diff --git a/src/components/ui/mention-textarea.test.tsx b/src/components/ui/mention-textarea.test.tsx
new file mode 100644
index 00000000..b2c7e51b
--- /dev/null
+++ b/src/components/ui/mention-textarea.test.tsx
@@ -0,0 +1,145 @@
+import { fireEvent, render, screen, act } from "@testing-library/react";
+import React from "react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { MentionTextarea } from "./mention-textarea";
+
+function ControlledMentionTextarea() {
+  const [value, setValue] = React.useState("");
+  return <MentionTextarea aria-label="comment" value={value} onChange={setValue} />;
+}
+
+function deferredResponse(
+  users: Array<{ id: string; username: string; avatar_url: string | null }>
+) {
+  let resolve!: (value: Response) => void;
+  const promise = new Promise<Response>((res) => {
+    resolve = res;
+  });
+  return {
+    promise,
+    resolve: () =>
+      resolve({
+        ok: true,
+        json: async () => ({ users }),
+      } as Response),
+  };
+}
+
+function deferredHttpError() {
+  let resolve!: (value: Response) => void;
+  const promise = new Promise<Response>((res) => {
+    resolve = res;
+  });
+  return {
+    promise,
+    resolve: () => resolve({ ok: false } as Response),
+  };
+}
+
+describe("MentionTextarea", () => {
+  afterEach(() => {
+    vi.useRealTimers();
+    vi.restoreAllMocks();
+  });
+
+  it("ignores stale mention search responses after a newer query resolves", async () => {
+    vi.useFakeTimers();
+    const oldQuery = deferredResponse([{ id: "1", username: "alice", avatar_url: null }]);
+    const newQuery = deferredResponse([{ id: "2", username: "adliebe", avatar_url: null }]);
+    const fetchMock = vi
+      .fn()
+      .mockReturnValueOnce(oldQuery.promise)
+      .mockReturnValueOnce(newQuery.promise);
+    vi.stubGlobal("fetch", fetchMock);
+
+    render(<ControlledMentionTextarea />);
+    const textarea = screen.getByLabelText("comment") as HTMLTextAreaElement;
+
+    fireEvent.change(textarea, { target: { value: "@a" } });
+    textarea.setSelectionRange(2, 2);
+    act(() => {
+      vi.advanceTimersByTime(300);
+    });
+    expect(fetchMock).toHaveBeenCalledTimes(1);
+
+    fireEvent.change(textarea, { target: { value: "@ad" } });
+    textarea.setSelectionRange(3, 3);
+    act(() => {
+      vi.advanceTimersByTime(300);
+    });
+    expect(fetchMock).toHaveBeenCalledTimes(2);
+    expect(fetchMock.mock.calls[0][0]).toContain("q=a");
+    expect(fetchMock.mock.calls[1][0]).toContain("q=ad");
+
+    await act(async () => {
+      newQuery.resolve();
+      await newQuery.promise;
+    });
+    expect(screen.getByText("@adliebe")).toBeInTheDocument();
+
+    await act(async () => {
+      oldQuery.resolve();
+      await oldQuery.promise;
+    });
+
+    expect(screen.getByText("@adliebe")).toBeInTheDocument();
+    expect(screen.queryByText("@alice")).not.toBeInTheDocument();
+  });
+
+  it("cancels pending mention search when the cursor leaves mention context", async () => {
+    vi.useFakeTimers();
+    const fetchMock = vi.fn();
+    vi.stubGlobal("fetch", fetchMock);
+
+    render(<ControlledMentionTextarea />);
+    const textarea = screen.getByLabelText("comment") as HTMLTextAreaElement;
+
+    fireEvent.change(textarea, { target: { value: "@a" } });
+    textarea.setSelectionRange(2, 2);
+    fireEvent.change(textarea, { target: { value: "@a done" } });
+    textarea.setSelectionRange(7, 7);
+
+    act(() => {
+      vi.advanceTimersByTime(300);
+    });
+
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+
+  it("clears stale suggestions when the active mention search returns an HTTP error", async () => {
+    vi.useFakeTimers();
+    const goodQuery = deferredResponse([{ id: "1", username: "alice", avatar_url: null }]);
+    const failedQuery = deferredHttpError();
+    const fetchMock = vi
+      .fn()
+      .mockReturnValueOnce(goodQuery.promise)
+      .mockReturnValueOnce(failedQuery.promise);
+    vi.stubGlobal("fetch", fetchMock);
+
+    render(<ControlledMentionTextarea />);
+    const textarea = screen.getByLabelText("comment") as HTMLTextAreaElement;
+
+    fireEvent.change(textarea, { target: { value: "@a" } });
+    textarea.setSelectionRange(2, 2);
+    act(() => {
+      vi.advanceTimersByTime(300);
+    });
+    await act(async () => {
+      goodQuery.resolve();
+      await goodQuery.promise;
+    });
+    expect(screen.getByText("@alice")).toBeInTheDocument();
+
+    fireEvent.change(textarea, { target: { value: "@ad" } });
+    textarea.setSelectionRange(3, 3);
+    act(() => {
+      vi.advanceTimersByTime(300);
+    });
+    await act(async () => {
+      failedQuery.resolve();
+      await failedQuery.promise;
+    });
+
+    expect(screen.queryByText("@alice")).not.toBeInTheDocument();
+  });
+});
diff --git a/src/components/ui/mention-textarea.tsx b/src/components/ui/mention-textarea.tsx
index bd8b797b..2b6603af 100644
--- a/src/components/ui/mention-textarea.tsx
+++ b/src/components/ui/mention-textarea.tsx
@@ -17,8 +17,10 @@ interface UserSuggestion {
   avatar_url: string | null;
 }
 
