forgetest: motion tests end on the machine's idle; the Grbl client survives a soft reset

wait_idle returned on a stale Idle before a just-commanded move began,
and the tests declared PASS on grblHAL's Idle while the kernel still
played the stream depth and the decel tail (the baseline caught
state=running after motion.pacing). Every motion test now ends on
forgectrl's idle (machine_idle), and wait_idle ignores an Idle inside a
short grace unless a non-Idle state was seen.

status_report re-sends '?' every 0.5 s until a report arrives: a soft
reset (^X) flushes the controller's read buffer and eats a '?' that lands
in it - the bench saw motion.cancel-abort error with no report for 5 s
after the abort while the controller answered the next '?' at once.

motion.deadman: the SIGSTOP drill waited for a running controller and
got the killed pid back before the supervisor reaped it (drill 1 already
waited for a different pid); and the forgectrl-restart drill expected the
busy controller's pid to survive the retake, but a retake under the
broker is stop-at-idle, re-probe, start a supervised controller (the old
inherited fd cannot be adopted) - the check is now: the move finished
unmanaged, supervision came back running and verified. Bench-proven
2026-08-16: kill respawn 1.3 s, hang -> underrun 0.21 s, retake at idle.

forgetest/forgetest/hw.py

@@ -276,10 +276,14 @@ class Grbl:
         self.send_raw(bytes([byte]))
 
     def status_report(self):
-        """One '?' report, parsed: {'state': 'Idle', 'MPos': (x,y,z), ...}."""
+        """One '?' report, parsed: {'state': 'Idle', 'MPos': (x,y,z), ...}.
+        The '?' is re-sent every 0.5 s until a report arrives: a soft
+        reset (^X) flushes the controller's read buffer and eats a '?'
+        that lands in it."""
         self.drain()
         self.send_raw(b"?")
         deadline = time.time() + self.timeout
+        resend = time.time() + 0.5
         self.sock.settimeout(0.2)
         while time.time() < deadline:
             try:
@@ -288,6 +292,9 @@ class Grbl:
                     self.buf += d
             except socket.timeout:
                 pass
+            if time.time() >= resend:
+                self.send_raw(b"?")
+                resend = time.time() + 0.5
             i = self.buf.find(b"<")
             j = self.buf.find(b">", i + 1) if i >= 0 else -1
             if i >= 0 and j > i: