Appendix B — Reserved ranges

Appendix B — Reserved ranges

TL;DR. The reserved-discriminant ranges for future protocol extensions: which message-ID slots are earmarked for which categories (lifecycle, hot path, control plane, events, L1 lifecycle), and the enum-allocation discipline for PhysicalKey and ErrorCode. Implementers extending the protocol pick from these ranges via PR.

1. Reserved message-ID ranges

For implementers extending the protocol:

  • Message IDs 0x04..=0x0F and 0x83..=0x8F: reserved for connection- lifecycle messages.
  • Message IDs 0x14..=0x1F and 0x93..=0x9F: reserved for hot-path messages.
  • Message IDs 0x24..=0x2F and 0xA3..=0xAF: reserved for further L1 Terminal lifecycle / per-pane control frames (phux-4li.10 allocated 0x22..=0x23 C→S and 0xA1..=0xA2 S→C from these ranges).
  • Message IDs 0x31..=0x3F and 0xC2..=0xCF: reserved for control plane.
  • Message IDs 0x41..=0x4F and 0xB3..=0xBF: reserved for events.

2. Reserved enum ranges

PhysicalKey enum values and ErrorCode enum values are allocated sequentially. Implementers proposing new values open a PR against this document.

(Earlier drafts of the SPEC reserved a DiffOp tag range here; per ADR-0013, Terminal content is now a VT byte stream and DiffOp no longer exists as a wire concept.)