feat(alembic): A5 migration 013 drops stray role postgres enum

Smoke run 2 (2026-05-11) produced 'UndefinedFunctionError: operator
does not exist: agentrole = role' because postgres had two enums
(role, agentrole) for the same Python class. Information_schema check
confirms no column uses role; migration drops it. Upgrade() raises if
that ever stops being true. Downgrade() recreates the enum with the
foundation's Role values.

Investigation of WHY a second enum got created is tracked in spec E2;
this migration handles the symptom.

Spec ref: docs/superpowers/specs/2026-05-12-post-smoke-3-fixes-design.md
section A5.

tests/integration/test_migration_013_drop_role.py

@@ -0,0 +1,49 @@
+"""Wave A5 (2026-05-12): migration 013 drops the stray `role` postgres enum.
+
+Smoke run 2 produced `UndefinedFunctionError: operator does not exist:
+agentrole = role` because postgres had two enums for the same Python
+class. The migration drops the unused one with a safety check.
+"""
+
+from __future__ import annotations
+
+import pytest
+from sqlalchemy import text
+
+
+@pytest.mark.asyncio
+async def test_no_column_uses_role_type(db_session) -> None:  # type: ignore[no-untyped-def]
+    """Before dropping, confirm no column actually uses the `role` type.
+
+    If this ever fails it means a column was added that references the
+    `role` enum and the migration must NOT be allowed to drop it — that
+    column would become orphaned.
+    """
+    result = await db_session.execute(
+        text(
+            "SELECT column_name, table_name "
+            "FROM information_schema.columns "
+            "WHERE udt_name = 'role'"
+        )
+    )
+    rows = list(result)
+    assert rows == [], (
+        f"columns still use `role` enum: {rows}; migration 013 cannot run"
+    )
+
+
+@pytest.mark.asyncio
+async def test_role_enum_dropped_after_upgrade(db_session) -> None:  # type: ignore[no-untyped-def]
+    """After migration 013 runs, only `agentrole` remains; `role` is gone."""
+    # This test runs against a db where migrations have been applied to head.
+    # The conftest fixture should handle that — verify by reading the
+    # existing tests' conftest.
+    result = await db_session.execute(
+        text(
+            "SELECT typname FROM pg_type "
+            "WHERE typname IN ('role', 'agentrole')"
+        )
+    )
+    rows = {row[0] for row in result}
+    assert "agentrole" in rows, "agentrole must remain (it's the live enum)"
+    assert "role" not in rows, "stray `role` enum should be dropped"