[hotfix][mcp] Skip listPrompts for MCP servers without prompt support (#539)

Author: avichaym

integrations/mcp/src/main/java/org/apache/flink/agents/integrations/mcp/MCPServer.java

@@ -42,6 +42,7 @@
 import java.net.http.HttpRequest;
 import java.time.Duration;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -360,6 +361,21 @@ private void validateHttpUrl() {
         }
     }
 
+    /**
+     * Check if the MCP server supports prompts based on its declared capabilities.
+     *
+     * @return true if the server declared prompt capabilities during initialization
+     */
+    public boolean supportsPrompts() {
+        try {
+            McpSyncClient mcpClient = getClient();
+            McpSchema.ServerCapabilities caps = mcpClient.getServerCapabilities();
+            return caps != null && caps.prompts() != null;
+        } catch (Exception e) {
+            return false;
+        }
+    }
+
     /**
      * List available tools from the MCP server.
      *
@@ -456,6 +472,9 @@ public List<Object> callTool(String toolName, Map<String, Object> arguments) {
      * @return List of MCPPrompt instances
      */
     public List<MCPPrompt> listPrompts() {
+        if (!supportsPrompts()) {
+            return Collections.emptyList();
+        }
         return getRetryExecutor()
                 .execute(
                         () -> {

integrations/mcp/src/test/java/org/apache/flink/agents/integrations/mcp/MCPServerTest.java

@@ -30,6 +30,7 @@
 
 import java.time.Duration;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 import static com.fasterxml.jackson.databind.DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES;
@@ -270,4 +271,14 @@ void testCustomRetryConfiguration() {
         assertThat(server.getInitialBackoffMs()).isEqualTo(200);
         assertThat(server.getMaxBackoffMs()).isEqualTo(5000);
     }
+
+    @Test
+    @DisabledOnJre(JRE.JAVA_11)
+    @DisplayName("listPrompts returns empty list when server does not support prompts")
+    void testListPromptsReturnsEmptyWhenNotSupported() {
+        MCPServer server = MCPServer.builder(DEFAULT_ENDPOINT).build();
+
+        List<MCPPrompt> prompts = server.listPrompts();
+        assertThat(prompts).isEmpty();
+    }
 }