ALTER TABLE outbox
    ADD COLUMN delivery_attempts INTEGER NOT NULL DEFAULT 0,
    ADD COLUMN last_delivery_error TEXT,
    ADD COLUMN dead_lettered_at TIMESTAMPTZ;

-- The unpublished dispatchers read oldest-first and previously stopped on the
-- first delivery error, so one permanently malformed payload blocked every
-- later event of that type forever. Dead-lettered rows leave the working set
-- via this partial index so a poison row degrades to one lost event instead of
-- a stalled queue.
DROP INDEX IF EXISTS outbox_unpublished_order;

CREATE INDEX outbox_unpublished_order
    ON outbox (created_at, event_id)
    WHERE published_at IS NULL AND dead_lettered_at IS NULL;