SaveSync: push null-slot exclusion into the SQL query

Three sync callsites (endpoints/sync.py, sync_watcher.py, and both
branches of tasks/sync_push_pull_task.py) ran get_saves(...) and then
discarded archival null-slot rows in a Python list comprehension. On
libraries with many archival/web-UI uploads that's a strict waste:
those rows are pulled from MariaDB, hydrated into Save model instances,
and then immediately filtered out.

Add a slot_not_null bool kwarg to DBSavesHandler.get_saves and apply
the filter in the SQL query. Update all four callsites to use it and
drop the Python-side comprehension. Default stays False so unrelated
callers keep the current behavior.

backend/endpoints/sync.py

@@ -118,12 +118,11 @@ def negotiate_sync(
     # Build a set of server saves for this user, keyed by (rom_id, file_name).
     # Only slot-bound saves participate in sync; null-slot saves are web-UI or
     # archival uploads and act as backups (clients can opt-in to import them
-    # outside the sync flow).
-    server_saves = [
-        s
-        for s in db_save_handler.get_saves(user_id=request.user.id)
-        if s.slot is not None
-    ]
+    # outside the sync flow). Filtering in SQL avoids materializing archival
+    # rows we'd immediately discard.
+    server_saves = db_save_handler.get_saves(
+        user_id=request.user.id, slot_not_null=True
+    )
     server_save_map: dict[tuple[int, str], Save] = {}
     for save in server_saves:
         server_save_map[(save.rom_id, save.file_name)] = save

backend/handler/database/saves_handler.py

@@ -68,6 +68,7 @@ class DBSavesHandler(DBBaseHandler):
         rom_id: int | None = None,
         platform_id: int | None = None,
         slot: str | None = None,
+        slot_not_null: bool = False,
         order_by: Literal["updated_at", "created_at"] | None = None,
         order_dir: Literal["asc", "desc"] = "desc",
         only_fields: Sequence[QueryableAttribute] | None = None,
@@ -86,6 +87,9 @@ class DBSavesHandler(DBBaseHandler):
         if slot is not None:
             query = query.filter(Save.slot == slot)
 
+        if slot_not_null:
+            query = query.filter(Save.slot.is_not(None))
+
         if order_by:
             order_col = getattr(Save, order_by)
             order_fn = asc if order_dir == "asc" else desc

backend/sync_watcher.py

@@ -224,15 +224,13 @@ def _process_incoming_file(
 
     # Try to find matching saves on this platform for this user. Only
     # slot-bound saves participate in sync; null-slot saves are web-UI /
-    # archival uploads and must never be paired with a device push.
-    saves_on_platform = [
-        s
-        for s in db_save_handler.get_saves(
-            user_id=device.user_id,
-            platform_id=platform.id,
-        )
-        if s.slot is not None
-    ]
+    # archival uploads and must never be paired with a device push. Filter
+    # in SQL so archival rows never load.
+    saves_on_platform = db_save_handler.get_saves(
+        user_id=device.user_id,
+        platform_id=platform.id,
+        slot_not_null=True,
+    )
 
     matched_save = None
     for save in saves_on_platform:

backend/tasks/sync_push_pull_task.py

@@ -237,14 +237,10 @@ async def _process_remote_save(
 
     # Find matching server save. Only slot-bound saves participate in sync;
     # null-slot saves are web-UI / archival uploads and must never be paired
-    # with a device push.
-    saves = [
-        s
-        for s in db_save_handler.get_saves(
-            user_id=device.user_id, platform_id=platform.id
-        )
-        if s.slot is not None
-    ]
+    # with a device push. Filter in SQL so archival rows never load.
+    saves = db_save_handler.get_saves(
+        user_id=device.user_id, platform_id=platform.id, slot_not_null=True
+    )
     matched_save = None
     for save in saves:
         if save.file_name == remote_save.file_name:
@@ -372,13 +368,10 @@ async def _push_missing_saves(
 
         # Only slot-bound saves participate in sync; null-slot saves are
         # web-UI / archival uploads and must never be pushed to a device.
-        server_saves = [
-            s
-            for s in db_save_handler.get_saves(
-                user_id=device.user_id, platform_id=platform.id
-            )
-            if s.slot is not None
-        ]
+        # Filter in SQL so archival rows never load.
+        server_saves = db_save_handler.get_saves(
+            user_id=device.user_id, platform_id=platform.id, slot_not_null=True
+        )
 
         remote_set = remote_files.get(platform_slug, set())
         remote_dir = platform_paths.get(platform_slug, "")

backend/tests/handler/database/test_saves_handler.py

@@ -444,6 +444,127 @@ class TestDBSavesHandlerGetSaveByContentHash:
         assert result.id == created.id
 
