fix: preserve isometric fallback rendering

Issue: #122
User-Visible: no

docs/ISOMETRIC.md

@@ -157,7 +157,8 @@ actions remain the only interactive opening surface.
 - `hide_openings: true`: panels and leaf shadows disappear, while masonry
   cuts, Glow/sun and contact/lock meaning remain;
 - `show_borders: false`: Stage 2 roots are absent and the established floor
-  symbols return (subject to `hide_openings`), avoiding floating panels;
+  symbols and Stage 1 projected frame return (subject to `hide_openings`),
+  avoiding floating panels or an invisible Stage 2 bound that reframes them;
 - Flat, editors and `houseplan-space-card` retain their old symbols and DOM.
 
 Stage 2 adds no window beam, Glow source, sun renderer, material config,

docs/adr/122-isometric-stage2-composition.md

@@ -73,7 +73,11 @@ exception enters the established `space|fingerprint` Flat fallback latch.
 These are presentation constants, not persisted fields. With visible borders,
 vertical panels replace the old floor symbols. `hide_openings` hides panels and
 leaf shadows. With borders disabled, every Stage 2 root is absent and the
-existing floor symbols return, so there are no floating vertical leaves.
+existing floor symbols return, so there are no floating vertical leaves. The
+no-borders branch also keeps the accepted Stage 1 projected frame (floor plus
+the fixed wall-height allowance): absent Stage 2 floor/opening geometry cannot
+contribute invisible bounds and reframe the live floor. With borders visible,
+fit includes every Stage 2 structural bound; blur capability never changes it.
 
 ## Consequences
 

src/houseplan-card.ts

@@ -4557,6 +4557,14 @@ class HouseplanCard extends LitElement {
 
   private _baseVb(): number[] {
     if (this._effectiveProjection() === 'iso') {
+      // No-borders is the accepted Stage 1 no-volume scene. Stage 2 structure
+      // is absent there, so its opening/floor-edge bounds must be absent too;
+      // otherwise merely hiding volume reframes every live floor pixel.
+      if (!this._spaceDisplayForRender().showBorders) {
+        const flat = this._frameOf().rect;
+        const frame = projectedFrame({ rect: flat, wallHeight: ISO_WALL_HEIGHT });
+        return [frame.x, frame.y, frame.w, frame.h];
+      }
       const frame = this._isoScene().frame;
       return [frame.x, frame.y, frame.w, frame.h];
     }
@@ -14170,12 +14178,13 @@ class HouseplanCard extends LitElement {
               preserveAspectRatio="xMidYMid meet" aria-hidden="true" pointer-events="none">
               ${this._renderIsoUnderlay(isoLayers)}
             </svg>` : nothing}
-          <svg class="plan-svg" viewBox=${iso
+          <svg class=${isoLayers?.structural ? 'plan-svg' : nothing}
+            viewBox=${isoLayers?.structural
               ? `${view.x} ${view.y} ${view.w} ${view.h}`
               : `${floorView.x} ${floorView.y} ${floorView.w} ${floorView.h}`}
-            preserveAspectRatio="xMidYMid meet">
-            <g class=${iso ? 'iso-floor-scene' : nothing}
-              transform=${iso ? isoFloorMatrixCss() : nothing}>
+            preserveAspectRatio=${isoLayers?.structural || !iso ? 'xMidYMid meet' : 'none'}>
+            <g class=${isoLayers?.structural ? 'iso-floor-scene' : nothing}
+              transform=${isoLayers?.structural ? isoFloorMatrixCss() : nothing}>
             ${''/* THE PAPER IS THE ROOMS (docs/BACKDROP.md §3, owner
                    2026-08-04). Opaque shapes stop the scene background —
                    bg_color or the 'daynight' sky — from bleeding through the

test/isometric-contract.test.mjs

@@ -46,6 +46,11 @@ test('structural cache includes opening flips and excludes live HA amount', () =
   assert.doesNotMatch(source, /_openingAmt|openingAmount|\.hass|matchMedia|CSS\.supports|theme|hover/);
   assert.match(card, /projectIsoOpening\(basis, this\._openingAmt\(opening\)\)/);
   assert.match(card, /isoLayers && !isoLayers\.floorSymbols/);
+  assert.match(card, /if \(!this\._spaceDisplayForRender\(\)\.showBorders\)/);
+  assert.match(card, /projectedFrame\(\{ rect: flat, wallHeight: ISO_WALL_HEIGHT \}\)/);
+  assert.match(card, /viewBox=\$\{isoLayers\?\.structural[\s\S]*?: `\$\{floorView\.x\}/);
+  assert.match(card, /preserveAspectRatio=\$\{isoLayers\?\.structural \|\| !iso \? 'xMidYMid meet' : 'none'\}/);
+  assert.match(card, /transform=\$\{isoLayers\?\.structural \? isoFloorMatrixCss\(\) : nothing\}/);
 });
 
 test('Stage 2 adds no schema, dependency, storage, network or HA action surface', () => {