fix: stop the Plotly canvas wedging on rapid or overlapping updates

Three defects in the view-preservation path could leave the plot frozen
(no updates, no orbit, stale colours):

1. The merge injected raw _fullLayout objects - including undefined when a
   push landed before the previous react resolved - and plotly validates
   layouts, so one bad value made every later react fail permanently.
   currentView() now deep-copies and validates eye/center/up and each
   range, and mergeView() is wrapped so it can never block an update.
2. Updates were not serialized: overlapping Plotly.react calls on one graph
   div left it unresponsive. otkoUpdate now queues and coalesces (one react
   at a time, latest payload wins), and logs instead of failing silently.
3. A style change re-framed the camera, so re-colouring yanked a view the
   user had orbited. Colour/opacity ride the traces and background/outline
   ride the layout, so set_style is now a non-framing push.

Verified in the browser: a user orbit survives colour changes, 30 rapid
preview updates land on the final value and stay responsive, and deleting
the live camera no longer wedges the plot.

src/otko/views/canvas_plotly/html.py

@@ -89,6 +89,90 @@ _PAGE = """<!DOCTYPE html>
     Plotly.restyle('plot', { x: [[]], y: [[]], z: [[]] }, [hoverIndex]);
   }
 
+  // --- view preservation -------------------------------------------------
+  // `Plotly.react` resets any scene attribute the incoming layout omits, so a
+  // non-framing update carries the live camera/ranges forward. Only plain,
+  // validated copies are merged: the raw `_fullLayout` objects are owned by
+  // plotly (react mutates them in place), and injecting an undefined value
+  // would make every later react fail, wedging the plot.
+  function toPlain(value) {
+    try { return JSON.parse(JSON.stringify(value)); } catch (err) { return null; }
+  }
+
+  function currentView() {
+    var gd = document.getElementById('plot');
+    var scene = gd && gd._fullLayout ? gd._fullLayout.scene : null;
+    if (!scene) return null;
+    var view = { ranges: {} };
+    var camera = toPlain(scene.camera);
+    if (camera && camera.eye && camera.center) {
+      view.camera = { eye: camera.eye, center: camera.center, up: camera.up };
+      if (camera.projection) view.camera.projection = camera.projection;
+    }
+    ['xaxis', 'yaxis', 'zaxis'].forEach(function (axis) {
+      var source = scene[axis];
+      if (!source || !Array.isArray(source.range) || source.range.length !== 2) return;
+      var low = Number(source.range[0]);
+      var high = Number(source.range[1]);
+      if (isFinite(low) && isFinite(high) && high > low) view.ranges[axis] = [low, high];
+    });
+    return view;
+  }
+
+  function mergeView(fig, view) {
+    try {
+      if (!view) return;
+      fig.layout.scene = fig.layout.scene || {};
+      if (view.camera) fig.layout.scene.camera = view.camera;
+      Object.keys(view.ranges).forEach(function (axis) {
+        fig.layout.scene[axis] = fig.layout.scene[axis] || {};
+        fig.layout.scene[axis].range = view.ranges[axis];
+        fig.layout.scene[axis].autorange = false;
+      });
+    } catch (err) {
+      // Never let view preservation block the figure update.
+      if (window.console) console.warn('otko: view merge skipped', err);
+    }
+  }
+
+  // --- update queue ------------------------------------------------------
+  // One react at a time, latest payload wins. Overlapping reacts on the same
+  // graph div are what left the plot unresponsive before.
+  var pendingUpdate = null;
+  var reactBusy = false;
+
+  function runUpdate() {
+    if (reactBusy || !pendingUpdate) return;
+    var job = pendingUpdate;
+    pendingUpdate = null;
+    reactBusy = true;
+
+    var fig;
+    try {
+      fig = JSON.parse(job.payload);
+    } catch (err) {
+      reactBusy = false;
+      if (window.console) console.error('otko: bad payload', err);
+      return;
+    }
+    mergeView(fig, job.preserve ? currentView() : null);
+
+    Plotly.react('plot', fig.data, fig.layout, config).then(function () {
+      findHover();
+      installHandlers();
+    }, function (err) {
+      if (window.console) console.error('otko: react failed', err);
+    }).then(function () {
+      reactBusy = false;
+      runUpdate();
+    });
+  }
+
+  window.otkoUpdate = function (payloadJson, preserveView) {
+    pendingUpdate = { payload: payloadJson, preserve: !!preserveView };
+    runUpdate();
+  };
+
   function installHandlers() {
     if (handlersReady) return;
     var gd = document.getElementById('plot');
@@ -122,32 +206,6 @@ _PAGE = """<!DOCTYPE html>
     gd.on('plotly_unhover', function () { clearHover(); });
   }
 
