Self-serve Stripe Connect Express onboarding. Mints (or reuses) a connected account for this publisher and returns a one-time onboarding URL the dashboard can redirect to. After onboarding the Stripe account.updated webhook flips charges_enabled + payouts_enabled on the publisher row, which the dashboard reads on next load to show the green-light state.

Never 5xxs on a Stripe failure. A payout rail that isn't ready is a state of the dashboard, not a server error: the publisher gets a 200 carrying status="pending_setup", a null onboarding_url and a plain-English message, so the rest of onboarding continues and the Connect button stays pressable. Same reasoning as _degraded_payload on the claim path — never a conversion-losing 500.

status is "ready" on the happy path and every pre-existing key keeps its meaning, so older dashboard builds that only look at onboarding_url are unaffected.