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>

1 files changed, 27 insertions, 0 deletions

diff --git a/ui/windows/channels_window.py b/ui/windows/channels_window.py
index f581851..31d1458 100644
--- a/ui/windows/channels_window.py
+++ b/ui/windows/channels_window.py
@@ -536,6 +536,8 @@ class PipelineTab(QWidget):
             if block:
                 self._on_remove_block(block)
         self._refresh_src_cb()
+        for blk in self._derived_blocks:
+            blk.refresh_missing_sources()
 
     def on_device_reconfigured(self, dev_id: str):
         dev = self.registry.get_instance(dev_id)
@@ -550,6 +552,8 @@ class PipelineTab(QWidget):
             if block:
                 self._on_remove_block(block)
         self._refresh_src_cb()
+        for blk in self._derived_blocks:
+            blk.refresh_missing_sources()
 
     def on_device_added(self):
         self._refresh_src_cb()
@@ -845,6 +849,11 @@ class ChannelBlock(QFrame):
         rm = QToolButton(); rm.setText("✕"); rm.setObjectName("plotRemoveBtn")
         rm.setFixedSize(22, 22); rm.clicked.connect(lambda: self.removed.emit(self))
         hl.addWidget(rm)
+        self._missing_lbl = QLabel("⚠")
+        self._missing_lbl.setObjectName("controlWidgetStale")
+        self._missing_lbl.setToolTip("A source signal is missing — reconfigured or removed")
+        self._missing_lbl.setVisible(False)
+        hl.addWidget(self._missing_lbl)
         self._toggle_btn = QToolButton(); self._toggle_btn.setText("▶")
         self._toggle_btn.setObjectName("traceRemoveBtn"); self._toggle_btn.setFixedSize(22, 22)
         self._toggle_btn.clicked.connect(self._toggle)
@@ -1013,6 +1022,24 @@ class ChannelBlock(QFrame):
         self._body = body
         self._update_vars_hint()
         self._update_visibility()
+        self.refresh_missing_sources()
+
+    def refresh_missing_sources(self):
+        """Update the header warning icon for a source signal that no longer
+        resolves (device removed, or Apply & Reconnect dropped that pin).
+        Called after any device add/remove/reconfigure — see PipelineTab."""
+        missing = False
+        for dev_id, ch_id in self.dc.sources:
+            if dev_id == "derived":
+                if ch_id not in self.processor.all_virtual_channel_ids():
+                    missing = True
+                    break
+            else:
+                dev = self.registry.get_instance(dev_id)
+                if dev is None or dev.get_signal(ch_id) is None:
+                    missing = True
+                    break
+        self._missing_lbl.setVisible(missing)
 
     def _toggle(self):
         self._expanded = not self._expanded