fix: make discussion answering model configurable

Merge #6113

## Summary
- Configure the discussion answering agents through `LLM_MODEL_NAME` instead of
hardcoding `gemini-3.5-flash`.
- Let the GitHub workflow override both the answering model and Vertex location
with repository variables.
- Downgrade the default model from `gemini-3.5-flash` to `gemini-2.5-flash` because
`gemini-3.5-flash` 404s on Vertex AI Search (#6104).
- Document the new knobs.

Fixes #6104

## Testing
- `git diff --check`
- `python3.12 -m py_compile contributing/samples/adk_team/adk_answering_agent/settings.py contributing/samples/adk_team/adk_answering_agent/agent.py contributing/samples/adk_team/adk_answering_agent/gemini_assistant/agent.py`

Co-authored-by: Kathy Wu <wukathy@google.com>
COPYBARA_INTEGRATE_REVIEW=#6113 from Haihan-Jiang:codex/adk-python-answering-model-config aea24ea
PiperOrigin-RevId: 947224603

Author: 2 people

.github/workflows/discussion_answering.yml

@@ -57,10 +57,11 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.ADK_TRIAGE_AGENT }}
           ADK_GCP_SA_KEY: ${{ secrets.ADK_GCP_SA_KEY }}
           GOOGLE_CLOUD_PROJECT: ${{ secrets.GOOGLE_CLOUD_PROJECT }}
-          GOOGLE_CLOUD_LOCATION: ${{ secrets.GOOGLE_CLOUD_LOCATION }}
+          GOOGLE_CLOUD_LOCATION: ${{ vars.ADK_ANSWERING_LOCATION || secrets.GOOGLE_CLOUD_LOCATION }}
           VERTEXAI_DATASTORE_ID: ${{ secrets.VERTEXAI_DATASTORE_ID }}
           GEMINI_API_DATASTORE_ID: ${{ secrets.GEMINI_API_DATASTORE_ID }}
           GOOGLE_GENAI_USE_VERTEXAI: 1
+          LLM_MODEL_NAME: ${{ vars.ADK_ANSWERING_MODEL || 'gemini-2.5-flash' }}
           OWNER: 'google'
           REPO: 'adk-python'
           INTERACTIVE: 0

contributing/samples/adk_team/adk_answering_agent/README.md

@@ -114,6 +114,7 @@ The following environment variables are required for the agent to connect to the
 - `GOOGLE_CLOUD_PROJECT=YOUR_PROJECT_ID`: **(Required)** The Google Cloud project ID.
 - `GOOGLE_CLOUD_LOCATION=LOCATION`: **(Required)** The Google Cloud region.
 - `VERTEXAI_DATASTORE_ID=YOUR_DATASTORE_ID`: **(Required)** The full Vertex AI datastore ID for the document store (i.e. knowledge base), with the format of `projects/{project_number}/locations/{location}/collections/{collection}/dataStores/{datastore_id}`.
+- `LLM_MODEL_NAME`: The Gemini model used by the answering agent. Defaults to `gemini-2.5-flash`.
 - `OWNER`: The GitHub organization or username that owns the repository (e.g., `google`). Needed for both modes.
 - `REPO`: The name of the GitHub repository (e.g., `adk-python`). Needed for both modes.
 - `INTERACTIVE`: Controls the agent's interaction mode. For the automated workflow, this is set to `0`. For interactive mode, it should be set to `1` or left unset.
@@ -124,4 +125,9 @@ The following environment variables are required to upload the docs to update th
 - `ADK_DOCS_ROOT_PATH=YOUR_ADK_DOCS_ROOT_PATH`: **(Required)** Path to the root of the downloaded adk-docs repo.
 - `ADK_PYTHON_ROOT_PATH=YOUR_ADK_PYTHON_ROOT_PATH`: **(Required)** Path to the root of the downloaded adk-python repo.
 
-For local execution in interactive mode, you can place these variables in a `.env` file in the project's root directory. For the GitHub workflow, they should be configured as repository secrets.
+For local execution in interactive mode, you can place these variables in a
+`.env` file in the project's root directory. For the GitHub workflow, required
+credentials should be configured as repository secrets. The workflow also
+supports the optional repository variables `ADK_ANSWERING_MODEL` and
+`ADK_ANSWERING_LOCATION` to override the default model and location without
+changing the workflow file.

contributing/samples/adk_team/adk_answering_agent/agent.py

@@ -15,6 +15,7 @@
 from adk_answering_agent.gemini_assistant.agent import root_agent as gemini_assistant_agent
 from adk_answering_agent.settings import BOT_RESPONSE_LABEL
 from adk_answering_agent.settings import IS_INTERACTIVE
+from adk_answering_agent.settings import LLM_MODEL_NAME
 from adk_answering_agent.settings import OWNER
 from adk_answering_agent.settings import REPO
 from adk_answering_agent.settings import VERTEXAI_DATASTORE_ID
@@ -38,7 +39,7 @@
 
 
 root_agent = Agent(
-    model="gemini-3.5-flash",
+    model=LLM_MODEL_NAME,
     name="adk_answering_agent",
     description="Answer questions about ADK repo.",
     instruction=f"""

contributing/samples/adk_team/adk_answering_agent/gemini_assistant/agent.py

@@ -19,6 +19,7 @@
 
 from adk_answering_agent.settings import ADK_GCP_SA_KEY
 from adk_answering_agent.settings import GEMINI_API_DATASTORE_ID
+from adk_answering_agent.settings import LLM_MODEL_NAME
 from adk_answering_agent.utils import error_response
 from google.adk.agents.llm_agent import Agent
 from google.api_core.exceptions import GoogleAPICallError
@@ -72,7 +73,7 @@ def search_gemini_api_docs(queries: List[str]) -> Dict[str, Any]:
 
 
 root_agent = Agent(
-    model="gemini-3.5-flash",
+    model=LLM_MODEL_NAME,
     name="gemini_assistant",
     description="Answer questions about Gemini API.",
     instruction="""

contributing/samples/adk_team/adk_answering_agent/settings.py

@@ -41,5 +41,7 @@
 REPO = os.getenv("REPO", "adk-python")
 BOT_RESPONSE_LABEL = os.getenv("BOT_RESPONSE_LABEL", "bot responded")
 DISCUSSION_NUMBER = os.getenv("DISCUSSION_NUMBER")
+DEFAULT_LLM_MODEL_NAME = "gemini-2.5-flash"
+LLM_MODEL_NAME = os.getenv("LLM_MODEL_NAME", DEFAULT_LLM_MODEL_NAME)
 
 IS_INTERACTIVE = os.getenv("INTERACTIVE", "1").lower() in ["true", "1"]