feat(telemetry): Add extensions to StartSessionEvent telemetry (#12261)

Co-authored-by: Shnatu <snatu@google.com>

docs/cli/telemetry.md

@@ -251,6 +251,9 @@ Captures startup configuration and user prompt submissions.
     - `debug_mode` (boolean)
     - `mcp_servers` (string)
     - `mcp_servers_count` (int)
+    - `extensions` (string)
+    - `extension_ids` (string)
+    - `extension_count` (int)
     - `mcp_tools` (string, if applicable)
     - `mcp_tools_count` (int, if applicable)
     - `output_format` ("text", "json", or "stream-json")

packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts

@@ -479,6 +479,7 @@ export class ClearcutLogger {
           EventMetadataKey.GEMINI_CLI_START_SESSION_EXTENSIONS_COUNT,
         value: event.extensions_count.toString(),
       },
+      // We deliberately do not log the names of extensions here, to be safe.
       {
         gemini_cli_key: EventMetadataKey.GEMINI_CLI_START_SESSION_EXTENSION_IDS,
         value: event.extension_ids.toString(),

packages/core/src/telemetry/loggers.test.ts

@@ -92,6 +92,7 @@ import * as metrics from './metrics.js';
 import { FileOperation } from './metrics.js';
 import * as sdk from './sdk.js';
 import { vi, describe, beforeEach, it, expect, afterEach } from 'vitest';
+import { type GeminiCLIExtension } from '@google/gemini-cli-core';
 import {
   FinishReason,
   type CallableTool,
@@ -200,7 +201,11 @@ describe('loggers', () => {
         getTargetDir: () => 'target-dir',
         getProxy: () => 'http://test.proxy.com:8080',
         getOutputFormat: () => OutputFormat.JSON,
-        getExtensions: () => [],
+        getExtensions: () =>
+          [
+            { name: 'ext-one', id: 'id-one' },
+            { name: 'ext-two', id: 'id-two' },
+          ] as GeminiCLIExtension[],
       } as unknown as Config;
 
       const startSessionEvent = new StartSessionEvent(mockConfig);
@@ -229,8 +234,9 @@ describe('loggers', () => {
           mcp_tools: undefined,
           mcp_tools_count: undefined,
           output_format: 'json',
-          extension_ids: '',
+          extension_ids: 'id-one,id-two',
-          extensions_count: 0,
+          extensions_count: 2,
+          extensions: 'ext-one,ext-two',
           auth_type: 'vertex-ai',
         },
       });

packages/core/src/telemetry/types.ts

@@ -67,6 +67,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
   mcp_tools?: string;
   output_format: OutputFormat;
   extensions_count: number;
+  extensions: string;
   extension_ids: string;
   auth_type?: string;
 
@@ -102,6 +103,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
     this.output_format = config.getOutputFormat();
     const extensions = config.getExtensions();
     this.extensions_count = extensions.length;
+    this.extensions = extensions.map((e) => e.name).join(',');
     this.extension_ids = extensions.map((e) => e.id).join(',');
     this.auth_type = generatorConfig?.authType;
     if (toolRegistry) {
@@ -135,6 +137,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
       mcp_tools: this.mcp_tools,
       mcp_tools_count: this.mcp_tools_count,
       output_format: this.output_format,
+      extensions: this.extensions,
       extensions_count: this.extensions_count,
       extension_ids: this.extension_ids,
       auth_type: this.auth_type,