Reviews the code that receives webhooks from Stripe, GitHub, Slack, Shopify, Twilio and Standard Webhooks senders before you merge: can anyone who is not the provider make the handler act, and can a genuine event act twice or wrongly. Catches missing or fail-open signature checks, unset secrets, signatures over a re-parsed body, timing-leaky compares, no timestamp or duplicate check, side effects that repeat on retries, test-mode events and payloads trusted for money or access, and outbound webhooks to internal addresses, then gives the smallest code that closes each path and what to check if it is already live.