Constant CREATE_OUTBOX_TABLE 

pub const CREATE_OUTBOX_TABLE: &str = "
CREATE TABLE IF NOT EXISTS outbox (
    dispatch_key TEXT NOT NULL UNIQUE,
    workflow_id TEXT NOT NULL,
    ordinal INTEGER NOT NULL,
    activity_type TEXT NOT NULL,
    input BLOB NOT NULL,
    status TEXT NOT NULL,
    attempt INTEGER NOT NULL,
    visible_after TEXT NOT NULL,
    run_id TEXT,
    claimed_at TEXT,
    PRIMARY KEY (dispatch_key)
)";

Durable fan-out dispatch outbox.

dispatch_key ("{workflow_id}:{ordinal}") is UNIQUE: it is the database-level idempotency guard, so a re-issued append of the same fan-out batch silently ignores the duplicate rows via INSERT OR IGNORE. status is one of pending/claimed/done/failed; visible_after fences retry backoff so a row is not re-claimed before its delay elapses; nullable claimed_at records the durable claim instant for live stale-claim reconciliation; nullable run_id records the concrete run that staged the row when known.