Add drag-and-snap tiling layout canvas to Plot Builder

Replace layout radio buttons (Stacked/Side-by-Side/Grid) with a visual
LayoutCanvas widget. Pane tiles snap to grid cells on drag-drop; dropping
on an occupied cell swaps positions. Ghost highlight shows snap target
during drag.

- PaneSpec gains row/col fields (None = unassigned; backward compat preserved)
- LayoutConfig gains "free" mode; strip_chart reads explicit positions
- PaneBlock loses ▲▼ move buttons; reordering is canvas-only
- QSS entries added for layoutTile, layoutTileDragging, layoutCanvasBar

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

4 files changed, 304 insertions, 74 deletions

diff --git a/ui/strip_chart.py b/ui/strip_chart.py
index 523102d..d855038 100644
--- a/ui/strip_chart.py
+++ b/ui/strip_chart.py
@@ -95,12 +95,14 @@ class StripChartWidget(QWidget):
         n  = len(cfg.panes)
 
         # Determine row/col for each pane
-        if cfg.layout_mode == "sidebyside":
+        if cfg.layout_mode == "free":
+            positions = [(spec.row or 0, spec.col or 0) for spec in cfg.panes]
+        elif cfg.layout_mode == "sidebyside":
             positions = [(0, c) for c in range(n)]
         elif cfg.layout_mode == "grid":
             cols = max(1, cfg.grid_cols)
             positions = [(i // cols, i % cols) for i in range(n)]
-        else:  # stacked
+        else:  # stacked (legacy default)
             positions = [(r, 0) for r in range(n)]
 
         ref_plot = None
@@ -112,7 +114,7 @@ class StripChartWidget(QWidget):
             plot.getAxis("left").setStyle(tickFont=mf)
             plot.getAxis("bottom").setStyle(tickFont=mf)
 
-            # Hide bottom axis labels for all but bottom row in stacked
+            # Hide bottom axis labels for non-bottom panes in stacked legacy mode
             if cfg.layout_mode == "stacked" and idx < n - 1:
                 plot.getAxis("bottom").setStyle(showValues=False)
                 plot.getAxis("bottom").setHeight(0)
@@ -133,10 +135,9 @@ class StripChartWidget(QWidget):
             else:
                 plot.enableAutoRange(axis="y")
 
-            # Set column stretch (relative weight)
+            # Apply weight to row and column stretch
             self._gw.ci.layout.setColumnStretchFactor(col, spec.weight)
-            if cfg.layout_mode == "stacked":
-                self._gw.ci.layout.setRowStretchFactor(row, spec.weight)
+            self._gw.ci.layout.setRowStretchFactor(row, spec.weight)
 
             for tr in spec.traces:
                 if not tr.visible: continue
diff --git a/ui/style_dark.qss b/ui/style_dark.qss
index 2c24d1c..e562365 100644
--- a/ui/style_dark.qss
+++ b/ui/style_dark.qss
@@ -563,3 +563,43 @@ QFrame#controlWidgetWrapper {
     background: transparent;
     border: none;
 }
+
+/* ── Layout canvas ───────────────────────────────────────────────── */
+QWidget#layoutCanvasBar {
+    background-color: #0f1521;
+    border-bottom: 1px solid #1c2540;
+}
+QLabel#layoutCanvasLabel {
+    font-family: "IBM Plex Mono", monospace;
+    font-size: 10px;
+    font-weight: 700;
+    letter-spacing: 2px;
+    color: #4338ca;
+    padding: 0 2px;
+}
+QFrame#layoutCanvasWidget {
+    background-color: #0b0e13;
+    border: 1px solid #2a3558;
+    border-radius: 4px;
+}
+QFrame#layoutTile {
+    background-color: #1c2540;
+    border: 1px solid #2a3558;
+    border-radius: 5px;
+}
+QFrame#layoutTile:hover {
+    border-color: #4338ca;
+    background-color: #212c52;
+}
+QFrame#layoutTileDragging {
+    background-color: #1e3a5f;
+    border: 2px solid #3b82f6;
+    border-radius: 5px;
+}
+QLabel#layoutTileLabel {
+    font-family: "IBM Plex Mono", monospace;
+    font-size: 11px;
+    font-weight: 700;
+    color: #8b9dc3;
+    background: transparent;
+}
diff --git a/ui/style_light.qss b/ui/style_light.qss
index 38b91f8..e0a1987 100644
--- a/ui/style_light.qss
+++ b/ui/style_light.qss
@@ -124,3 +124,11 @@ QMenu#profileMenu { background:#ffffff; border:1px solid #e2e8f0; border-radius:
 QMenu#profileMenu::item { padding:7px 20px; color:#334155; }
 QMenu#profileMenu::item:selected { background:#dbeafe; color:#1d4ed8; }
 QMenu#profileMenu::separator { height:1px; background:#e2e8f0; margin:3px 8px; }
+/* Layout canvas */
+QWidget#layoutCanvasBar { background-color:#f8fafc; border-bottom:1px solid #e2e8f0; }
+QLabel#layoutCanvasLabel { font-family:"IBM Plex Mono",monospace; font-size:10px; font-weight:700; letter-spacing:2px; color:#4338ca; }
+QFrame#layoutCanvasWidget { background-color:#f1f5f9; border:1px solid #cbd5e1; border-radius:4px; }
+QFrame#layoutTile { background-color:#e2e8f0; border:1px solid #94a3b8; border-radius:5px; }
+QFrame#layoutTile:hover { border-color:#4338ca; background-color:#c7d2fe; }
+QFrame#layoutTileDragging { background-color:#bfdbfe; border:2px solid #3b82f6; border-radius:5px; }
+QLabel#layoutTileLabel { font-family:"IBM Plex Mono",monospace; font-size:11px; font-weight:700; color:#334155; background:transparent; }
diff --git a/ui/windows/plot_window.py b/ui/windows/plot_window.py
index 0207af1..91799f9 100644
--- a/ui/windows/plot_window.py
+++ b/ui/windows/plot_window.py
@@ -4,8 +4,8 @@ ui/windows/plot_window.py
 PLOT window — toolbar section 4.
 
