extension-guide-v3

The supplied fragment is a comprehensive documentation/guidance scaffold for Sindri V3 extensions. It is consistent with a descriptive, non-executable blueprint and does not contain code that would execute or exfiltrate data. No suspicious network activity, credential harvesting, or supply-chain exploit vectors are evident within the fragment itself. From a security-review perspective, it should be considered benign in isolation, though any future implementation should ensure proper secret handling (avoid hardcoding, use secure storage) and strict validation of extension manifests before execution.