fix(mcp): Ensure that stdio MCP server execution has the GEMINI_CLI=1 env variable populated.

packages/core/src/services/shellExecutionService.ts

@@ -32,6 +32,18 @@ const { Terminal } = pkg;
 
 const MAX_CHILD_PROCESS_BUFFER_SIZE = 16 * 1024 * 1024; // 16MB
 
+/**
+ * An environment variable that is set for shell executions. This can be used
+ * by downstream executables and scripts to identify that they were executed
+ * from within Gemini CLI.
+ */
+export const GEMINI_CLI_IDENTIFICATION_ENV_VAR = 'GEMINI_CLI';
+
+/**
+ * The value of {@link GEMINI_CLI_IDENTIFICATION_ENV_VAR}
+ */
+export const GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE = '1';
+
 // We want to allow shell outputs that are close to the context window in size.
 // 300,000 lines is roughly equivalent to a large context window, ensuring
 // we capture significant output from long-running commands.
@@ -302,7 +314,8 @@ export class ShellExecutionService {
         detached: !isWindows,
         env: {
           ...sanitizeEnvironment(process.env, sanitizationConfig),
-          GEMINI_CLI: '1',
+          [GEMINI_CLI_IDENTIFICATION_ENV_VAR]:
+            GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE,
           TERM: 'xterm-256color',
           PAGER: 'cat',
           GIT_PAGER: 'cat',

packages/core/src/tools/mcp-client.test.ts

@@ -1639,6 +1639,28 @@ describe('mcp-client', () => {
       });
     });
 
+    it('sets an env variable GEMINI_CLI=1 for stdio MCP servers', async () => {
+      const mockedTransport = vi
+        .spyOn(SdkClientStdioLib, 'StdioClientTransport')
+        .mockReturnValue({} as SdkClientStdioLib.StdioClientTransport);
+
+      await createTransport(
+        'test-server',
+        {
+          command: 'test-command',
+          args: ['--foo', 'bar'],
+          env: {},
+          cwd: 'test/cwd',
+        },
+        false,
+        EMPTY_CONFIG,
+      );
+
+      const callArgs = mockedTransport.mock.calls[0][0];
+      expect(callArgs.env).toBeDefined();
+      expect(callArgs.env!['GEMINI_CLI']).toBe('1');
+    });
+
     it('should exclude extension settings with undefined values from environment', async () => {
       const mockedTransport = vi
         .spyOn(SdkClientStdioLib, 'StdioClientTransport')

packages/core/src/tools/mcp-client.ts

@@ -67,6 +67,10 @@ import {
   sanitizeEnvironment,
   type EnvironmentSanitizationConfig,
 } from '../services/environmentSanitization.js';
+import {
+  GEMINI_CLI_IDENTIFICATION_ENV_VAR,
+  GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE,
+} from '../services/shellExecutionService.js';
 
 export const MCP_DEFAULT_TIMEOUT_MSEC = 10 * 60 * 1000; // default to 10 minutes
 
@@ -1897,10 +1901,11 @@ export async function createTransport(
     let transport: Transport = new StdioClientTransport({
       command: mcpServerConfig.command,
       args: mcpServerConfig.args || [],
-      // eslint-disable-next-line @typescript-eslint/no-unsafe-type-assertion
       env: {
         ...sanitizeEnvironment(process.env, sanitizationConfig),
         ...(mcpServerConfig.env || {}),
+        [GEMINI_CLI_IDENTIFICATION_ENV_VAR]:
+          GEMINI_CLI_IDENTIFICATION_ENV_VAR_VALUE,
       } as Record<string, string>,
       cwd: mcpServerConfig.cwd,
       stderr: 'pipe',