Name every machine after its own MAC address, and drop mDNS

One name for every machine was wrong: an operator with two of them on a
network had one forgefirm.local, and mDNS does not work on many networks
at all. The machine now calls itself forgefirm-<xxxx>, from the last four
hex digits of its WiFi MAC address, and sends that name with its DHCP
request, so a network with dynamic DNS publishes it and a router lists
the machine by name. The name is the same at every boot, two machines
take different names, and no serial number leaves the machine.

forgefirm-hostname (new): reads the wlan0 MAC address (eth0 on a machine
with no WiFi) at S38 in rcS, after udev has probed the network drivers
and before poky's hostname.sh reads the file and before the network
starts. The rootfs is read-only, so the name is written through a
bind-mounted copy under /run/forgefirm. A bounded wait covers a slow
probe. hostname:pn-base-files is "forgefirm": the name before S38, and
the fallback when no MAC address can be read.

avahi is deleted - the bbappend, the daemon configuration, the service
file, the image install and the distro block. The address is the way in
that works on every network, and the DHCP name covers the rest.

forgefirm-banner: the marker lines are gone. "# ForgeFIRM addresses" and
"# end" delimited the address block inside /etc/issue, and getty prints
every line of that file, so both markers were on the console. The script
now keeps the image's own text in a second copy under /run/forgefirm,
captured once per boot before the first write, and renders the whole
banner from it. The block is the addresses alone: no mDNS name.

forgefirm-image.bb: the ForgeFIRM mark, under the OpenGlow one the base
image carries, with the version on the mark's own last line,
right-justified to the mark's last column. The mark is written once and
rendered per reader, because /etc/issue is parsed by busybox getty (a
backslash or a percent sign starts an escape, so the art goes in with
every backslash doubled) while /etc/motd is written out as it is. Widths
are measured in columns, not bytes: the color sequences take no room on
the screen. /etc/issue.net stays unused - the machine tells a client that
has not logged in nothing.

Acceptance: commission.mdns-announce is replaced by
commission.machine-name, which checks the name against the MAC address,
the bind-mounted /etc/hostname, the DHCP client's hostname option, the
banner's addresses, and that no mDNS responder is on the image; it covers
nothing by design, like the test it replaces. forgectrl.auth gains the
own-name Host check and its refusal with a domain on it. image.health
checks the /etc/hostname mount and the version on the mark's last line in
both files. commission.ssh-until-reboot asserts there is no
pre-authentication banner. commission_dark's lens coverage widens to
src/lenshome.* so src/lenshome.h is covered; the lint is clean at 83
tests.

Pins: forgectrl 0.1.14 (9e5330f, the hostname certificate and the Host
rule), meta-openglow ced2af2 (the DHCP hostname option and the motd mark)
in the kas lock.

Proven on the bench reference, hot-deployed and rebooted (image
20260910000208 dev): hostname forgefirm-b00a from MAC 2c:6b:7d:0d:b0:0a,
live and in the bind-mounted file; the DHCP client running with
-x hostname:forgefirm-b00a; the console banner and the motd carrying both
marks with the version aligned to the mark's last column, no marker line
and no .local name; forgectrl regenerating its certificate for the new
name. Host tests: 357 forgetest unit tests, forgectrl clean under
-Werror, tls_test and sanitize_test.

forgetest/tests/test_commission_suite.py

@@ -1,13 +1,11 @@
 """The commission.* suite on the host: the registration (ids, kinds, the
 takeover tests, the operator tests' hands), the record builders, the
-mDNS packet code, the cookie parsing, the LED cue, the settle rule for a
+machine's name, the cookie parsing, the LED cue, the settle rule for a
 gated supervisor, and the cloud-off surface test driven end to end
 against the fake daemon."""
 import json
 import os
 import shutil
-import socket
-import struct
 import tempfile
 import unittest
 
@@ -19,7 +17,7 @@ from forgetest.suite import commission
 IDS = ("commission.gate-blocks-controllers", "commission.override-until-reboot",
        "commission.advisories-rehash", "commission.account-login", "commission.https-only-writes",
        "commission.ssh-until-reboot", "commission.cloud-disabled-surface",
-       "commission.factory-return", "commission.mdns-announce", "commission.first-run-flow",
+       "commission.factory-return", "commission.machine-name", "commission.first-run-flow",
        "commission.first-run-page", "commission.what-changed", "commission.record-export",
        "commission.mirror")
 OPERATOR = ("commission.first-run-flow", "commission.first-run-page")
@@ -104,8 +102,8 @@ class RegistrationTests(unittest.TestCase):
         self.assertEqual(t.kind, "auto")                 # the return itself is a bench drill, not a test
         self.assertFalse(t.hands)
 