 Lets operators:
-  • Choose layout: Stacked (rows) or Side-by-Side (columns) or Grid (N×M)
-  • Add/remove/reorder subplot panes
+  • Arrange subplot panes by dragging tiles on the layout canvas (tiling WM style)
+  • Add/remove subplot panes
   • Assign any channel (physical or derived) to any pane
   • Set X-axis: Time (elapsed s) OR any channel (e.g. strain → stress vs strain)
   • Name axes, set Y auto/fixed range, grid, relative size weight
@@ -19,16 +19,16 @@ from __future__ import annotations
 import json
 from copy import deepcopy
 from dataclasses import dataclass, field, asdict
-from typing import List, Optional, Tuple
+from typing import Dict, List, Optional, Tuple
 
 from PyQt6.QtWidgets import (
     QWidget, QVBoxLayout, QHBoxLayout, QLabel, QPushButton,
     QScrollArea, QFrame, QLineEdit, QDoubleSpinBox, QSpinBox,
-    QCheckBox, QComboBox, QColorDialog, QToolButton, QButtonGroup,
-    QFileDialog, QMessageBox, QRadioButton, QGroupBox, QSizePolicy,
+    QCheckBox, QComboBox, QColorDialog, QToolButton,
+    QFileDialog, QMessageBox,
 )
-from PyQt6.QtCore import Qt, pyqtSignal
-from PyQt6.QtGui import QColor, QCloseEvent
+from PyQt6.QtCore import Qt, pyqtSignal, QPoint, QRect
+from PyQt6.QtGui import QColor, QCloseEvent, QPainter, QPen
 
 from devices.device_registry import DeviceRegistry
 from core.signal_processor import SignalProcessor
@@ -60,11 +60,13 @@ class PaneSpec:
     grid:     bool             = True
     weight:   int              = 1       # relative size
     traces:   List[TraceSpec]  = field(default_factory=list)
+    row:      Optional[int]    = None   # canvas grid position; None = unassigned
+    col:      Optional[int]    = None
 
 @dataclass
 class LayoutConfig:
     panes:         List[PaneSpec] = field(default_factory=list)
-    layout_mode:   str            = "stacked"   # stacked | sidebyside | grid
+    layout_mode:   str            = "stacked"   # stacked | sidebyside | grid | free
     grid_cols:     int            = 2
     time_window_s: float          = 30.0
     link_x:        bool           = True
@@ -169,10 +171,9 @@ class TraceRow(QFrame):
 # ══════════════════════════════════════════════════════════════════════════════
 
 class PaneBlock(QFrame):
-    removed  = pyqtSignal(object)
-    changed  = pyqtSignal()
-    move_up  = pyqtSignal(object)
-    move_dn  = pyqtSignal(object)
+    removed       = pyqtSignal(object)
+    changed       = pyqtSignal()
+    title_changed = pyqtSignal(object, str)   # (self, new_title)
 
