Helios diode current: stop the status poll overwriting the setpoint

The current spin box could not hold a typed value: the 1 Hz status poll
read LDS and wrote it straight into the spin box, so the operator's number
was replaced by the laser's within a second — before Set could be pressed.
The spin box is now seeded once on connect and belongs to the operator
after that; the poll's reading goes to a read-back label beside the Set
button, so the value about to be sent and the value the laser holds are
separate readouts.

The write itself was also unverified. Section 6 of the operator's manual:
"Commands or set values can be discarded by the controller unintentionally.
It is recommended to query the set value after the command is entered to
confirm the actual value." set_current_ma() wrote LDS and returned True
regardless, so a discarded write looked exactly like a good one.
_write_verified() now writes, reads back, and retries up to three times;
set_current_ma() and set_frequency_hz() use it, and HeliosWorker reports a
refusal on the status line instead of echoing the requested value.

Also from the manual, recorded but not acted on: LDS accepts 0-7000 mA
(the driver's 2000 mA ceiling is this rig's, not the protocol's), LDF has
to be re-sent after LDG changes, and the power-monitor mnemonic is HMP —
which this laser does not implement, per the operator.

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

hardware/helios_laser.py

@@ -210,6 +210,38 @@ class HeliosLaser:
             logger.error(f"Failed to read the reply to '{command}': {e}")
         return True
 
+    # Section 6 of the operator's manual, under Syntax:
+    #
+    #     Commands or set values can be discarded by the controller
+    #     unintentionally.  It is recommended to query the set value after
+    #     the command is entered to confirm the actual value.
+    #
+    # (The command table repeats it: "Query the command to confirm it was
+    # accepted.")  A setter that only writes therefore cannot report whether
+    # it worked, and the panel's next status poll reads back the old value —
+    # which looks exactly like the GUI refusing the operator's number.
+    SET_RETRIES = 3
+    SET_SETTLE_S = 0.05         # let the controller store it before reading
+
+    def _write_verified(self, mnemonic: str, value: int) -> bool:
+        """Write `value` to `mnemonic`, and confirm the controller took it.
+
+        Returns False if the read-back never matches, leaving the controller
+        holding whatever value it kept — the caller is expected to say so
+        rather than let the discarded write pass for a successful one.
+        """
+        for attempt in range(1, self.SET_RETRIES + 1):
+            if not self._write_command(f"{mnemonic} {value}"):
+                return False
+            time.sleep(self.SET_SETTLE_S)
+            readback = self._query_int(mnemonic)
+            if readback == value:
+                return True
+            logger.warning(
+                f"'{mnemonic} {value}' not accepted: controller reports "
+                f"{readback} (attempt {attempt}/{self.SET_RETRIES})")
+        return False
+
     def _query_int(self, command: str) -> Optional[int]:
         """Query a value that should parse as an int; None if absent/unparseable."""
         raw = self._query(command)
@@ -235,20 +267,28 @@ class HeliosLaser:
             logger.error(f"Period {period_ns} ns out of range (8000-60000)")
             return False
 
-        command = f"LDF {period_ns}"
-        return self._write_command(command)
+        return self._write_verified("LDF", period_ns)
 
     def set_current_ma(self, current: int) -> bool:
-        """Set pump diode current in mA."""
+        """Set pump diode pulse current (LDS) in mA.
+
+        False means the controller did not take the value — see
+        _write_verified.  The manual's range for LDS is 0-7000 mA; the
+        2000 mA ceiling here is this rig's limit, not the protocol's.
+        """
         if not (0 <= current <= 2000):
             logger.error(f"Current {current} mA out of range (0-2000)")
             return False
 
-        command = f"LDS {current}"
-        return self._write_command(command)
+        return self._write_verified("LDS", current)
 
     def set_pulse_mode(self, mode: PulseMode) -> bool:
-        """Set pulse mode."""
+        """Set pulse mode.
+
+        Note from the manual's LDG entry: "LDF has to be set again after LDG
+        is changed, except for single pulse triggering" — so a caller that
+        changes the mode has to re-send the frequency.
+        """
         command = f"LDG {mode.value}"
         return self._write_command(command)