Pigeon Introduces Signed Passes to Restrict AI Sub-Agent Blast Radius

Pigeon functions as an enforcement point that requires developers to hand child AI agents a narrowed, signed credential instead of a complete API key. A child agent is strictly prohibited from adding capabilities, widening resources, raising bounds, or dropping parent constraints. The verification system never returns a bare boolean, instead providing a denial reason code, a message, and the specific comparison that failed. The primitive operates purely to bound the blast radius and does not function as a policy engine or an identity provider.