     def __init__(self, spec: PaneSpec, registry: DeviceRegistry,
                  processor: SignalProcessor):
@@ -188,11 +189,11 @@ class PaneBlock(QFrame):
         hdr = QWidget(); hdr.setObjectName("plotBlockHeader"); hdr.setFixedHeight(32)
         hl = QHBoxLayout(hdr); hl.setContentsMargins(8,0,6,0); hl.setSpacing(4)
         self._title = QLineEdit(self.spec.title); self._title.setObjectName("plotBlockTitle")
-        self._title.textChanged.connect(lambda t: setattr(self.spec,"title",t))
-        hl.addWidget(self._title,1)
-        for txt, sig in [("▲",self.move_up),("▼",self.move_dn)]:
-            b = QToolButton(); b.setText(txt); b.setObjectName("plotMoveBtn")
-            b.setFixedSize(22,22); b.clicked.connect(lambda _,s=sig: s.emit(self)); hl.addWidget(b)
+        self._title.textChanged.connect(lambda t: (
+            setattr(self.spec, "title", t),
+            self.title_changed.emit(self, t),
+        ))
+        hl.addWidget(self._title, 1)
         rm = QToolButton(); rm.setText("✕"); rm.setObjectName("plotRemoveBtn")
         rm.setFixedSize(22,22); rm.clicked.connect(lambda: self.removed.emit(self)); hl.addWidget(rm)
         outer.addWidget(hdr)
@@ -214,7 +215,6 @@ class PaneBlock(QFrame):
         for dc in self.processor.get_derived():
             self._x_cb.addItem(f"[virtual] {dc.channel_id}",
                                userData=f"derived/{dc.channel_id}")
-        # Select current
         for i in range(self._x_cb.count()):
             if self._x_cb.itemData(i) == self.spec.x_source:
                 self._x_cb.setCurrentIndex(i); break
@@ -305,6 +305,200 @@ class PaneBlock(QFrame):
 
