-- ==========================================
-- Chat Switchboard — 017 Unread Counts
-- ==========================================
-- Adds last_read_message_id to channel_participants for
-- per-user unread count computation.
-- ICD §3 (Channels & Conversations) — v0.23.2
-- ==========================================

ALTER TABLE channel_participants
    ADD COLUMN IF NOT EXISTS last_read_message_id UUID;