diff --git a/src/lib/pwa/__tests__/query-persister.test.ts b/src/lib/pwa/__tests__/query-persister.test.ts
index 9ddf27bdb..d04314362 100644
--- a/src/lib/pwa/__tests__/query-persister.test.ts
+++ b/src/lib/pwa/__tests__/query-persister.test.ts
@@ -323,3 +323,125 @@ describe("persister round-trips through a fake IndexedDB", () => {
     expect(store.get("react-query")).toBeUndefined();
   });
 });
+
+describe("persister is bounded and surfaces quota failures", () => {
+  const original = (globalThis as { indexedDB?: unknown }).indexedDB;
+
+  afterEach(() => {
+    if (original !== undefined) {
+      (globalThis as { indexedDB?: unknown }).indexedDB = original;
+    } else {
+      delete (globalThis as { indexedDB?: unknown }).indexedDB;
+    }
+    vi.restoreAllMocks();
+  });
+
+  const makeReq = (run: () => void) => {
+    const req: Record<string, unknown> = {};
+    queueMicrotask(() => {
+      run();
+      (req.onsuccess as (() => void) | undefined)?.();
+    });
+    return req;
+  };
+
+  function installFakeIdb(opts: {
+    onPut: (value: unknown, key: string) => void;
+    store: Map<string, unknown>;
+  }) {
+    const fakeDb = {
+      close() {},
+      transaction() {
+        return {
+          objectStore() {
+            return {
+              put(value: unknown, key: string) {
+                opts.onPut(value, key);
+                return makeReq(() => {});
+              },
+              get(key: string) {
+                const req = makeReq(() => {});
+                (req as { result?: unknown }).result = opts.store.get(key);
+                return req;
+              },
+              delete(key: string) {
+                opts.store.delete(key);
+                return makeReq(() => {});
+              },
+            };
+          },
+          set oncomplete(fn: () => void) {
+            queueMicrotask(fn);
+          },
+          set onerror(_fn: () => void) {},
+        };
+      },
+    };
+    (globalThis as { indexedDB?: unknown }).indexedDB = {
+      open() {
+        const req: Record<string, unknown> = { result: fakeDb };
+        queueMicrotask(() => (req.onsuccess as () => void)?.());
+        return req;
+      },
+    };
+  }
+
+  it("skips a snapshot that exceeds the size cap, leaving the last write intact", async () => {
+    const store = new Map<string, unknown>();
+    let putCount = 0;
+    installFakeIdb({ store, onPut: () => (putCount += 1) });
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+
+    const source = new QueryClient();
+    // A persistable family with a payload well over the 2 MB ceiling.
+    const huge = "x".repeat(3 * 1024 * 1024);
+    source.setQueryData(["chart-data", "WEIGHT"], [{ blob: huge }]);
+    const stop = startPersistingQueryCache(source, "v1.18.6");
+    vi.useFakeTimers();
+    source.setQueryData(["chart-data", "WEIGHT"], [{ blob: huge }]);
+    vi.advanceTimersByTime(1100);
+    vi.useRealTimers();
+    await new Promise((r) => setTimeout(r, 0));
+    stop();
+
+    // The oversized snapshot was never written, and the skip was logged
+    // rather than silently dropped.
+    expect(putCount).toBe(0);
+    expect(store.get("react-query")).toBeUndefined();
+    expect(warn).toHaveBeenCalled();
+  });
+
+  it("clears the cache and warns on an IndexedDB quota error instead of swallowing it", async () => {
+    const store = new Map<string, unknown>();
+    let firstPut = true;
+    installFakeIdb({
+      store,
+      onPut: (value, key) => {
+        if (firstPut) {
+          firstPut = false;
+          // First write hits the storage quota.
+          throw new DOMException("quota", "QuotaExceededError");
+        }
+        store.set(key, value);
+      },
+    });
+    const warn = vi.spyOn(console, "warn").mockImplementation(() => {});
+
+    const source = new QueryClient();
+    source.setQueryData(["dashboard", "snapshot"], { weightKg: 81 });
+    const stop = startPersistingQueryCache(source, "v1.18.6");
+    vi.useFakeTimers();
+    source.setQueryData(["chart-data", "WEIGHT"], [{ v: 81 }]);
+    vi.advanceTimersByTime(1100);
+    vi.useRealTimers();
+    await new Promise((r) => setTimeout(r, 0));
+    // Let the clear-on-quota microtasks settle.
+    await new Promise((r) => setTimeout(r, 0));
+    stop();
+
+    // The quota failure was surfaced, not swallowed, and the cache key was
+    // cleared so the next flush has room.
+    expect(warn).toHaveBeenCalled();
+    expect(store.get("react-query")).toBeUndefined();
+  });
+});
diff --git a/src/lib/pwa/query-persister.ts b/src/lib/pwa/query-persister.ts
index e512f54b7..2701f6431 100644
--- a/src/lib/pwa/query-persister.ts
+++ b/src/lib/pwa/query-persister.ts
@@ -38,6 +38,17 @@ const KEY = "react-query";
 const VERSION_KEY = "react-query-version";
 const MAX_AGE_MS = 24 * 60 * 60 * 1000; // discard anything older than a day
 
