arcint 1.2.4 — the loop guard's door

This is not the current release. The current one is here, with its changes in CHANGELOG.md.

The loop guard gains a door rung; every switch stays off by default, and
with none set a request is served as in 1.2.3. The coder unit's ladder now
includes the door (operator, 2026-10-24).

• Door rung — --loop-guard door|ladder|ladder-nodoor, with
  --loop-guard-door-grace (20) and the same three names in the request
  field. At detection, while the think block is open, the sampler masks every
  vocabulary id whose decoded piece consists only of newline characters and
  has two or more of them; the single-newline token stays legal. Nothing is
  injected and no token is forced: the model draws normally and may close by
  its own draw. The order is detect → door → nudge → slap → abort; the
  door opens at detection and stays open through the nudge (after the door
  grace) and the slap, and is gone once the block closes. door is the mask
  alone (never nudge or slap); ladder includes the door; ladder-nodoor is
  1.2.3's ladder exactly (nudge at detection, no mask), so one binary can
  compare both. The door ids are scanned once at model load from the
  vocabulary the backend owns. In a speculative lane the mask applies inside
  sample(), so a draft the mask forbids is a mismatch and drops the rest.
  The response's loop_guard object and the decode line count self_closes
  (the model's own close while the mask was open, not a slap) and
  door_masked (draws at which a masked token sat in the row's candidate
  set). /props reports the mode and door_grace.
• Answer watched after a door self-close — after a turn in which the door
  opened, the content phase feeds the detector too, and a looping answer ends
  on finish_reason loop exactly as after a slap. The answer starts from a
  clean window at the block's close, so reasoning lines (including the loop
  that opened the door) do not count against it; an answer that restates a
  line or two of its reasoning once stays normal. A turn whose door never
  opened keeps 1.2.3's unwatched answer, and detect/nudge/slap never
  open the door.
• No end of turn inside the open block — while the door is open and the
  think block is open, the turn-ending ids are illegal next tokens, applied to
  the logits in the same place as the newline mask (before penalties and the
  draw); the closer is never masked, and ignore_eos turns it off. With
  think_eog_mask set the mask is the same one and applied once. The
  loop_guard object and the decode line add door_eog_masked, last after
  door_masked: draws at which an end-of-generation id was a finite candidate
  the door removed.
• The door on the card (measured-here, the coder on the A770, its
  model card's thinking row, seed 1, 64k cap). On the 9 tasks that had hit
  the cap in the screening, with the door in the ladder all 7 looping runs
  ended fully correct; all 7 closed by the model's own draw, 5 by the door
  alone within seconds of opening and 2 after the nudge, and no forced token
  was needed in the whole round. The same set without the door needed the
  slap 4 times. README, "New: loop guard for small models".
• ladder now includes the door. On a unit that set ladder in 1.2.3 a
  detection now (a) waits the door grace (20 counted lines) before the nudge
  instead of nudging at once, (b) masks the multi-newline tokens until the
  block closes, (c) with think_eog_mask off also masks the turn-ending ids
  in the open block, and (d) watches the answer after the model's own close,
  so a turn that 1.2.3 recovered with the nudge and an unwatched answer can
  now end on loop. ladder-nodoor restores 1.2.3's ladder.
• Known residual (code, from the release review, not observed): the nudge
  and the slap fire only on a line where the repeat share is at or above the
  threshold. If the door is open with think_eog_mask off and the share then
  falls below it without the model closing the block, nothing escalates and
  the turn-ending ids stay masked, so the turn runs to the token cap where
  1.2.3 could have ended it. The counters door_masked and door_eog_masked
  count against the whole row when top_k is 0 (observability only).

Runtime: llama.cpp 3e4dfa8 with contrib/llama.cpp/patches (60
patches), unchanged from 1.2.3; dependencies unchanged. arcint-stt (1.2.0)
and arcint-imggen (1.1.1) are unchanged.

Release check (2026-10-25): the device-free suite 305 cases and ctest -L unit 6/6 on the tagged tree, the package build's own tests; the
mutations of the gap fixes red (measured-here, on the branch). The card
numbers above and the answer watch's offline replay (0 of 391 recorded
non-loop answers would abort) are from dev builds of the same mechanism. Not
run on the release candidate, by the operator's decision: the same-window
speed A/B against 1.2.3 and the acceptance task; every switch off is 1.2.3's
path (code).

Published (2026-10-25): arcint 1.2.4-1 built by its recipe from the
v1.2.4 tag tarball (sha256 a12aabde…) and published to the trixie
repository (index verified); installed from the pool on the card host, where
the coder runs it with --loop-guard ladder (now with the door) and the
agent with the switches as before, each answering the stop-string check.
arcint-stt stays at 1.2.0-1, arcint-imggen at 1.1.1-1.