diff --git a/web/src/features/messages/MentionPicker.tsx b/web/src/features/messages/MentionPicker.tsx
index 3e6b8e5b..c1a2983e 100644
--- a/web/src/features/messages/MentionPicker.tsx
+++ b/web/src/features/messages/MentionPicker.tsx
@@ -50,28 +50,38 @@ export function MentionPicker({ topicId, query, onPick }: MentionPickerProps) {
               <span className="text-sm text-text-body">所有人</span>
             </button>
           ) : null}
-          {items.map((m) => (
-            <button
-              key={m.user_id}
-              type="button"
-              onClick={() => onPick({ userId: m.user_id, label: m.display_name || m.user_id })}
-              className="flex w-full items-center gap-2 px-3 py-2 text-left hover:bg-[#f2f6fd]"
-            >
-              <span className={`grid h-7 w-7 flex-none place-items-center rounded-lg text-xs font-medium text-white ${avatarBgClass(m.user_id)}`}>
-                {avatarLetter(m.display_name)}
-              </span>
-              <span className="min-w-0 flex-1 truncate text-sm text-text-body">{m.display_name || m.user_id}</span>
-              {m.role !== 'member' ? (
-                <span
-                  className={`flex-none rounded-[3px] border px-1 text-[10px] leading-[14px] ${
-                    m.role === 'owner' ? 'border-warn text-warn' : 'border-accent text-accent'
-                  }`}
-                >
-                  {ROLE_LABEL[m.role]}
+          {items.map((m) => {
+            // Real, reported bug: `display_name` here silently prefers the CURRENT viewer's own
+            // private remark for this member (see GroupMember.display_name's own doc comment) --
+            // fine for a list only the viewer sees, wrong for an @mention, whose label gets baked
+            // into the message's shared content once and read by every OTHER member from then on,
+            // who have no idea what the sender's personal remark for this person means. `nickname`
+            // is that member's own real public name, unaffected by anyone's remark, so it stays
+            // correct for whoever else ends up reading the mention.
+            const label = m.nickname || m.display_name || m.user_id;
+            return (
+              <button
+                key={m.user_id}
+                type="button"
+                onClick={() => onPick({ userId: m.user_id, label })}
+                className="flex w-full items-center gap-2 px-3 py-2 text-left hover:bg-[#f2f6fd]"
+              >
+                <span className={`grid h-7 w-7 flex-none place-items-center rounded-lg text-xs font-medium text-white ${avatarBgClass(m.user_id)}`}>
+                  {avatarLetter(label)}
                 </span>
-              ) : null}
-            </button>
-          ))}
+                <span className="min-w-0 flex-1 truncate text-sm text-text-body">{label}</span>
+                {m.role !== 'member' ? (
+                  <span
+                    className={`flex-none rounded-[3px] border px-1 text-[10px] leading-[14px] ${
+                      m.role === 'owner' ? 'border-warn text-warn' : 'border-accent text-accent'
+                    }`}
+                  >
+                    {ROLE_LABEL[m.role]}
+                  </span>
+                ) : null}
+              </button>
+            );
+          })}
         </>
       )}
     </div>
diff --git a/web/src/lib/api/groups.ts b/web/src/lib/api/groups.ts
index d3dd340b..04d8e4f7 100644
--- a/web/src/lib/api/groups.ts
+++ b/web/src/lib/api/groups.ts
@@ -147,7 +147,23 @@ export type GroupRole = 'owner' | 'admin' | 'member';
 
 export interface GroupMember {
   user_id: string;
+  /**
+   * Real, live-confirmed gotcha (2026-09-24): this is NOT always the member's own real name.
+   * Reading server/im_http.go's userSummaryPayload confirms `display_name` here unconditionally
+   * prefers the CALLING viewer's own private remark for that member when one is set, falling back
+   * to their real public nickname only when the viewer has no remark for them -- correct and
+   * intended for rendering a list to yourself (README's member list/search), completely wrong for
+   * anything that gets baked into shared message CONTENT once and read by everyone from then on
+   * (an @mention's label): a real reported bug was exactly this -- a group owner's own private
+   * remark for a member ("小号1") ended up as that member's permanent @mention text, which every
+   * OTHER member then saw with no idea who it meant. Use `nickname` (below) instead for that case.
+   */
   display_name?: string;
+  /** The member's own real public profile nickname -- same backend response, but from
+   *  copyUserNickname(), which reads straight off their public profile and is NEVER shadowed by the
+   *  viewer's own remark the way `display_name` above is. This is what stays correct for everyone
+   *  once baked into shared content (an @mention's label), not just for the viewer's own screen. */
+  nickname?: string;
   avatar_file_id?: string;
   role: GroupRole;
   mentionable?: boolean;