Texture fills show in the vector tab as soon as they load (#196)

After signing out and back in, a texture fill stayed in its base
colour until something else redrew the vector tab. The texture
library is a singleton that outlives the editor. Four widgets
subscribed to it and never unsubscribed. After a new sign-in the
first loaded texture called a destroyed canvas, which threw and
stopped the loop before the vector tab heard about the image.

- TextureCanvas, TileCanvas, ShaderPreview and WorldViewport now
  unsubscribe in destroy(). This is the pattern FontPreview and
  VectorArtCanvas already use. WorldViewport leaves both the
  texture and the font library.
- FileLibrary.notifyChange catches errors per listener. A broken
  listener no longer starves the others. The error is still
  logged as "[textures] a listener failed".
- e2e 47i no longer forces a redraw. It waits up to 3 s for the
  tab to show the texture on its own.

Findings:
- The trigger was e2e module 45 (sign out, sign in), not the
  texture fill. My note in #196 that the browser showed no
  exception was wrong. The counter-check shows it clearly.

Tests:
- ./check.sh: 137 files, 2051 tests, exit 0 (before 136 / 2049)
- 2 new unit tests in tests/viewport/file-library.test.ts
- GM_STEPS=45,47 after a fresh seed: ALL PASSED, 71 checks
- Counter-check with the old source and the new check: 1 FAIL
  (shape stays #0000ff) plus the TypeError. Old FileLibrary.ts
  fails the first unit test.
- No full e2e run locally. The check count is unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/editor/shader/ShaderPreview.ts

@@ -32,6 +32,7 @@ export class ShaderPreview extends Widget {
   private clockOrigin = 0;
   /** Null: the clock runs. A number: the preview stands at that second. */
   private held: number | null = null;
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -39,7 +40,7 @@ export class ShaderPreview extends Widget {
     this.content.addChild(this.mesh);
     this.content.mask = this.clip;
     this.addChild(this.bg, this.content, this.clip);
-    textureLibrary.onChange(() => this.invalidate());
+    this.stopPictures = textureLibrary.onChange(() => this.invalidate());
   }
 
   override measure(): Size {
@@ -107,6 +108,7 @@ export class ShaderPreview extends Widget {
   }
 
   override destroy(): void {
+    this.stopPictures();
     disposeSpriteMesh(this.mesh);
     super.destroy();
   }

src/editor/texture/TextureCanvas.ts

@@ -136,6 +136,7 @@ export class TextureCanvas extends Widget {
   private collision = false;
   /** The outline a click adds corners to; for another frame, or one gone, the frame's last one. */
   private active = { frameId: '', index: -1 };
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -159,7 +160,13 @@ export class TextureCanvas extends Widget {
       this.redraw();
     });
     // A picture arrives asynchronously; until then there is nothing to fit the view to.
-    textureLibrary.onChange(() => this.redraw());
+    this.stopPictures = textureLibrary.onChange(() => this.redraw());
+  }
+
+  /** The library outlives a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    this.stopPictures();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/editor/tile/TileCanvas.ts

@@ -68,6 +68,7 @@ export class TileCanvas extends Widget {
   private board = { w: 0, h: 0 };
   private info: TileInfo | null = null;
   private needsFit = true;
+  private readonly stopPictures: () => void;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -90,7 +91,13 @@ export class TileCanvas extends Widget {
     state.on('project', () => this.redraw());
     state.on('load', () => this.show(''));
     // A picture arrives asynchronously; the board is empty until it does.
-    textureLibrary.onChange(() => this.redraw());
+    this.stopPictures = textureLibrary.onChange(() => this.redraw());
+  }
+
+  /** The library outlives a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    this.stopPictures();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/editor/viewport/WorldViewport.ts

@@ -61,6 +61,7 @@ export abstract class WorldViewport extends Widget {
   private visibleCount = 0;
   private animated = false;
   protected lastItems: DrawItem[] = [];
+  private readonly stopFiles: (() => void)[];
 
   protected constructor(protected readonly state: EditorState) {
     super();
@@ -78,8 +79,16 @@ export abstract class WorldViewport extends Widget {
       if (this.visible && !this.animated) this.redraw();
     });
     // Unconditional: a picture or a typeface arriving fires once per file, not per frame.
-    textureLibrary.onChange(() => this.redraw());
-    fontLibrary.onChange(() => this.redraw());
+    this.stopFiles = [
+      textureLibrary.onChange(() => this.redraw()),
+      fontLibrary.onChange(() => this.redraw()),
+    ];
+  }
+
+  /** The libraries outlive a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    for (const stop of this.stopFiles) stop();
+    super.destroy(options);
   }
 
