fix: allow session to be used while half-open (#34)

Author: ggoodman

internal/engine/engine.go

@@ -264,12 +264,6 @@ func (e *Engine) InitializeSession(ctx context.Context, userID string, req *mcp.
 }
 
 func (e *Engine) HandleRequest(ctx context.Context, sess *SessionHandle, req *jsonrpc.Request) (*jsonrpc.Response, error) {
-	// Require session to be open before serving requests (except initialize, which
-	// doesn't reach here).
-	if st := sess.State(); st != "" && st != sessions.SessionStateOpen {
-		return jsonrpc.NewErrorResponse(req.ID, jsonrpc.ErrorCodeInvalidRequest, "session not initialized", nil), nil
-	}
-
 	switch req.Method {
 	case string(mcp.ToolsListMethod):
 		return e.handleToolsList(ctx, sess, req)

stdio/handler_test.go

@@ -338,17 +338,17 @@ func TestTools_ListAndCall(t *testing.T) {
 	}
 }
 
-// Handshake gating: requests must fail until client sends notifications/initialized.
-func TestHandshake_PendingRejectsRequests(t *testing.T) {
+// Half-open sessions: requests are now allowed (no gating InvalidRequest error) before client sends notifications/initialized.
+func TestHandshake_PreInitializedRequestsAllowed(t *testing.T) {
 	srv := mcpservice.NewServer(
 		mcpservice.WithToolsCapability(mcpservice.NewToolsContainer()),
 	)
 	th := newHarness(t, srv)
 
-	// Initialize session
+	// Initialize session (server responds) but do NOT send notifications/initialized yet.
 	_ = th.initialize(t, "init-1", defaultInitializeRequest())
 
-	// Immediately send a ping request before initialized; expect InvalidRequest error
+	// Send a ping request before initialized; it should NOT fail with "session not initialized".
 	ping := &jsonrpc.Request{JSONRPCVersion: jsonrpc.ProtocolVersion, Method: string(mcp.PingMethod), ID: jsonrpc.NewRequestID("1")}
 	if err := th.send(ping); err != nil {
 		t.Fatal(err)
@@ -357,8 +357,8 @@ func TestHandshake_PendingRejectsRequests(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	if res.Error == nil || res.Error.Code != jsonrpc.ErrorCodeInvalidRequest {
-		t.Fatalf("expected invalid request error before initialized, got: %+v", res.Error)
+	if res.Error != nil && res.Error.Message == "session not initialized" {
+		t.Fatalf("did not expect gating error before initialized: %+v", res.Error)
 	}
 }