feat(arch): SECTION 25 opens - walls, openings, stairs and exterior chains as tools

engineering/arch/draw.py is the only module of the track that touches a
backend. It draws through draw_prims(role_layer=ARCH_ROLE_LAYER) and the
generic contract members, so it runs on both engines as written, and it writes
the plan onto the drawing: each element's ACADMCP_ARCH record on one of its own
entities (a wall's first face line, a door's leaf, a window's frame, a stair's
first riser) and, beside it under ACADMCP_ARCH_H, the handles that element
owns. read_plan reads the records back and never modifies the drawing.

arch_wall computes the whole network before and after the new walls and
redraws only the drawn walls whose outline changes - erasing exactly the
entities they own - and says which under redrawn. arch_opening hosts a door or
a window in a drawn wall found by id and redraws that wall cut; its tag
defaults to the next D1/W1 (K1/P1 in Turkish). A new wall that would leave a
drawn opening uncuttable, and an opening that runs into a junction, are refused
before anything is erased. arch_stair reports the Blondel value; it does not
enforce it.

exterior_chains gives each side up to three rows, nearest first: every jamb in
that facade, both faces of every wall meeting it, and the overall - from the
wall engine's own faces. A row that would only restate a farther one is not
emitted (ISO 129-1: each measurement once). The 10 mm / 8 mm row spacing is a
declared drafting default times the plot scale, not a standard value.

The arch tag is ranked after mech so the four tools file under a new
architecture group; alias records carry WALLADD/MLINE, DOORADD/WINDOWADD and
STAIRADD with English and Turkish shop words. Inventory regenerated; README
snapshot 233 tools (228 advertised) in 26 groups; registry snapshot
architecture: 4.

No new ActiveX member is called. Measured on AutoCAD 2026 in a scratch
document through ComBackend: shell + teed partition, D1 + W1, a straight 17-riser stair
and the bottom chains gave the same 20 wall LINEs (identical endpoints),
9 poche HATCHes, 1+1 door, 4 window lines, 11 dimensions and a read_plan
round trip as the headless engine.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/arch/__init__.py

@@ -6,6 +6,13 @@ and alphabetical - keep every side's names.
 
 from __future__ import annotations
 
+from .dimension import (
+    FIRST_OFFSET_PAPER_MM,
+    ROWS,
+    SIDES,
+    STEP_PAPER_MM,
+    exterior_chains,
+)
 from .lang import LANGS, fmt_area_m2, fmt_number, tag_prefix, vocab
 from .layers import ARCH_LAYER_DEFS, ARCH_LAYER_ROLES, ARCH_LAYERS, ARCH_ROLE_LAYER
 from .materials import WALL_HATCH_TABLE, WALL_MATERIALS, wall_hatch
@@ -58,12 +65,16 @@ __all__ = [
     "ARCH_ROLE_LAYER",
     "ARROW_PAPER_MM",
     "BLONDEL_RANGE",
+    "FIRST_OFFSET_PAPER_MM",
     "KINDS",
     "LANGS",
     "MIN_JOIN_ANGLE_DEG",
     "Opening",
+    "ROWS",
     "Room",
+    "SIDES",
     "STAIR_KINDS",
+    "STEP_PAPER_MM",
     "Stair",
     "TEXT_PAPER_MM",
     "TURNS",
@@ -75,6 +86,7 @@ __all__ = [
     "blondel",
     "decode",
     "encode",
+    "exterior_chains",
     "face_offsets",
     "fmt_area_m2",
     "fmt_number",