents.Select((definition, index) => (definition, index)))
             {
                 CopilotClient client = new(clientOptions);
                 await client.StartAsync(cancellationToken).ConfigureAwait(false);
@@ -449,7 +449,7 @@ public sealed class CopilotWorkflowRunner : ITurnWorkflowRunner
                     ReasoningEffort = definition.ReasoningEffort,
                     SystemMessage = new SystemMessageConfig
                     {
-                        Content = definition.Instructions,
+                        Content = AgentInstructionComposer.Compose(pattern, definition, agentIndex),
                     },
                     WorkingDirectory = projectPath,
                     OnPermissionRequest = ApprovePermissionAsync,