fix: hidden architecture no longer widens the fit: house frame (#384)

Wall bodies, extras and zero walls vote in the tight frame only while
show_borders renders them — mirroring the hideOpenings guard for opening
symbols. needsCanonicalWallGeometry returns to its pre-#373 form: the
union is no longer forced for extras-only plans just for the frame.

User-Visible: yes
Issue: #384

scripts/mutation-gate.mjs

@@ -735,6 +735,17 @@ const MUTANT_DEFINITIONS = [
       replace: "      this._persistDecorStyle();\n    }, 0);",
     }],
   },
+  {
+    id: 'fit-house-hidden-walls-vote',
+    guard: 'node demo/smoke_space_card.mjs',
+    because: 'hidden architecture silently widening the tight frame is exactly the #384 bug: '
+      + 'only the twin-frames smoke sees the rendered viewBox difference',
+    patches: [{
+      file: 'src/space-render.ts',
+      find: "    if (disp.showBorders) for (const body of extras) {",
+      replace: "    for (const body of extras) {",
+    }],
+  },
   {
     id: 'space-card-null-title-compact-narrowed',
     guard: 'node --test test/space-card-audit-lows.test.mjs',