diff --git a/clients/web/src/test/core/auth/oauth-persist-browser-safe.test.ts b/clients/web/src/test/core/auth/oauth-persist-browser-safe.test.ts
new file mode 100644
index 00000000..b689adaa
--- /dev/null
+++ b/clients/web/src/test/core/auth/oauth-persist-browser-safe.test.ts
@@ -0,0 +1,47 @@
+import { describe, it, expect } from "vitest";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import { dirname, resolve } from "node:path";
+
+/**
+ * Regression guard for the browser bundle. `core/auth/oauth-persist.ts` is
+ * imported by browser code (App.tsx -> RemoteOAuthStorage -> oauth-persist),
+ * so it must stay Node-free. It previously imported `store-io.js`, which pulls
+ * `node:fs` + `atomically` (-> `stubborn-fs` -> `node:process.getuid`) into the
+ * browser bundle and blanked the app at runtime. The Node-only file backend
+ * now lives in `core/auth/node/oauth-persist-file.ts`; the isomorphic module
+ * must only import the Node-free `store-serialize` helpers.
+ */
+
+const here = dirname(fileURLToPath(import.meta.url));
+const coreAuth = resolve(here, "../../../../../../core/auth");
+
+function importSpecifiers(source: string): string[] {
+  const specs: string[] = [];
+  const re = /(?:import|export)[^;]*?from\s*["']([^"']+)["']/g;
+  let m: RegExpExecArray | null;
+  while ((m = re.exec(source)) !== null) {
+    specs.push(m[1]);
+  }
+  return specs;
+}
+
+describe("oauth-persist.ts stays browser-safe", () => {
+  const source = readFileSync(resolve(coreAuth, "oauth-persist.ts"), "utf-8");
+  const specs = importSpecifiers(source);
+
+  it("does not import the Node-only store-io module", () => {
+    expect(specs).not.toContain("../storage/store-io.js");
+  });
+
+  it("does not import node: builtins or atomically", () => {
+    const forbidden = specs.filter(
+      (s) => s.startsWith("node:") || s === "atomically",
+    );
+    expect(forbidden).toEqual([]);
+  });
+
+  it("gets its (de)serializers from the Node-free store-serialize module", () => {
+    expect(specs).toContain("../storage/store-serialize.js");
+  });
+});
diff --git a/clients/web/src/test/core/auth/oauth-persist.test.ts b/clients/web/src/test/core/auth/oauth-persist.test.ts
index 62f8eadd..ac0c42ab 100644
--- a/clients/web/src/test/core/auth/oauth-persist.test.ts
+++ b/clients/web/src/test/core/auth/oauth-persist.test.ts
@@ -1,8 +1,21 @@
-import { describe, it, expect } from "vitest";
+import { describe, it, expect, vi } from "vitest";
 import {
   parseOAuthPersistBlob,
   serializeOAuthPersistBlob,
+  createRemoteOAuthPersistBackend,
+  createSessionOAuthPersistBackend,
+  OAUTH_PERSIST_STORAGE_KEY,
 } from "@inspector/core/auth/oauth-persist.js";
+import type { OAuthPersistSnapshot } from "@inspector/core/auth/oauth-persist.js";
+
+const SNAPSHOT: OAuthPersistSnapshot = {
+  servers: { "http://s": { scope: "read" } },
+  idpSessions: {},
+};
+
+function jsonResponse(body: unknown, status = 200): Response {
+  return new Response(JSON.stringify(body), { status });
+}
 
 describe("parseOAuthPersistBlob", () => {
   it("returns null for empty input", () => {
@@ -69,3 +82,141 @@ describe("serializeOAuthPersistBlob", () => {
     expect(raw).not.toMatch(/"state"\s*:/);
   });
 });
+
+describe("createRemoteOAuthPersistBackend", () => {
+  const baseUrl = "http://remote.example/";
+  const storeId = "oauth";
+  const url = "http://remote.example/api/storage/oauth";
+
+  it("read() returns the parsed snapshot and sends the auth header", async () => {
+    const fetchFn = vi.fn(async () => jsonResponse(SNAPSHOT));
+    const backend = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      authToken: "tok",
+      fetchFn: fetchFn as unknown as typeof fetch,
+    });
+    expect(await backend.read()).toEqual(SNAPSHOT);
+    expect(fetchFn).toHaveBeenCalledWith(url, {
+      method: "GET",
+      headers: { "x-mcp-remote-auth": "Bearer tok" },
+    });
+  });
+
+  it("read() returns null for the empty-object missing-file response", async () => {
+    const backend = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () => jsonResponse({})) as unknown as typeof fetch,
+    });
+    expect(await backend.read()).toBeNull();
+  });
+
+  it("read() returns null on 404 and throws on other errors", async () => {
+    const notFound = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () =>
+        new Response("", { status: 404 })) as unknown as typeof fetch,
+    });
+    expect(await notFound.read()).toBeNull();
+
+    const failing = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () =>
+        new Response("", { status: 500 })) as unknown as typeof fetch,
+    });
+    await expect(failing.read()).rejects.toThrow(/Failed to read store: 500/);
+  });
+
+  it("write() POSTs the serialized snapshot and throws on failure", async () => {
+    const ok = vi.fn(async () => new Response("", { status: 200 }));
+    const backend = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: ok as unknown as typeof fetch,
+    });
+    await backend.write(SNAPSHOT);
+    expect(ok).toHaveBeenCalledWith(
+      url,
