Split zip volumes (.zNN) and .xNN as volumes, but not .x32/.x64/.x86

87e15d8's .[s-v]NN let "Licence 700790900887990.z18" and "….x31" uploads
fall apart again (+1,740 releases on the corpus). .zNN is a split zip volume;
.xNN is a volume unless it's a build.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/release/identity.ts

@@ -49,8 +49,9 @@ const SUFFIXES = [
 /** Strips per-file suffixes (volume numbers, archive and par2 extensions) from a filename. */
 export function fileStem(name: string): string {
   // Old-style rar volumes after .r99 ("BD_NoTHing018.s41", "….s00", ".t91", ".v81"): only as the file's own extension, in
-  // lower case, so a season ("show.s01.rar", "Show.S01") stays; not x or z (".x64", ".x86" builds; ".z01" goes with .zip).
-  let stem = name.trim().replace(/\.[s-v]\d{2}$/, '')
+  // lower case, so a season ("show.s01.rar", "Show.S01") stays. Split zip volumes (".z18"), and .xNN but not the builds
+  // ".x32", ".x64", ".x86" ("Licence 700790900887990.z18", "….x31"; "….v1.0.142.x64" stays).
+  let stem = name.trim().replace(/\.(?:[s-vz]\d{2}|x(?!32$|64$|86$)\d{2})$/, '')
   let changed = true
   while (changed) {
     changed = false