feat(seafile): support deleted-file sync via slim snapshot (#14499)

### What problem does this PR solve?

Incremental Seafile sync only ingests files whose modification time
falls in the poll window; documents removed in Seafile were never
removed from the knowledge base. This contributes to
[#14362](https://github.com/infiniflow/ragflow/issues/14362) (datasource
“sync deleted files” coordination).

This PR adds a **slim snapshot** (`retrieve_all_slim_docs_perm_sync`)
that enumerates current remote file IDs **without downloading content**,
using the same logical IDs as full ingest
(`seafile:{repo_id}:{file_id}`). When **`sync_deleted_files`** is
enabled on incremental runs, **`SeaFile._generate`** returns
**`(document_generator, file_list)`** so **`SyncBase`** can run
**`cleanup_stale_documents_for_task`** and remove stale KB documents.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
### What changed

- **`common/data_source/seafile_connector.py`**: `SeaFileConnector`
implements **`SlimConnectorWithPermSync`**;
**`_list_files_recursive(..., filter_by_mtime=...)`** supports full-tree
listing for snapshots; **`retrieve_all_slim_docs_perm_sync()`** reuses
the same library/root scan as ingest and applies the same **size**
ceiling; logging for snapshot start/end and counts.
- **`rag/svr/sync_data_source.py`**: **`SeaFile._generate`** validates
**`batch_size`**, captures **`end_ts`** before snapshot +
**`poll_source`**, wraps slim retrieval in **`try`/`except`** (
**`file_list = None`** on failure so ingest continues), returns
**`(generator, file_list)`**.
- **`web/src/pages/user-setting/data-source/constant/index.tsx`**:
**`syncDeletedFiles`** for Seafile in
**`DataSourceFeatureVisibilityMap`**.

common/data_source/seafile_connector.py

@@ -20,17 +20,19 @@ from common.data_source.exceptions import (
     CredentialExpiredError,
     InsufficientPermissionsError,
 )
-from common.data_source.interfaces import LoadConnector, PollConnector
+from common.data_source.interfaces import LoadConnector, PollConnector, SlimConnectorWithPermSync
 from common.data_source.models import (
     Document,
     SecondsSinceUnixEpoch,
     GenerateDocumentsOutput,
+    GenerateSlimDocumentOutput,
     SeafileSyncScope,
+    SlimDocument,
 )
 
 logger = logging.getLogger(__name__)
 
-class SeaFileConnector(LoadConnector, PollConnector):
+class SeaFileConnector(LoadConnector, PollConnector, SlimConnectorWithPermSync):
     """SeaFile connector supporting account-, library- and directory-level sync.
 
     API endpoints used:
@@ -357,8 +359,18 @@ class SeaFileConnector(LoadConnector, PollConnector):
         return self._get_repo_info_via_account(self.repo_id)
 
     @retry(tries=3, delay=1, backoff=2)
-    def _get_directory_entries(self, repo_id: str, path: str = "/") -> list[dict]:
-        """List directory contents using the appropriate endpoint."""
+    def _get_directory_entries(
+        self,
+        repo_id: str,
+        path: str = "/",
+        *,
+        raise_on_failure: bool = False,
+    ) -> list[dict]:
+        """List directory contents using the appropriate endpoint.
+
+        When ``raise_on_failure`` is True (used for slim snapshots), HTTP/API errors
+        propagate so callers do not treat a failed listing as an empty directory.
+        """
         try:
             if self._use_repo_token:
                 # GET /api/v2.1/via-repo-token/dir/?path=/foo
@@ -380,6 +392,8 @@ class SeaFileConnector(LoadConnector, PollConnector):
             logger.warning(
                 "Error fetching directory %s in repo %s: %s", path, repo_id, e,
             )
+            if raise_on_failure:
+                raise
             return []
 
