refactor(assets): database layer — split queries into modules and merge migrations

- Split monolithic queries.py into modular query modules (asset, asset_reference, common, tags)
- Absorb bulk_ops.py and tags.py into query modules
- Merge migrations 0002-0005 into single migration (0002_merge_to_asset_references)
- Update models.py (merge AssetInfo/AssetCacheState into AssetReference)
- Enable SQLite foreign key enforcement
- Add comprehensive query-layer tests

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019c917d-82b5-7448-a04f-9cd59c69d0a2

tests-unit/assets_test/queries/test_asset.py

@@ -0,0 +1,144 @@
+import uuid
+
+import pytest
+from sqlalchemy.orm import Session
+
+from app.assets.helpers import get_utc_now
+from app.assets.database.models import Asset
+from app.assets.database.queries import (
+    asset_exists_by_hash,
+    get_asset_by_hash,
+    upsert_asset,
+    bulk_insert_assets,
+)
+
+
+class TestAssetExistsByHash:
+    @pytest.mark.parametrize(
+        "setup_hash,query_hash,expected",
+        [
+            (None, "nonexistent", False),  # No asset exists
+            ("blake3:abc123", "blake3:abc123", True),  # Asset exists with matching hash
+            (None, "", False),  # Null hash in DB doesn't match empty string
+        ],
+        ids=["nonexistent", "existing", "null_hash_no_match"],
+    )
+    def test_exists_by_hash(self, session: Session, setup_hash, query_hash, expected):
+        if setup_hash is not None or query_hash == "":
+            asset = Asset(hash=setup_hash, size_bytes=100)
+            session.add(asset)
+            session.commit()
+
+        assert asset_exists_by_hash(session, asset_hash=query_hash) is expected
+
+
+class TestGetAssetByHash:
+    @pytest.mark.parametrize(
+        "setup_hash,query_hash,should_find",
+        [
+            (None, "nonexistent", False),
+            ("blake3:def456", "blake3:def456", True),
+        ],
+        ids=["nonexistent", "existing"],
+    )
+    def test_get_by_hash(self, session: Session, setup_hash, query_hash, should_find):
+        if setup_hash is not None:
+            asset = Asset(hash=setup_hash, size_bytes=200, mime_type="image/png")
+            session.add(asset)
+            session.commit()
+
+        result = get_asset_by_hash(session, asset_hash=query_hash)
+        if should_find:
+            assert result is not None
+            assert result.size_bytes == 200
+            assert result.mime_type == "image/png"
+        else:
+            assert result is None
+
+
+class TestUpsertAsset:
+    @pytest.mark.parametrize(
+        "first_size,first_mime,second_size,second_mime,expect_created,expect_updated,final_size,final_mime",
+        [
+            # New asset creation
+            (None, None, 1024, "application/octet-stream", True, False, 1024, "application/octet-stream"),
+            # Existing asset, same values - no update
+            (500, "text/plain", 500, "text/plain", False, False, 500, "text/plain"),
+            # Existing asset with size 0, update with new values
+            (0, None, 2048, "image/png", False, True, 2048, "image/png"),
+            # Existing asset, second call with size 0 - no update
+            (1000, None, 0, None, False, False, 1000, None),
+        ],
+        ids=["new_asset", "existing_no_change", "update_from_zero", "zero_size_no_update"],
+    )
+    def test_upsert_scenarios(
+        self,
+        session: Session,
+        first_size,
+        first_mime,
+        second_size,
+        second_mime,
+        expect_created,
+        expect_updated,
+        final_size,
+        final_mime,
+    ):
+        asset_hash = f"blake3:test_{first_size}_{second_size}"
+
+        # First upsert (if first_size is not None, we're testing the second call)
+        if first_size is not None:
+            upsert_asset(
+                session,
+                asset_hash=asset_hash,
+                size_bytes=first_size,
+                mime_type=first_mime,
+            )
+            session.commit()
+
+        # The upsert call we're testing
+        asset, created, updated = upsert_asset(
+            session,
+            asset_hash=asset_hash,
+            size_bytes=second_size,
+            mime_type=second_mime,
+        )
+        session.commit()
+
+        assert created is expect_created
+        assert updated is expect_updated
+        assert asset.size_bytes == final_size
+        assert asset.mime_type == final_mime
+
+
+class TestBulkInsertAssets:
+    def test_inserts_multiple_assets(self, session: Session):
+        now = get_utc_now()
+        rows = [
+            {"id": str(uuid.uuid4()), "hash": "blake3:bulk1", "size_bytes": 100, "mime_type": "text/plain", "created_at": now},
+            {"id": str(uuid.uuid4()), "hash": "blake3:bulk2", "size_bytes": 200, "mime_type": "image/png", "created_at": now},
+            {"id": str(uuid.uuid4()), "hash": "blake3:bulk3", "size_bytes": 300, "mime_type": None, "created_at": now},
+        ]
+        bulk_insert_assets(session, rows)
+        session.commit()
+
+        assets = session.query(Asset).all()
+        assert len(assets) == 3
+        hashes = {a.hash for a in assets}
+        assert hashes == {"blake3:bulk1", "blake3:bulk2", "blake3:bulk3"}
+
+    def test_empty_list_is_noop(self, session: Session):
+        bulk_insert_assets(session, [])
+        session.commit()
+        assert session.query(Asset).count() == 0
+
+    def test_handles_large_batch(self, session: Session):
+        """Test chunking logic with more rows than MAX_BIND_PARAMS allows."""
+        now = get_utc_now()
+        rows = [
+            {"id": str(uuid.uuid4()), "hash": f"blake3:large{i}", "size_bytes": i, "mime_type": None, "created_at": now}
+            for i in range(200)
+        ]
+        bulk_insert_assets(session, rows)
+        session.commit()
+
+        assert session.query(Asset).count() == 200