tsb/tsb.hpp holds the link, the handshake and command bytes, the guard policy and SPM interlock, the boot geometry, act_min/comm_window and a consteval builder for the 16-byte info block, whose BUILDSTATE and ATmega marker bytes are now named rather than commented. Every tier's image is byte-identical to before. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>