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>

3 files changed, 99 insertions, 22 deletions

diff --git a/ui/windows/channels_window.py b/ui/windows/channels_window.py
index 2388b83..87d7840 100644
--- a/ui/windows/channels_window.py
+++ b/ui/windows/channels_window.py
@@ -38,6 +38,7 @@ from core.signal_processor import (
     SignalProcessor, ChannelPipeline, DerivedChannel,
     FilterBase, FILTER_CLASSES,
 )
+from ui.windows.plot_window import _DragHandle, _DragReorderContainer
 
 _DERIVED_COLORS = [
     "#f72585","#7209b7","#4361ee","#4cc9f0",
@@ -473,7 +474,7 @@ class PipelineTab(QWidget):
         virt_scroll = QScrollArea(); virt_scroll.setWidgetResizable(True)
         virt_scroll.setObjectName("deviceScroll")
         virt_scroll.setHorizontalScrollBarPolicy(Qt.ScrollBarPolicy.ScrollBarAlwaysOff)
-        self._virt_cont = QWidget()
+        self._virt_cont = _DragReorderContainer(self)
         self._virt_inner = QVBoxLayout(self._virt_cont)
         self._virt_inner.setContentsMargins(10, 10, 10, 10); self._virt_inner.setSpacing(6)
         self._virt_inner.addStretch()
@@ -645,6 +646,8 @@ class PipelineTab(QWidget):
         blk = DerivedBlock(dc, self.registry, self.processor)
         blk.removed.connect(self._rm_virtual)
         blk.applied.connect(lambda _: self.derived_changed.emit())
+        blk.id_renamed.connect(self.refresh_derived)
+        blk._drag_handle.set_drag_source(self, blk)
         self._derived_blocks.append(blk)
         return blk
 
@@ -654,6 +657,56 @@ class PipelineTab(QWidget):
         self._virt_inner.removeWidget(blk); blk.deleteLater()
         self.derived_changed.emit()
 
+    # ── Drag-to-reorder — see _DragReorderContainer in ui/windows/plot_window.py
+
+    def _index_of(self, block: DerivedBlock) -> int:
+        return self._derived_blocks.index(block)
+
+    def _drop_index(self, y: float) -> int:
+        """Insertion index for a drop at container-relative y."""
+        n = self._virt_inner.count() - 1   # exclude trailing stretch
+        for i in range(n):
+            w = self._virt_inner.itemAt(i).widget()
+            if y < w.y() + w.height() / 2:
+                return i
+        return n
+
+    def _indicator_y_for(self, idx: int) -> int:
+        """Container-relative y for the drop-line at insertion index idx."""
+        n = self._virt_inner.count() - 1   # exclude trailing stretch
+        spacing = self._virt_inner.spacing()
+        if n == 0:
+            return self._virt_inner.contentsMargins().top()
+        if idx <= 0:
+            w = self._virt_inner.itemAt(0).widget()
+            return w.y() - spacing // 2
+        if idx >= n:
+            w = self._virt_inner.itemAt(n - 1).widget()
+            return w.y() + w.height() + spacing // 2
+        prev = self._virt_inner.itemAt(idx - 1).widget()
+        nxt  = self._virt_inner.itemAt(idx).widget()
+        return (prev.y() + prev.height() + nxt.y()) // 2
+
+    def _reorder(self, src_idx: int, dst_idx: int):
+        """Move the Channel at src_idx to dst_idx (drop-target index,
+        pre-removal) — same semantics as ControlPanel._reorder(). Also
+        reorders processor._derived so evaluation order stays matched to
+        the visual order: a Channel sourced from another Channel needs that
+        source evaluated first in the same pass (SignalProcessor.
+        _evaluate_derived), or it lags by one sample."""
+        if dst_idx > src_idx:
+            dst_idx -= 1
+        if dst_idx == src_idx:
+            return
+
+        blk = self._derived_blocks.pop(src_idx)
+        self._derived_blocks.insert(dst_idx, blk)
+        self._virt_inner.removeWidget(blk)
+        self._virt_inner.insertWidget(dst_idx, blk)
+
+        self.processor.reorder_derived(src_idx, dst_idx)
+        self.derived_changed.emit()
+
     def refresh_derived(self):
         """Rebuild DerivedBlock widgets from processor state (called after profile load)."""
         for blk in self._derived_blocks:
@@ -754,8 +807,10 @@ def _sub_xrefs(code: str, names: list) -> str:
 
