fix(mcp): check project dir exists (#8607)

Author: mbleigh

src/mcp/index.ts

@@ -21,6 +21,7 @@ import { trackGA4 } from "../track.js";
 import { Config } from "../config.js";
 import { loadRC } from "../rc.js";
 import { EmulatorHubClient } from "../emulator/hubClient.js";
+import { existsSync } from "node:fs";
 
 const SERVER_VERSION = "0.0.1";
 
@@ -185,9 +186,13 @@ export class FirebaseMcpServer {
 
     const projectId = await this.getProjectId();
     const accountEmail = await this.getAuthenticatedUser();
-    if (!this.cachedProjectRoot) {
-      return mcpError("No project root set. Please set the project root before calling tools.");
-    }
+    if (
+      tool.mcp.name !== "firebase_update_environment" && // allow this tool only, to fix the issue
+      (!this.cachedProjectRoot || !existsSync(this.cachedProjectRoot))
+    )
+      return mcpError(
+        `The current project directory '${this.cachedProjectRoot || "<NO PROJECT DIRECTORY FOUND>"}' does not exist. Please use the 'update_firebase_environment' tool to target a different project directory.`,
+      );
     if (tool.mcp._meta?.requiresAuth && !accountEmail) return mcpAuthError();
     if (tool.mcp._meta?.requiresProject && !projectId) return NO_PROJECT_ERROR;
 

src/mcp/tools/core/update_environment.ts

@@ -1,8 +1,9 @@
 import { z } from "zod";
 import { tool } from "../../tool.js";
-import { toContent } from "../../util.js";
+import { mcpError, toContent } from "../../util.js";
 import { setNewActive } from "../../../commands/use.js";
 import { assertAccount, setProjectAccount } from "../../../auth.js";
+import { existsSync } from "node:fs";
 
 export const update_environment = tool(
   {
@@ -41,6 +42,10 @@ export const update_environment = tool(
   async ({ project_dir, active_project, active_user_account }, { config, rc, host }) => {
     let output = "";
     if (project_dir) {
+      if (!existsSync(project_dir))
+        return mcpError(
+          `Cannot update project directory to '${project_dir}' as it does not exist.`,
+        );
       host.setProjectRoot(project_dir);
       output += `- Updated project directory to '${project_dir}'\n`;
     }