"""Make musehub_snapshots.manifest_blob nullable.

snapshot_id = sha256(sorted manifest entries) — the ID is the proof.
Snapshots pushed via the delta-mpack path store manifest_blob=NULL;
the manifest can be reconstructed from the delta chain in MinIO.

Revision ID: 0053
Revises: 0052
"""
from __future__ import annotations

import sqlalchemy as sa
from alembic import op


revision: str = "0053"
down_revision: str = "0052"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.alter_column(
        "musehub_snapshots",
        "manifest_blob",
        existing_type=sa.LargeBinary(),
        nullable=True,
    )


def downgrade() -> None:
    op.execute(
        "UPDATE musehub_snapshots SET manifest_blob = '\\x80' WHERE manifest_blob IS NULL"
    )
    op.alter_column(
        "musehub_snapshots",
        "manifest_blob",
        existing_type=sa.LargeBinary(),
        nullable=False,
    )