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