fix(tests): isolate database and module state

tests/helpers/database.py

@@ -0,0 +1,51 @@
+"""Disposable databases for tests that exercise the real ORM and session manager."""
+
+from contextlib import contextmanager
+from tempfile import TemporaryDirectory
+
+import pytest
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import NullPool
+
+
+@contextmanager
+def disposable_database(tmp_path):
+    """Own the database file and engine; keep the canonical ORM classes intact."""
+    import core.database as database
+
+    with TemporaryDirectory(prefix="database-", dir=tmp_path) as directory:
+        engine = create_engine(
+            f"sqlite:///{directory}/test.db",
+            connect_args={"check_same_thread": False},
+            poolclass=NullPool,
+        )
+        try:
+            database.Base.metadata.create_all(engine)
+            yield sessionmaker(bind=engine, autoflush=False, autocommit=False)
+        finally:
+            engine.dispose()
+
+
+@contextmanager
+def isolated_session_database(tmp_path):
+    """Temporarily bind the real manager and database aliases without reloading.
+
+    Reloading core.database changes its ORM classes while existing imports keep
+    the old classes and factories. Patch only resource bindings instead, and
+    undo them before disposing the owned engine and removing its files.
+    """
+    import core.database as database
+    import core.session_manager as manager
+    import src.database as compatibility_database
+
+    with disposable_database(tmp_path) as factory:
+        engine = factory.kw["bind"]
+        with pytest.MonkeyPatch.context() as patcher:
+            patcher.setenv("DATABASE_URL", str(engine.url))
+            for module in (database, compatibility_database):
+                patcher.setattr(module, "DATABASE_URL", str(engine.url))
+                patcher.setattr(module, "engine", engine)
+                patcher.setattr(module, "SessionLocal", factory)
+            patcher.setattr(manager, "SessionLocal", factory)
+            yield manager.SessionManager(), database