web/src/routes/admin/duplicates/+page.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
   import { pageTitle } from '$lib/branding';
-  import { Copy } from 'lucide-svelte';
+  import { Copy, TriangleAlert } from 'lucide-svelte';
   import {
     createDuplicatesQuery,
     runDuplicateSweep,
@@ -122,6 +122,27 @@
     return n === 1 ? `1 ${one}` : `${n} ${many}`;
   }
 
+  // Identical audio under different titles means at least one file's tags are
+  // wrong, and the recording the other title names may not be in the library at
+  // all. #3885: "WWW" was a second copy of the instrumental, and the vocal was
+  // missing with nothing to say so. Exact tier only: an acoustic match spans
+  // encodings, where a "Remastered" suffix is routine rather than a lie.
+  function differingTitles(g: AdminDuplicateGroup): string[] {
+    if (g.tier !== 'exact') return [];
+    const byKey = new Map<string, string>();
+    for (const m of g.members) {
+      const title = m.title.trim().replace(/\s+/g, ' ');
+      const key = title.toLowerCase();
+      if (!byKey.has(key)) byKey.set(key, title);
+    }
+    return byKey.size > 1 ? [...byKey.values()] : [];
+  }
+
+  function quotedList(titles: string[]): string {
+    const q = titles.map((t) => `“${t}”`);
+    return q.length <= 2 ? q.join(' and ') : `${q.slice(0, -1).join(', ')} and ${q[q.length - 1]}`;
+  }
+
   // What the copy carries is the fact that decides which to keep.
   function historyLabel(m: AdminDuplicateMember): string {
     if (m.like_count === 0 && m.play_count === 0) return 'no likes or plays';
@@ -224,6 +245,7 @@
   {:else}
     <ul class="space-y-4">
       {#each groups as group (group.id)}
+        {@const titles = differingTitles(group)}
         <li class="overflow-hidden rounded-lg border border-border bg-surface" data-testid="duplicate-group">
           <div class="flex items-center justify-between gap-4 border-b border-border px-4 py-3">
             <div class="min-w-0">
@@ -258,6 +280,20 @@
             </div>
           </div>
 
+          {#if titles.length > 0}
+            <p
+              class="flex items-start gap-2 border-b border-border bg-surface-hover px-4 py-3 text-xs text-text-secondary"
+              data-testid="title-mismatch"
+            >
+              <TriangleAlert size={14} class="mt-0.5 flex-shrink-0 text-warning-fg" aria-hidden="true" />
+              <span>
+                The audio is identical, but the copies are titled {quotedList(titles)}. If those
+                name different recordings, one file is mislabelled and the other recording isn't in
+                your library. Keep the copy whose title matches what you hear.
+              </span>
+            </p>
+          {/if}
+
           {#if confirmingMerge === group.id}
             <!-- What the second click will do, said plainly before it is done. -->
             <div class="space-y-2 border-b border-border bg-surface-hover px-4 py-3 text-sm" data-testid="merge-confirm">

web/src/routes/admin/duplicates/duplicates.test.ts

@@ -124,6 +124,61 @@ describe('admin duplicates', () => {
     expect(text(screen.getByTestId('duplicate-tier'))).toBe('Same recording · 96% match');
   });
 
+  // #3885: identical audio titled "WWW" and "WWW (instrumental)". One file
+  // claimed to be the vocal and wasn't, and nothing said the vocal was missing.
+  describe('identical audio under different titles', () => {
+    function www() {
+      const r = response();
+      r.groups[0] = {
+        ...r.groups[0],
+        members: [member('www-01'), member('www-02', { title: 'WWW (instrumental)' })]
+      };
+      return r;
+    }
+
+    test('says the copies are titled differently and names both titles', () => {
+      renderWith(www());
+      const notice = text(screen.getByTestId('title-mismatch'));
+      expect(notice).toContain('titled “WWW” and “WWW (instrumental)”');
+      expect(notice).toContain("isn't in your library");
+    });
+
+    test('three different titles are all named', () => {
+      const r = www();
+      r.groups[0].members.push(member('www-03', { title: 'WWW (Radio Edit)' }));
+      renderWith(r);
+      expect(text(screen.getByTestId('title-mismatch'))).toContain(
+        '“WWW”, “WWW (instrumental)” and “WWW (Radio Edit)”'
+      );
+    });
+
+    test('titles differing only in case or spacing are the same title', () => {
+      const r = response();
+      r.groups[0] = {
+        ...r.groups[0],
+        members: [
+          member('www-01', { title: 'WWW (Instrumental)' }),
+          member('www-02', { title: ' www  (instrumental) ' })
+        ]
+      };
+      renderWith(r);
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+
+    test('matching titles raise nothing', () => {
+      renderWith(response());
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+
+    // Across encodings a "Remastered" suffix is routine, not a mislabel.
+    test('an acoustic group with different titles raises nothing', () => {
+      const r = www();
+      r.groups[0] = { ...r.groups[0], tier: 'acoustic', worst_bit_error_rate: 0.04 };
+      renderWith(r);
+      expect(screen.queryByTestId('title-mismatch')).toBeNull();
+    });
+  });
+
   // Three states all show zero groups. Each must say which it is.
   test('empty while still fingerprinting says so', () => {
     renderWith(