diff --git a/src/app/api/dashboard/chart-overlay-prefs/__tests__/route.test.ts b/src/app/api/dashboard/chart-overlay-prefs/__tests__/route.test.ts
index cfc2b2d3e..51cf6b4c9 100644
--- a/src/app/api/dashboard/chart-overlay-prefs/__tests__/route.test.ts
+++ b/src/app/api/dashboard/chart-overlay-prefs/__tests__/route.test.ts
@@ -51,10 +51,13 @@ function putReq(body: unknown): NextRequest {
   });
 }
 
+import { __resetAuditDedupMemoForTests } from "@/lib/audit-dedup";
+
 beforeEach(() => {
   vi.resetAllMocks();
   vi.mocked(getSession).mockResolvedValue(SESSION_OK as never);
   vi.mocked(prisma.auditLog.create).mockResolvedValue({} as never);
+  __resetAuditDedupMemoForTests();
 });
 
 describe("PUT /api/dashboard/chart-overlay-prefs — 422 multi-issue (v1.4.43 W6)", () => {
diff --git a/src/app/api/dashboard/chart-overlay-prefs/route.ts b/src/app/api/dashboard/chart-overlay-prefs/route.ts
index 89c69a5ab..87a8f4050 100644
--- a/src/app/api/dashboard/chart-overlay-prefs/route.ts
+++ b/src/app/api/dashboard/chart-overlay-prefs/route.ts
@@ -22,6 +22,7 @@ import {
   safeJson,
   sanitiseZodIssues,
 } from "@/lib/api-response";
+import { shouldEmitAuditRow } from "@/lib/audit-dedup";
 import { annotate } from "@/lib/logging/context";
 import { prisma, toJson } from "@/lib/db";
 import {
@@ -57,23 +58,30 @@ export const PUT = apiHandler(async (request: NextRequest) => {
     // v1.4.43 W6 — sibling of `/api/dashboard/widgets`; the per-chart
     // overlay popover hits this on every toggle so the multi-issue
     // envelope matches widgets exactly. Audit breadcrumb keyed
-    // `dashboard.chart-overlay.validation-failed`.
+    // `dashboard.chart-overlay.validation-failed`, deduped via the
+    // shared `shouldEmitAuditRow` 60 s `(userId, action)` window so a
+    // misbehaving iOS client looping the popover cannot flood the
+    // audit ledger.
     const issues = sanitiseZodIssues(parsed.error.issues);
     annotate({
       action: { name: "dashboard.chart-overlay.validation-failed" },
       meta: { issue_count: issues.length },
     });
-    prisma.auditLog
-      .create({
-        data: {
-          userId: user.id,
-          action: "dashboard.chart-overlay.validation-failed",
-          details: JSON.stringify({ issues }),
-        },
-      })
-      .catch(() => {
-        /* swallow — 422 response is the contract */
-      });
+    if (
+      shouldEmitAuditRow(user.id, "dashboard.chart-overlay.validation-failed")
+    ) {
+      prisma.auditLog
+        .create({
+          data: {
+            userId: user.id,
+            action: "dashboard.chart-overlay.validation-failed",
+            details: JSON.stringify({ issues }),
+          },
+        })
+        .catch(() => {
+          /* swallow — 422 response is the contract */
+        });
+    }
     return returnAllZodIssues(parsed.error, 422);
   }
 
diff --git a/src/app/api/dashboard/widgets/route.ts b/src/app/api/dashboard/widgets/route.ts
index 17af5d029..ca3873505 100644
--- a/src/app/api/dashboard/widgets/route.ts
+++ b/src/app/api/dashboard/widgets/route.ts
@@ -42,39 +42,11 @@ import type { NextRequest } from "next/server";
 // the enum from `DASHBOARD_WIDGET_IDS` so the two lists cannot drift.
 const widgetIdEnum = z.enum(DASHBOARD_WIDGET_IDS);
 
