feat(backend): fix T4 index drift, lazy import, FK policy, expand test coverage

backend/tests/test_db_models.py

@@ -78,3 +78,80 @@ def test_create_and_query_claim_with_default_state():
         assert loaded.state == ClaimState.SUBMITTED
         assert loaded.charge_amount == Decimal("124.00")
         assert loaded.service_date_from == date(2026, 6, 1)
+
+
+def test_claim_uses_db_default_when_state_omitted():
+    """The `state` column has a DB-side DEFAULT of 'submitted' (per migration
+    and ORM `default=`). When the caller omits `state=`, the loaded value
+    must be ClaimState.SUBMITTED, not None."""
+    with db.SessionLocal()() as s:
+        s.add(Batch(
+            id="b1", kind="837p", input_filename="x",
+            parsed_at=datetime(2026, 6, 19, tzinfo=timezone.utc),
+        ))
+        c = Claim(
+            id="CLM-1",
+            batch_id="b1",
+            patient_control_number="CLM-1",
+            charge_amount=Decimal("0"),
+        )
+        s.add(c)
+        s.commit()
+
+    with db.SessionLocal()() as s:
+        loaded = s.get(Claim, "CLM-1")
+        assert loaded is not None
+        assert loaded.state == ClaimState.SUBMITTED
+
+
+def test_state_before_reversal_round_trips():
+    """`state_before_reversal` is nullable but stores a ClaimState enum.
+    Setting it to PAID must round-trip as ClaimState.PAID after commit+reload."""
+    with db.SessionLocal()() as s:
+        s.add(Batch(
+            id="b1", kind="837p", input_filename="x",
+            parsed_at=datetime(2026, 6, 19, tzinfo=timezone.utc),
+        ))
+        c = Claim(
+            id="CLM-1",
+            batch_id="b1",
+            patient_control_number="CLM-1",
+            charge_amount=Decimal("50.00"),
+            state_before_reversal=ClaimState.PAID,
+        )
+        s.add(c)
+        s.commit()
+
+    with db.SessionLocal()() as s:
+        loaded = s.get(Claim, "CLM-1")
+        assert loaded is not None
+        assert loaded.state_before_reversal == ClaimState.PAID
+
+
+def test_batch_cascade_delete_drops_claims():
+    """Deleting a Batch must cascade-delete its claims (FK is ON DELETE CASCADE
+    in migration; ORM relationship uses cascade='all, delete-orphan' which makes
+    SQLAlchemy emit the child DELETE at flush time even without
+    PRAGMA foreign_keys=ON)."""
+    with db.SessionLocal()() as s:
+        s.add(Batch(
+            id="b1", kind="837p", input_filename="x",
+            parsed_at=datetime(2026, 6, 19, tzinfo=timezone.utc),
+        ))
+        s.add(Claim(
+            id="CLM-1",
+            batch_id="b1",
+            patient_control_number="CLM-1",
+            charge_amount=Decimal("0"),
+        ))
+        s.commit()
+
+    with db.SessionLocal()() as s:
+        batch = s.get(Batch, "b1")
+        assert batch is not None
+        s.delete(batch)
+        s.commit()
+
+    with db.SessionLocal()() as s:
+        assert s.get(Batch, "b1") is None
+        assert s.get(Claim, "CLM-1") is None