   override measure(): Size {

src/viewport/FileLibrary.ts

@@ -30,7 +30,13 @@ export abstract class FileLibrary<T> {
 
   /** Runs the listeners: something they draw from has changed without a file arriving here. */
   notifyChange(): void {
-    for (const listener of this.listeners) listener();
+    // One listener that throws must not keep the file from the ones after it (#196).
+    for (const listener of this.listeners)
+      try {
+        listener();
+      } catch (error) {
+        console.error(`[${this.tag}] a listener failed`, error);
+      }
   }
 
   protected abstract fetchFile(url: string, file: string): Promise<T>;

tests/viewport/file-library.test.ts

@@ -0,0 +1,67 @@
+/**
+ * The base of the picture and font libraries: a file asked for is fetched once, and the listeners
+ * hear when it lands. The libraries are module singletons and outlive an editor that was signed out
+ * of, so a listener can belong to a widget that is gone (#196).
+ */
+import { describe, expect, it, vi } from 'vitest';
+import { FileLibrary } from '../../src/viewport/FileLibrary';
+
+/** A library whose loads a test resolves by hand. */
+class HandLibrary extends FileLibrary<string> {
+  readonly kept = new Map<string, string>();
+  private readonly pending: (() => void)[] = [];
+
+  constructor() {
+    super('/files', 'test');
+  }
+
+  ask(file: string): void {
+    if (!this.kept.has(file)) this.startLoading(file);
+  }
+
+  land(): Promise<void> {
+    for (const resolve of this.pending.splice(0)) resolve();
+    return new Promise((resolve) => setTimeout(resolve, 0));
+  }
+
+  protected fetchFile(url: string): Promise<string> {
+    return new Promise((resolve) => this.pending.push(() => resolve(url)));
+  }
+
+  protected keep(file: string, loaded: string): void {
+    this.kept.set(file, loaded);
+  }
+}
+
+describe('the file library', () => {
+  it('tells every listener when a file lands, even after one of them threw', async () => {
+    const library = new HandLibrary();
+    const error = vi.spyOn(console, 'error').mockImplementation(() => {});
+    // First in line, as the canvas of an editor signed out of is: its graphics are destroyed.
+    library.onChange(() => {
+      throw new TypeError("Cannot read properties of null (reading 'clear')");
+    });
+    const later = vi.fn();
+    library.onChange(later);
+
+    library.ask('a.png');
+    await library.land();
+
+    expect(library.kept.get('a.png')).toBe('/files/a.png');
+    expect(later).toHaveBeenCalledTimes(1);
+    // Not swallowed: the broken listener still shows in the console.
+    expect(error).toHaveBeenCalledWith('[test] a listener failed', expect.any(TypeError));
+    error.mockRestore();
+  });
+
+  it('forgets a listener once its unsubscribe has run', async () => {
+    const library = new HandLibrary();
+    const gone = vi.fn();
+    const stop = library.onChange(gone);
+    stop();
+
+    library.ask('a.png');
+    await library.land();
+    expect(gone).not.toHaveBeenCalled();
+  });
+});

tools/e2e/47-vectorart.mjs

@@ -843,15 +843,17 @@ export async function vectorArt(t) {
   const halvesEntry = Boolean(halvesName) && filteredOffers.includes(halvesName);
   await press(halvesEntry ? 'Enter' : 'Escape');
   await settle();
-  // The picture loads asynchronously and the shape keeps its plain fill until it is there. In the
-  // full run the tab then waits for the next redraw instead of drawing when the picture lands
-  // (#196), so the check asks for that redraw itself. Remove the preview() with #196.
-  await sleep(300);
-  await evaluate('__gm.state.preview()');
-  await settle();
+  // The picture loads asynchronously and the shape keeps its plain fill until it is there; the tab
+  // redraws by itself when it lands. Nothing here asks for that redraw: after module 45 had signed
+  // out and in, a canvas of the old editor used to swallow the news (#196).
+  let leftHalf = await tabPixel(60, 100);
+  let rightHalf = await tabPixel(196, 100);
+  for (let waited = 0; waited < 3000 && colourDistance(rightHalf, HALVES_RIGHT) >= 20; waited += 100) {
+    await sleep(100);
+    leftHalf = await tabPixel(60, 100);
+    rightHalf = await tabPixel(196, 100);
+  }
   const tiled = (await sky())?.paint;
-  const leftHalf = await tabPixel(60, 100);
-  const rightHalf = await tabPixel(196, 100);
   check(
     'Texture offers the uploaded pictures but no drawing, and fills the shape with the one picked',
     halvesEntry &&