A comment that still describes the old arrangement

IMAGE_EXTENSIONS claimed to be "the same list the daemon's own upload
code uses" and to be what "decides which host a file is offered to".
Neither has been true since the host listing learned to say what it
takes: the daemon's postimg table has no avif and this list does, and
the host is chosen by asking the daemon rather than by this predicate.

Left as it was, the comment invites exactly the drift it warns about -
the next reader to take it at its word would either add avif to the
daemon's table, which postimg refuses, or drop it from here, which
would stop an avif being drawn as the picture it is.

The list and the routing are both already correct and are unchanged;
only the account of them is.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/renderer/src/lib/util.ts

@@ -224,10 +224,20 @@ export const MEDIA_SCHEME = 'moho-media'
 /**
  * Whether this is a picture, by its name.
  *
- * The same list the daemon's own upload code uses, because the two have to
- * agree: this decides which host a file is offered to, and that one decides
- * whether the host will take it. A file called an image here and refused
- * there is the trap the uploads setting used to spring.
+ * Deliberately the broad answer - every format worth drawing as a picture
+ * rather than as a paperclip - and deliberately *not* the list of what any
+ * particular image host will take. It once tried to be both, and could not
+ * be: avif is an image by any ordinary reading, and postimg.cc refuses it,
+ * so a single list either called an avif something other than a picture or
+ * offered it to a host that would reject it.
+ *
+ * The two questions are asked separately now. This one decides whether to
+ * show a preview (see Composer) and which of somebody's two upload
+ * preferences applies, images or media. Whether the chosen host will
+ * actually accept the file is asked of the daemon instead - it is the one
+ * performing the upload, so it is the one that knows - by way of
+ * `listUploadHosts` and `hostAccepts` in the store, which sends a file the
+ * picture host refuses to the other one rather than letting it fail there.
  */
 const IMAGE_EXTENSIONS = /\.(png|jpe?g|gif|webp|bmp|avif)$/i