fix(mcp): emit properties:{} in list_agents inputSchema (#1889)

go/core/internal/mcp/mcp_handler.go

@@ -8,6 +8,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/google/jsonschema-go/jsonschema"
 	"github.com/kagent-dev/kagent/go/api/v1alpha2"
 	"github.com/kagent-dev/kagent/go/core/internal/a2a"
 	authimpl "github.com/kagent-dev/kagent/go/core/internal/httpserver/auth"
@@ -81,12 +82,21 @@ func NewMCPHandler(kubeClient client.Client, a2aBaseURL string, authenticator au
 	server := mcpsdk.NewServer(impl, nil)
 	handler.server = server
 
-	// Add list_agents tool
+	// Add list_agents tool.
+	// InputSchema is set explicitly (rather than reflected from the empty
+	// ListAgentsInput struct) so the serialized schema includes "properties": {}.
+	// OpenAI strict mode rejects object schemas without a properties key.
+	// See https://github.com/kagent-dev/kagent/issues/1889.
 	mcpsdk.AddTool[ListAgentsInput, ListAgentsOutput](
 		server,
 		&mcpsdk.Tool{
 			Name:        "list_agents",
 			Description: "List invokable kagent agents (accepted + deploymentReady)",
+			InputSchema: &jsonschema.Schema{
+				Type:                 "object",
+				Properties:           map[string]*jsonschema.Schema{},
+				AdditionalProperties: &jsonschema.Schema{Not: &jsonschema.Schema{}},
+			},
 		},
 		handler.handleListAgents,
 	)

go/core/internal/mcp/mcp_handler_test.go

@@ -0,0 +1,76 @@
+package mcp
+
+import (
+	"context"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/kagent-dev/kagent/go/api/v1alpha2"
+	mcpsdk "github.com/modelcontextprotocol/go-sdk/mcp"
+	"github.com/stretchr/testify/require"
+	"k8s.io/apimachinery/pkg/runtime"
+	"sigs.k8s.io/controller-runtime/pkg/client/fake"
+)
+
+// TestListAgentsInputSchemaHasProperties asserts that the list_agents tool
+// advertises an inputSchema containing an explicit "properties" key, even
+// though it accepts no arguments. OpenAI strict mode requires this.
+// Regression test for https://github.com/kagent-dev/kagent/issues/1889.
+func TestListAgentsInputSchemaHasProperties(t *testing.T) {
+	scheme := runtime.NewScheme()
+	require.NoError(t, v1alpha2.AddToScheme(scheme))
+	kubeClient := fake.NewClientBuilder().WithScheme(scheme).Build()
+
+	h, err := NewMCPHandler(kubeClient, "http://unused", nil, time.Minute)
+	require.NoError(t, err)
+
+	clientTransport, serverTransport := mcpsdk.NewInMemoryTransports()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+
+	// Run the server in a goroutine; it returns when the transport closes.
+	serverDone := make(chan error, 1)
+	go func() {
+		serverDone <- h.server.Run(ctx, serverTransport)
+	}()
+	// Registered first so it runs last (LIFO): after session.Close below has
+	// disconnected the client, cancel the context and drain the server's
+	// return value so the goroutine cannot leak and unexpected errors surface.
+	t.Cleanup(func() {
+		cancel()
+		if err := <-serverDone; err != nil && err != context.Canceled {
+			t.Errorf("MCP server returned unexpected error: %v", err)
+		}
+	})
+
+	client := mcpsdk.NewClient(&mcpsdk.Implementation{Name: "test", Version: "0.0.0"}, nil)
+	session, err := client.Connect(ctx, clientTransport, nil)
+	require.NoError(t, err)
+	t.Cleanup(func() { session.Close() })
+
+	tools, err := session.ListTools(ctx, &mcpsdk.ListToolsParams{})
+	require.NoError(t, err)
+
+	var listAgents *mcpsdk.Tool
+	for i := range tools.Tools {
+		if tools.Tools[i].Name == "list_agents" {
+			listAgents = tools.Tools[i]
+			break
+		}
+	}
+	require.NotNil(t, listAgents, "list_agents tool not registered")
+
+	raw, err := json.Marshal(listAgents.InputSchema)
+	require.NoError(t, err)
+
+	var schema map[string]any
+	require.NoError(t, json.Unmarshal(raw, &schema))
+
+	require.Equal(t, "object", schema["type"], "inputSchema type must be object")
+	props, ok := schema["properties"]
+	require.True(t, ok, "inputSchema must include a properties key (got %s)", string(raw))
+	require.IsType(t, map[string]any{}, props, "properties must be a JSON object")
+	require.Empty(t, props, "list_agents takes no args, properties should be empty")
+	require.Equal(t, false, schema["additionalProperties"], "additionalProperties must remain false")
+}