-export interface MentionTextareaProps
-  extends Omit<React.TextareaHTMLAttributes<HTMLTextAreaElement>, "onChange"> {
+export interface MentionTextareaProps extends Omit<
+  React.TextareaHTMLAttributes<HTMLTextAreaElement>,
+  "onChange"
+> {
   value: string;
   onChange: (value: string) => void;
 }
@@ -35,25 +37,37 @@ const MentionTextarea = forwardRef<HTMLTextAreaElement, MentionTextareaProps>(
     const [query, setQuery] = useState("");
     const [dropdownPos, setDropdownPos] = useState({ top: 0, left: 0 });
     const debounceRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+    const requestSeqRef = useRef(0);
     const dropdownRef = useRef<HTMLDivElement>(null);
 
     // Fetch user suggestions
-    const fetchSuggestions = useCallback(async (q: string) => {
+    const fetchSuggestions = useCallback(async (q: string, seq: number) => {
       if (q.length < 1) {
-        setSuggestions([]);
-        setShowDropdown(false);
+        if (requestSeqRef.current === seq) {
+          setSuggestions([]);
+          setShowDropdown(false);
+        }
         return;
       }
       try {
         const res = await fetch(`/api/users/search?q=${encodeURIComponent(q)}&limit=8`);
-        if (res.ok) {
-          const data = await res.json();
-          setSuggestions(data.users || []);
-          setShowDropdown((data.users || []).length > 0);
-          setSelectedIndex(0);
+        if (!res.ok) {
+          if (requestSeqRef.current === seq) {
+            setSuggestions([]);
+            setShowDropdown(false);
+          }
+          return;
         }
+        const data = await res.json();
+        if (requestSeqRef.current !== seq) return;
+        setSuggestions(data.users || []);
+        setShowDropdown((data.users || []).length > 0);
+        setSelectedIndex(0);
       } catch {
-        setSuggestions([]);
+        if (requestSeqRef.current === seq) {
+          setSuggestions([]);
+          setShowDropdown(false);
+        }
       }
     }, []);
 
@@ -83,8 +97,12 @@ const MentionTextarea = forwardRef<HTMLTextAreaElement, MentionTextareaProps>(
         });
 
         if (debounceRef.current) clearTimeout(debounceRef.current);
-        debounceRef.current = setTimeout(() => fetchSuggestions(q), 300);
+        const seq = ++requestSeqRef.current;
+        debounceRef.current = setTimeout(() => fetchSuggestions(q, seq), 300);
       } else {
+        if (debounceRef.current) clearTimeout(debounceRef.current);
+        requestSeqRef.current++;
+        setSuggestions([]);
         setShowDropdown(false);
         setMentionStart(null);
         setQuery("");