perf: taper multi-wall exterior corridors

Keep the finite #272 exit as a safe subset of the square connector while removing two contour corners per bevel. The simpler canonical path preserves the zero-hole and finite-ray contracts and restores headroom in the large-house Glow gate.

Issue: #272
User-Visible: no

src/wall-thickness.ts

@@ -2075,18 +2075,16 @@ function multiWallBevelCutsAt(
           );
           const ux = dx / length, uy = dy / length;
           const vx = -uy, vy = ux;
-          // A tiny local corridor overlaps the triangle just before `hit`
-          // and the exterior sector just after it. Keeping this as a second
-          // patch avoids rotating the long bevel edges across an acute arm.
+          // This tapered connector is a strict subset of the original square
+          // corridor: it keeps the same finite cross-section at `hit` and the
+          // same exterior reach, but avoids two extra contour corners in every
+          // large-plan junction path.
           const connector = stableJunctionPatch([
             [hit[0] - ux * bridge + vx * bridge,
               hit[1] - uy * bridge + vy * bridge],
             [hit[0] - ux * bridge - vx * bridge,
               hit[1] - uy * bridge - vy * bridge],
-            [hit[0] + ux * bridge - vx * bridge,
-              hit[1] + uy * bridge - vy * bridge],
-            [hit[0] + ux * bridge + vx * bridge,
-              hit[1] + uy * bridge + vy * bridge],
+            [hit[0] + ux * bridge, hit[1] + uy * bridge],
           ], map.coordinateScale);
           if (connector) cuts.push(connector);
         }

test/wall-thickness.test.mjs

@@ -1583,7 +1583,7 @@ test('issue #197 keeps the full masonry when one virtual-junction patch has ULP
   // #271 removes only the area that the old node-wide 8H rectangles invented
   // after finite ray endpoints; all semantic #197/#249/#261 probes above stay.
   // #272 additionally opens any point-contact bevel cut to the exterior.
-  closeTo(geometryArea(geometry.geom), 124242.78593276718, 1e-6);
+  closeTo(geometryArea(geometry.geom), 124243.7732289006, 1e-6);
   closeTo(geometryArea(geometry.paperGeom), 727303.8153386558, 1e-6);
   assert.equal(
     JSON.stringify({ rooms, walls, cuts, openings, extraBodies }), before,