"""v3 second_brain: sources.claimed_by / claimed_at

Revision ID: c8f1d9e34b7a
Revises: 7b3e8a5c1f29
Create Date: 2026-05-25 12:30:00.000000

Adds a lightweight claim mechanism so the tower and dev sides never grab
the same row off the queue. The claim flow used by both workers is:

    BEGIN;
    SELECT id, status, source_type
      FROM second_brain.sources
     WHERE <filter>
       AND claimed_by IS NULL
     ORDER BY ingested_at ASC
     LIMIT 1
     FOR UPDATE SKIP LOCKED;
    UPDATE second_brain.sources
       SET claimed_by = :worker, claimed_at = now() AT TIME ZONE 'UTC'
     WHERE id = :id;
    COMMIT;

`FOR UPDATE SKIP LOCKED` is the actual race-safety primitive — the column
pair is observability (who has it, since when, for stale-claim recovery).
A partial index would help once we have a real queue depth; deliberately
not added now per Travis's "no gold-plating".
"""

from __future__ import annotations

from collections.abc import Sequence

from alembic import op

revision: str = "c8f1d9e34b7a"
down_revision: str | Sequence[str] | None = "7b3e8a5c1f29"
branch_labels: str | Sequence[str] | None = None
depends_on: str | Sequence[str] | None = None


def upgrade() -> None:
    op.execute("SET search_path TO second_brain")
    op.execute("ALTER TABLE sources ADD COLUMN claimed_by VARCHAR(100)")
    op.execute("ALTER TABLE sources ADD COLUMN claimed_at TIMESTAMP")


def downgrade() -> None:
    op.execute("SET search_path TO second_brain")
    op.execute("ALTER TABLE sources DROP COLUMN IF EXISTS claimed_at")
    op.execute("ALTER TABLE sources DROP COLUMN IF EXISTS claimed_by")