feat: surface the Plotly page console in the Console dock

A plotly failure inside the WebEngine page was invisible from Python - the
react promise just rejected and the canvas looked frozen with no evidence.
PlotlyCanvas now installs a QWebEnginePage that forwards
javaScriptConsoleMessage into the Console dock with the right severity
(error/warning/info), so the next silent failure is diagnosable.

src/otko/views/canvas_plotly/plotly_canvas.py

@@ -18,11 +18,13 @@ from __future__ import annotations
 
 import json
 import math
+from collections.abc import Callable
 from dataclasses import replace
 from typing import Any
 
-from PySide6.QtCore import QUrl, Signal
+from PySide6.QtCore import QObject, QUrl, Signal
 from PySide6.QtWebChannel import QWebChannel
+from PySide6.QtWebEngineCore import QWebEnginePage
 from PySide6.QtWebEngineWidgets import QWebEngineView
 from PySide6.QtWidgets import QVBoxLayout, QWidget
 
@@ -47,6 +49,34 @@ _VIEW_DIRECTIONS = {
 }
 
 
+class _LoggingPage(QWebEnginePage):
+    """A web page that forwards the JS console to the app's console dock.
+
+    A plotly failure inside the page is otherwise invisible from Python (the
+    ``react`` promise just rejects), which makes a frozen canvas very hard to
+    diagnose.
+    """
+
+    def __init__(self, log: Callable[[str, str], None], parent: QObject | None = None) -> None:
+        super().__init__(parent)
+        self._log = log
+
+    def javaScriptConsoleMessage(
+        self,
+        level: QWebEnginePage.JavaScriptConsoleMessageLevel,
+        message: str,
+        line_number: int,
+        source_id: str,
+    ) -> None:
+        names = {
+            QWebEnginePage.JavaScriptConsoleMessageLevel.ErrorMessageLevel: "error",
+            QWebEnginePage.JavaScriptConsoleMessageLevel.WarningMessageLevel: "warning",
+        }
+        severity = names.get(level, "info")
+        source = source_id.rsplit("/", 1)[-1] or "plotly"
+        self._log(f"[web] {source}:{line_number} {message}", severity)
+
+
 class _CameraShim:
     """Mimics ``canvas.camera.parallel_projection`` as consumed elsewhere."""
 
@@ -126,8 +156,10 @@ class PlotlyCanvas(QWidget):
         parent: QWidget | None = None,
         style: RenderStyle | None = None,
         selection: SelectionState | None = None,
+        log: Callable[[str, str], None] | None = None,
     ) -> None:
         super().__init__(parent)
+        self._log = log
         self._style = style or RenderStyle()
         self.selection = selection or SelectionState(self)
         self._builder = PlotlyTraceBuilder(self._style)
@@ -153,6 +185,8 @@ class PlotlyCanvas(QWidget):
         layout = QVBoxLayout(self)
         layout.setContentsMargins(0, 0, 0, 0)
         self._web = QWebEngineView(self)
+        if self._log is not None:
+            self._web.setPage(_LoggingPage(self._log, self._web))
         self._channel = QWebChannel(self._web.page())
         self._bridge = _Bridge(self)
         self._channel.registerObject("otkoBridge", self._bridge)

src/otko/views/main_window.py

@@ -119,7 +119,12 @@ class MainWindow(
             # Imported lazily so a plotly-less install still boots PyVista.
             from otko.views.canvas_plotly import PlotlyCanvas
 
-            canvas = PlotlyCanvas(self, style=self._style, selection=self._selection)
+            canvas = PlotlyCanvas(
+                self,
+                style=self._style,
+                selection=self._selection,
+                log=self._log_canvas_message,
+            )
         else:
             canvas = ModelCanvas(self, style=self._style, selection=self._selection)
         self._canvases[backend] = canvas
@@ -149,6 +154,16 @@ class MainWindow(
         """Name of the active canvas backend (``"pyvista"`` or ``"plotly"``)."""
         return self._canvas_backend
 
+    def _log_canvas_message(self, message: str, severity: str = "info") -> None:
+        """Route a JS console line from the Plotly page to the Console dock.
+
+        The dock may not exist yet while canvases are being constructed, so
+        the lookup is guarded.
+        """
+        dock = getattr(self, "_console_dock", None)
+        if dock is not None:
+            dock.log(message, severity=severity)
+
     # ── plot style ───────────────────────────────────────────────────
     def _load_plot_style(self) -> RenderStyle:
         """Style from the last session, ignoring anything unrecognised."""

tests/gui/test_plotly_view_preservation.py

@@ -99,3 +99,25 @@ def test_style_change_keeps_the_view_but_updates_the_layout(qtbot) -> None:  # t
     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
+
+
+@pytest.mark.gui
+def test_js_console_messages_reach_the_log(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """A plotly failure inside the page must not be invisible from Python."""
+    from PySide6.QtWebEngineCore import QWebEnginePage
+
+    from otko.views.canvas_plotly.plotly_canvas import _LoggingPage
+
+    messages: list[tuple[str, str]] = []
+    page = _LoggingPage(lambda msg, severity="info": messages.append((severity, msg)))
+
+    levels = QWebEnginePage.JavaScriptConsoleMessageLevel
+    page.javaScriptConsoleMessage(levels.ErrorMessageLevel, "boom", 7, "file:///tmp/plot.html")
+    page.javaScriptConsoleMessage(levels.WarningMessageLevel, "careful", 8, "file:///tmp/plot.html")
+    page.javaScriptConsoleMessage(levels.InfoMessageLevel, "hello", 9, "")
+
+    assert messages == [
+        ("error", "[web] plot.html:7 boom"),
+        ("warning", "[web] plot.html:8 careful"),
+        ("info", "[web] plotly:9 hello"),
+    ]