Add tests for File Search tool when stores are available

[evansenter]

Summary

The with_file_search() and with_file_search_config() builder methods exist but have no integration tests.

Current State

• with_file_search() - implemented in src/request_builder/mod.rs:1594
• with_file_search_config() - implemented in src/request_builder/mod.rs:1638
• Wire format documented in docs/ENUM_WIRE_FORMATS.md
• No tests exist

Why Blocked

File Search requires configured file search stores, which requires:

1. Creating file search stores via the API
2. Uploading files to those stores
3. Then querying them

This is different from the Files API - file search stores are a separate concept.

When to Unblock

• When we have a test harness for creating/managing file search stores
• Or when Google provides a simpler way to test file search

Action Items

• Research file search store creation process
• Add unit tests for builder methods
• Add integration test with test store (if feasible)
• Document file search setup process

[evansenter]

Audit Update (2026-03-28)

Stale References

The methods referenced in this issue were refactored in PR #382 (unified tool config API):

• with_file_search() → add_tool(FileSearchConfig::new(store_names))
• with_file_search_config() → add_tool(FileSearchConfig::new(store_names).with_top_k(k))

Already Completed

• ✅ Unit tests for builder methods — Exist in src/request_builder/tests.rs:1109-1213 (4 tests covering FileSearchConfig via add_tool)

Still Remaining

• Research file search store creation process
• Add integration test with test store (when feasible)
• Document file search setup process