dwt/screenshot: --stretch for the real unit's 1024->1280 display; record geometry and the background stipple

dwt/notes/REAL_UNIT.md

@@ -45,3 +45,20 @@ The remaining unproven step on this unit is the write path: `poke`/`jump` and
 then the COFF loader + `create_process`. The loader already refuses a target
 outside a free-list block (status 8), so a first attempt with `marker.coff`
 will tell us whether the linked ranges are free before anything runs.
+
+## Display geometry and background (measured)
+
+* Framebuffer **1024×1024, 128 bytes/row**, LSB-first. A 160-byte pitch shears;
+  128 bytes is coherent. The 160-byte figure is the **total raster**
+  (1280/8), not the memory pitch (`RENDER_REPORT.md`).
+* Visible raster **1280×1024** (monitor OSD: 77.2 kHz / 73 Hz; Samsung
+  SyncMaster 770 native 1280×1024). The 1024-wide canvas is displayed 5:4, so
+  `dwt/screenshot.py --stretch 1280x1024` matches the screen. `--screen`'s
+  emulator 1280×901 geometry pads/crops and looks line-doubled.
+* The `101010` background is **real data**, not a decode error. It is a 50%
+  stipple: rows alternate `55` (`01010101`) and `ff`. The root background has a
+  setting; setting it to **100% white** changed the root to solid `ff` (verified
+  by a fresh grab). The Terminal Manager window kept its own stipple, so its
+  window background is a **separate setting** (or was taken at creation).
+* The bottom message box `Ethernet Port Error - 24` is present in VRAM; it is a
+  real terminal error, not a capture artifact.