-- Migration: 002_dedup_unique_index
-- Add a UNIQUE index on (camera_id, recorded_at) to enforce hub-side
-- deduplication for ESP32 offline status replay (CUB-239).
-- This prevents race-condition double-inserts that a pure SELECT COUNT(*)
-- check cannot guard against.

CREATE UNIQUE INDEX IF NOT EXISTS idx_status_logs_unique_entry
    ON status_logs(camera_id, recorded_at);