-- Migration: 0002_positions_faulty
-- Adds the faulty column to positions and ensures the (device_id, ts DESC) index
-- needed by the snapshot-on-subscribe query exists.
--
-- The faulty column is set post-hoc by operators in Directus when a position is
-- flagged as unrealistic. The snapshot-on-subscribe query (task 1.5.5) filters
-- WHERE faulty = false to exclude flagged positions from the initial map state.
-- The live broadcast path (Redis stream → fan-out) never touches this column
-- because faulty flags are applied after the fact.

ALTER TABLE positions
  ADD COLUMN IF NOT EXISTS faulty boolean NOT NULL DEFAULT false;

-- Index for the snapshot DISTINCT ON query:
-- SELECT DISTINCT ON (device_id) ... ORDER BY device_id, ts DESC
-- TimescaleDB scans only the latest chunks for devices with recent activity,
-- but the (device_id, ts DESC) index makes per-device latest-position lookups
-- efficient regardless of chunk age.
CREATE INDEX IF NOT EXISTS positions_device_ts_idx ON positions (device_id, ts DESC);