mini-dhcpd: stop reporting ARP as a corrupted frame

Swiss got a DHCP lease on hardware (10.0.0.64/24), but the script flagged
every ARP from the GC as "frame did NOT parse as DHCP ... this is what a
corrupted TX frame looks like".  That was wrong and actively misleading: the
frames are valid lwIP duplicate-address probes (sender 0.0.0.0, target =
the offered address), sent to check the lease is free before accepting it.

The parser conflated "not DHCP" with "corrupted".  A diagnostic that cries
wolf on normal traffic is worse than none, because 'malformed' then means
nothing.  Now:

  'info'      from the client but not DHCP -- ARP decoded properly (probe vs
              request vs reply, with addresses), other ethertypes named
  'malformed' CLAIMED IPv4/UDP->67 and then failed to parse, i.e. what a
              genuinely damaged TX frame would look like

So the corruption diagnostic still works -- that was the point of using a raw
socket -- but it only fires when it means something.

scripts/test-mini-dhcpd.py keeps the self-test, now including the exact
60-byte frame from the console (T6), a damaged DHCP packet that must still be
flagged (T7), and a raw ethertype (T8).

One note for anyone extending that test: the real frame goes in as ONE string
literal.  Splitting the hex across two adjacent literals is how the first
version of T6 silently lost a byte and blamed the parser for decoding the
target as 0.10.0.0 -- the parser was correct.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -1353,6 +1353,34 @@ parallel master is the default — see "W5100 vs W5500".)
 
 ---
 
+## ✅ SWISS GETS A DHCP LEASE ON HARDWARE (2026-10-10)
+
+`DISCOVER → OFFER → REQUEST → ACK`, lease `10.0.0.64/24`, served by
+`scripts/mini-dhcpd.py` on a direct link. This is the first end-to-end proof
+of the two paths our own test suite **structurally cannot** exercise:
+
+- **The command-level interrupt works.** Receiving the OFFER requires
+  `bba_event_handler` → `bba_cmd_in8(0x03) & 0x80` → `bba_interrupt()` →
+  `bba_start_rx()`. That chain was dead until the `cmd_ir[7]` fix;
+  `gc_bba_test` and `netboot` poll `RWP`/`IR` and would never have noticed.
+- **libogc2's TX path works** — no TWD write, `EXI_Dma` payload, NCRA ST1 —
+  so the GC's documented DMA-write 1-bit-shift bug is NOT biting us.
+- **The MACRAW MF filter accepts unicast to `SHAR`**: both replies were sent
+  unicast to `00:09:bf:00:00:01` and arrived.
+
+Getting there needed, in order: the packed RX descriptor, both command-space
+forms, the counted TX length, the command-level interrupt, removing the
+device-ID one-shot, and the MF filter. Any one of them missing stops DHCP.
+
+⚠️ **ARP from the GC is expected, not a fault.** lwIP sends an ARP probe
+(`sender 0.0.0.0`, `target` = the offered address) to check the lease is free
+before accepting it. The first version of `mini-dhcpd.py` reported every ARP
+as a corrupted TX frame; it now decodes them. Its padding is uninitialised
+junk rather than zeros, which is also normal — lwIP pads to the 60-byte
+ethernet minimum with whatever is in the pbuf.
+
+---
+
 ## ⚠️ Open compatibility gaps — see `docs/bba_compat_todo.md`
 
 Known differences between this implementation and what real GC software