dwt/screenshot: real geometry is 1280x1024 with a 256-byte stride (160B image + 96B mask); --real captures the full screen

dwt/notes/REAL_UNIT.md

@@ -132,3 +132,26 @@ bottom — the whole screen.
 framebuffer; it is **not** 1:1 and the nearest-neighbour version produces the
 uneven-pixel artefacts. Use it only for an approximate visual match, not as
 evidence.
+
+### Final geometry: 1280x1024, 256-byte row stride
+
+The real unit is **1280x1024** with a **256-byte row stride**. Each row's first
+**160 bytes (1280 px)** are the image; the remaining **96 bytes** are a `0x55`
+mask. The earlier "1024x2048, even rows" reading was an artifact of treating
+that 96-byte gap as an alternate row.
+
+This is why the 1024-wide reads lost the right quarter: the Icon Box really is
+1280 px wide and its resize buttons are at the far right, outside a 1024-px
+crop. The mask bytes are what looked like "line doubling".
+
+Correct 1:1 capture:
+
+```sh
+python3 dwt/screenshot.py --host 100.103.100.103 --real --out screen.png
+```
+
+`--real` = width 1280, stride 256, 1024 rows, no resampling.
+`dwt/evidence/real-unit-1280-1to1.png` is the full 1280x1024 screen, including
+the Icon Box resize buttons and the `Ethernet Port Error - 24` box.
+
+The emulator geometry is unchanged: 1024x1024 with a 128-byte stride.