-- Additive support for local customer merges. No existing rows are changed.
ALTER TABLE customers ADD COLUMN IF NOT EXISTS merged_into_customer_id INTEGER REFERENCES customers(id);
CREATE TABLE IF NOT EXISTS customer_merge_history (
    id BIGSERIAL PRIMARY KEY,
    target_customer_id INTEGER NOT NULL REFERENCES customers(id),
    source_customer_ids INTEGER[] NOT NULL,
    actor_id INTEGER NOT NULL,
    created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
    snapshot JSONB NOT NULL,
    movements JSONB NOT NULL
);