diff --git a/frontend/src/components/ui/Combobox.tsx b/frontend/src/components/ui/Combobox.tsx
index aa87f9ee..5b1eebfc 100644
--- a/frontend/src/components/ui/Combobox.tsx
+++ b/frontend/src/components/ui/Combobox.tsx
@@ -1,7 +1,8 @@
 import clsx from "clsx";
 import { useCallback, useEffect, useMemo, useRef, useState, type ReactNode } from "react";
 import { useTranslation } from "react-i18next";
-import { Check, ChevronDown } from "lucide-react";
+import { ChevronDown } from "lucide-react";
+import { MenuCheck } from "./MenuCheck";
 import { PopoverSurface, PopoverItem } from "./AnchoredPopover";
 import { useAnchoredPopover } from "./anchoredPopoverHooks";
 import { useScrollFade } from "../../lib/useScrollFade";
@@ -285,13 +286,7 @@ export default function Combobox({
                       renderOption(o, on)
                     ) : (
                       <>
-                        <span
-                          className={`flex h-3.5 w-3.5 shrink-0 items-center justify-center rounded border ${
-                            on ? "border-accent bg-accent text-accent-fg" : "border-border"
-                          }`}
-                        >
-                          {on && <Check className="h-2.5 w-2.5" />}
-                        </span>
+                        <MenuCheck kind={multiple ? "many" : "one"} on={on} />
                         <span className="flex-1 truncate">{o.label ?? o.value}</span>
                         {o.count != null && (
                           <span className="shrink-0 text-2xs tabular-nums text-muted">
diff --git a/frontend/src/components/ui/FilterSelect.tsx b/frontend/src/components/ui/FilterSelect.tsx
index 49a821be..d310cc06 100644
--- a/frontend/src/components/ui/FilterSelect.tsx
+++ b/frontend/src/components/ui/FilterSelect.tsx
@@ -1,5 +1,5 @@
 import { useState } from "react";
-import { Check } from "lucide-react";
+import { MenuCheck } from "./MenuCheck";
 import { SelectTrigger } from "./SelectTrigger";
 import { PopoverItem, PopoverSurface } from "./AnchoredPopover";
 import { useAnchoredPopover } from "./anchoredPopoverHooks";
@@ -129,17 +129,7 @@ export default function FilterSelect({
                   on ? "text-fg" : "text-muted"
                 }`}
               >
-                {multiple ? (
-                  <span
-                    className={`flex h-3.5 w-3.5 shrink-0 items-center justify-center rounded border ${
-                      on ? "border-accent bg-accent text-accent-fg" : "border-border"
-                    }`}
-                  >
-                    {on && <Check className="h-2.5 w-2.5" />}
-                  </span>
-                ) : (
-                  <Check className={`h-3.5 w-3.5 shrink-0 ${on ? "text-accent" : "opacity-0"}`} />
-                )}
+                <MenuCheck kind={multiple ? "many" : "one"} on={on} />
                 <span className="flex-1 truncate">{o.label}</span>
                 {o.count != null && (
                   <span className="shrink-0 text-2xs tabular-nums text-muted">{o.count}</span>
diff --git a/frontend/src/components/ui/menuCheck.contract.test.ts b/frontend/src/components/ui/menuCheck.contract.test.ts
new file mode 100644
index 00000000..3d9a97f0
--- /dev/null
+++ b/frontend/src/components/ui/menuCheck.contract.test.ts
@@ -0,0 +1,19 @@
+import { readdirSync, readFileSync } from "node:fs";
+import { describe, expect, it } from "vitest";
+
+// E28 review L2: `ui/MenuCheck` is the ONE drawn check box of a checkable row (S3e3b replaced seven
+// hand-drawn copies), yet FilterSelect and Combobox still painted their own — a 14px box beside the
+// menus' 16px one. The filled-box paint is the tell: it may live in MenuCheck only.
+describe("the drawn check box", () => {
+  it("is painted by MenuCheck alone", () => {
+    const root = new URL("../", import.meta.url);
+    const offenders = readdirSync(root, { recursive: true, encoding: "utf8" })
+      .filter((f) => f.endsWith(".tsx") && !f.includes(".test.") && !f.endsWith("MenuCheck.tsx"))
+      .filter((f) =>
+        /border-accent bg-accent text-accent-fg/.test(
+          readFileSync(new URL(f.replace(/\\/g, "/"), root), "utf8"),
+        ),
+      );
+    expect(offenders).toEqual([]);
+  });
+});