Fix(findrive): resolve missing negative-limit guard in search_files

[Jean-Regis-M]

Summary

Fixes #353 search_files accepted negative limit values and forwarded them directly to the database layer, triggering undefined SQL LIMIT behavior.

Root Cause

No lower-bound validation existed on the limit parameter in search_files. The raw value was passed unchecked into repo.search_files(query, limit=limit).

Solution

Added a two-line early-return guard at the top of search_files, before the db_session block, that returns a structured error response when limit < 0. Matches the existing error-return pattern used in upload_file.

if limit < 0:
    return {"error": f"limit must be non-negative, got {limit}"}

Impact

• No breaking changes
• Deterministic error response for invalid input
• Zero change to the valid-input path

Testing

pytest tests/unit/mcp/test_findrive.py::TestIntFieldEdgeCases::test_fd_int_006_search_files_negative_limit_raises -v
pytest tests/unit/mcp/test_findrive.py::test_fd_srch_001_returns_matching_files_by_filename -v

Tasks

• Root cause identified (limit forwarded to DB without validation)
• Guard added before db_session block in search_files
• Error response matches existing pattern in upload_file
• Negative limit test passes (test_fd_int_006_search_files_negative_limit_raises)
• Valid search regression test passes (test_fd_srch_001_returns_matching_files_by_filename)