update(telemetry): OTel API response event with finish reasons (#13849)

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

docs/cli/telemetry.md

@@ -361,6 +361,7 @@ Captures Gemini API requests, responses, and errors.
     - `response_text` (string, optional)
     - `prompt_id` (string)
     - `auth_type` (string)
+    - `finish_reasons` (array of strings)
 
 - `gemini_cli.api_error`: API request failed.
   - **Attributes**:

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

@@ -409,6 +409,7 @@ describe('loggers', () => {
         attributes: expect.objectContaining({
           'event.name': EVENT_API_RESPONSE,
           prompt_id: 'prompt-id-1',
+          finish_reasons: ['stop'],
         }),
       });
 

packages/core/src/telemetry/types.ts

@@ -31,6 +31,7 @@ import type { AgentTerminateMode } from '../agents/types.js';
 import { getCommonAttributes } from './telemetryAttributes.js';
 import { SemanticAttributes } from '@opentelemetry/semantic-conventions';
 import { safeJsonStringify } from '../utils/safeJsonStringify.js';
+import type { OTelFinishReason } from './semantic.js';
 import {
   toInputMessages,
   toOutputMessages,
@@ -545,6 +546,7 @@ export class ApiResponseEvent implements BaseTelemetryEvent {
   prompt: GenAIPromptDetails;
   response: GenAIResponseDetails;
   usage: GenAIUsageDetails;
+  finish_reasons: OTelFinishReason[];
 
   constructor(
     model: string,
@@ -573,6 +575,7 @@ export class ApiResponseEvent implements BaseTelemetryEvent {
       tool_token_count: usage_data?.toolUsePromptTokenCount ?? 0,
       total_token_count: usage_data?.totalTokenCount ?? 0,
     };
+    this.finish_reasons = toFinishReasons(this.response.candidates);
   }
 
   toLogRecord(config: Config): LogRecord {
@@ -591,6 +594,7 @@ export class ApiResponseEvent implements BaseTelemetryEvent {
       prompt_id: this.prompt.prompt_id,
       auth_type: this.auth_type,
       status_code: this.status_code,
+      finish_reasons: this.finish_reasons,
     };
     if (this.response_text) {
       attributes['response_text'] = this.response_text;
@@ -613,9 +617,7 @@ export class ApiResponseEvent implements BaseTelemetryEvent {
       'event.name': EVENT_GEN_AI_OPERATION_DETAILS,
       'event.timestamp': this['event.timestamp'],
       'gen_ai.response.id': this.response.response_id,
-      'gen_ai.response.finish_reasons': toFinishReasons(
-        this.response.candidates,
-      ),
+      'gen_ai.response.finish_reasons': this.finish_reasons,
       'gen_ai.output.messages': JSON.stringify(
         toOutputMessages(this.response.candidates),
       ),