feat(backend): harden db_migrate — rollback test, non-sql filter test, doc convention

backend/tests/test_db_migrate.py

@@ -6,6 +6,7 @@ from pathlib import Path
 
 import pytest
 import sqlalchemy as sa
+import sqlalchemy.exc
 
 from cyclone import db_migrate
 
@@ -64,4 +65,51 @@ def test_run_raises_on_missing_version_header(tmp_path: Path, monkeypatch: pytes
 
     engine = _fresh_engine(tmp_path)
     with pytest.raises(RuntimeError, match="missing '-- version"):
-        db_migrate.run(engine)
+        db_migrate.run(engine)
+
+
+def test_run_rolls_back_version_on_failed_statement(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """If a DDL statement fails, the version bump must also roll back."""
+    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
+    (tmp_path / "0001_initial.sql").write_text(
+        "-- version: 1\nCREATE TABLE t (id INTEGER);\n"
+    )
+
+    engine = _fresh_engine(tmp_path)
+    db_migrate.run(engine)  # applies 0001, user_version=1
+    assert _user_version(engine) == 1
+
+    # Now drop in a second migration whose DDL conflicts with the first.
+    # The runner should apply 0001 and 0002 in one call; 0002 fails, the
+    # transaction rolls back, and user_version must stay at 1 (not bump to 2).
+    (tmp_path / "0002_bad.sql").write_text(
+        "-- version: 2\nCREATE TABLE t (id INTEGER);\n"  # table already exists!
+    )
+
+    with pytest.raises(sqlalchemy.exc.SQLAlchemyError):
+        db_migrate.run(engine)
+
+    assert _user_version(engine) == 1  # bumped atomically, rolled back on failure
+
+
+def test_run_ignores_non_sql_files(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """README.md and similar files in MIGRATIONS_DIR must not be executed."""
+    monkeypatch.setattr(db_migrate, "MIGRATIONS_DIR", tmp_path)
+    (tmp_path / "0001_initial.sql").write_text(
+        "-- version: 1\nCREATE TABLE t (id INTEGER);\n"
+    )
+    (tmp_path / "README.md").write_text("Don't run me!\nCREATE TABLE should_not_exist (x INT);\n")
+
+    engine = _fresh_engine(tmp_path)
+    db_migrate.run(engine)
+
+    with engine.connect() as c:
+        rows = c.exec_driver_sql(
+            "SELECT name FROM sqlite_master WHERE type='table' AND name='should_not_exist'"
+        ).all()
+    assert len(rows) == 0
+    assert _user_version(engine) == 1