+      expect.objectContaining({ method: "POST" }),
+    );
+    const body = ok.mock.calls[0][1].body;
+    expect(JSON.parse(body)).toEqual(SNAPSHOT);
+
+    const failing = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () =>
+        new Response("", { status: 500 })) as unknown as typeof fetch,
+    });
+    await expect(failing.write(SNAPSHOT)).rejects.toThrow(
+      /Failed to write store: 500/,
+    );
+  });
+
+  it("remove() DELETEs, tolerates 404, and throws on other errors", async () => {
+    const ok = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      authToken: "tok",
+      fetchFn: (async () =>
+        new Response("", { status: 200 })) as unknown as typeof fetch,
+    });
+    await expect(ok.remove!()).resolves.toBeUndefined();
+
+    const gone = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () =>
+        new Response("", { status: 404 })) as unknown as typeof fetch,
+    });
+    await expect(gone.remove!()).resolves.toBeUndefined();
+
+    const failing = createRemoteOAuthPersistBackend({
+      baseUrl,
+      storeId,
+      fetchFn: (async () =>
+        new Response("", { status: 500 })) as unknown as typeof fetch,
+    });
+    await expect(failing.remove!()).rejects.toThrow(
+      /Failed to delete store: 500/,
+    );
+  });
+});
+
+describe("createSessionOAuthPersistBackend", () => {
+  function fakeStorage() {
+    const map = new Map<string, string>();
+    return {
+      getItem: (k: string) => map.get(k) ?? null,
+      setItem: (k: string, v: string) => void map.set(k, v),
+      removeItem: (k: string) => void map.delete(k),
+      map,
+    } as unknown as Storage & { map: Map<string, string> };
+  }
+
+  it("round-trips a snapshot through the default storage key", async () => {
+    const storage = fakeStorage();
+    const backend = createSessionOAuthPersistBackend({
+      getStorage: () => storage,
+    });
+    expect(await backend.read()).toBeNull();
+    await backend.write(SNAPSHOT);
+    expect(storage.map.has(OAUTH_PERSIST_STORAGE_KEY)).toBe(true);
+    expect(await backend.read()).toEqual(SNAPSHOT);
+    await backend.remove!();
+    expect(await backend.read()).toBeNull();
+  });
+
+  it("honors a custom storage key", async () => {
+    const storage = fakeStorage();
+    const backend = createSessionOAuthPersistBackend({
+      storageKey: "custom-key",
+      getStorage: () => storage,
+    });
+    await backend.write(SNAPSHOT);
+    expect(storage.map.has("custom-key")).toBe(true);
+  });
+});
diff --git a/clients/web/src/test/core/auth/store.test.ts b/clients/web/src/test/core/auth/store.test.ts
new file mode 100644
index 00000000..131a5ab8
--- /dev/null
+++ b/clients/web/src/test/core/auth/store.test.ts
@@ -0,0 +1,84 @@
+import { describe, it, expect } from "vitest";
+import { OAuthMemoryStore } from "@inspector/core/auth/store.js";
+
+describe("OAuthMemoryStore", () => {
+  it("returns empty defaults for unknown server / issuer", () => {
+    const store = new OAuthMemoryStore();
+    expect(store.getState().getServerState("http://x")).toEqual({});
+    expect(store.getState().getIdpSession("http://idp")).toEqual({});
+  });
+
+  it("merges partial updates immutably via setServerState / setIdpSession", () => {
+    const store = new OAuthMemoryStore();
+    const s = store.getState();
+    s.setServerState("http://x", { scope: "read" });
+    s.setServerState("http://x", { codeVerifier: "v" });
+    expect(store.getState().getServerState("http://x")).toEqual({
+      scope: "read",
+      codeVerifier: "v",
+    });
+    s.setIdpSession("http://idp", { idToken: "t" });
+    expect(store.getState().getIdpSession("http://idp")).toEqual({
+      idToken: "t",
+    });
+  });
+
+  it("clears a single server and a single idp session", () => {
+    const store = new OAuthMemoryStore({
+      servers: { "http://x": { scope: "read" } },
+      idpSessions: { "http://idp": { idToken: "t" } },
+    });
+    store.getState().clearServerState("http://x");
+    store.getState().clearIdpSession("http://idp");
+    expect(store.getState().getServerState("http://x")).toEqual({});
+    expect(store.getState().getIdpSession("http://idp")).toEqual({});
+  });
+
+  it("clears only enterprise-managed servers", () => {
+    const store = new OAuthMemoryStore({
+      servers: {
+        "http://managed": { enterpriseManaged: true },
+        "http://plain": { scope: "read" },
+      },
+      idpSessions: {},
+    });
+    store.getState().clearEnterpriseManagedResourceServers();
+    expect(store.getState().getServerState("http://managed")).toEqual({});
+    expect(store.getState().getServerState("http://plain")).toEqual({
+      scope: "read",
+    });
+  });
+
+  it("snapshot() returns a shallow copy of current state", () => {
+    const store = new OAuthMemoryStore({
+      servers: { "http://x": { scope: "read" } },
+      idpSessions: {},
+    });
+    const snap = store.snapshot();
+    expect(snap).toEqual({
+      servers: { "http://x": { scope: "read" } },
+      idpSessions: {},
+    });
+    // Mutating the store afterward must not change the earlier snapshot.
