Process 05 — payment-saga cascade

Process 05 — payment-saga cascade

Charge fails on the top bidder → strike increment → fall through ranked list (top 2..5) → ultimately house-ad if exhausted.

Cascade invariants

• instance_id stays auction_id across all cascade iterations — no sub-workflows spawned.
• Stripe Idempotency-Key increments via the attempt counter; never reuses keys across users.
• Workflow step.do names are unique per attempt: invoice-create:attempt-2:user-u2. Replay safety is preserved by name uniqueness.
• Strike API is idempotent on (saga_instance_id, user_id) so workflow restarts mid-strike are safe.
• First attempt uses 6h SCA window; cascaded attempts use 30min to stay within 24h pre-activate budget.
• Max 5 attempts → guaranteed HOUSE_AD fallback before slot time.