fsp-server: implement GET_PRO (0x47), which Swiss asks for first

Swiss sent CC_GET_PRO 'swiss/patches' and the server replied "unsupported".
Reply shape, from fsplib's fsp_getpro:

  * pos MUST equal FSP_PRO_BYTES (1), or fsplib fails with ENOMSG
  * the flags byte is at buf[len] -- the first byte of the EXTRA region,
    after the echoed name, NOT inside the data field
  * a missing directory must be CC_ERR so fsplib reports ENOENT, because
    Swiss probes "swiss/patches", then "swiss", then "" and relies on that
    fallback chain

Those bits are not cosmetic.  deviceHandler-FSP.c does:

  if ((pro & (MKDIR|ADD|DEL|GET)) == (MKDIR|ADD|DEL) || (pro & OWNER)) {
      features |= FEAT_PATCHES;  emulable |= EMU_ETHERNET;
  } else { ... clears both ... }

so a plain read-only answer makes Swiss DISABLE patch support on this device.
Default is therefore the honest GET|LIST (0x50) with patches disabled, and
--claim-owner reports OWNER to turn them back on -- flagged in the help as
unsafe for now, because this server has no UP_LOAD or MAKE_DIR, so Swiss
believing it can write here would make a patch write fail rather than degrade.
Try without it first.

T9 checks pos == 1 and that the flags land at buf[len] with GET|LIST and
without OWNER; T10 checks a missing directory gives CC_ERR so the fallback
chain works.

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

scripts/test-fsp-server.py

@@ -124,6 +124,36 @@ try:
         fails.append(f"T8 traversal escaped the root: type {ty} size {sz}")
     else:
         print("T8 ../../etc/passwd refused")
+    # T9 GET_PRO: flags go in the EXTRA region at buf[len], and pos must
+    # equal FSP_PRO_BYTES (1) or fsplib returns ENOMSG.
+    CC_GET_PRO = 0x47
+    r = rt(req(CC_GET_PRO, 20, 0, ""))
+    if r["cmd"] != CC_GET_PRO:
+        fails.append(f"T9 GET_PRO cmd {r['cmd']:#04x}")
+    elif r["pos"] != 1:
+        fails.append(f"T9 GET_PRO pos {r['pos']}, want 1 (FSP_PRO_BYTES) "
+                     f"- fsplib returns ENOMSG otherwise")
+    else:
+        s.sendto(req(CC_GET_PRO, 21, 0, ""), A)
+        raw = s.recv(2048)
+        ln = struct.unpack("!H", raw[8:10])[0]
+        pro = raw[HSIZE + ln]          # buf[len] -- the first extra byte
+        if not (pro & 0x10) or not (pro & 0x40):
+            fails.append(f"T9 GET_PRO flags {pro:#04x} lack GET|LIST")
+        elif pro & 0x01:
+            fails.append(f"T9 GET_PRO claims OWNER without --claim-owner")
+        else:
+            print(f"T9 GET_PRO -> pos=1, flags {pro:#04x} (GET|LIST) at buf[len]")
+
+    # T10 a missing directory must be CC_ERR, so fsplib reports ENOENT and
+    # Swiss falls back from "swiss/patches" to "swiss" to "".
+    r = rt(req(CC_GET_PRO, 22, 0, "swiss/patches"))
+    if r["cmd"] != CC_ERR:
+        fails.append(f"T10 GET_PRO on a missing dir returned {r['cmd']:#04x}, "
+                     f"want CC_ERR -- Swiss's fallback chain needs ENOENT")
+    else:
+        print("T10 GET_PRO 'swiss/patches' -> CC_ERR (Swiss falls back to root)")
+
 finally:
     srv.terminate()