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.

alembic/versions/013_drop_role_enum.py

@@ -0,0 +1,67 @@
+"""Drop stray `role` postgres enum.
+
+Smoke run 2 (2026-05-11) surfaced `UndefinedFunctionError: operator
+does not exist: agentrole = role` because postgres ended up with two
+enums (`role` and `agentrole`) for the same Python `Role` class. Only
+agents.role column uses `agentrole`; nothing uses `role`. This migration
+drops the orphan.
+
+The cause (E2 in the spec) is a SQLAlchemy parameter-binding edge case
+where a query parameter wasn't bound with the column's enum name,
+letting SQLAlchemy infer a new type from the Python class name.
+Investigation tracked in E2; this migration handles the symptom.
+
+Revision ID: 013_drop_role_enum
+Revises: 012_align_agentrole_foundation
+Create Date: 2026-05-12
+"""
+
+from __future__ import annotations
+
+from alembic import context, op
+from sqlalchemy import text
+
+revision = "013_drop_role_enum"
+down_revision = "012_align_agentrole_foundation"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    """Drop the orphan `role` enum after confirming no column uses it."""
+    if context.is_offline_mode():
+        # Offline mode: emit the SQL but skip the safety check.
+        op.execute("DROP TYPE IF EXISTS role")
+        return
+
+    conn = op.get_bind()
+    # Safety check: no column may still reference the type
+    result = conn.execute(
+        text(
+            "SELECT column_name, table_name "
+            "FROM information_schema.columns "
+            "WHERE udt_name = 'role'"
+        )
+    )
+    rows = list(result)
+    if rows:
+        raise RuntimeError(
+            f"refusing to DROP TYPE role: columns still reference it: {rows}"
+        )
+
+    conn.execute(text("DROP TYPE IF EXISTS role"))
+
+
+def downgrade() -> None:
+    """Recreate the enum with the foundation's Role values.
+
+    Used if we ever need to revert this migration. No rows reference
+    the type after the upgrade ran, so recreation is a no-op for app
+    state.
+    """
+    op.execute(
+        "CREATE TYPE role AS ENUM ("
+        "'system', 'developer', 'qa', 'documenter', 'cell_pm', 'main_pm', "
+        "'product_owner', 'head_marketing', 'auditor', 'ceo'"
+        ")"
+    )