fix: restore original conftest.py from last working state

Revert to the exact per-test create/drop conftest that worked at
25cff5e4. The session-scoped and module-level patching approaches
both broke e2e tests in CI.

tests/conftest.py

@@ -1,17 +1,11 @@
-"""Shared test fixtures — async DB session using a test database.
-
-Unit tests use the ``session`` fixture, which provides a per-test
-savepoint-isolated session on a dedicated test engine.  E2E tests do NOT
-use this fixture and are therefore unaffected — they keep using the real
-``wiregui.db.async_session`` that talks to the app's database.
-"""
+"""Shared test fixtures — async DB session using a test database."""
 
 import os
 from collections.abc import AsyncGenerator
 
 import pytest_asyncio
 from sqlalchemy import text
-from sqlalchemy.ext.asyncio import AsyncSession, create_async_engine
+from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 from sqlmodel import SQLModel
 
 from wiregui.config import get_settings
@@ -57,34 +51,19 @@ def _ensure_test_db_sync():
 
 _ensure_test_db_sync()
 
-# Test engine — only used by the ``session`` fixture and unit tests.
-# NOT assigned to wiregui.db so e2e tests are unaffected.
-_test_engine = create_async_engine(TEST_DATABASE_URL)
-
-
-@pytest_asyncio.fixture(scope="session")
-async def _test_tables():
-    """Create all tables once per test session, drop at end."""
-    async with _test_engine.begin() as conn:
-        await conn.run_sync(SQLModel.metadata.create_all)
-    yield
-    async with _test_engine.begin() as conn:
-        await conn.run_sync(SQLModel.metadata.drop_all)
-    await _test_engine.dispose()
-
 
 @pytest_asyncio.fixture
-async def session(_test_tables) -> AsyncGenerator[AsyncSession]:
-    """Per-test session with transaction isolation.
+async def session() -> AsyncGenerator[AsyncSession]:
+    """Fresh engine + session per test, with table setup/teardown."""
+    engine = create_async_engine(TEST_DATABASE_URL)
+    async with engine.begin() as conn:
+        await conn.run_sync(SQLModel.metadata.create_all)
 
-    The session is bound to a connection-level transaction that is always
-    rolled back at teardown.  When tested code calls ``session.commit()``,
-    SQLAlchemy only releases a SAVEPOINT — the outer transaction is never
-    committed, so no test data persists between tests.
-    """
-    async with _test_engine.connect() as conn:
-        txn = await conn.begin()
-        sess = AsyncSession(bind=conn, expire_on_commit=False, join_transaction_mode="create_savepoint")
+    factory = async_sessionmaker(engine, expire_on_commit=False)
+    async with factory() as sess:
         yield sess
-        await sess.close()
-        await txn.rollback()
+        await sess.rollback()
+
+    async with engine.begin() as conn:
+        await conn.run_sync(SQLModel.metadata.drop_all)
+    await engine.dispose()