Hand focus back to the globe canvas after a render failure

When the control that had focus is gone or cannot take it, focus went to
the #cesiumContainer div, where Enter no longer finished a drawing. It now
goes to the globe's canvas, which the map's keys read as the map; the canvas
is focusable only until focus moves on or the globe is pressed. A control
disabled while the notice was up no longer leaves focus on the page, and
neither focus call scrolls.

docs/CURRENT-STATE.md

@@ -2225,9 +2225,12 @@ black globe behind controls that still respond. `installRenderFailureNotice()`
 Cesium stops its render loop, and for the canvas' `webglcontextlost`. It logs
 the error and publishes a notice to the status store, which
 `RenderFailure.vue` renders as an alert dialog that takes focus. When the
-globe draws again, focus goes back to the element that had it, or to the map
-(`#cesiumContainer`, made focusable with `tabindex="-1"`) if that element is
-gone, unless the user has moved focus since. The
+globe draws again, focus goes back to the element that had it, or, if that
+element is gone or cannot take focus, to the globe's canvas, which the map's
+keys (Enter to finish a drawing, Space to talk) read as the map. The canvas
+gets `tabindex="-1"` only until focus moves on or the globe is pressed, and a
+press leaves focus on the page, as Cesium has it. Focus the user moved
+meanwhile stays put. The
 application scene creates its viewer with `showRenderLoopErrors: false`, so
 Cesium's own "Rendering has stopped" panel, which offers no way back, no longer
 appears; `applicationViewerOptions()` and `createApplicationViewer()` keep