feat: enable capability-based routing in HandoffTool

The LLM can now delegate tasks by capability instead of requiring a
specific agent_id. The handoff tool resolves the first matching agent
via FindAgentsByCapability.

- HandoffTool.Execute: accept "capability" as alternative to "agent_id"
- HandoffTool.Description: display agent capabilities in tool listing
- HandoffTool.Parameters: "task" is the only required field now
- 4 new tests (route by capability, not found, no target, description)

pkg/multiagent/handoff_test.go

@@ -192,6 +192,73 @@ func TestHandoffTool_Description(t *testing.T) {
 	}
 }
 
+func TestHandoffTool_Description_WithCapabilities(t *testing.T) {
+	resolver := newMockResolver(
+		&AgentInfo{ID: "main", Name: "Main"},
+		&AgentInfo{ID: "coder", Name: "Coder", Role: "coding", Capabilities: []string{"coding", "review"}},
+	)
+	bb := NewBlackboard()
+	tool := NewHandoffTool(resolver, bb, "main")
+
+	desc := tool.Description()
+	if !strings.Contains(desc, "coding, review") {
+		t.Errorf("Description = %q, expected capabilities", desc)
+	}
+}
+
+func TestHandoffTool_ExecuteByCapability(t *testing.T) {
+	provider := &mockProvider{response: "capability result"}
+	resolver := newMockResolver(
+		&AgentInfo{ID: "main", Name: "Main", Provider: provider, Tools: tools.NewToolRegistry(), MaxIter: 5},
+		&AgentInfo{ID: "coder", Name: "Coder", Capabilities: []string{"coding"}, Provider: provider, Tools: tools.NewToolRegistry(), MaxIter: 5},
+	)
+	bb := NewBlackboard()
+	tool := NewHandoffTool(resolver, bb, "main")
+
+	result := tool.Execute(context.Background(), map[string]any{
+		"capability": "coding",
+		"task":       "write a function",
+	})
+
+	if result.IsError {
+		t.Fatalf("handoff by capability failed: %s", result.ForLLM)
+	}
+	if !strings.Contains(result.ForLLM, "capability result") {
+		t.Errorf("ForLLM = %q, expected 'capability result'", result.ForLLM)
+	}
+}
+
+func TestHandoffTool_ExecuteByCapability_NotFound(t *testing.T) {
+	resolver := newMockResolver(
+		&AgentInfo{ID: "main", Name: "Main"},
+	)
+	bb := NewBlackboard()
+	tool := NewHandoffTool(resolver, bb, "main")
+
+	result := tool.Execute(context.Background(), map[string]any{
+		"capability": "nonexistent",
+		"task":       "do something",
+	})
+
+	if !result.IsError {
+		t.Error("expected error for unknown capability")
+	}
+}
+
+func TestHandoffTool_ExecuteNoAgentNoCapability(t *testing.T) {
+	resolver := newMockResolver()
+	bb := NewBlackboard()
+	tool := NewHandoffTool(resolver, bb, "main")
+
+	result := tool.Execute(context.Background(), map[string]any{
+		"task": "do something",
+	})
+
+	if !result.IsError {
+		t.Error("expected error when neither agent_id nor capability provided")
+	}
+}
+
 func TestListAgentsTool_Execute(t *testing.T) {
 	resolver := newMockResolver(
 		&AgentInfo{ID: "main", Name: "Main Agent", Role: "general"},

pkg/multiagent/handoff_tool.go

@@ -51,6 +51,9 @@ func (t *HandoffTool) Description() string {
 		if a.Role != "" {
 			fmt.Fprintf(&sb, ": %s", a.Role)
 		}
+		if len(a.Capabilities) > 0 {
+			fmt.Fprintf(&sb, " [%s]", strings.Join(a.Capabilities, ", "))
+		}
 		sb.WriteString("\n")
 	}
 	return sb.String()
@@ -63,7 +66,11 @@ func (t *HandoffTool) Parameters() map[string]any {
 		"properties": map[string]any{
 			"agent_id": map[string]any{
 				"type":        "string",
-				"description": "The ID of the target agent to hand off to",
+				"description": "The ID of the target agent to hand off to (required if capability is not set)",
+			},
+			"capability": map[string]any{
+				"type":        "string",
+				"description": "Route to an agent with this capability instead of by ID (e.g. \"coding\", \"research\")",
 			},
 			"task": map[string]any{
 				"type":        "string",
@@ -74,7 +81,7 @@ func (t *HandoffTool) Parameters() map[string]any {
 				"description": "Optional key-value context to share via blackboard before handoff",
 			},
 		},
-		"required": []string{"agent_id", "task"},
+		"required": []string{"task"},
 	}
 }
 
@@ -86,22 +93,26 @@ func (t *HandoffTool) SetContext(channel, chatID string) {
 
 // Execute delegates a task to the specified target agent.
 func (t *HandoffTool) Execute(ctx context.Context, args map[string]any) *tools.ToolResult {
-	agentID, ok := args["agent_id"].(string)
-	if !ok {
-		agentID = ""
-	}
-	task, ok := args["task"].(string)
-	if !ok {
-		task = ""
-	}
+	agentID, _ := args["agent_id"].(string)
+	capability, _ := args["capability"].(string)
+	task, _ := args["task"].(string)
 
-	if agentID == "" {
-		return tools.ErrorResult("agent_id is required")
-	}
 	if task == "" {
 		return tools.ErrorResult("task is required")
 	}
 
+	// Resolve agent: by ID or by capability
+	if agentID == "" && capability != "" {
+		matches := FindAgentsByCapability(t.resolver, capability)
+		if len(matches) == 0 {
+			return tools.ErrorResult(fmt.Sprintf("no agent found with capability %q", capability))
+		}
+		agentID = matches[0].ID
+	}
+	if agentID == "" {
+		return tools.ErrorResult("agent_id or capability is required")
+	}
+
 	// Parse optional context map
 	var contextMap map[string]string
 	if ctxRaw, ok := args["context"].(map[string]any); ok {