 
 # ══════════════════════════════════════════════════════════════════════════════
+#  Layout canvas — drag-and-snap tiling pane arranger
+# ══════════════════════════════════════════════════════════════════════════════
+
+_CANVAS_CELL_W = 120
+_CANVAS_CELL_H = 76
+_CANVAS_GAP    = 6
+_CANVAS_COLS   = 4
+
+
+class PaneTile(QFrame):
+    def __init__(self, pane_index: int, title: str, parent: QWidget) -> None:
+        super().__init__(parent)
+        self.pane_index = pane_index
+        self.setObjectName("layoutTile")
+        self.setAttribute(Qt.WidgetAttribute.WA_TransparentForMouseEvents, True)
+        lay = QVBoxLayout(self)
+        lay.setContentsMargins(4, 4, 4, 4)
+        self._lbl = QLabel(title)
+        self._lbl.setObjectName("layoutTileLabel")
+        self._lbl.setAlignment(Qt.AlignmentFlag.AlignCenter)
+        self._lbl.setWordWrap(True)
+        lay.addWidget(self._lbl)
+
+    def set_title(self, title: str) -> None:
+        self._lbl.setText(title)
+
+    def set_dragging(self, v: bool) -> None:
+        self.setObjectName("layoutTileDragging" if v else "layoutTile")
+        self.style().unpolish(self)
+        self.style().polish(self)
+        self._lbl.setObjectName("layoutTileLabel")
+        self._lbl.style().unpolish(self._lbl)
+        self._lbl.style().polish(self._lbl)
+
+
+class LayoutCanvas(QFrame):
+    arrangement_changed = pyqtSignal()
+
+    def __init__(self, panes: List[PaneSpec], parent: Optional[QWidget] = None) -> None:
+        super().__init__(parent)
+        self.setObjectName("layoutCanvasWidget")
+        self.setMouseTracking(True)
+        self._panes: List[PaneSpec] = panes
+        self._tiles: List[PaneTile] = []
+        self._grid:  Dict[Tuple[int, int], int] = {}
+        self._drag_tile:   Optional[PaneTile]      = None
+        self._drag_offset: QPoint                  = QPoint()
+        self._ghost_cell:  Optional[Tuple[int,int]] = None
+        self._assign_legacy_positions()
+        self._rebuild_tiles()
+
+    # ── Public ────────────────────────────────────────────────────────────────
+
+    def sync_panes(self, panes: List[PaneSpec]) -> None:
+        self._panes = panes
+        self._drag_tile = None
+        self._ghost_cell = None
+        self._assign_legacy_positions()
+        self._rebuild_tiles()
+
+    def update_tile_title(self, pane_index: int, title: str) -> None:
+        if 0 <= pane_index < len(self._tiles):
+            self._tiles[pane_index].set_title(title)
+
+    # ── Position assignment ───────────────────────────────────────────────────
+
+    def _assign_legacy_positions(self) -> None:
+        occupied = {(p.row, p.col) for p in self._panes
+                    if p.row is not None and p.col is not None}
+        for pane in self._panes:
+            if pane.row is None or pane.col is None:
+                row = 0
+                while (row, 0) in occupied:
+                    row += 1
+                pane.row, pane.col = row, 0
+                occupied.add((row, 0))
+
+    # ── Rebuild ───────────────────────────────────────────────────────────────
+
+    def _rebuild_tiles(self) -> None:
+        for t in self._tiles:
+            t.deleteLater()
+        self._tiles.clear()
+        self._grid.clear()
+        for i, pane in enumerate(self._panes):
+            tile = PaneTile(i, pane.title, self)
+            tile.setGeometry(self._cell_rect(pane.row, pane.col))
+            tile.show()
+            self._tiles.append(tile)
+            self._grid[(pane.row, pane.col)] = i
+        self._resize_canvas()
+
+    def _resize_canvas(self) -> None:
+        if not self._panes:
+            self.setFixedSize(
+                _CANVAS_COLS * (_CANVAS_CELL_W + _CANVAS_GAP) + _CANVAS_GAP,
+                _CANVAS_CELL_H + 2 * _CANVAS_GAP,
+            )
+            return
+        max_row = max((p.row for p in self._panes if p.row is not None), default=0)
+        h = (max_row + 1) * (_CANVAS_CELL_H + _CANVAS_GAP) + _CANVAS_GAP
+        w = _CANVAS_COLS * (_CANVAS_CELL_W + _CANVAS_GAP) + _CANVAS_GAP
+        self.setFixedSize(w, h)
+
+    def _cell_rect(self, row: int, col: int) -> QRect:
+        x = _CANVAS_GAP + col * (_CANVAS_CELL_W + _CANVAS_GAP)
+        y = _CANVAS_GAP + row * (_CANVAS_CELL_H + _CANVAS_GAP)
+        return QRect(x, y, _CANVAS_CELL_W, _CANVAS_CELL_H)
+
+    def _tile_at(self, pos: QPoint) -> Optional[PaneTile]:
+        for tile in reversed(self._tiles):
+            if tile.geometry().contains(pos):
+                return tile
+        return None
+
+    def _nearest_cell(self, pos: QPoint) -> Tuple[int, int]:
+        max_row = max((p.row for p in self._panes if p.row is not None), default=0)
+        max_rows = max(max_row + 2, len(self._panes))
+        col = max(0, min(_CANVAS_COLS - 1, pos.x() // (_CANVAS_CELL_W + _CANVAS_GAP)))
+        row = max(0, min(max_rows - 1,     pos.y() // (_CANVAS_CELL_H + _CANVAS_GAP)))
+        return (int(row), int(col))
+
+    # ── Drag ─────────────────────────────────────────────────────────────────
+
+    def mousePressEvent(self, event) -> None:
+        if event.button() != Qt.MouseButton.LeftButton:
+            return
+        tile = self._tile_at(event.pos())
+        if tile is None:
+            return
+        self._drag_tile = tile
+        self._drag_offset = event.pos() - tile.pos()
+        tile.set_dragging(True)
+        tile.raise_()
+
+    def mouseMoveEvent(self, event) -> None:
+        if self._drag_tile is None:
+            return
+        self._drag_tile.move(event.pos() - self._drag_offset)
+        snap = self._nearest_cell(event.pos())
+        if snap != self._ghost_cell:
+            self._ghost_cell = snap
+            self.update()
+
+    def mouseReleaseEvent(self, event) -> None:
+        if self._drag_tile is None:
+            return
+        snap = self._nearest_cell(event.pos())
+        self._do_drop(self._drag_tile.pane_index, snap)
+        self._drag_tile.set_dragging(False)
+        self._drag_tile = None
+        self._ghost_cell = None
+        self.update()
+
+    def _do_drop(self, pane_index: int, target: Tuple[int, int]) -> None:
+        dragged = self._panes[pane_index]
+        old = (dragged.row, dragged.col)
+
+        if old == target:
+            self._tiles[pane_index].setGeometry(self._cell_rect(*old))
+            return
+
+        occupant_idx = self._grid.get(target)
+
+        if occupant_idx is not None:
+            occupant = self._panes[occupant_idx]
+            occupant.row, occupant.col = old
+            self._tiles[occupant_idx].setGeometry(self._cell_rect(*old))
+            self._grid[old] = occupant_idx
+        else:
+            self._grid.pop(old, None)
+
+        dragged.row, dragged.col = target
+        self._tiles[pane_index].setGeometry(self._cell_rect(*target))
+        self._grid[target] = pane_index
+
+        self._resize_canvas()
+        self.arrangement_changed.emit()
+
+    # ── Ghost highlight ───────────────────────────────────────────────────────
+
+    def paintEvent(self, event) -> None:
+        super().paintEvent(event)
+        if self._ghost_cell is None:
+            return
+        painter = QPainter(self)
+        painter.setRenderHint(QPainter.RenderHint.Antialiasing)
+        r = self._cell_rect(*self._ghost_cell)
+        painter.setPen(QPen(QColor("#3b82f6"), 2))
+        painter.setBrush(QColor(59, 130, 246, 40))
+        painter.drawRoundedRect(r, 4, 4)
+
+
+# ══════════════════════════════════════════════════════════════════════════════
 #  PlotWindow
 # ══════════════════════════════════════════════════════════════════════════════
 
