feat(arch): the wall engine - L/T/X junctions, opening gaps and material poche

engineering/arch/walls.py turns a wall network - axis polylines with a
thickness, a justification and a material - into clean outlines. One rule
resolves every junction: at each node the segment ends are sorted by angle and
the left face of each meets the right face of the next one counter-clockwise.
That mitres an L, stops a T's stem on the crossing wall's near face (cut there,
while the far face stays one line) and cuts all four faces of an X. A T is an
axis end lying inside another wall: it is carried onto the crossing axis and
the crossing segment is split. The hub a three- or four-way node leaves is a
region of its own, so the poche has no hole.

Openings remove their width from both faces and are closed by jambs; a free
end is closed by a jamb. Each solid piece is one CCW region and one HatchArea
in the wall's material. The two face lines across each opening are kept as
thresholds - never drawn - so room_segments hands the face finder closed rooms
instead of rooms merged through their doorways.

Refused by name before any geometry: a duplicate id, an unknown material or
justification, a zero-length segment, a junction below 5 degrees, a corner
inside another wall off its axis, an end whose axis meets the other wall past
its end, a segment lying wholly inside the wall it joins, and one too short
for its junctions (engineering.measure.is_self_intersecting on its outline).
An opening that runs into a junction is returned in omitted, never dropped.

Every corner in the tests is hand-computed: two 200 mm walls at the origin
meet at (100, 100) inside and (-100, -100) outside.

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

engineering/arch/__init__.py

@@ -30,6 +30,15 @@ from .model import (
     wall_from_dict,
     wall_length,
 )
+from .walls import (
+    MIN_JOIN_ANGLE_DEG,
+    WallGeometry,
+    face_offsets,
+    room_segments,
+    wall_geometry,
+    wall_geometry_by_wall,
+    wall_segments,
+)
 
 __all__ = [
     "APP_ID",
@@ -39,20 +48,24 @@ __all__ = [
     "ARCH_ROLE_LAYER",
     "KINDS",
     "LANGS",
+    "MIN_JOIN_ANGLE_DEG",
     "Opening",
     "Room",
     "Stair",
     "WALL_HATCH_TABLE",
     "WALL_MATERIALS",
     "Wall",
+    "WallGeometry",
     "axis_segments",
     "decode",
     "encode",
+    "face_offsets",
     "fmt_area_m2",
     "fmt_number",
     "from_payload",
     "opening_from_dict",
     "room_from_dict",
+    "room_segments",
     "segment_of",
     "stair_from_dict",
     "tag_prefix",
@@ -61,6 +74,9 @@ __all__ = [
     "validate_openings",
     "vocab",
     "wall_from_dict",
+    "wall_geometry",
+    "wall_geometry_by_wall",
     "wall_hatch",
     "wall_length",
+    "wall_segments",
 ]