-// v1.4.43 B2 — in-process dedup memo for the validation-failed audit row.
-// A misbehaving iOS client looping on a 422 can otherwise write thousands
-// of identical audit rows per minute. We dedup on `(userId, action)` with
-// a 60 s window: only the first 422 inside the window writes; subsequent
-// 422s still return the full multi-issue envelope but skip the breadcrumb.
-// In-memory only — a process restart resets the map, which is the safe
-// failure mode (worst case: one extra audit row per restart). Cluster
-// deployments still get one row per process per minute, which is fine for
-// the operator-grep use case the audit row exists for.
-const AUDIT_DEDUP_WINDOW_MS = 60_000;
-const auditDedupMemo = new Map<string, number>();
-
-function shouldEmitAuditRow(userId: string, action: string, now: number): boolean {
-  const key = `${userId}:${action}`;
-  const last = auditDedupMemo.get(key);
-  if (last !== undefined && now - last < AUDIT_DEDUP_WINDOW_MS) {
-    return false;
-  }
-  auditDedupMemo.set(key, now);
-  // Opportunistic GC — drop entries older than the window on every miss so
-  // the map cannot grow unbounded across a long-running process.
-  if (auditDedupMemo.size > 512) {
-    for (const [k, t] of auditDedupMemo) {
-      if (now - t >= AUDIT_DEDUP_WINDOW_MS) auditDedupMemo.delete(k);
-    }
-  }
-  return true;
-}
-
-/** @internal — exported for the dedup unit test only. */
-export function __resetAuditDedupMemoForTests(): void {
-  auditDedupMemo.clear();
-}
+// v1.4.43 B2 — dedup helper extracted to `src/lib/audit-dedup.ts` so both
+// `/api/dashboard/widgets` and `/api/dashboard/chart-overlay-prefs` share
+// the same 60 s `(userId, action)` window.
+export { __resetAuditDedupMemoForTests } from "@/lib/audit-dedup";
+import { shouldEmitAuditRow } from "@/lib/audit-dedup";
 
 const layoutSchema = z.object({
   version: z.literal(1),
diff --git a/src/lib/audit-dedup.ts b/src/lib/audit-dedup.ts
new file mode 100644
index 000000000..664294ac3
--- /dev/null
+++ b/src/lib/audit-dedup.ts
@@ -0,0 +1,44 @@
+/**
+ * In-process dedup helper for fire-and-forget audit-log rows.
+ *
+ * A misbehaving iOS client looping on a 422 can otherwise write
+ * thousands of identical audit rows per minute. Routes that emit a
+ * `<route>.validation-failed` audit row alongside a multi-issue Zod
+ * 422 envelope wrap the write through `shouldEmitAuditRow` to gate
+ * on a 60 s `(userId, action)` window — only the first 422 inside
+ * the window writes; subsequent 422s still return the full envelope
+ * but skip the breadcrumb.
+ *
+ * In-memory only — a process restart resets the map, which is the
+ * safe failure mode (worst case: one extra audit row per restart).
+ * Cluster deployments still get one row per process per minute,
+ * which is fine for the operator-grep use case the audit row
+ * exists for.
+ */
+
+const AUDIT_DEDUP_WINDOW_MS = 60_000;
+const auditDedupMemo = new Map<string, number>();
+
+export function shouldEmitAuditRow(
+  userId: string,
+  action: string,
+  now: number = Date.now(),
+): boolean {
+  const key = `${userId}:${action}`;
+  const last = auditDedupMemo.get(key);
+  if (last !== undefined && now - last < AUDIT_DEDUP_WINDOW_MS) {
+    return false;
+  }
+  auditDedupMemo.set(key, now);
+  if (auditDedupMemo.size > 512) {
+    for (const [k, t] of auditDedupMemo) {
+      if (now - t >= AUDIT_DEDUP_WINDOW_MS) auditDedupMemo.delete(k);
+    }
+  }
+  return true;
+}
+
+/** @internal — exported for unit tests only. */
+export function __resetAuditDedupMemoForTests(): void {
+  auditDedupMemo.clear();
+}