feat(understand): drawing_topology_check and the three topo_* critique focuses

engineering/understand/topology.py reads a line network (LINE, polylines
with true bulge arcs, ARC) on the chosen layers and reports dangling
ends, near misses (end-end and end-segment within gap, one row per pair)
and interior crossings of two straight segments of one layer. An end on
another network line is joined; an end on any curve of another layer or
inside a block reference's box is attached; a line drawn twice is not a
join, so a doubled pipe still dangles. gap defaults to 0.2 % of the
network diagonal, never under ten tol.

drawing_topology_check joins drawing_diff in SECTION 26: default layers
are those classify_layer calls piping or electrical at >= 0.9, reported
with their classification; no such layer is a refusal, not a pass.

topo_dangling_endpoint (warning), topo_near_miss (error) and
topo_interior_crossing (info) join the closed enum and run under
focus=None, excluding the P&ID and architectural layer sets, so a
pid_from_spec sheet and an arch_plan_from_spec plan get none of them;
a drawing with no candidate layer is never snapshotted.

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

engineering/plan_spec.py

@@ -36,6 +36,9 @@ CritiqueFocus = Literal[
     "arch_room_unlabelled",
     "arch_wall_gap",
     "arch_opening_clash",
+    "topo_dangling_endpoint",
+    "topo_near_miss",
+    "topo_interior_crossing",
 ]
 SnapType = Literal["end", "mid", "center", "quad", "int", "perp", "near"]
 
@@ -62,6 +65,9 @@ ALL_CRITIQUE_FOCUSES: tuple[CritiqueFocus, ...] = (
     "arch_room_unlabelled",
     "arch_wall_gap",
     "arch_opening_clash",
+    "topo_dangling_endpoint",
+    "topo_near_miss",
+    "topo_interior_crossing",
 )