 
 class DerivedBlock(QFrame):
-    removed = pyqtSignal(object)
-    applied = pyqtSignal(object)  # DerivedChannel
+    removed     = pyqtSignal(object)
+    applied     = pyqtSignal(object)  # DerivedChannel
+    id_renamed  = pyqtSignal()        # this Channel's ID changed — other blocks'
+                                       # source pickers may now be stale
 
     def __init__(self, dc: DerivedChannel, registry: DeviceRegistry,
                  processor: SignalProcessor):
@@ -764,6 +819,7 @@ class DerivedBlock(QFrame):
         self.setObjectName("plotBlock")
         self._src_combos: List[QComboBox] = []
         self._expanded = False
+        self._orig_id = dc.channel_id
         self._build()
 
     def _build(self):
@@ -772,6 +828,8 @@ class DerivedBlock(QFrame):
         # Header
         hdr = QWidget(); hdr.setObjectName("plotBlockHeader"); hdr.setFixedHeight(32)
         hl  = QHBoxLayout(hdr); hl.setContentsMargins(8, 0, 6, 0)
+        self._drag_handle = _DragHandle()
+        hl.addWidget(self._drag_handle)
         self._name = QLineEdit(self.dc.name); self._name.setObjectName("plotBlockTitle")
         self._name.textChanged.connect(lambda t: setattr(self.dc, "name", t))
         hl.addWidget(self._name, 1)
@@ -1133,6 +1191,14 @@ class DerivedBlock(QFrame):
             self._st.setText(f"⚠ ID '{channel_id}' is already used by another channel")
             self._st.setStyleSheet("color:#ef4444;")
             return
+        renamed = channel_id != self._orig_id
+        if renamed:
+            # Other channels sourced from this one under the old ID would
+            # otherwise keep pointing at a reference that no longer exists —
+            # fix their sources up front, carry the ring buffer + latest
+            # value over so the rename doesn't reset their plotted history.
+            self.processor.rename_derived(self._orig_id, channel_id)
+            self._orig_id = channel_id
         sources = [cb.currentData() for cb in self._src_combos if cb.currentData()]
         if self.dc.kind in ("derivative", "second_derivative"):
             wrt = "channel" if self._wrt_cb.currentIndex() == 1 else "time"
@@ -1149,6 +1215,11 @@ class DerivedBlock(QFrame):
         elif self.dc.kind in ("function", "custom_script"):
             self.dc.script = self._code.toPlainText()
         err = self.processor.add_derived(self.dc)
+        # The rename above already committed regardless of whether this
+        # channel's own expression/script compiles — other blocks' source
+        # pickers need to refresh either way.
+        if renamed:
+            self.id_renamed.emit()
         if err:
             self._st.setText(f"⚠ {err[:100]}")
             self._st.setStyleSheet("color:#ef4444;")
diff --git a/ui/windows/config_window.py b/ui/windows/config_window.py
index 3bd3dc6..34cc789 100644
--- a/ui/windows/config_window.py
+++ b/ui/windows/config_window.py
@@ -34,7 +34,7 @@ from ui.windows.devices_window import DeviceRow, ChannelsTab
 from ui.windows.channels_window import PipelineTab, _slug_id, _dedupe_name
 from ui.windows.plot_window import (
     PlotWindow, LayoutConfig, LayoutCanvas, PaneBlock,
-    build_default_layout, _PlotDropContainer,
+    build_default_layout, _DragReorderContainer,
 )
 from ui.namespace_panel import NamespacePanel
 
@@ -242,7 +242,7 @@ class _PlotTab(PlotWindow):
 
         scroll = QScrollArea(); scroll.setWidgetResizable(True)
         scroll.setObjectName("deviceScroll")
-        self._cont = _PlotDropContainer(self)
+        self._cont = _DragReorderContainer(self)
         self._blay = QVBoxLayout(self._cont)
         self._blay.setContentsMargins(10, 10, 10, 10); self._blay.setSpacing(12)
         self._blay.addStretch()
diff --git a/ui/windows/plot_window.py b/ui/windows/plot_window.py
index 93ce776..e810365 100644
--- a/ui/windows/plot_window.py
+++ b/ui/windows/plot_window.py
@@ -377,42 +377,45 @@ class TraceChannelPickerDialog(QDialog):
 # ══════════════════════════════════════════════════════════════════════════════
 #  Drag-to-reorder — same mechanics as ControlPanel (ui/control_panel.py):
 #  a small drag handle starts a QDrag carrying the source index, the config
-#  list container accepts the drop and reorders. The pane title here is an
-#  editable QLineEdit (unlike ControlPanel's static label), so the whole
-#  header can't be made transparent-for-mouse — a dedicated grip is used
-#  instead of the whole header.
+#  list container accepts the drop and reorders. Reused by PipelineTab
+#  (ui/windows/channels_window.py) for the Channels list — owner just needs
+#  to implement _index_of / _drop_index / _indicator_y_for / _reorder.
+#  A dedicated grip is used instead of making the whole header a drag
+#  source (unlike ControlPanel) because these headers hold an editable
+#  QLineEdit title, which needs real mouse focus to edit.
 # ══════════════════════════════════════════════════════════════════════════════
 
