dwt/tcpip: LAN TFTP client (100.103.255.254) and a verified self-contained fetch + load on the real unit

dwt/notes/REAL_UNIT.md

@@ -282,3 +282,25 @@ The LANCE address ROM at bit `0x6800000` reads (low bytes of the words):
 
 byte-identical to the MAME model. The `Ethernet Address ROM Test` passing is
 consistent with this.
+
+### Self-contained TFTP loader on the real unit
+
+Retargeted `tftpc.asm` to the LAN (`100.103.255.254:69`) as
+`dwt/tcpip/tftpl.asm`; the RRQ name stays `dwt/tcpip/probe.bin` because the
+server serves the chosen COFF for any requested name. The DOS 8.3 build name
+must be <= 8 characters: `tftpc_lan` silently truncates and GSPLNK produces no
+`TFTPC_LAN.OUT`; `tftpl` is safe.
+
+```
+server: dwt/tcpip/serve_probe.py 100.103.255.254 --file dwt/loader/build/xhello.coff
+RRQ:    100.103.100.103:1036 requested 'dwt/tcpip/probe.bin' (774 bytes)
+fetch:  sha256 a8b3014d27deb97adcebb418a5d14da51fc3c11559e84923ede72e260d3e7271
+loader: status 0, entry 0x01840000, pcb 0x00849a10
+app:    xhello stage=6 strlen=4
+```
+
+Evidence: `dwt/loader/evidence/real-unit-tftp/hostload_tftp_xhello.png`.
+
+This is the first fully self-contained delivery on the real unit: the terminal
+fetched the COFF over TFTP into `malloc` memory and ran it in a created
+process, with only the rdebug jump used to start the fetch.