dwt: trace the bottom diagnostics message box to @0xCB640 and the RAM message table

dwt/notes/REAL_UNIT.md

@@ -388,3 +388,25 @@ The build name must be <= 8 characters: `tftpc_real` silently fails (no
 
 Evidence: `dwt/loader/evidence/real-unit-xtext/` (loads, markers, server logs,
 screenshots, emulator runs, `xtext_probe.lua`).
+
+### Bottom diagnostics box: live state (2026-10-18, read-only)
+
+The separate bottom X window is owned by the Terminal Manager; its window id is
+the global at bit `0xB7C60`. The text is selected from the status mask at bit
+`0xCB640` and a pointer list at bit `0x19F150` (20-byte entries, string pointer
+at +8 bytes). Live reads, two samples 2 s apart:
+
+```
+peek 0xCB640 4   -> 00 00 00 00      mask 0 -> "All Diagnostics Passed"
+peek 0xB7C60 4   -> 2d 00 10 00      box window 0x0010002d
+peek 0x19F190 4  -> a0 b9 4a 3f      list[0] -> 0x3F4AB9A0
+peek 0x19F230 4  -> 00 00 00 00      null terminator
+peek 0x19FF10 2  -> 00 00            language 0 (English)
+peek 0x19E8D0 4  -> 90 b0 4a 3f      record 8: "Ethernet Port Error - 24"
+peek 0x27C190 4  -> 00 00 00 00      DIAGNOSTIC MAILBOX pointer is NULL
+peek 0x3F4AB9A0  -> "All Diagnostics Passed"
+```
+
+The mask bit mapping (bit 15 = Ethernet Port Error - 24, bit 8 = Video RAM
+Error - 22, ...) was verified dynamically in MAME by setting `@0xCB640` before
+the builder at frame 569. Full trace: `dwt/notes/MESSAGEBOX.md`.