fix(downloads): a conversion's commit, a stopped upload, the fast join and a clip's copy hold up

- The fast join gives each ffconcat entry its own media-only format whitelist, so a library file
  can no longer be opened as a nested concat list (the list's whitelist was handed down to it).
- A file the guarded probe cannot read is a download-only file, not a guess from yt-dlp's info.
- A conversion's or an ingest's commit that raises is re-read in a fresh session before any file
  is removed: a commit that landed keeps the file its row now names.
- An original that cannot be removed after conversion is logged; the upload stays ready.
- An upload whose conversion is cancelled or deleted midway is freed once nothing holds it; a
  paused one is kept.
- A shared link says "preparing" only while its video's job is queued or running.
- The admin storage view counts every file on disk ("Files on disk"), not only ready ones.
- A clip's failure title, unknown failure and cancel dialog, and a clip's and an upload's delete
  dialog speak of what the job made; an upload's quota refusal explains that the original is kept.
- /watch announces "preparing" as an alert and moves focus to the new Retry after an action.

frontend/src/lib/downloadFailure.ts

@@ -1,27 +1,38 @@
-import type { DownloadJob } from "./api";
+import type { DownloadJob, DownloadJobKind } from "./api";
 
 // The i18n keys that explain a failed download, most specific first — the list form `t()` takes, so
 // the first key a locale has wins. A failure-catalog entry (`error_detail`, e.g. `facebook.login_wall`)
 // names what went wrong on that site and what to do; the category (`error_code`) is the generic
 // sentence, and the fallback when an older client meets a detail it has no copy for; a category it has
-// no copy for falls back to the unknown one, so the row never prints a key. One helper for the queue
-// row's headline and the failure window, so the two can never explain the same job differently.
+// no copy for falls back to the unknown one, so the row never prints a key. A job that is not a
+// download (an upload's conversion, a clip) may word a category its own way, ahead of the shared
+// sentence — "this download was stopped" is not what happened to it — and its own unknown sentence
+// comes before the download's. One helper for the queue row's headline and the failure window, so
+// the two can never explain the same job differently.
 export function failCopyKeys(
-  job: Pick<DownloadJob, "error_code" | "error_detail">,
+  job: Pick<DownloadJob, "error_code" | "error_detail" | "job_kind">,
   part: "short" | "body",
 ): string[] {
-  const category = (code: string) => `downloads.errors.fail.cat.${code}.${part}`;
+  const kind = job.job_kind ?? "download";
+  const category = (code: string) => [
+    ...(kind === "download" ? [] : [`downloads.errors.fail.${kind}.${code}.${part}`]),
+    `downloads.errors.fail.cat.${code}.${part}`,
+  ];
   const code = job.error_code || "unknown";
   return [
     ...(job.error_detail ? [`downloads.errors.fail.catalog.${job.error_detail}.${part}`] : []),
-    category(code),
-    ...(code === "unknown" ? [] : [category("unknown")]),
+    ...category(code),
+    ...(code === "unknown" ? [] : category("unknown")),
   ];
 }
 
-/** The title over a failed job's explanation: an upload's failure is a conversion, not a download. */
+const TITLE_KEYS: Record<DownloadJobKind, string> = {
+  download: "downloads.errors.fail.title",
+  upload: "downloads.errors.fail.titleUpload", // its failure is a conversion, not a download
+  edit: "downloads.errors.fail.titleEdit", // a clip being cut
+};
+
+/** The title over a failed job's explanation, worded for what the job was making. */
 export function failTitleKey(job: Pick<DownloadJob, "job_kind">): string {
-  return job.job_kind === "upload"
-    ? "downloads.errors.fail.titleUpload"
-    : "downloads.errors.fail.title";
+  return TITLE_KEYS[job.job_kind ?? "download"];
 }