Invoke a function (POST)

Invokes a deployed function. Free functions return the direct function response. Paid functions require Idempotency-Key for retry-safe billing. A new paid call creates one idempotency record and one durable run, returns the retained result when it finishes within the bounded wait, or returns 202 with run_id/operation_id and next_actions[] for polling. Reusing the same key with the same canonical JSON intent replays the terminal result/error; reusing it with a different intent returns 409 idempotency_conflict. Insufficient allowance and other pre-dispatch failures do not consume the key.