-    def test_mdns_covers_nothing_by_design(self):
-        self.assertEqual(self.reg["commission.mdns-announce"].covers, ())
+    def test_the_machine_name_covers_nothing_by_design(self):
+        self.assertEqual(self.reg["commission.machine-name"].covers, ())
 
     def test_the_login_test_makes_its_own_account(self):
         # No bench credentials, no precheck: the test installs a temporary
@@ -184,35 +182,45 @@ class RecordTests(unittest.TestCase):
             os.environ.pop("GF_RUN_DIR", None)
 
 
-class MdnsTests(unittest.TestCase):
-    def test_query_is_a_unicast_response_question(self):
-        q = commission.mdns_query("forgefirm.local", qid=0x1234)
-        qid, flags, qd, an, ns, ar = struct.unpack(">HHHHHH", q[:12])
-        self.assertEqual((qid, flags, qd, an, ns, ar), (0x1234, 0, 1, 0, 0, 0))
-        self.assertEqual(q[12:], b"\x09forgefirm\x05local\x00" + struct.pack(">HH", 1, 0x8001))
+class MachineNameTests(unittest.TestCase):
+    def setUp(self):
+        self.root = tempfile.mkdtemp()
+        self.addCleanup(shutil.rmtree, self.root, ignore_errors=True)
 
-    def _response(self, qid, name_bytes, addr, flags=0x8400, extra=b""):
-        q = b"\x09forgefirm\x05local\x00" + struct.pack(">HH", 1, 1)
-        rr = name_bytes + struct.pack(">HHIH", 1, 0x8001, 120, 4) + socket.inet_aton(addr)
-        return struct.pack(">HHHHHH", qid, flags, 1, 1, 0, 0) + q + rr + extra
+    def _net(self, **devs):
+        """A /sys/class/net tree; commission.mac_suffix reads it through
+        commission.read_file, which takes an absolute path."""
+        for dev, mac in devs.items():
+            d = os.path.join(self.root, dev)
+            os.makedirs(d)
+            with open(os.path.join(d, "address"), "w") as f:
+                f.write(mac + "\n")
+        real = commission.read_file
 
-    def test_answers_follow_a_compression_pointer(self):
-        pkt = self._response(7, b"\xc0\x0c", "192.168.1.9")
-        self.assertEqual(commission.mdns_answers(pkt, 7), [("forgefirm.local", "192.168.1.9")])
+        def read(path):
+            head = "/sys/class/net/"
+            if path.startswith(head):
+                return real(os.path.join(self.root, path[len(head):]))
+            return real(path)
 
-    def test_answers_with_the_name_spelled_out(self):
-        pkt = self._response(0, b"\x09forgefirm\x05local\x00", "10.0.0.5")
-        self.assertEqual(commission.mdns_answers(pkt), [("forgefirm.local", "10.0.0.5")])
+        commission.read_file = read
+        self.addCleanup(setattr, commission, "read_file", real)
 
-    def test_wrong_id_or_a_query_yields_nothing(self):
-        pkt = self._response(7, b"\xc0\x0c", "192.168.1.9")
-        self.assertEqual(commission.mdns_answers(pkt, 8), [])
-        self.assertEqual(commission.mdns_answers(self._response(7, b"\xc0\x0c", "1.2.3.4", flags=0), 7), [])
-        self.assertEqual(commission.mdns_answers(b"\x00" * 5), [])
+    def test_the_wifi_address_names_the_machine(self):
+        self._net(wlan0="2C:6B:7D:0D:B0:0A", eth0="00:11:22:33:44:55")
+        self.assertEqual(commission.mac_suffix(), "b00a")
 
-    def test_a_truncated_packet_yields_nothing(self):
-        pkt = self._response(7, b"\xc0\x0c", "192.168.1.9")
-        self.assertEqual(commission.mdns_answers(pkt[:20], 7), [])
+    def test_a_machine_with_no_wifi_falls_back_to_the_wired_address(self):
+        self._net(eth0="00:11:22:33:44:55")
+        self.assertEqual(commission.mac_suffix(), "4455")
+
+    def test_an_unread_address_is_no_address(self):
+        self._net(wlan0="00:00:00:00:00:00")
+        self.assertEqual(commission.mac_suffix(), "")
+
+    def test_no_interface_is_no_address(self):
+        self._net()
+        self.assertEqual(commission.mac_suffix(), "")
 
 
 class SmallHelpersTests(unittest.TestCase):