@@ -321,7 +515,7 @@ class PlotWindow(QWidget):
                          else build_default_layout(registry, processor)
         self.setWindowTitle("Plot Builder")
         self.setMinimumSize(720, 560)
-        self.resize(820, 700)
+        self.resize(820, 760)
         self._blocks: List[PaneBlock] = []
         self._build()
         self._populate()
@@ -337,31 +531,10 @@ class PlotWindow(QWidget):
         div = QFrame(); div.setFrameShape(QFrame.Shape.HLine)
         div.setObjectName("devWindowDivider"); root.addWidget(div)
 
-        # Global settings
+        # Global settings bar
         glob = QWidget(); glob.setObjectName("cfgGlobalBar")
         gl   = QHBoxLayout(glob); gl.setContentsMargins(12,7,12,7); gl.setSpacing(12)
 
-        # Layout mode
-        gl.addWidget(QLabel("Layout:"))
-        self._stacked_rb = QRadioButton("Stacked")
-        self._side_rb    = QRadioButton("Side-by-Side")
-        self._grid_rb    = QRadioButton("Grid")
-        mode_grp = QButtonGroup(self)
-        for rb in (self._stacked_rb, self._side_rb, self._grid_rb):
-            rb.setObjectName("cfgLiveChk"); mode_grp.addButton(rb)
-        mode_map = {"stacked": self._stacked_rb,
-                    "sidebyside": self._side_rb, "grid": self._grid_rb}
-        mode_map.get(self.cfg.layout_mode, self._stacked_rb).setChecked(True)
-        for rb, key in [(self._stacked_rb,"stacked"),(self._side_rb,"sidebyside"),(self._grid_rb,"grid")]:
-            rb.toggled.connect(lambda v, k=key: self._set_mode(k) if v else None)
-            gl.addWidget(rb)
-
-        gl.addWidget(QLabel("Cols:"))
-        self._cols = QSpinBox(); self._cols.setRange(1,6); self._cols.setValue(self.cfg.grid_cols)
-        self._cols.setFixedWidth(44); self._cols.setObjectName("traceWidthSpin")
-        self._cols.valueChanged.connect(lambda v: setattr(self.cfg,"grid_cols",v))
-        gl.addWidget(self._cols)
-
         gl.addWidget(QLabel("Window:"))
         self._win = QDoubleSpinBox(); self._win.setRange(1,3600)
         self._win.setSuffix(" s"); self._win.setValue(self.cfg.time_window_s)
@@ -387,6 +560,18 @@ class PlotWindow(QWidget):
         add_btn.clicked.connect(self._add_pane); gl.addWidget(add_btn)
         root.addWidget(glob)
 
