"""git_sources.branch: per-source branch to mirror (phase 135, task 01)

Revision ID: 0024
Revises: 0023
Create Date: 2026-09-27

Phase 135 (a git source can pin the branch it mirrors — task 01, storage
only):

* ``git_sources.branch`` — TEXT NULLABLE, no server default: the branch
  the owner specifies for a git source (TODO-derived phase). NULL =
  the repo's DEFAULT branch — every pre-phase-135 row and every
  env-fallback synthetic row is a default-branch source by definition,
  so no row is touched and no backfill runs. A non-NULL value is
  validated at the API boundary
  (``app.rag.git_sources.validate_branch_name`` — task 02); the column
  itself is plain ``Text`` (the ``git_sources.token`` (0021)
  precedent: the column stores, the boundary validates).

One additive, fully reversible migration (A13); no other schema
change. The branch-aware clone/pull wiring (``clone_or_pull(…, branch)``
— task 03) and the API tri-state (task 02) are code — this revision
only carries the column.
"""
from __future__ import annotations

import sqlalchemy as sa

from alembic import op

revision = "0024"
down_revision = "0023"
branch_labels = None
depends_on = None


def upgrade() -> None:
    op.add_column("git_sources", sa.Column("branch", sa.Text(), nullable=True))


def downgrade() -> None:
    # The branch column is the only 0024 artefact — dropping it leaves
    # 0023's schema byte-identical (A13, fully reversible). NULL =
    # default branch, so no data migration in either direction.
    op.drop_column("git_sources", "branch")