Shorten the render failure notice's comments and docs

Comments keep only the why: the loop-running flag, the mid-raise events and
the one-time canvas focus. The CURRENT-STATE section lists behaviour and
pitfalls instead of retelling the code, and no longer says every tileset
event is raised outside Scene's error handling.

docs/CURRENT-STATE.md

@@ -2445,66 +2445,47 @@ during viewer construction, before any tile builds a draw command.
 ## Render failure notice
 
 When the globe stops drawing, the scene chrome says so instead of leaving a
-black globe behind controls that still respond. `installRenderFailureNotice()`
-(`src/ui/renderFailure.js`) listens for Cesium's `renderError`, after which
-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, 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
-Cesium's panel by default for other callers. An error thrown outside Scene's
-own error handling (a `preRender` or `postRender` listener, the clock's
-`onTick`, a resize) also stops the loop without a `renderError`, so the notice
-wraps the widget's `render()` and `resize()` and raises such an error as a
-render error before Cesium's loop handles it as before; one Scene has raised
-already and throws on (`rethrowRenderErrors`) is not raised again. A lost
-context fails every later frame, and those errors are only logged, so the
-notice keeps saying why. The notice sits above floating panels such as the
-Québec camera viewer, and its buttons are 44 px tall on touch screens.
+black globe behind working controls. `installRenderFailureNotice()`
+(`src/ui/renderFailure.js`) listens for Cesium's `renderError` and the canvas'
+`webglcontextlost`, logs the error, and publishes a notice that
+`RenderFailure.vue` shows as an alert dialog with focus on its first action.
+The app's viewer uses `showRenderLoopErrors: false`, so Cesium's dead-end
+"Rendering has stopped" panel no longer appears; `applicationViewerOptions()`
+keeps it by default for other callers.
 
-- **Retry** after a render error restarts the render loop. The notice stays
-  until a frame starts and ends without a render error (Cesium raises
-  `postRender` after a failed frame too), and a loop that fails again keeps it.
-  A listener that throws leaves its Cesium event mid-raise, with listeners
-  added or removed since only queued, so the `render()` and `resize()` wrapper
-  finishes the events it cut short (`finishRaise()`) before it raises the
-  render error. These are the events Cesium raises outside Scene's error
-  handling (`frameEvents()`): Scene's frame events, the camera's and the
-  clock's, the globe's tile load progress, and the load events of the scene's
-  top-level tilesets. So the notice's frame watchers start with the next
-  frame, a listener removed while the loop is stopped, for a layer turned off,
-  is not called again, and one turned off and on again keeps running.
-- **Reload** after a lost context reloads the page: Cesium cannot draw into a
-  context it has lost, and the address keeps the view.
-- **Reset view** opens the app's root address (`appRootUrl()`), without the
-  hash or `/share/<code>` path the view was restored from; the query, such as
-  `?lang=`, is kept.
+- **Retry** restarts the render loop. The notice stays until a frame starts
+  and ends without an error: Cesium raises `postRender` after a failed frame
+  too.
+- **Reload**, after a lost context, reloads the page; the address keeps the
+  view.
+- **Reset view** opens `appRootUrl()`, without the hash or `/share/<code>`
+  path; the query, such as `?lang=`, is kept.
 
-An inline conversation panel never reloads or navigates its host's page, so it
+Pitfalls:
+
+- An error thrown outside Scene's error handling (a frame listener, `onTick`,
+  a resize) stops the loop without a `renderError`. The notice wraps the
+  widget's `render()` and `resize()` and raises it as one, once even with
+  `rethrowRenderErrors`.
+- A throwing listener leaves its Cesium event mid-raise, with listener changes
+  only queued. The wrapper finishes those raises first (`finishRaise()` over
+  `frameEvents()`), so a layer turned off or on meanwhile behaves.
+- A render error marks the loop stopped while its next frame is still queued.
+  The wrapper keeps the loop marked running, so a Retry or a shown tab
+  (`src/app/tools.js`) before that frame starts no second loop.
+- After a lost context, later render errors are only logged, so the notice
+  keeps saying why. The listener neither prevents nor restores the loss.
+- When the globe draws again, focus goes back where it was, or to the globe's
+  canvas, which the map's keys read as the map; the canvas is focusable only
+  until focus leaves or the globe is pressed. Focus the user moved stays put.
+- The notice sits above floating panels such as the Québec camera viewer, and
+  its buttons are 44 px tall on touch screens.
+
+An inline conversation panel never reloads or navigates its host's page: it
 offers Retry after a render error only, and nothing after a lost context, where
-the panel runtime's own notice applies. The panel's timer
-(`keepPanelRendering()`) draws only while Cesium's render loop is on, so it
-stops after a render error and draws again after Retry. An error a frame of
-the timer throws stops there: it has been raised as a render error, and
-thrown on it would only reach the host page.
-
-A render error marks Cesium's loop stopped, but a frame drawn while the loop
-ran leaves its next animation frame queued: an error Scene catches itself
-returns to the loop, which queues the frame, and a frame the panel's timer
-draws leaves it queued. The `render()` and `resize()` wrapper keeps the loop
-marked running after such a call, so a Retry before that frame, or a tab shown
-again (`src/app/tools.js`), does not start a second loop that would draw every
-frame twice. The queued frame stops the loop itself if nothing restarted it.
-
-The `webglcontextlost` listener does not `preventDefault()` the context loss or
-restore the context; it only reports it.
+the panel runtime's own notice applies. Its timer (`keepPanelRendering()`)
+draws only while the render loop is on. An error a timer frame throws is caught
+there: it has already been raised as a render error.
 
