feat: Download the uploaded files (#31068)

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api/agent-notes/tests/unit_tests/services/test_file_service_zip_and_lookup.py.md

@@ -0,0 +1,18 @@
+## Purpose
+
+Unit tests for `api/services/file_service.py` helper methods that are not covered by higher-level controller tests.
+
+## What’s covered
+
+- `FileService.build_upload_files_zip_tempfile(...)`
+  - ZIP entry name sanitization (no directory components / traversal)
+  - name deduplication while preserving extensions
+  - writing streamed bytes from `storage.load(...)` into ZIP entries
+  - yields a tempfile path so callers can open/stream the ZIP without holding a live file handle
+- `FileService.get_upload_files_by_ids(...)`
+  - returns `{}` for empty id lists
+  - returns an id-keyed mapping for non-empty lists
+
+## Notes
+
+- These tests intentionally stub `storage.load` and `db.session.scalars(...).all()` to avoid needing a real DB/storage.