+        # Layout canvas section
+        canvas_bar = QWidget(); canvas_bar.setObjectName("layoutCanvasBar")
+        cb_lay = QVBoxLayout(canvas_bar)
+        cb_lay.setContentsMargins(10, 6, 10, 8); cb_lay.setSpacing(4)
+        clbl = QLabel("LAYOUT  —  drag tiles to arrange")
+        clbl.setObjectName("layoutCanvasLabel")
+        cb_lay.addWidget(clbl)
+        self._canvas = LayoutCanvas(self.cfg.panes, self)
+        self._canvas.arrangement_changed.connect(self._maybe_live)
+        cb_lay.addWidget(self._canvas)
+        root.addWidget(canvas_bar)
+
         div2 = QFrame(); div2.setFrameShape(QFrame.Shape.HLine)
         div2.setObjectName("devWindowDivider"); root.addWidget(div2)
 
@@ -412,45 +597,39 @@ class PlotWindow(QWidget):
         ap.clicked.connect(self._apply); bl.addWidget(ap)
         root.addWidget(btm)
 
-    def _set_mode(self, mode: str):
-        self.cfg.layout_mode = mode
-        self._maybe_live()
-
     def _populate(self):
-        for b in self._blocks: self._blay.removeWidget(b); b.deleteLater()
+        for b in self._blocks:
+            self._blay.removeWidget(b); b.deleteLater()
         self._blocks.clear()
-        for spec in self.cfg.panes: self._insert(spec)
+        for spec in self.cfg.panes:
+            self._insert(spec)
+        self._canvas.sync_panes(self.cfg.panes)
+        self.cfg.layout_mode = "free"
 
     def _insert(self, spec: PaneSpec):
         blk = PaneBlock(spec, self.registry, self.processor)
-        blk.removed.connect(self._rm); blk.changed.connect(self._maybe_live)
-        blk.move_up.connect(self._mv_up); blk.move_dn.connect(self._mv_dn)
+        blk.removed.connect(self._rm)
+        blk.changed.connect(self._maybe_live)
+        blk.title_changed.connect(self._on_tile_title)
         self._blocks.append(blk)
         self._blay.insertWidget(self._blay.count()-1, blk)
 
+    def _on_tile_title(self, blk: PaneBlock, title: str) -> None:
+        if blk in self._blocks:
+            self._canvas.update_tile_title(self._blocks.index(blk), title)
+
     def _add_pane(self):
         spec = PaneSpec(title=f"Plot {len(self.cfg.panes)+1}")
-        self.cfg.panes.append(spec); self._insert(spec); self._maybe_live()
+        self.cfg.panes.append(spec)
+        self._insert(spec)
+        self._canvas.sync_panes(self.cfg.panes)
+        self.cfg.layout_mode = "free"
+        self._maybe_live()
 
     def _rm(self, blk):
         if blk.spec in self.cfg.panes: self.cfg.panes.remove(blk.spec)
         self._blocks.remove(blk); self._blay.removeWidget(blk); blk.deleteLater()
-        self._maybe_live()
-
-    def _mv_up(self, blk):
-        i = self._blocks.index(blk)
-        if i==0: return
-        self.cfg.panes.insert(i-1,self.cfg.panes.pop(i))
-        self._blocks.insert(i-1,self._blocks.pop(i))
-        self._blay.removeWidget(blk); self._blay.insertWidget(i-1,blk)
-        self._maybe_live()
-
-    def _mv_dn(self, blk):
-        i = self._blocks.index(blk)
-        if i>=len(self._blocks)-1: return
-        self.cfg.panes.insert(i+1,self.cfg.panes.pop(i))
-        self._blocks.insert(i+1,self._blocks.pop(i))
-        self._blay.removeWidget(blk); self._blay.insertWidget(i+1,blk)
+        self._canvas.sync_panes(self.cfg.panes)
         self._maybe_live()
 
     def _maybe_live(self):
@@ -461,7 +640,8 @@ class PlotWindow(QWidget):
     def _reset(self):
         self.cfg = build_default_layout(self.registry, self.processor)
         self._win.setValue(self.cfg.time_window_s)
-        self._populate(); self._maybe_live()
+        self._populate()
+        self._maybe_live()
 
     def _export(self):
         path, _ = QFileDialog.getSaveFileName(self,"Export","layout.json","JSON (*.json)")
@@ -473,7 +653,8 @@ class PlotWindow(QWidget):
             try:
                 self.cfg = LayoutConfig.from_json(open(path).read())
                 self._win.setValue(self.cfg.time_window_s)
-                self._populate(); self._maybe_live()
+                self._populate()
+                self._maybe_live()
             except Exception as e:
                 QMessageBox.critical(self,"Import failed",str(e))