-- Phase 1: N-way group rooms.
-- The threads/thread_participants/thread_messages schema (0001) is already
-- N-way; this adds only what rooms need for audit + UX. Existing rows default
-- to kind='dm' so 1:1 routing is unchanged.

ALTER TABLE threads
    ADD COLUMN kind       TEXT NOT NULL DEFAULT 'dm'
        CHECK (kind IN ('dm', 'room')),
    ADD COLUMN created_by UUID REFERENCES agents (id);

-- Soft-remove participants so message history stays attributable after someone
-- leaves a room. added_by/joined_at record who pulled a participant in + when.
ALTER TABLE thread_participants
    ADD COLUMN added_by  UUID REFERENCES agents (id),
    ADD COLUMN joined_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    ADD COLUMN active    BOOLEAN NOT NULL DEFAULT true;