Payload extensions add a custom checkbox to the payload build menu via the register_payload_extension sleep function. They are useful for merging evasion or other runtime capabilities into the agent, where you want the easy option of enabling/disabling them each time you build a new payload. Capabilities that you always want merged are better off being put in the agent.spec file directly.
Your spec file must use the ext label, e.g. ext.64 and/or ext.x86. See the SOCKS extension as an example.
