I believe I have a proof for 1 more holdout (identified and proved halting with AI-assistance). Skelet 1-like Class 2 again, but this one halts! :skull_crossbones:

`1RB0RD_1LC0RA_---1RD_1RA1LE_1RC0LF_1LE0LB` halts after 176,522,930,997,643,289,094,015,905,898,381,767,890,130,463 ≈ 1.77 × 10^44 steps. That count is computed from per-rule step formulas checked against simulation; the Coq proof shows only that it halts.
File: <FILE_LINK>
PR: <PR_LINK>
Informal write-up: attached

Watched each time the head reaches new ground on the right, the tape is a binary counter, and every carry burns fuel in each digit it touches. A digit that runs dry sheds a spare wall toward the head (walls drift right and refill the digits there), but a digit with a single marker has none to shed. New digits are born at the right end, and the time between births grows by a ratio that oscillates with growing swings; when the third swing crosses 2, a single-marker digit is left with bit 0 and no fuel, and the next carry into it halts the machine.

The .v replays the whole run in 107,781 checked moves (closed-form batches between structural events). It compiles against unmodified busycoq, Print Assumptions lists only functional_extensionality_dep (from flip_halts_iff), and coqchk passes.

AI disclosure: as before, produced with Claude Code (Opus 5.5). The results rest on the Coq files; extra verification and feedback are very welcome!