-  window.otkoUpdate = function (payloadJson, preserveView) {
-    var fig = JSON.parse(payloadJson);
-    // `Plotly.react` resets any scene attribute the incoming layout omits,
-    // which would snap the camera and the padded ranges back on every data
-    // update. When this is not an explicit re-frame, carry the user's
-    // current view forward into the incoming layout.
-    if (preserveView) {
-      var gd = document.getElementById('plot');
-      var scene = gd && gd._fullLayout ? gd._fullLayout.scene : null;
-      if (scene) {
-        fig.layout.scene = fig.layout.scene || {};
-        fig.layout.scene.camera = scene.camera;
-        ['xaxis', 'yaxis', 'zaxis'].forEach(function (axis) {
-          if (!scene[axis]) return;
-          fig.layout.scene[axis] = fig.layout.scene[axis] || {};
-          fig.layout.scene[axis].range = scene[axis].range;
-          fig.layout.scene[axis].autorange = false;
-        });
-      }
-    }
-    Plotly.react('plot', fig.data, fig.layout, config).then(function () {
-      findHover();
-      installHandlers();
-    });
-  };
-
   window.otkoSetCamera = function (cameraJson) {
     Plotly.relayout('plot', { 'scene.camera': JSON.parse(cameraJson) });
   };

src/otko/views/canvas_plotly/plotly_canvas.py

@@ -277,12 +277,13 @@ class PlotlyCanvas(QWidget):
     def set_style(self, style: RenderStyle) -> None:
         """Swap the visual style and repaint the figure.
 
-        Treated as a re-frame because the background and axis outline are
-        layout-level (``Plotly.restyle`` cannot carry them).
+        Deliberately *not* a re-frame: colour/opacity are trace props and the
+        background/outline ride the layout, so a style change (including the
+        live preview while dragging a colour) updates without snapping the
+        camera the user has moved.
         """
         self._style = style
         self._builder.set_style(style)
-        self._framing_dirty = True
         self.render()
 
     def set_display_options(self, *, show_node_labels: bool, show_element_labels: bool) -> None:
@@ -306,7 +307,8 @@ class PlotlyCanvas(QWidget):
         selection change. So a non-framing push marks itself
         ``preserveView`` and the JS side carries the live camera/ranges
         forward; only an explicit re-frame (new project, view preset,
-        ``reset_camera``, style change) sends the computed framing.
+        ``reset_camera``) sends the computed framing. Style changes are
+        non-framing: they re-colour in place.
         """
         self._scene = self._builder.build(self._project, self._options)
         if not self._ready:

tests/gui/test_plotly_view_preservation.py

@@ -85,7 +85,8 @@ def test_view_presets_and_reset_re_frame(qtbot) -> None:  # type: ignore[no-unty
 
 
 @pytest.mark.gui
-def test_style_change_re_frames_for_layout_only_attrs(qtbot) -> None:  # type: ignore[no-untyped-def]
+def test_style_change_keeps_the_view_but_updates_the_layout(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """Re-colouring must not snap the camera back to the preset."""
     from otko.views.canvas3d.style import RenderStyle
 
     canvas, calls = _canvas_with_captured_js(qtbot)
@@ -94,4 +95,7 @@ def test_style_change_re_frames_for_layout_only_attrs(qtbot) -> None:  # type: i
 
     canvas.set_style(RenderStyle(show_axis_outline=True))
 
-    assert calls[-1].endswith(", false)"), "background/outline live in the layout"
+    assert calls, "a style change must push"
+    payload, preserve = _parse_call(calls[-1])
+    assert preserve is True, "colour changes must not re-frame the view"
+    assert payload["layout"]["scene"]["xaxis"]["showgrid"] is True  # layout applied