fix(tests): drop_all before create_all to clear stale PostgreSQL enums

If a previous test run was interrupted before teardown, PostgreSQL enum
types persist with stale values, causing create_all to fail. Adding
drop_all first ensures a clean slate.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.beans/nuzlocke-tracker-9xac--fix-stale-postgresql-enum-causing-test-failures.md

@@ -0,0 +1,50 @@
+---
+# nuzlocke-tracker-9xac
+title: Fix stale PostgreSQL enum causing test failures
+status: completed
+type: bug
+priority: normal
+created_at: 2026-03-21T10:27:53Z
+updated_at: 2026-03-21T10:29:14Z
+---
+
+## Problem
+
+The backend smoke tests fail with:
+```
+sqlalchemy.exc.DBAPIError: invalid input value for enum run_visibility: "public"
+```
+
+This happens during `Base.metadata.create_all` in the `engine` fixture (`backend/tests/conftest.py:27`).
+
+## Root Cause
+
+The `engine` fixture only calls `create_all` during setup and `drop_all` during teardown. If a previous test run was interrupted before teardown, the `run_visibility` PostgreSQL enum type persists in the test database with stale/incorrect values. On the next run, `create_all` (with `checkfirst=True` default) sees the enum exists and skips recreating it, but the existing enum lacks valid values, causing the `DEFAULT 'public'` to fail.
+
+PostgreSQL native enum types are not automatically dropped with `DROP TABLE` — they require explicit `DROP TYPE`.
+
+## Fix
+
+In the `engine` fixture at `backend/tests/conftest.py:23-31`, add `Base.metadata.drop_all` before `create_all` to ensure a clean slate:
+
+```python
+@pytest.fixture(scope="session")
+async def engine():
+    eng = create_async_engine(TEST_DATABASE_URL, echo=False)
+    async with eng.begin() as conn:
+        await conn.run_sync(Base.metadata.drop_all)   # <-- add this
+        await conn.run_sync(Base.metadata.create_all)
+    yield eng
+    async with eng.begin() as conn:
+        await conn.run_sync(Base.metadata.drop_all)
+    await eng.dispose()
+```
+
+## Checklist
+
+- [x] Add `drop_all` before `create_all` in the `engine` fixture (`backend/tests/conftest.py`)
+- [x] Verify tests pass with `pytest backend/tests/test_smoke.py`
+
+## Summary of Changes
+
+Added `drop_all` before `create_all` in the test engine fixture to ensure stale PostgreSQL enum types are cleared before recreating the schema. This prevents test failures when a previous test run was interrupted before cleanup.