 ## Map Source control ownership
 

src/ui/renderFailure.js

@@ -4,14 +4,11 @@ import { describeError } from '../app/errors.js';
 import { appRootUrl } from '../share/shareLinkPath.js';
 
 /**
- * Tell the user when the globe stops drawing, rather than leave a black globe
- * behind controls that still respond. Cesium stops its render loop after a
- * render error, and a page whose WebGL context was lost never draws again.
- *
- * Retry restarts the loop, and the notice stays until a frame renders without
- * an error; after a context loss Retry reloads the page. Reset opens the app's
- * root address. With `allowReload: false`, Reset is left out, and so is Retry
- * after a context loss. Returns a function that removes the notice.
+ * Show a recoverable notice when the globe stops drawing, instead of a black
+ * globe behind working controls. Retry restarts the render loop, or reloads
+ * after a lost WebGL context; Reset opens the app's root address. With
+ * `allowReload: false`, Reset is dropped, and so is Retry after a context loss.
+ * Returns a function that removes the notice.
  */
 export function installRenderFailureNotice(
   viewer,
@@ -27,8 +24,8 @@ export function installRenderFailureNotice(
   const canvas = viewer.canvas ?? scene.canvas;
   let notice = null;
   let contextLost = false;
-  // The error Scene raised as a render error and, with rethrowRenderErrors,
-  // throws on: the render() wrapper must not raise it a second time.
+  // With rethrowRenderErrors, Scene throws the error it has just raised;
+  // the render() wrapper must not raise it again.
   let raisedByScene = null;
   let frameFailed = false;
   let removeFrameListeners = null;
@@ -104,14 +101,10 @@ export function installRenderFailureNotice(
   };
 
   const removeRenderError = scene.renderError.addEventListener(onRenderError);
-  // An error thrown outside Scene's own error handling (a preRender or
-  // postRender listener, the clock's onTick, a resize) also stops Cesium's
-  // render loop, but raises no renderError, and Cesium reports it only in the
-  // panel the app turns off. Raise it as a render error, so Cesium's handler,
-  // an inline panel's timer and this notice all see it. Such an error passes
-  // here before anything else runs, so finish the raises of frameEvents() it
-  // cut short first: listeners added or removed while the loop is stopped
-  // then apply at once, in order.
+  // An error thrown outside Scene's error handling (a frame listener, onTick,
+  // resize) stops the loop without a renderError. Raise one, so Cesium, an
+  // inline panel's timer and this notice all see it. First finish the event
+  // raises it cut short, so listeners added or removed meanwhile apply.
   const unguard = ['resize', 'render'].map((name) =>
     reportThrown(viewer.cesiumWidget, name, (error) => {
       frameEvents(viewer).forEach(finishRaise);
@@ -130,11 +123,8 @@ export function installRenderFailureNotice(
 }
 
 /**
- * The events Cesium raises in a frame outside Scene's own error handling, so
- * that a listener's error cuts their raise short: Scene's frame events, the
- * camera's and the clock's, and those raised after the frame renders, the
- * globe's tile load progress and the load events of the scene's tilesets.
- * Tilesets nested in a collection are not reached.
+ * Events Cesium raises in a frame outside Scene's error handling, which a
+ * listener's error can leave mid-raise. Only top-level tilesets are reached.
  */
 function frameEvents(viewer) {
   const { scene } = viewer;
@@ -164,10 +154,8 @@ function frameEvents(viewer) {
 }
 
 /**
- * Finish the raise a throwing listener cut short. Cesium's `Event.raiseEvent`
- * marks the event as raising until every listener returns, and until then it
- * only queues the listeners added or removed. Apply the queue as the raise
- * would have, so listeners added or removed from here on take effect at once.
+ * Finish a raise a throwing listener cut short. Until a raise ends, Cesium's
+ * `Event` only queues added and removed listeners; apply that queue.
  */
 function finishRaise(event) {
   if (!event?._invokingListeners) return;
@@ -187,15 +175,12 @@ function finishRaise(event) {
 }
 
