Replace grid-snap canvas with BSP-tree drag-to-split tiling

Dragging a tile to the edge (left/right/top/bottom) of another tile
splits that tile's space and inserts the dragged tile on that side.
Drop zones occupy the outer third of each tile edge; center has no zone.
Ghost overlay shows the split target during drag.

Data model: LayoutConfig.tree (BSP tree as nested dict). PaneSpec.row/col
removed. strip_chart uses tree_to_grid() → rowspan/colspan for pyqtgraph.
Backward compat: tree=None falls back to layout_mode stacking path.

Example: 3 stacked → drag Tile 3 to left of Tile 1 → Tile 3|Tile 1 on
top (side-by-side), Tile 2 spans full bottom.

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

1 files changed, 16 insertions, 10 deletions

diff --git a/ui/strip_chart.py b/ui/strip_chart.py
index d855038..5a1d1e9 100644
--- a/ui/strip_chart.py
+++ b/ui/strip_chart.py
@@ -42,7 +42,8 @@ if _HAS_PG:
 from devices.device_registry import DeviceRegistry
 from core.acquisition import AcquisitionEngine
 from core.signal_processor import SignalProcessor
-from ui.windows.plot_window import LayoutConfig, PaneSpec, TraceSpec, build_default_layout
+from ui.windows.plot_window import (LayoutConfig, PaneSpec, TraceSpec,
+                                    build_default_layout, tree_to_grid, _tree_grid_size)
 
 _STYLES = {
     "solid": Qt.PenStyle.SolidLine,
@@ -94,20 +95,26 @@ class StripChartWidget(QWidget):
         mf = QFont("IBM Plex Mono", 8)
         n  = len(cfg.panes)
 
-        # Determine row/col for each pane
-        if cfg.layout_mode == "free":
-            positions = [(spec.row or 0, spec.col or 0) for spec in cfg.panes]
+        # Determine row/col/rowspan/colspan for each pane
+        if cfg.layout_mode == "free" and cfg.tree is not None:
+            gs = _tree_grid_size(cfg.tree)
+            grid_pos: dict = {}
+            tree_to_grid(cfg.tree, 0, 0, gs, gs, grid_pos)
+            # grid_pos[pane_idx] = (row, col, rowspan, colspan)
         elif cfg.layout_mode == "sidebyside":
-            positions = [(0, c) for c in range(n)]
+            grid_pos = {i: (0, i, 1, 1) for i in range(n)}
         elif cfg.layout_mode == "grid":
             cols = max(1, cfg.grid_cols)
-            positions = [(i // cols, i % cols) for i in range(n)]
+            grid_pos = {i: (i // cols, i % cols, 1, 1) for i in range(n)}
         else:  # stacked (legacy default)
-            positions = [(r, 0) for r in range(n)]
+            grid_pos = {i: (i, 0, 1, 1) for i in range(n)}
 
         ref_plot = None
-        for idx, (spec, (row, col)) in enumerate(zip(cfg.panes, positions)):
-            plot = self._gw.addPlot(row=row, col=col)
+        for idx, spec in enumerate(cfg.panes):
+            if idx not in grid_pos:
+                continue
+            row, col, rowspan, colspan = grid_pos[idx]
+            plot = self._gw.addPlot(row=row, col=col, rowspan=rowspan, colspan=colspan)
             plot.setLabel("left",   spec.y_label or spec.title)
             plot.setLabel("bottom", spec.x_label or "Elapsed (s)")
             plot.showGrid(x=spec.grid, y=spec.grid, alpha=0.12)
@@ -135,7 +142,6 @@ class StripChartWidget(QWidget):
             else:
                 plot.enableAutoRange(axis="y")
 
-            # Apply weight to row and column stretch
             self._gw.ci.layout.setColumnStretchFactor(col, spec.weight)
             self._gw.ci.layout.setRowStretchFactor(row, spec.weight)