feat: handle location in DiscoveryEngineSearchTool

[ranand12]

PR Title
feat: support regional endpoints in DiscoveryEngineSearchTool

---

PR Description

1. Link to an existing issue:

• Closes: discovery engine not working for non-global endpoints (400 error) #4049

Problem:
DiscoveryEngineSearchTool was defaulting to the global Discovery Engine API endpoint. This caused failures (400 Incorrect API endpoint used. The current endpoint can only serve traffic from "global" region, but got "us" region from the API request. Please follow https://cloud.google.com/generative-ai-app-builder/docs/locations to use the correct regional API endpoint) when attempting to access Data Stores or Search Engines located in specific regions like us or eu.

Solution:
Updated the tool to dynamically detect the region from the resource ID:

1. Parses the location from data_store_id or search_engine_id (e.g., projects/.../locations/us/...).
2. Configures the SearchServiceClient with regional ClientOptions (e.g., us-discoveryengine.googleapis.com) when a
   specific region is detected.
3. Falls back to the global endpoint if no region is specified or if it is explicitly global.

Testing Plan

Unit Tests:

• I have added or updated unit tests for my change.
• All unit tests pass locally.

Summary of passed pytest results:
1 $ uv run pytest tests/unittests/tools/test_discovery_engine_search_tool.py
2 ============================= 9 passed in 3.90s ==============================
(Verified against the full suite of 3680 tests, all passed.)

Manual End-to-End (E2E) Tests:
To verify, initialize the tool using a regional Data Store ID and observe the client configuration:

1 from google.adk.tools.discovery_engine_search_tool import DiscoveryEngineSearchTool
2
3 # Regional ID
4 ds_id = "projects/my-project/locations/us/collections/default_collection/dataStores/my-ds"
5 tool = DiscoveryEngineSearchTool(data_store_id=ds_id)
6
7 # The internal client now uses the 'us-discoveryengine.googleapis.com' endpoint.

Checklist

• I have read the [CONTRIBUTING.md (https://github.com/google/adk-python/blob/main/CONTRIBUTING.md) document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context
The implementation ensures that regional Data Stores work out-of-the-box without requiring users to manually configure API endpoints, while maintaining full backward compatibility for global stores.

[google-cla]

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[gemini-code-assist]

Summary of Changes

Hello @ranand12, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the DiscoveryEngineSearchTool to intelligently handle regional Google Cloud Discovery Engine instances. Previously, the tool would default to a global API endpoint, leading to errors when interacting with regionally deployed Data Stores or Search Engines. The updated implementation automatically parses the region from resource IDs and configures the underlying client to use the correct regional API endpoint, ensuring seamless operation across different geographical deployments while maintaining compatibility with global instances.

Highlights

• Regional Endpoint Support: The DiscoveryEngineSearchTool now dynamically detects and utilizes regional API endpoints for Google Cloud Discovery Engine, resolving issues with accessing regional Data Stores or Search Engines.
• Location Extraction: The tool extracts the location (e.g., 'us', 'eu') from the data_store_id or search_engine_id provided during initialization.
• Dynamic Client Configuration: Based on the extracted location, the SearchServiceClient is configured with a specific regional API endpoint (e.g., us-discoveryengine.googleapis.com) using ClientOptions.
• Global Endpoint Fallback: The tool maintains backward compatibility by falling back to the global Discovery Engine API endpoint if no specific region is identified or if 'global' is explicitly specified.
• New Unit Test: A new unit test, test_init_with_location, has been added to verify that the SearchServiceClient is correctly initialized with the appropriate regional API endpoint.

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[adk-bot]

Response from ADK Triaging Agent

Hello @ranand12, thank you for your contribution!

Before we can merge this pull request, you'll need to sign the Contributor License Agreement (CLA). You can do so by following the instructions in the "cla/google" check at the bottom of the pull request.

Thanks!

[gemini-code-assist]

Code Review

This pull request effectively adds support for regional endpoints in DiscoveryEngineSearchTool by dynamically detecting the location from the resource ID. The change is well-implemented and includes a corresponding unit test to ensure correctness. I have one suggestion to simplify the location parsing logic for improved code clarity and maintainability.