Fix Signal name reset and orphaned references on device reconfigure

Apply & Reconnect rebuilt a device's whole Signal list from hardware
defaults on every call, silently discarding user/profile-set names,
units, and colors even when pins hadn't changed. Add
merge_signal_metadata() and call it from ArduinoDevice.remap_pins()
and SerialDevice.reconfigure() to reapply the same fields
ProfileManager already treats as user overrides, keyed by signal_id.

Also close a related gap: removing a pin that a Channel/Plot/Control
still referenced left it silently dangling, and SignalProcessor never
pruned its latest-value cache, so a derived Channel kept computing off
a permanently frozen stale reading. Add SignalProcessor.
on_device_reconfigured() to purge that cache, reference_registry.
find_references() for a console breadcrumb, and live "missing source"
indicators on Plot traces and Channel blocks reusing ControlWidget's
existing stale/QSS pattern. Also fixes ControlWidget._write() still
enqueuing writes to a channel that no longer exists.

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

3 files changed, 21 insertions, 4 deletions

diff --git a/devices/arduino_device.py b/devices/arduino_device.py
index 5c954c8..1512223 100644
--- a/devices/arduino_device.py
+++ b/devices/arduino_device.py
@@ -15,7 +15,7 @@ from PyQt6.QtWidgets import (
 )
 from PyQt6.QtCore import Qt, QThread, pyqtSignal
 
-from devices.base_device import BaseDevice, SignalConfig, DeviceInfo, DeviceStatus
+from devices.base_device import BaseDevice, SignalConfig, DeviceInfo, DeviceStatus, merge_signal_metadata
 from api_layers.arduino_layer import ArduinoLayer
 
 _ANALOG_COLORS = [
@@ -268,7 +268,7 @@ class ArduinoDevice(BaseDevice):
             self._do_pins = list(do_pins)
             self._do_map  = {f"do{i}": p for i, p in enumerate(do_pins)}
 
-        self.info.signals     = self._build_channels()
+        self.info.signals     = merge_signal_metadata(self.info.signals, self._build_channels())
         self.info.description = self._description()
         self._output_state = {f"do{i}": self._output_state.get(f"do{i}", 0) for i in range(len(self._do_pins))}
         self._di_state = {f"di{i}": self._di_state.get(f"di{i}", 0) for i in range(len(self._di_pins))}
diff --git a/devices/base_device.py b/devices/base_device.py
index e3eed65..ae7f438 100644
--- a/devices/base_device.py
+++ b/devices/base_device.py
@@ -104,3 +104,20 @@ class BaseDevice(ABC):
 
     def __repr__(self):
         return f"<{self.__class__.__name__} id={self.info.device_id} status={self.status.value}>"
+
+
+def merge_signal_metadata(old_signals: List[SignalConfig], new_signals: List[SignalConfig]) -> List[SignalConfig]:
+    """Reapply user-customized Signal metadata (name/unit/enabled/color) onto a
+    freshly rebuilt signal list, keyed by signal_id. Mirrors exactly the fields
+    ProfileManager treats as user overrides (core/profile.py capture/apply) so
+    identity set at profile-load time survives a later device reconfigure too —
+    otherwise a device's own reconfigure()/remap_pins() rebuilding info.signals
+    from scratch silently resets names back to hardware defaults. Signal ids
+    not present in old_signals (new pins) keep their fresh defaults; ids no
+    longer in new_signals (removed pins) are simply dropped."""
+    old_by_id = {s.signal_id: s for s in old_signals}
+    for sig in new_signals:
+        old = old_by_id.get(sig.signal_id)
+        if old is not None:
+            sig.name, sig.unit, sig.enabled, sig.color = old.name, old.unit, old.enabled, old.color
+    return new_signals
diff --git a/devices/serial_device.py b/devices/serial_device.py
index 86d5e80..53f9275 100644
--- a/devices/serial_device.py
+++ b/devices/serial_device.py
@@ -31,7 +31,7 @@ from PyQt6.QtWidgets import (
     QStackedWidget, QTableWidget, QTableWidgetItem, QTextEdit, QVBoxLayout, QWidget,
 )
 
-from devices.base_device import BaseDevice, SignalConfig, DeviceInfo, DeviceStatus
+from devices.base_device import BaseDevice, SignalConfig, DeviceInfo, DeviceStatus, merge_signal_metadata
 from api_layers.arduino_layer import ArduinoLayer
 
 _COLORS = ["#7fff6e", "#4cc9f0", "#f72585", "#00d4ff",
@@ -274,7 +274,7 @@ class SerialDevice(BaseDevice):
         self._mb_channels     = modbus_channels or self._mb_channels
         self._motors          = motors          or self._motors
 
-        self.info.signals    = self._build_channel_configs()
+        self.info.signals    = merge_signal_metadata(self.info.signals, self._build_channel_configs())
         self.info.description = self._description()
         self._layer = self._make_layer()