+/**
+ * Upper bound on the serialized snapshot. The allowlist already caps WHAT is
+ * persisted (dashboard snapshot + widget layout + daily series), but a tenant
+ * with a long chart history can still grow a single series past what's worth
+ * keeping on disk — and an oversized write is the most likely trigger for an
+ * IndexedDB `QuotaExceededError`. A snapshot above this ceiling is skipped
+ * rather than written: the offline read value of a multi-megabyte blob is
+ * marginal, and skipping keeps the last good (smaller) snapshot in place.
+ */
+const MAX_PERSIST_BYTES = 2 * 1024 * 1024; // 2 MB
+
 /**
  * Strict allowlist of the only query families written to disk — the
  * low-sensitivity reads the dashboard needs to paint last-known values when
@@ -78,13 +89,30 @@ function openDb(): Promise<IDBDatabase> {
 
 async function idbSet(value: unknown): Promise<void> {
   const db = await openDb();
-  await new Promise<void>((resolve, reject) => {
-    const tx = db.transaction(STORE, "readwrite");
-    tx.objectStore(STORE).put(value, KEY);
-    tx.oncomplete = () => resolve();
-    tx.onerror = () => reject(tx.error);
-  });
-  db.close();
+  try {
+    await new Promise<void>((resolve, reject) => {
+      const tx = db.transaction(STORE, "readwrite");
+      tx.objectStore(STORE).put(value, KEY);
+      tx.oncomplete = () => resolve();
+      tx.onerror = () => reject(tx.error);
+    });
+  } finally {
+    db.close();
+  }
+}
+
+/** True for the storage-quota error class across browsers. */
+function isQuotaError(err: unknown): boolean {
+  if (err instanceof DOMException) {
+    // Chromium/WebKit throw `QuotaExceededError`; Firefox historically
+    // throws `NS_ERROR_DOM_QUOTA_REACHED` (code 22).
+    return (
+      err.name === "QuotaExceededError" ||
+      err.name === "NS_ERROR_DOM_QUOTA_REACHED" ||
+      err.code === 22
+    );
+  }
+  return false;
 }
 
 async function idbGet<T>(): Promise<T | undefined> {
@@ -211,8 +239,32 @@ export function startPersistingQueryCache(
       userId: currentUserId(queryClient),
       state,
     };
-    void idbSet(payload).catch(() => {
-      /* best effort */
+
+    // Size-cap before touching disk: a snapshot past the ceiling is the
+    // likeliest quota trigger and its marginal offline value isn't worth
+    // evicting the last good (smaller) snapshot. Skip the write, keep what's
+    // there.
+    const serialized = JSON.stringify(payload);
+    if (serialized.length > MAX_PERSIST_BYTES) {
+      console.warn(
+        `[query-persister] skipping persist: snapshot ${serialized.length}B exceeds ${MAX_PERSIST_BYTES}B cap`,
+      );
+      return;
+    }
+
+    void idbSet(payload).catch((err) => {
+      // Don't silently swallow a full-disk failure: a quota error means the
+      // offline cache stopped updating, and a clear signal beats a stale
+      // snapshot the user can't explain. Drop the persisted blob so the next
+      // flush has room rather than failing again against a full store.
+      if (isQuotaError(err)) {
+        console.warn(
+          "[query-persister] IndexedDB quota exceeded; dropping persisted cache",
+        );
+        void clearPersistedQueryCache();
+        return;
+      }
+      console.warn("[query-persister] persist failed", err);
     });
   };