Uploads carry the name the file came with (#83)

An upload sends its file name next to the raw bytes, and the server keeps
it in a sidecar next to the content-addressed file. Both pickers caption
every tile and row with it, and an asset made there is named after the
file instead of "Texture" / "Font". Last upload of the same content wins.

The API's own set_error_handler ignores error_reporting(), so @-silenced
warnings still throw: a missing sidecar took the whole listing down with a
500. Existence is checked instead of suppressed.

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

src/editor/texture/ImagePicker.ts

@@ -81,6 +81,11 @@ class ImageGrid extends Widget {
     return this.items.filter((item) => item.assetName !== null).map((item) => item.file);
   }
 
+  /** The captions as drawn, read off the tiles themselves rather than recomputed (test hook). */
+  get captions(): string[] {
+    return this.tiles.map((tile) => tile.caption.text);
+  }
+
   select(file: string | null): void {
     if (file === this.selectedFile) return;
     this.selectedFile = file;
@@ -139,8 +144,10 @@ class ImageGrid extends Widget {
         node.sprite.height = fitted.h;
       }
 
-      // The asset name is the useful caption where there is one; a bare hash tells nobody anything.
-      const text = item.width > 0 ? (item.assetName ?? `${item.width} × ${item.height}`) : 'unreadable';
+      // The asset name is the useful caption where there is one, then the name the file was
+      // uploaded under; a bare hash tells nobody anything, and the size is the last resort.
+      const text =
+        item.width > 0 ? (item.assetName ?? (item.name || `${item.width} × ${item.height}`)) : 'unreadable';
       node.caption.style = textStyle(item.assetName ? 'accent' : 'muted');
       node.caption.text = truncate(text, node.caption.style, side);
       node.caption.position.set(0, side + 1);
@@ -210,10 +217,11 @@ export class ImagePicker extends Popup {
   }
 
   /** What the dialog offers, which of it the project already wears, and what is picked (test hook). */
-  debugInfo(): { files: string[]; used: string[]; selected: string | null } {
+  debugInfo(): { files: string[]; used: string[]; captions: string[]; selected: string | null } {
     return {
       files: this.grid.fileList,
       used: this.grid.usedFiles,
+      captions: this.grid.captions,
       selected: this.grid.selected?.file ?? null,
     };
   }
@@ -270,7 +278,8 @@ export class ImagePicker extends Popup {
 
 function describe(item: PickerItem): string {
   if (item.width <= 0) return 'The server cannot read this file as an image.';
-  const size = `${item.width} × ${item.height} px, ${formatBytes(item.bytes)}`;
+  const measurements = `${item.width} × ${item.height} px, ${formatBytes(item.bytes)}`;
+  const size = item.name ? `${item.name} – ${measurements}` : measurements;
   return item.assetName ? `${size} – already in the project as "${item.assetName}"` : size;
 }