The original title is: "The Webhook Bug That Passed Every Test and Every Code Review"

Short summary

A developer discovered a multi-tenancy bug in their bounce handler that silently unsubscribed contacts across all tenants when a bounce occurred. The handler queried by email without a customer_id filter, so a bounce for Customer A's subscriber also unsubscribed the same email under Customer B. No errors or logs were raised, making the bug invisible to tests and code reviews.

• •Bounce handler queried Contact.email without tenant scoping, causing cross-tenant unsubscribes
• •Same email can legitimately exist under multiple tenants in multi-tenant systems
• •Bug was invisible to all tests and security review passes

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