Helios: don't let an unlabelled reply pass for a register's value

_value_in()'s last resort was to accept any line it could not attribute as
the answer to whatever had just been asked.  That fallback exists for the
serial numbers, which come back bare — but it applied to every query, so a
stray "32" could be read as a diode current of 32 mA.  32 is also what a
status register reads with bit 5 set (LER "Over voltage laser diode", LCE
"Door switch open", CCE "Q-switch under/over temperature"), which is
exactly the value the panel is stuck on.

Only CSR and HSR now accept an unlabelled reply; every other read has to
see its own mnemonic in the line.  A read that cannot be attributed returns
None, and the panel shows "laser: ? mA" instead of leaving the last good
value on screen looking live — a stale reading and a setpoint that refuses
to move are indistinguishable otherwise.

tools/helios_lds_probe.py is the diagnostic for the underlying question:
it talks to the controller with no reply parsing at all and prints every
byte, so the transcript says whether LDS answers for itself, whether the
write is taken, and which flags the registers hold before and after.  The
status-register tables move to hardware/helios_registers.py so the probe
can decode them without importing the Qt app.

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

hardware/helios_laser.py

@@ -130,15 +130,21 @@ class HeliosLaser:
                 return lines
             time.sleep(0.005)
 
-    @staticmethod
-    def _value_in(line: str, mnemonic: str) -> Optional[str]:
+    # The only replies that come back without naming what they answer.
+    # Every other line has to identify itself: an unlabelled number is not
+    # evidence that it is *this* register's number, and taking one on faith
+    # is how a status register's value ends up displayed as a diode current.
+    UNLABELLED_REPLIES = frozenset({"CSR", "HSR"})
+
+    @classmethod
+    def _value_in(cls, line: str, mnemonic: str) -> Optional[str]:
         """The value `line` holds for `mnemonic`, or None if it isn't its reply.
 
         The controller answers "LDF = 20000 ns".  A line naming a different
         mnemonic is the tail of an earlier reply, and "Bit 15..0: ..." is a
         status register's decode line; neither is an answer to this query.
-        A line naming nothing is taken as the value — that is how the serial
-        numbers come back.
+        A line naming nothing counts only for the serial numbers, which is
+        the one reply known to come back bare.
         """
         head, sep, tail = line.partition('=')
         if sep:
@@ -152,7 +158,9 @@ class HeliosLaser:
         fields = line.split()
         if fields and fields[0].upper() == mnemonic:
             return fields[1] if len(fields) > 1 else None
-        return line
+        if mnemonic in cls.UNLABELLED_REPLIES:
+            return line
+        return None
 
     def _query(self, command: str) -> Optional[str]:
         """Send a query and return the value from its response.

hardware/helios_registers.py

@@ -0,0 +1,102 @@
+"""Helios status-register bit definitions (Tables 8-1, 8-2, 8-3).
+
+Kept out of the driver and out of the Qt apps so that a command-line
+diagnostic can decode a register without importing either.
+
+Each entry: bit_number -> (severity, description, comment)
+  severity: 'C' = critical error, 'S' = status, 'I' = input error, '' = none
+"""
+
+LER_FLAGS = {
+    0:  ('C', 'Controller temperature failure (resonator/SHG/q-switch)',
+         'Check CCE register for details'),
+    1:  ('S', 'Trigger input active',
+         'High when trigger signal applied or laser in continuous pulsing'),
+    2:  ('I', 'Command error',
+         'Unknown command sent to controller'),
+    3:  ('C', 'Laser disable pin open (utility connector)',
+         'Shuts down pump diodes; reset LER 0 required to restart'),
+    4:  ('C', 'Internal hardware failure',
+         'Contact Coherent'),
+    5:  ('C', 'Over voltage laser diode',
+         'Check for open circuit or voltage spikes'),
+    6:  ('C', 'Internal hardware failure',
+         'Contact Coherent'),
+    7:  ('C', 'Controller temperature failure at pump diodes',
+         'Check LCE register for details'),
+    8:  ('S', 'Laser start delay (60 s warmup)',
+         'Laser cannot be started yet; status error LED flashing'),
+    9:  ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    10: ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    11: ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    12: ('S', 'Slave controller error (remote input)',
+         'Valid only for master controller coupled with a slave'),
+    13: ('',  'Laserhead not found',
+         'Head not connected / not found; check EMI; ignore for double-electronic slave'),
+    14: ('',  'Laserhead I\u00b2C acknowledge error',
+         'Check environment for strong EMI; ignore for double-electronic slave'),
+    15: ('S', 'Range-Error (not critical)',
+         'Input value out of range'),
+}
+
+LCE_FLAGS = {
+    0:  ('C', 'Pump diode over/under temperature',
+         'Limit exceeded (<10\u00b0C or >60\u00b0C); check head cooling'),
+    1:  ('C', 'Internal hardware failure',
+         'Contact Coherent'),
+    2:  ('C', 'Pump diode temperature out of range',
+         'Actual temp >2\u00b0C off setpoint for >1 min'),
+    3:  ('C', 'Pump diode current critical',
+         'Current set too close to current limit'),
+    4:  ('C', 'Pump diode temperature out of limit',
+         'Pump diode temperature is out of limit'),
+    5:  ('S', 'Door switch open',
+         'Close utility connector pin 2 permanently to pin 9 (GND)'),
+    7:  ('C', 'Pump diode NTC error',
+         'Invalid temperature measured or NTC broken'),
+    8:  ('C', 'Laser diode power stage over temperature',
+         'Temp <10\u00b0C or >65\u00b0C at controller; check controller cooling'),
+    9:  ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    10: ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    11: ('C', 'Internal hardware failure',
+         'Check environment for strong EMI; contact Coherent'),
+    15: ('S', 'Range-Error (not critical)',
+         'Input value out of range'),
+}
+
+CCE_FLAGS = {
+    0:  ('C', 'Resonator/SHG under/over temperature',
+         'Limit exceeded (<10\u00b0C or >60\u00b0C); temperature controller deactivated'),
+    1:  ('C', 'Resonator/SHG NTC failure',
+         'Temperature sensor broken or disconnected'),
+    2:  ('C', 'Resonator/SHG temperature out of range',
+         'Actual temp >2\u00b0C off setpoint for >1 min'),
+    3:  ('C', 'Q-switch ADC / temperature readout failure',
+         'Internal hardware error or no NTC connected'),
+    4:  ('C', 'Q-switch temperature out of range',
+         'Actual temp >2\u00b0C off setpoint for >1 min'),
+    5:  ('C', 'Q-switch under/over temperature',
+         'Limit exceeded (<10\u00b0C or >60\u00b0C); temperature controller deactivated'),
+    7:  ('C', 'Q-switch NTC failure',
+         'Internal hardware error or no NTC connected'),
+    8:  ('C', 'Internal hardware failure',
+         'Contact Coherent'),
+    15: ('S', 'Range-Error (not critical)',
+         'Input value out of range'),
+}
+
+SEVERITY_LABEL = {'C': '[CRIT]', 'S': '[STAT]', 'I': '[INPT]', '': '[INFO]'}
+
+
+def decode_register(flags_dict: dict, value: int) -> list:
+    """Return list of (bit, severity, description, comment) for each set bit."""
+    active = []
+    for bit, (sev, desc, comment) in flags_dict.items():
+        if value & (1 << bit):
+            active.append((bit, sev, desc, comment))
+    return active