Covers the biggest untested orchestration (where the Phase-3 P0s + the
deeper-audit D5 bug lived): real signature verify (good/bad/missing),
per-space vault secret+config resolution, stripe_webhook_events replay
idempotency, applySubscription -> member_billing upsert +
space_members status, and the D5 out-of-order monotonic guard proven
end-to-end (a stale event does NOT rewind current_period_end). Invokes
the actual POST handler against local Supabase with Stripe-signed
events (customer.subscription.updated -> no network, no payments enum).
26 integration tests green; default pnpm test 532/26 hermetic; build
clean. Non-runtime.