 /**
- * Report an error the widget's `name` method throws, and throw it on.
+ * Report an error the widget's `name` method throws, and rethrow it.
  *
- * A render error marks Cesium's render loop stopped, but a call made while
- * the loop ran leaves the loop's next animation frame queued: the loop queues
- * it after a call that returns, and a frame an inline panel's timer draws
- * leaves it queued. That frame stops the loop itself, and a Retry or a shown
- * tab that comes first must not start a second loop beside it, so the loop
- * stays marked running. A call from the loop that throws is still marked
- * stopped by the loop's own catch.
+ * A render error marks the loop stopped, but a call made while it ran leaves
+ * its next frame queued, and that frame stops it. Keep the loop marked
+ * running, so a Retry or a shown tab before that frame starts no second loop.
+ * After a throw, the loop's own catch still marks it stopped.
  */
 function reportThrown(widget, name, report) {
   const original = widget?.[name];

src/ui/renderFailureEventRetry.test.mjs

@@ -1,8 +1,6 @@
-// Retry after an error thrown by a scene event listener. Cesium's
-// Event.raiseEvent has no try/finally: a throwing listener leaves the event
-// with _invokingListeners = true, so listeners added or removed afterwards are
-// only queued (_toAdd/_toRemove) until the next raise of that event completes.
-// Drives Cesium's real Event and startRenderLoop (CesiumWidget.prototype).
+// Retry after a scene event listener throws. Cesium's Event.raiseEvent has no
+// try/finally, so the event stays mid-raise and only queues listener changes.
+// Drives Cesium's real Event and startRenderLoop.
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import * as Cesium from 'cesium';

src/ui/renderFailureLoopErrors.test.mjs

@@ -1,7 +1,5 @@
-// Errors thrown in the render loop outside Scene's tryAndCatchError (a
-// preRender/postRender listener, clock.onTick, resize). Drives Cesium's real
-// startRenderLoop through the CesiumWidget.prototype.useDefaultRenderLoop
-// setter.
+// Errors thrown in the render loop outside Scene's tryAndCatchError. Drives
+// Cesium's real startRenderLoop through the useDefaultRenderLoop setter.
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import * as Cesium from 'cesium';

src/ui/renderFailureSecondLoop.test.mjs

@@ -1,9 +1,6 @@
-// Retry after an error Scene catches itself (Scene.tryAndCatchError raises
-// renderError and returns). CesiumWidget's renderError handler marks the loop
-// stopped, but startRenderLoop still queues the loop's next animation frame.
-// A Retry that lands before that frame runs must not start a second loop.
-// Drives Cesium's real startRenderLoop and useDefaultRenderLoop setter
-// (CesiumWidget.prototype).
+// Retry after an error Scene catches itself: the loop is marked stopped but
+// its next frame is still queued, so an early Retry must not start a second
+// loop. Drives Cesium's real startRenderLoop and useDefaultRenderLoop setter.
 import test from 'node:test';
 import assert from 'node:assert/strict';
 import * as Cesium from 'cesium';

src/ui/renderFailureView.test.mjs

@@ -1,5 +1,4 @@
-// src/ui/renderFailureView.test.mjs — the scene chrome renders the render
-// failure notice installRenderFailureNotice() publishes, with its actions.
+// The scene chrome renders the render failure notice and its actions.
 import '../testSupport/registerDom.mjs';
 import test from 'node:test';
 import assert from 'node:assert/strict';

src/ui/views/panels/RenderFailure.vue

@@ -5,8 +5,7 @@ import { msg, t } from '../../../i18n/index.js';
 import { useStatusStore } from '../../stores/status.js';
 import UiButton from '../../kit/UiButton.vue';
 
-// The notice installRenderFailureNotice() (src/ui/renderFailure.js) publishes
-// while the globe cannot draw, with the actions it offers.
+// Published by installRenderFailureNotice() (src/ui/renderFailure.js).
 const { renderFailure: failure } = storeToRefs(useStatusStore());
 const panel = ref(null);
 const MESSAGES = {
@@ -17,10 +16,8 @@ const MESSAGES = {
     'Rendering stopped after an error. Layers and controls still work, but the map is not updating.',
   ),
 };
-// Focus moves to the first action each time the notice appears, so a
-// keyboard user can act on it at once. When the globe draws again, it goes
-// back where it was, or to the map if that cannot take it, unless the user
-// has moved it since.
+// Focus goes to the first action when the notice appears. When the globe
+// draws again, it goes back, or to the map, unless the user moved it.
 let focusBefore;
 watch(
   () => Boolean(failure.value),
@@ -39,7 +36,7 @@ watch(
     if (active && active !== document.body) return;
     if (previous?.isConnected && previous !== document.body) {
       previous.focus({ preventScroll: true });
-      // A control disabled, hidden or made inert since does not take it.
+      // A control disabled, hidden or made inert meanwhile does not take it.
       if (document.activeElement === previous) return;
     }
     focusMap();
@@ -47,10 +44,9 @@ watch(
   { immediate: true },
 );
 
-// The globe's canvas, which the map's keys (Enter to finish a drawing, Space
-// to talk) read as the map. It takes focus only this once: when focus moves
-// on, or the globe is pressed, it goes back to a canvas that cannot take
-// focus, and a press leaves focus on the page, as Cesium has it.
+// The map's keys (Enter to finish a drawing, Space to talk) read the canvas
+// as the map. It stays focusable only until focus leaves or the globe is
+// pressed; a press leaves focus on the page, as in Cesium.
 function focusMap() {
   const canvas = document.querySelector(
     '#cesiumContainer .cesium-widget canvas',