hero: make the portals real recesses and land the facade on Z 0

The portal detail shot failed for a modelling reason, not a camera reason: the
doors were 0.1 m panels on a solid plinth, so they read as shading. The plinth is
now four piers plus a lintel band, with a 1.2 m reveal, stone jambs and lintels
standing 0.10 m proud and three mullions per opening. review-06 frames them from
8 m at eye height.

Two defects fixed while doing it: the jamb boxes hung 0.15 m below the pavement,
so the facade imported with min Z -15 cm; and a rebuild run against a read-only
.blend silently skipped the save, which is why screenshots kept showing the old
geometry.

MEMORY.md

@@ -120,3 +120,9 @@ Scope: facts and traps that cost time to establish. Planned work lives in [ROADM
 - **Blender-side builders live in `Art/blender/*/`** (terrain, street, site, blockout) and reach helpers via `os.path.join(HERE, "..","..","..","Geo","tools")`. Moving them breaks the old `"..", "Geo", "scripts"` path silently until the script is run.
 - **Height provenance:** 3 of the 15 block buildings carry no OSM height and Blosm renders them at a placeholder 6.4 m. `Geo/tools/block_height_report.py` lists them; they need heights measured off the photographs before the skyline is believable.
 
+## 2026-11-07 — Blender rebuilds that silently did nothing
+
+- **A read-only `.blend` makes Blender skip the save without failing the run.** `Tools/hero_facade_build.py` printed its part list and "bounds" as normal, then went straight to the export: the `.blend` and the report stayed at their old timestamps, and the Unreal re-import brought back the old mesh. Symptom to watch for: the imported bounds do not change after a rebuild. Fix: `chmod u+w` the `.blend` first, then confirm the timestamp moved.
+- **Model bottom must land on Z 0.** The hero portal jambs were sized `PORTAL_H + 0.3` and centred at `PORTAL_H / 2`, so they hung 0.15 m below the pavement and the whole facade imported with `min z = -15 cm`. Always check the asset's `bounds_m.min.z` in the build report.
+- **Rebuilding a facade is not enough to make a detail shot work**: doors modelled as thin panels on a solid plinth read as shading, not openings. Cutting the plinth into piers with a lintel band is what makes them legible from 8 m.
+