@@ -388,7 +388,7 @@ func (client *Client) readLoop() {
 		// A message with a Method is a server-initiated request or notification.
 		// It must never be routed as a response to a pending client request.
 		if message.Method != "" {
-			if message.ID != nil {
+			if message.ID != nil && jsonRPCIDEchoable(message.ID) {
 				// Send the courtesy -32601 reply asynchronously off the read loop so
 				// an undrained server stdin pipe never stalls readLoop or holds client.mu.
 				id := message.ID
@@ -493,6 +493,27 @@ func rpcIDMatches(value any, id int) bool {
 	}
 }
 
+// jsonRPCIDEchoable reports whether id is a valid JSON-RPC 2.0 identifier type
+// (string, integer, or float with no fractional part) that is safe to echo back.
+func jsonRPCIDEchoable(id any) bool {
+	if id == nil {
+		return false
+	}
+	switch v := id.(type) {
+	case string:
+		return true
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64:
+		return true
+	case float64:
+		return v == float64(int64(v))
+	case json.Number:
+		_, err := v.Int64()
+		return err == nil
+	default:
+		return false
+	}
+}
+
 func (client *Client) notify(method string, params any) error {
 	rawParams, err := json.Marshal(params)
 	if err != nil {
 
@@ -949,3 +949,41 @@ func TestStdioClientUndrainedServerDoesNotStallReadLoop(t *testing.T) {
 		t.Fatal("readLoop stalled on undrained error write; pending response was not delivered")
 	}
 }
+
+func TestStdioClientDropsInvalidServerRequestIDs(t *testing.T) {
+	inReader, inWriter := io.Pipe()
+	outReader, outWriter := io.Pipe()
+
+	client := &Client{
+		reader:  newMessageReader(inReader),
+		writer:  newMessageWriter(outWriter),
+		pending: make(map[int]chan dispatchResult),
+	}
+	defer func() {
+		_ = inWriter.Close()
+		_ = outReader.Close()
+	}()
+
+	client.ensureReader()
+
+	// Server sends request with boolean ID (invalid JSON-RPC id)
+	serverReq := `{"jsonrpc":"2.0","id":true,"method":"roots/list","params":{}}` + "\n"
+	go func() {
+		_, _ = inWriter.Write([]byte(serverReq))
+	}()
+
+	// Read should not produce any output response for invalid ID
+	buf := make([]byte, 1024)
+	readChan := make(chan int, 1)
+	go func() {
+		n, _ := outReader.Read(buf)
+		readChan <- n
+	}()
+
+	select {
+	case n := <-readChan:
+		t.Fatalf("unexpected reply for invalid ID: %s", string(buf[:n]))
+	case <-time.After(100 * time.Millisecond):
+		// Expected: dropped cleanly
+	}
+}