"""Add committed_at_raw to musehub_commits

musehub#195 (narrow fix): committed_at is identity-bearing -- a commit's
content-addressed id is a hash whose preimage includes the exact ISO-8601
committed_at string the client used. musehub_commits.timestamp is a
Postgres timestamptz, which normalizes any non-UTC offset to UTC on
write. When the wire-serve path (_to_wire_commit) reconstructs a commit's
bytes from `timestamp.isoformat()` to send it back to a client, a commit
originally authored with a non-UTC offset gets served with a DIFFERENT
committed_at string than the one baked into its id -- the client correctly
rejects the download as an integrity failure.

This is an instance of the broader problem tracked in musehub#63 (commits
are DB-only, reconstructed from DB fields rather than served as stored
canonical bytes). This migration is the deliberately narrow, additive fix:
capture the exact original string alongside the normalized timestamptz, so
the serve path can use it verbatim instead of re-deriving a lossy one.
Still correct after #63 eventually lands (canonical-bytes storage would
make this column redundant, not wrong).

Additive and nullable -- existing rows get NULL. The serve path
(musehub/services/musehub_wire_shared.py::_to_wire_commit) falls back to
`timestamp.isoformat()` for NULL rows and verifies the reconstructed bytes
actually reproduce the stored commit_id, refusing to serve (fail closed)
rather than silently serving a mismatched reconstruction if they don't.

Revision ID: 0077
Revises: 0076
"""
from __future__ import annotations

from typing import Sequence, Union

import sqlalchemy as sa
from alembic import op


# revision identifiers, used by Alembic.
revision: str = '0077'
down_revision: Union[str, None] = '0076'
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None


def upgrade() -> None:
    op.add_column(
        'musehub_commits',
        sa.Column('committed_at_raw', sa.Text(), nullable=True),
    )


def downgrade() -> None:
    op.drop_column('musehub_commits', 'committed_at_raw')