Add diagnostic logs for HeadsetMicGain fallback + bridge TX payloads

If the HeadsetMicGain GetInfo probe goes wrong, we were silently
falling back to the int8 default range with no log. Now we log each
fallback path distinctly so field diagnostics can tell:
- Exception during GetInfo (transport error)
- GetInfo returned non-None but too short (truncated response)
- GetInfo returned nonsense range (max <= min, probably wrong feature
  format)

Separately, centurion_bridge_request now logs outgoing sub-messages at
INFO level showing sub_idx, function, sw_id, and payload hex. This
pairs with the existing "bridge sub-device error" INFO log so when a
NACK fires we can see both the rejected value and the device's error
code in one place. Verbose during normal operation — dial back to
DEBUG once the G522 writes are confirmed working.

lib/logitech_receiver/device.py

@@ -714,6 +714,17 @@ class Device:
 
         timeout = base.DEFAULT_TIMEOUT
         with base.acquire_timeout(base.handle_lock(handle), handle, timeout):
+            # Log the outgoing sub-message at INFO so field diagnostics can
+            # correlate bridge NACKs with the exact payload we sent (e.g. to
+            # verify mic-gain byte landed in the device's accepted range).
+            if logger.isEnabledFor(logging.INFO):
+                logger.info(
+                    "bridge TX: sub_idx=%d func=0x%02X sw_id=%d payload=%s",
+                    sub_feat_idx,
+                    sub_function,
+                    sw_id,
+                    sub_params.hex() if sub_params else "",
+                )
             if sub_len <= first_chunk:
                 # Single-frame path
                 layer3 = bridge_prefix + bridge_hdr + sub_msg

lib/logitech_receiver/settings_templates.py

@@ -1680,12 +1680,19 @@ class HeadsetMicGain(settings.Setting):
         # LGHUB caches these once at startup to rescale SetMicGain writes.
         try:
             info = device.feature_request(cls.feature, 0x00)
-        except Exception:
+        except Exception as e:
+            logger.info("HeadsetMicGain: GetInfo raised %s, using fallback int8 range", e)
             info = None
         if info and len(info) >= 2:
             min_gain = struct.unpack("b", bytes([info[0]]))[0]
             max_gain = struct.unpack("b", bytes([info[1]]))[0]
             if max_gain <= min_gain:  # sanity — fall back to class defaults
+                logger.info(
+                    "HeadsetMicGain: GetInfo returned nonsense range [%d, %d] (hex=%s), using fallback int8 range",
+                    min_gain,
+                    max_gain,
+                    info.hex(),
+                )
                 min_gain, max_gain = cls.min_value, cls.max_value
             else:
                 logger.info(
@@ -1694,6 +1701,10 @@ class HeadsetMicGain(settings.Setting):
                     max_gain,
                 )
         else:
+            logger.info(
+                "HeadsetMicGain: GetInfo returned %s, using fallback int8 range",
+                info.hex() if info else info,
+            )
             min_gain, max_gain = cls.min_value, cls.max_value
         rw = settings.FeatureRW(cls.feature, **cls.rw_options)
         validator = settings_validator.RangeValidator(min_value=min_gain, max_value=max_gain, byte_count=1, signed=True)