fix: only drop exact role-folder name duplicates from the folder tree (#771)

src/lib/__tests__/mailbox-tree.test.ts

@@ -140,3 +140,42 @@ describe('account scoping helpers', () => {
     expect(mailboxesForSiblingOf(all, null).map((m) => m.id)).toEqual(['inbox', 'trash']);
   });
 });
+
+describe('role-folder deduplication (#771)', () => {
+  it('keeps user folders whose name merely contains a role folder name', () => {
+    const tree = buildMailboxTree([
+      own('inbox', 'Inbox', { role: 'inbox' }),
+      own('sent', 'Sent', { role: 'sent' }),
+      own('archive', 'Archive', { role: 'archive' }),
+      own('old-inbox', 'Old Inbox'),
+      own('arch-2025', '2025 Archive'),
+      own('sent-acc', 'Sent to Accounting'),
+      own('in', 'In'),
+    ]);
+    expect(tree.map((n) => n.id)).toEqual([
+      'inbox', 'sent', 'archive', 'arch-2025', 'in', 'old-inbox', 'sent-acc',
+    ]);
+  });
+
+  it('drops only an exact (trimmed, case-insensitive) duplicate of a role folder', () => {
+    const tree = buildMailboxTree([
+      own('sent', 'Sent', { role: 'sent' }),
+      own('sent-dup', ' sent '),
+      own('sent-mail', 'Sent Mail'),
+    ]);
+    expect(tree.map((n) => n.id)).toEqual(['sent', 'sent-mail']);
+  });
+
+  it('never drops a nested folder or a duplicate that has children', () => {
+    const tree = buildMailboxTree([
+      own('inbox', 'Inbox', { role: 'inbox' }),
+      own('sent', 'Sent', { role: 'sent' }),
+      own('proj', 'Projects'),
+      own('proj-sent', 'Sent', { parentId: 'proj' }),
+      own('inbox-dup', 'Inbox'),
+      own('inbox-dup-child', 'Child', { parentId: 'inbox-dup' }),
+    ]);
+    expect(tree.map((n) => n.id)).toEqual(['inbox', 'sent', 'inbox-dup', 'proj']);
+    expect(tree.find((n) => n.id === 'proj')?.children.map((n) => n.id)).toEqual(['proj-sent']);
+  });
+});

src/lib/mailbox-tree.ts

@@ -44,8 +44,12 @@ const ROLE_PRIORITY: Record<string, number> = {
 };
 
 // Drop root-level folders whose name collides with an existing role mailbox
-// (e.g. "Sent Mail" when a role=sent mailbox already exists). Mirrors the
-// webmail's `deduplicateMailboxes`; kept minimal (single account only).
+// (e.g. a plain "Sent" folder when a role=sent mailbox already exists).
+// Mirrors the webmail's `deduplicateMailboxes`; kept minimal (single account
+// only). Only an *exact* (trimmed, case-insensitive) name collision counts:
+// substring matching silently hid legitimate user folders whose name merely
+// contained a role folder's name — "Old Inbox", "2025 Archive",
+// "Sent to Accounting" (GitHub #771).
 function deduplicate(mailboxes: Mailbox[]): Mailbox[] {
   const roles = mailboxes.filter((m) => m.role);
   const referencedParentIds = new Set<string>();
@@ -56,12 +60,11 @@ function deduplicate(mailboxes: Mailbox[]): Mailbox[] {
   const result: Mailbox[] = [];
   for (const m of mailboxes) {
     if (m.role) { result.push(m); continue; }
+    // Never deduplicate nested folders — removing one would orphan its
+    // children to the root (GitHub #118).
     if (m.parentId) { result.push(m); continue; }
-    const lower = m.name.toLowerCase();
-    const dup = roles.find((r) => {
-      const rn = r.name.toLowerCase();
-      return lower.includes(rn) || rn.includes(lower);
-    });
+    const lower = m.name.trim().toLowerCase();
+    const dup = roles.find((r) => r.name.trim().toLowerCase() === lower);
     if (!dup || referencedParentIds.has(m.id)) result.push(m);
   }
   return result;