-class _PaneDragHandle(QLabel):
+class _DragHandle(QLabel):
     def __init__(self):
         super().__init__("⠿")
         self._owner = None
-        self._block = None
+        self._item  = None
         self.setObjectName("paneDragHandle")
         self.setFixedWidth(18)
         self.setAlignment(Qt.AlignmentFlag.AlignCenter)
         self.setCursor(Qt.CursorShape.OpenHandCursor)
         self.setToolTip("Drag to reorder")
 
-    def set_drag_source(self, owner: "PlotWindow", block: "PaneBlock"):
+    def set_drag_source(self, owner, item):
         self._owner = owner
-        self._block = block
+        self._item  = item
 
     def mousePressEvent(self, event):
         if event.button() == Qt.MouseButton.LeftButton and self._owner is not None:
             drag = QDrag(self)
             mime = QMimeData()
-            mime.setText(str(self._owner._blocks.index(self._block)))
+            mime.setText(str(self._owner._index_of(self._item)))
             drag.setMimeData(mime)
             drag.exec(Qt.DropAction.MoveAction)
         super().mousePressEvent(event)
 
 
-class _PlotDropContainer(QWidget):
-    """Holds the pane config blocks; drops reorder them — same drag-to-reorder
-    mechanics as ControlPanel's _DropContainer."""
+class _DragReorderContainer(QWidget):
+    """Holds a vertical list of config blocks; drops reorder them — same
+    drag-to-reorder mechanics as ControlPanel's _DropContainer. Owner must
+    implement _drop_index(y), _indicator_y_for(idx), _reorder(src, dst)."""
 
-    def __init__(self, owner: "PlotWindow"):
+    def __init__(self, owner):
         super().__init__()
         self._owner = owner
         self._indicator_y = None
@@ -438,7 +441,7 @@ class _PlotDropContainer(QWidget):
             src_idx = int(event.mimeData().text())
         except ValueError:
             return
-        self._owner._reorder_panes(src_idx, self._owner._drop_index(event.position().y()))
+        self._owner._reorder(src_idx, self._owner._drop_index(event.position().y()))
         event.acceptProposedAction()
 
     def _show_indicator(self, y: float):
@@ -474,7 +477,7 @@ class PaneBlock(QFrame):
 
         hdr = QWidget(); hdr.setObjectName("plotBlockHeader"); hdr.setFixedHeight(32)
         hl = QHBoxLayout(hdr); hl.setContentsMargins(8,0,6,0); hl.setSpacing(4)
-        self._drag_handle = _PaneDragHandle()
+        self._drag_handle = _DragHandle()
         hl.addWidget(self._drag_handle)
         self._title = QLineEdit(self.spec.title); self._title.setObjectName("plotBlockTitle")
         self._title.textChanged.connect(lambda t: (
@@ -1075,7 +1078,7 @@ class PlotWindow(QWidget):
 
         scroll = QScrollArea(); scroll.setWidgetResizable(True)
         scroll.setObjectName("deviceScroll")
-        self._cont = _PlotDropContainer(self)
+        self._cont = _DragReorderContainer(self)
         self._blay = QVBoxLayout(self._cont)
         self._blay.setContentsMargins(10,10,10,10); self._blay.setSpacing(12)
         self._blay.addStretch()
@@ -1173,7 +1176,10 @@ class PlotWindow(QWidget):
         nxt  = self._blay.itemAt(idx).widget()
         return (prev.y() + prev.height() + nxt.y()) // 2
 
-    def _reorder_panes(self, src_idx: int, dst_idx: int):
+    def _index_of(self, block: "PaneBlock") -> int:
+        return self._blocks.index(block)
+
+    def _reorder(self, src_idx: int, dst_idx: int):
         """Move the pane at src_idx to dst_idx (drop-target index, pre-removal)
         — same semantics as ControlPanel._reorder(). Also walks the BSP tree's
         leaf pane-index labels through the same chain of adjacent swaps so