feat: Download the uploaded files (#31068)

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
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api/agent-notes/controllers/console/datasets/datasets_document.py.md

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+## Purpose
+
+`api/controllers/console/datasets/datasets_document.py` contains the console (authenticated) APIs for managing dataset documents (list/create/update/delete, processing controls, estimates, etc.).
+
+## Storage model (uploaded files)
+
+- For local file uploads into a knowledge base, the binary is stored via `extensions.ext_storage.storage` under the key:
+  - `upload_files/<tenant_id>/<uuid>.<ext>`
+- File metadata is stored in the `upload_files` table (`UploadFile` model), keyed by `UploadFile.id`.
+- Dataset `Document` records reference the uploaded file via:
+  - `Document.data_source_info.upload_file_id`
+
+## Download endpoint
+
+- `GET /datasets/<dataset_id>/documents/<document_id>/download`
+
+  - Only supported when `Document.data_source_type == "upload_file"`.
+  - Performs dataset permission + tenant checks via `DocumentResource.get_document(...)`.
+  - Delegates `Document -> UploadFile` validation and signed URL generation to `DocumentService.get_document_download_url(...)`.
+  - Applies `cloud_edition_billing_rate_limit_check("knowledge")` to match other KB operations.
+  - Response body is **only**: `{ "url": "<signed-url>" }`.
+
+- `POST /datasets/<dataset_id>/documents/download-zip`
+
+  - Accepts `{ "document_ids": ["..."] }` (upload-file only).
+  - Returns `application/zip` as a single attachment download.
+  - Rationale: browsers often block multiple automatic downloads; a ZIP avoids that limitation.
+  - Applies `cloud_edition_billing_rate_limit_check("knowledge")`.
+  - Delegates dataset permission checks, document/upload-file validation, and download-name generation to
+    `DocumentService.prepare_document_batch_download_zip(...)` before streaming the ZIP.
+
+## Verification plan
+
+- Upload a document from a local file into a dataset.
+- Call the download endpoint and confirm it returns a signed URL.
+- Open the URL and confirm:
+  - Response headers force download (`Content-Disposition`), and
+  - Downloaded bytes match the uploaded file.
+- Select multiple uploaded-file documents and download as ZIP; confirm all selected files exist in the archive.
+
+## Shared helper
+
+- `DocumentService.get_document_download_url(document)` resolves the `UploadFile` and signs a download URL.
+- `DocumentService.prepare_document_batch_download_zip(...)` performs dataset permission checks, batches
+  document + upload file lookups, preserves request order, and generates the client-visible ZIP filename.
+- Internal helpers now live in `DocumentService` (`_get_upload_file_id_for_upload_file_document(...)`,
+  `_get_upload_file_for_upload_file_document(...)`, `_get_upload_files_by_document_id_for_zip_download(...)`).
+- ZIP packing is handled by `FileService.build_upload_files_zip_tempfile(...)`, which also:
+  - sanitizes entry names to avoid path traversal, and
+  - deduplicates names while preserving extensions (e.g., `doc.txt` → `doc (1).txt`).
+    Streaming the response and deferring cleanup is handled by the route via `send_file(path, ...)` + `ExitStack` +
+    `response.call_on_close(...)` (the file is deleted when the response is closed).