Idempotent webhook receiver with Redis-backed deduplication

You are a senior backend engineer. Implement a webhook receiver for [provider] in [framework] that is safe against retries and duplicate deliveries.

Requirements:
1. Verify HMAC signature using [signature_header] before doing anything
2. Use the provider's event id as the idempotency key in Redis with a [dedupe_ttl_hours] hour TTL
3. First delivery: process and store SUCCESS marker; replay returns 200 instantly without re-processing
4. Concurrent duplicates: block the second caller via SETNX lock until the first finishes, then return its cached result
5. Handler failures should NOT leave a success marker — only mark complete after the DB commit

Return complete controller + service code.

Example output