feat: the library's albums go on the wanted list as held, once; after that the list is the truth (M502 #5567)

A one-time job in the wanted worker lists every album in the library as a
held want, one per release group, with a record that it happened
(acquisition_settings.library_listed_at). Albums whose tags name only a
release are named on MusicBrainz first, 120 a pass; what nothing names is
counted and shown on the Held tab.

Re-acquisition now wants back only albums on the list. Taking a held album
off the list leaves its files, and it is never fetched back; albums put in
the library folder by hand afterwards are not added.

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

web/src/lib/components/wanted/WantList.svelte

@@ -13,7 +13,9 @@
   // One tab of the Wanted view (M502 #5520–#5522): the albums still wanted,
   // the missing albums wanted back, or the ones held. Each open want says
   // what its last search found and how its download is getting on; Releases
-  // lists every candidate with its verdict, and Search runs one now.
+  // lists every candidate with its verdict, and Search runs one now. The
+  // library's albums were put on the list as held once (#5567); taking one
+  // off leaves its files and stops it being fetched back if they go.
 
   let { list }: { list: WantState } = $props();
 
@@ -21,6 +23,7 @@
   const wantsStore = $derived(createWantsQuery(list));
   const wants = $derived($wantsStore);
   const items = $derived((wants.data?.pages ?? []).flatMap((p) => p.items) as Want[]);
+  const library = $derived(wants.data?.pages[0]?.library);
 
   let busy = $state<string | null>(null);
   let searching = $state<string | null>(null);
@@ -30,7 +33,11 @@
     busy = w.id;
     try {
       await removeWant(w.id);
-      pushToast(`${w.title} is off the wanted list.`);
+      pushToast(
+        w.held_at
+          ? `${w.title} is off the list. Its files stay, and it won't be fetched back if they go missing.`
+          : `${w.title} is off the wanted list.`
+      );
       await client.invalidateQueries({ queryKey: ['adminWants'] });
     } catch (e) {
       pushToast(errMessage(e), 'error');
@@ -137,6 +144,7 @@
   function why(w: Want): string {
     if (w.reason === 'request') return w.requested_by ? `Requested by ${w.requested_by}` : 'Requested';
     if (w.reason === 'follow') return 'New from a followed artist';
+    if (w.reason === 'library') return 'In your library when the list began';
     return 'Its files went missing';
   }
 
@@ -151,6 +159,22 @@
   }
 </script>
 
+{#if list === 'held' && library}
+  {#if !library.listed_at}
+    <p class="mb-3 text-sm text-text-secondary" data-testid="library-listing">
+      Your library's albums are being added to this list as held. Albums whose tags name only a
+      release are looked up on MusicBrainz first, about one a second.
+    </p>
+  {:else if library.unlisted > 0}
+    <p class="mb-3 text-sm text-text-secondary" data-testid="library-listing">
+      {library.unlisted === 1 ? '1 album' : `${library.unlisted} albums`} in your library
+      {library.unlisted === 1 ? "isn't" : "aren't"} on this list: nothing in {library.unlisted === 1 ? 'its' : 'their'}
+      tags names {library.unlisted === 1 ? 'it' : 'them'} to MusicBrainz. Those are never fetched back if
+      their files go missing.
+    </p>
+  {/if}
+{/if}
+
 {#if wants.isPending}
   <p class="text-text-secondary">Reading the wanted list…</p>
 {:else if wants.isError && !wants.isFetchNextPageError}
@@ -216,6 +240,17 @@
               <div class="truncate text-xs text-text-secondary" data-testid="want-arrived">{arrived(w)}</div>
             {/if}
           </div>
+          {#if w.held_at}
+            <button
+              type="button"
+              onclick={() => onRemove(w)}
+              disabled={busy === w.id}
+              aria-label="Take {w.title} off the list"
+              class="inline-flex shrink-0 items-center gap-1 rounded-md border border-border px-2.5 py-1 text-xs text-text-secondary hover:bg-surface-hover hover:text-text-primary disabled:opacity-50"
+            >
+              <X size={12} strokeWidth={2} /> Remove
+            </button>
+          {/if}
           {#if !w.held_at}
             <div class="flex shrink-0 flex-wrap justify-end gap-1.5">
               <button