forgetest: the fixture spaces its presses; an unattended refusal is an error; the baseline resets out of a hold

The first campaign with the bench actuator wired failed
motion.button-hold-resume on the tool, not the machine: the second press
was asked while the first 200 ms pulse was still on, the fixture answered
409, the runner handed the step to an operator who was not in the room,
and the post pass could not jog a controller left in Hold.

- fixture.py: a press waits for the last pulse to end (the fixture's
  pulse_ms) plus a 300 ms release, so the controller sees the edge; a
  409 for a pulse in progress is waited out against button_pulsing and
  retried once.
- runner.py: in an unattended run a fixture refusal ends the test at
  once as ERROR naming the refusal; the operator fallback stays for
  attended runs.
- baseline.py: a controller in Hold or Door gets a soft reset before the
  return jog, position kept.
- tests: the fake fixture refuses a press while one is in progress and
  reports button_pulsing; FakeGrbl records ^X and can land a reset in a
  chosen state; five new tests.
- docs: ACCEPTANCE.md fixture rules, fixture/README.md tool's side.

No catalog consequence: tool-side change, no covers map moves.
Bench: campaign c-20260824174545-0bdc 25/25 with every action by the
fixture; the hold reset proven by a dry drill.

forgetest/tests/helpers.py

@@ -184,6 +184,8 @@ class FakeGrbl:
         self.mpos = [0.0, 0.0, 0.0]
         self.sent = []
         self.extra = b""            # text pushed to the client on the next poll
+        self.reset_to = None        # the state a soft reset (^X) lands in, when set
+        self.on_command = None      # called with every command line received
         self._sock = _socket.socket()
         self._sock.setsockopt(_socket.SOL_SOCKET, _socket.SO_REUSEADDR, 1)
         self._sock.bind(("127.0.0.1", 0))
@@ -228,10 +230,16 @@ class FakeGrbl:
                         buf = buf[1:]
                         out += ("<%s|MPos:%.3f,%.3f,%.3f|FS:0,0>\r\n" % (self.state, *self.mpos)).encode()
                     elif buf[0] in (0x18, 0x85, 0x7E, 0x21):
+                        if buf[0] == 0x18:
+                            self.sent.append("^X")
+                            if self.reset_to:
+                                self.state = self.reset_to
                         buf = buf[1:]
                     elif b"\n" in buf:
                         line, buf = buf.split(b"\n", 1)
                         self.sent.append(line.strip().decode("utf-8", "replace"))
+                        if self.on_command:
+                            self.on_command(self.sent[-1])
                         out += b"ok\r\n"
                     else:
                         break