Add support for running available commands prior to MCP servers loading (#15596)

packages/cli/src/ui/hooks/slashCommandProcessor.ts

@@ -28,6 +28,9 @@ import {
   ToolConfirmationOutcome,
   Storage,
   IdeClient,
+  addMCPStatusChangeListener,
+  removeMCPStatusChangeListener,
+  MCPDiscoveryState,
 } from '@google/gemini-cli-core';
 import { useSessionStats } from '../contexts/SessionContext.js';
 import type {
@@ -269,6 +272,10 @@ export const useSlashCommandProcessor = (
       ideClient.addStatusChangeListener(listener);
     })();
 
+    // Listen for MCP server status changes (e.g. connection, discovery completion)
+    // to reload slash commands (since they may include MCP prompts).
+    addMCPStatusChangeListener(listener);
+
     // TODO: Ideally this would happen more directly inside the ExtensionLoader,
     // but the CommandService today is not conducive to that since it isn't a
     // long lived service but instead gets fully re-created based on reload
@@ -289,6 +296,7 @@ export const useSlashCommandProcessor = (
         const ideClient = await IdeClient.getInstance();
         ideClient.removeStatusChangeListener(listener);
       })();
+      removeMCPStatusChangeListener(listener);
       appEvents.off('extensionsStarting', extensionEventListener);
       appEvents.off('extensionsStopping', extensionEventListener);
     };
@@ -572,9 +580,16 @@ export const useSlashCommandProcessor = (
           }
         }
 
+        const isMcpLoading =
+          config?.getMcpClientManager()?.getDiscoveryState() ===
+          MCPDiscoveryState.IN_PROGRESS;
+        const errorMessage = isMcpLoading
+          ? `Unknown command: ${trimmed}. Command might have been from an MCP server but MCP servers are not done loading.`
+          : `Unknown command: ${trimmed}`;
+
         addMessage({
           type: MessageType.ERROR,
-          content: `Unknown command: ${trimmed}`,
+          content: errorMessage,
           timestamp: new Date(),
         });