"""phase14 — add created_at to facilities

Adds a nullable DateTime column to the facilities table so that facility
creation time is tracked consistently with every other core model.

Existing rows receive NULL (unknown creation time) — nullable=True is
intentional for backward compatibility with pre-existing data.

Revision ID: phase14_facility_created_at
Revises: phase13_issue_facility
"""

revision      = 'phase14_facility_created_at'
down_revision = 'phase13_issue_facility'
branch_labels = None
depends_on    = None

from alembic import op
import sqlalchemy as sa


def upgrade():
    with op.batch_alter_table('facilities') as batch_op:
        batch_op.add_column(
            sa.Column('created_at', sa.DateTime(), nullable=True)
        )


def downgrade():
    with op.batch_alter_table('facilities') as batch_op:
        batch_op.drop_column('created_at')