setup: init-db e reset-db stampano head in un thread (TieMeasureFlow#80)

_stamp_head esegue env.py di alembic, che fa asyncio.run() e dentro il loop
di FastAPI dava RuntimeError (500). Ora gira con asyncio.to_thread. Nuovo
test_setup_stamp.py senza monkeypatch di _stamp_head, su file SQLite.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/tests/test_setup_stamp.py

@@ -0,0 +1,81 @@
+"""init-db / reset-db con _stamp_head REALE su un file SQLite (TieMeasureFlow#80).
+
+_stamp_head esegue migrations/env.py, che chiama asyncio.run(): dentro il loop
+gia' attivo di FastAPI dava RuntimeError -> 500. test_setup.py e
+test_station_seed.py sostituiscono _stamp_head con un no-op e non lo vedevano:
+qui NON si fa monkeypatch di _stamp_head.
+"""
+import logging.config
+import sqlite3
+
+import pytest
+from alembic.config import Config
+from alembic.script import ScriptDirectory
+from httpx import ASGITransport, AsyncClient
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+from src.backend.config import settings
+from src.backend.main import app
+
+SETUP_PWD = "test-setup-password"
+
+
+@pytest.fixture
+def file_db(tmp_path, monkeypatch):
+    """Punta settings, engine e session factory del router setup a un file SQLite."""
+    import src.backend.api.routers.setup as setup_mod
+
+    db_file = tmp_path / "t.db"
+    url = f"sqlite+aiosqlite:///{db_file.as_posix()}"
+    # env.py ricava sqlalchemy.url da settings.database_url (property su db_url)
+    monkeypatch.setattr(settings, "db_url", url)
+    monkeypatch.setattr(settings, "setup_password", SETUP_PWD)
+    file_engine = create_async_engine(url, echo=False)
+    monkeypatch.setattr(setup_mod, "engine", file_engine)
+    monkeypatch.setattr(
+        setup_mod, "async_session_factory",
+        async_sessionmaker(file_engine, expire_on_commit=False),
+    )
+    # env.py chiama fileConfig, che disattiverebbe i logger degli altri test
+    monkeypatch.setattr(logging.config, "fileConfig", lambda *a, **k: None)
+    return db_file, setup_mod, file_engine
+
+
+def _head() -> str:
+    from src.backend.api.routers.setup import _alembic_ini
+    cfg = Config(str(_alembic_ini))
+    return ScriptDirectory.from_config(cfg).get_current_head()
+
+
+def _versions(db_file) -> list[str]:
+    con = sqlite3.connect(db_file)
+    try:
+        return [r[0] for r in con.execute("SELECT version_num FROM alembic_version")]
+    finally:
+        con.close()
+
+
+@pytest.fixture
+async def http():
+    async with AsyncClient(transport=ASGITransport(app=app), base_url="http://testserver") as ac:
+        yield ac
+
+
+@pytest.mark.asyncio
+async def test_init_db_stamps_head(file_db, http):
+    db_file, _, file_engine = file_db
+    resp = await http.post("/api/setup/init-db", json={"password": SETUP_PWD})
+    assert resp.status_code == 200, resp.text
+    assert _versions(db_file) == [_head()]
+    await file_engine.dispose()
+
+
+@pytest.mark.asyncio
+async def test_reset_db_stamps_head(file_db, http):
+    db_file, _, file_engine = file_db
+    resp = await http.post("/api/setup/init-db", json={"password": SETUP_PWD})
+    assert resp.status_code == 200, resp.text
+    resp = await http.post("/api/setup/reset-db", json={"password": SETUP_PWD, "confirm": True})
+    assert resp.status_code == 200, resp.text
+    assert _versions(db_file) == [_head()]
+    await file_engine.dispose()