Channels tab drag-to-reorder, Namespace absolute references, fix stale Channel ID renames

Generalized the Plot pane drag-to-reorder (_PaneDragHandle/_PlotDropContainer
-> _DragHandle/_DragReorderContainer) and reused it for the Channels tab's
derived-channel list; reordering also updates SignalProcessor's evaluation
order (list order matters for chained Channels) via new reorder_derived().

Namespace panel: added an ID column (bare channel_id, matching the actual
channels.get(...) script convention) and fixed the Source column for
Channels to show resolved absolute references (dev_id/ch_id for a Signal,
bare id for a chained Channel) instead of the operation kind, so a chain
is traceable by eye.

Fixed a real bug this surfaced: renaming a Channel's ID never propagated
to other Channels' sources, leaving dangling ("derived", old_id)
references that silently stopped updating. Added
SignalProcessor.rename_derived() to fix up sources plus carry the ring
buffer/latest-value cache to the new key, wired to DerivedBlock's Apply.

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

1 files changed, 41 insertions, 0 deletions

diff --git a/core/signal_processor.py b/core/signal_processor.py
index 8abaff8..4781e91 100644
--- a/core/signal_processor.py
+++ b/core/signal_processor.py
@@ -437,6 +437,47 @@ class SignalProcessor(QObject):
             self._derived = [d for d in self._derived if d.channel_id != channel_id]
             self._derived_bufs.pop(channel_id, None)
 
+    def rename_derived(self, old_id: str, new_id: str):
+        """Propagate a Channel ID rename to every other derived channel's
+        sources — otherwise anything chained from it keeps a dangling
+        ("derived", old_id) reference (SignalProcessor._evaluate_derived
+        looks sources up by exact match) and silently stops updating.
+        Also carries the ring buffer and latest-value cache over under the
+        new key so the rename doesn't reset plotted history or blank the
+        Value column for a poll cycle. Does NOT touch source_names or
+        expression/script text — those are display labels / user-authored
+        code, out of scope for an automatic rewrite."""
+        if old_id == new_id:
+            return
+        with self._lock:
+            for dc in self._derived:
+                if dc.channel_id == new_id:
+                    continue
+                new_sources = [
+                    ("derived", new_id) if d == "derived" and c == old_id else (d, c)
+                    for d, c in dc.sources
+                ]
+                if new_sources != dc.sources:
+                    dc.sources = new_sources
+
+            buf = self._derived_bufs.pop(old_id, None)
+            if buf is not None:
+                self._derived_bufs[new_id] = buf
+
+            entry = self._latest.pop(("derived", old_id), None)
+            if entry is not None:
+                self._latest[("derived", new_id)] = entry
+
+    def reorder_derived(self, src_idx: int, dst_idx: int):
+        """Move the derived channel at src_idx to dst_idx — list order is
+        evaluation order (see _evaluate_derived): a Channel sourced from
+        another Channel needs that source evaluated earlier in the same
+        pass, or it reads a stale value and lags by one sample cycle."""
+        with self._lock:
+            if 0 <= src_idx < len(self._derived) and 0 <= dst_idx < len(self._derived):
+                dc = self._derived.pop(src_idx)
+                self._derived.insert(dst_idx, dc)
+
     def get_derived(self) -> List[DerivedChannel]:
         return list(self._derived)