chore: Add agent engine telemetry

PiperOrigin-RevId: 765346182

src/google/adk/models/google_llm.py

@@ -18,6 +18,7 @@ from __future__ import annotations
 import contextlib
 from functools import cached_property
 import logging
+import os
 import sys
 from typing import AsyncGenerator
 from typing import cast
@@ -40,6 +41,8 @@ logger = logging.getLogger('google_adk.' + __name__)
 
 _NEW_LINE = '\n'
 _EXCLUDED_PART_FIELD = {'inline_data': {'data'}}
+_AGENT_ENGINE_TELEMETRY_TAG = 'remote_reasoning_engine'
+_AGENT_ENGINE_TELEMETRY_ENV_VARIABLE_NAME = 'GOOGLE_CLOUD_AGENT_ENGINE_ID'
 
 
 class Gemini(BaseLlm):
@@ -181,6 +184,8 @@ class Gemini(BaseLlm):
   @cached_property
   def _tracking_headers(self) -> dict[str, str]:
     framework_label = f'google-adk/{version.__version__}'
+    if os.environ.get(_AGENT_ENGINE_TELEMETRY_ENV_VARIABLE_NAME):
+      framework_label = f'{framework_label}+{_AGENT_ENGINE_TELEMETRY_TAG}'
     language_label = 'gl-python/' + sys.version.split()[0]
     version_header_value = f'{framework_label} {language_label}'
     tracking_headers = {