     @retry(tries=3, delay=1, backoff=2)
@@ -412,9 +426,14 @@ class SeaFileConnector(LoadConnector, PollConnector):
         path: str,
         start: datetime,
         end: datetime,
+        *,
+        filter_by_mtime: bool = True,
+        strict_listing: bool = False,
     ) -> list[tuple[str, dict, dict]]:
         files = []
-        entries = self._get_directory_entries(repo_id, path)
+        entries = self._get_directory_entries(
+            repo_id, path, raise_on_failure=strict_listing,
+        )
 
         for entry in entries:
             entry_type = entry.get("type")
@@ -424,15 +443,33 @@ class SeaFileConnector(LoadConnector, PollConnector):
             if entry_type == "dir":
                 files.extend(
                     self._list_files_recursive(
-                        repo_id, repo_name, entry_path, start, end,
+                        repo_id,
+                        repo_name,
+                        entry_path,
+                        start,
+                        end,
+                        filter_by_mtime=filter_by_mtime,
+                        strict_listing=strict_listing,
                     )
                 )
             elif entry_type == "file":
                 modified = self._parse_mtime(entry.get("mtime"))
-                if start < modified <= end:
+                if filter_by_mtime:
+                    if start < modified <= end:
+                        files.append(
+                            (
+                                entry_path,
+                                entry,
+                                {"id": repo_id, "name": repo_name},
+                            )
+                        )
+                else:
                     files.append(
-                        (entry_path, entry,
-                        {"id": repo_id, "name": repo_name})
+                        (
+                            entry_path,
+                            entry,
+                            {"id": repo_id, "name": repo_name},
+                        )
                     )
 
         return files
@@ -473,6 +510,8 @@ class SeaFileConnector(LoadConnector, PollConnector):
             try:
                 files = self._list_files_recursive(
                     lib["id"], lib["name"], root, start, end,
+                    filter_by_mtime=True,
+                    strict_listing=False,
                 )
                 all_files.extend(files)
             except Exception as e:
@@ -539,4 +578,59 @@ class SeaFileConnector(LoadConnector, PollConnector):
         for batch in self._yield_seafile_documents(start_dt, end_dt):
             yield batch
 
-    
+    def retrieve_all_slim_docs_perm_sync(
+        self,
+        callback: Any = None,
+    ) -> GenerateSlimDocumentOutput:
+        """Full snapshot of file IDs eligible for indexing (no downloads).
+
+        Uses ``seafile:{repo_id}:{file_id}`` matching :meth:`_yield_seafile_documents`.
+        Listing uses strict directory reads (errors propagate) so partial snapshots
+        are never treated as authoritative for stale-document cleanup.
+        """
+        del callback
+        logger.info(
+            "Starting SeaFile slim snapshot: scope=%s url=%s",
+            self.sync_scope.value,
+            self.seafile_url,
+        )
+
+        libraries = self._resolve_libraries_to_scan()
+        all_files: list[tuple[str, dict, dict]] = []
+        for lib in libraries:
+            root = self._root_path_for_repo(lib["id"])
+            span_start = datetime(1970, 1, 1, tzinfo=timezone.utc)
+            span_end = datetime.now(timezone.utc)
+            listed = self._list_files_recursive(
+                lib["id"],
+                lib["name"],
+                root,
+                span_start,
+                span_end,
+                filter_by_mtime=False,
+                strict_listing=True,
+            )
+            all_files.extend(listed)
+
+        batch: list[SlimDocument] = []
+        total = 0
+        for file_path, file_entry, library in all_files:
+            file_size = file_entry.get("size", 0)
+            if file_size > self.size_threshold:
+                continue
+            file_id = file_entry.get("id", "")
+            repo_id = library["id"]
+            batch.append(SlimDocument(id=f"seafile:{repo_id}:{file_id}"))
+            total += 1
+            if len(batch) >= self.batch_size:
+                yield batch
+                batch = []
+
+        if batch:
+            yield batch
+
+        logger.info(
+            "Completed SeaFile slim snapshot: %d documents (listed_paths=%d)",
+            total,
+            len(all_files),
+        )