diff --git a/frontend/sync-client/src/persistence/settings.test.ts b/frontend/sync-client/src/persistence/settings.test.ts
index 2f4bcee0..feb81715 100644
--- a/frontend/sync-client/src/persistence/settings.test.ts
+++ b/frontend/sync-client/src/persistence/settings.test.ts
@@ -20,4 +20,20 @@ describe("Settings logging", () => {
         assert.doesNotMatch(messages, /loaded-secret|updated-secret/u);
         assert.match(messages, /\[REDACTED\]/u);
     });
+
+    it("retains and persists the configured diff cache size", async () => {
+        let saved = 0;
+        const settings = new Settings(
+            new Logger(),
+            { diffCacheSizeMB: 7 },
+            async (value) => {
+                saved = value.diffCacheSizeMB;
+            }
+        );
+
+        assert.equal(settings.getSettings().diffCacheSizeMB, 7);
+        await settings.setSetting("diffCacheSizeMB", 9);
+        assert.equal(settings.getSettings().diffCacheSizeMB, 9);
+        assert.equal(saved, 9);
+    });
 });
diff --git a/frontend/sync-client/src/persistence/settings.ts b/frontend/sync-client/src/persistence/settings.ts
index bac7c69d..3e046b03 100644
--- a/frontend/sync-client/src/persistence/settings.ts
+++ b/frontend/sync-client/src/persistence/settings.ts
@@ -10,6 +10,7 @@ export interface SyncSettings {
     maxFileSizeMB: number;
     ignorePatterns: string[];
     webSocketRetryIntervalMs: number;
+    diffCacheSizeMB: number;
     enableTelemetry: boolean;
     requestTimeoutMs: number;
     networkRetryIntervalMs: number;
@@ -24,6 +25,7 @@ export const DEFAULT_SETTINGS: SyncSettings = {
     maxFileSizeMB: 10,
     ignorePatterns: [],
     webSocketRetryIntervalMs: 3500,
+    diffCacheSizeMB: 4,
     enableTelemetry: false,
     requestTimeoutMs: 30_000,
     networkRetryIntervalMs: 1000,