 
+class TestDBSavesHandlerSlotNotNullFilter:
+    """Pin the slot_not_null kwarg: when true, archival/null-slot saves are
+    excluded; when false (default), they are returned alongside slot-bound
+    rows. Sync callsites use slot_not_null=True so the database does the
+    filter instead of pulling the whole table into Python."""
+
+    def test_slot_not_null_false_returns_both(self, admin_user: User, rom: Rom):
+        slot_save = Save(
+            rom_id=rom.id,
+            user_id=admin_user.id,
+            file_name="slotted.sav",
+            file_name_no_tags="slotted",
+            file_name_no_ext="slotted",
+            file_extension="sav",
+            emulator="test_emu",
+            file_path=f"{rom.platform_slug}/saves",
+            file_size_bytes=100,
+            slot="autosave",
+        )
+        archival_save = Save(
+            rom_id=rom.id,
+            user_id=admin_user.id,
+            file_name="archival.sav",
+            file_name_no_tags="archival",
+            file_name_no_ext="archival",
+            file_extension="sav",
+            emulator="test_emu",
+            file_path=f"{rom.platform_slug}/saves",
+            file_size_bytes=100,
+            slot=None,
+        )
+        db_save_handler.add_save(slot_save)
+        db_save_handler.add_save(archival_save)
+
+        saves = db_save_handler.get_saves(user_id=admin_user.id, rom_id=rom.id)
+
+        names = {s.file_name for s in saves}
+        assert "slotted.sav" in names
+        assert "archival.sav" in names
+
+    def test_slot_not_null_true_excludes_null_slot(self, admin_user: User, rom: Rom):
+        slot_save = Save(
+            rom_id=rom.id,
+            user_id=admin_user.id,
+            file_name="slotted_only.sav",
+            file_name_no_tags="slotted_only",
+            file_name_no_ext="slotted_only",
+            file_extension="sav",
+            emulator="test_emu",
+            file_path=f"{rom.platform_slug}/saves",
+            file_size_bytes=100,
+            slot="autosave",
+        )
+        archival_save = Save(
+            rom_id=rom.id,
+            user_id=admin_user.id,
+            file_name="archival_only.sav",
+            file_name_no_tags="archival_only",
+            file_name_no_ext="archival_only",
+            file_extension="sav",
+            emulator="test_emu",
+            file_path=f"{rom.platform_slug}/saves",
+            file_size_bytes=100,
+            slot=None,
+        )
+        db_save_handler.add_save(slot_save)
+        db_save_handler.add_save(archival_save)
+
+        saves = db_save_handler.get_saves(
+            user_id=admin_user.id, rom_id=rom.id, slot_not_null=True
+        )
+
+        names = {s.file_name for s in saves}
+        assert "slotted_only.sav" in names
+        assert "archival_only.sav" not in names
+        assert all(s.slot is not None for s in saves)
+
+    def test_slot_not_null_true_composes_with_slot_value(
+        self, admin_user: User, rom: Rom
+    ):
+        """slot_not_null and slot can both be set; the explicit slot filter
+        wins (and is implicitly not-null), so slot_not_null=True is a no-op
+        in that case. Pin that behavior so callers don't have to reason
+        about the interaction."""
+        db_save_handler.add_save(
+            Save(
+                rom_id=rom.id,
+                user_id=admin_user.id,
+                file_name="compose_a.sav",
+                file_name_no_tags="compose_a",
+                file_name_no_ext="compose_a",
+                file_extension="sav",
+                emulator="test_emu",
+                file_path=f"{rom.platform_slug}/saves",
+                file_size_bytes=100,
+                slot="A",
+            )
+        )
+        db_save_handler.add_save(
+            Save(
+                rom_id=rom.id,
+                user_id=admin_user.id,
+                file_name="compose_b.sav",
+                file_name_no_tags="compose_b",
+                file_name_no_ext="compose_b",
+                file_extension="sav",
+                emulator="test_emu",
+                file_path=f"{rom.platform_slug}/saves",
+                file_size_bytes=100,
+                slot="B",
+            )
+        )
+
+        saves = db_save_handler.get_saves(
+            user_id=admin_user.id, rom_id=rom.id, slot="A", slot_not_null=True
+        )
+
+        assert len(saves) == 1
+        assert saves[0].slot == "A"
+
+
 class TestDBSavesHandlerGetSavesAfterId:
     """Cover keyset pagination used by the recompute_save_content_hashes
     maintenance task. Per-page bounded reads avoid materializing the full