+    store.getState().setServerState("http://y", { scope: "write" });
+    expect(snap.servers["http://y"]).toBeUndefined();
+  });
+
+  it("replace() tolerates a snapshot missing servers or idpSessions", () => {
+    // Exercises both `?? {}` fallbacks in replace().
+    const noServers = new OAuthMemoryStore({
+      idpSessions: { "http://idp": { idToken: "t" } },
+    } as never);
+    expect(noServers.snapshot()).toEqual({
+      servers: {},
+      idpSessions: { "http://idp": { idToken: "t" } },
+    });
+    const noSessions = new OAuthMemoryStore({
+      servers: { "http://x": { scope: "read" } },
+    } as never);
+    expect(noSessions.snapshot()).toEqual({
+      servers: { "http://x": { scope: "read" } },
+      idpSessions: {},
+    });
+  });
+});
diff --git a/clients/web/src/test/integration/auth/node/storage.test.ts b/clients/web/src/test/integration/auth/node/storage.test.ts
index 9eea463d..0bb328ad 100644
--- a/clients/web/src/test/integration/auth/node/storage.test.ts
+++ b/clients/web/src/test/integration/auth/node/storage.test.ts
@@ -579,6 +579,18 @@ describe("NodeOAuthStorage with custom storagePath", () => {
     resetNodeOAuthStorageCache();
   });
 
+  it("clearAllOAuthClientState is a no-op when no store file exists", async () => {
+    // Exercises the null-snapshot branch: read() returns null, so
+    // `snapshot?.servers ?? {}` yields no urls and nothing is cleared.
+    const filePath = getStateFilePath();
+    resetNodeOAuthStorageCache();
+    await fs.unlink(filePath).catch(() => {});
+
+    await expect(clearAllOAuthClientState()).resolves.toBeUndefined();
+
+    resetNodeOAuthStorageCache();
+  });
+
   it("should isolate state from default store", async () => {
     const customPath = path.join(
       os.tmpdir(),
diff --git a/clients/web/src/test/integration/storage/adapters.test.ts b/clients/web/src/test/integration/storage/adapters.test.ts
index a48663a9..998e60e7 100644
--- a/clients/web/src/test/integration/storage/adapters.test.ts
+++ b/clients/web/src/test/integration/storage/adapters.test.ts
@@ -12,7 +12,7 @@ import type { ServerType } from "@hono/node-server";
 import { NodeOAuthStorage } from "@inspector/core/auth/node/storage-node.js";
 import { RemoteOAuthStorage } from "@inspector/core/auth/remote/storage-remote.js";
 import { OAuthMemoryStore } from "@inspector/core/auth/store.js";
-import { createFileOAuthPersistBackend } from "@inspector/core/auth/oauth-persist.js";
+import { createFileOAuthPersistBackend } from "@inspector/core/auth/node/oauth-persist-file.js";
 import { createRemoteApp } from "@inspector/core/mcp/remote/node/server.js";
 import {
   writeStoreFile,
diff --git a/core/auth/node/oauth-persist-file.ts b/core/auth/node/oauth-persist-file.ts
new file mode 100644
index 00000000..dc0714fb
--- /dev/null
+++ b/core/auth/node/oauth-persist-file.ts
@@ -0,0 +1,42 @@
+/**
+ * Node-only file backend for OAuth persistence. Kept out of the isomorphic
+ * `core/auth/oauth-persist.ts` because it imports `store-io.js` (which pulls
+ * `node:fs`/`atomically`); the browser must never load that. Node consumers
+ * (e.g. `NodeOAuthStorage`) import the file backend from here, while the
+ * shared blob (de)serialization and browser/remote backends stay isomorphic.
+ */
+
+import {
+  readStoreFile,
+  writeStoreFile,
+  deleteStoreFile,
+} from "../../storage/store-io.js";
+import {
+  parseOAuthPersistBlob,
+  serializeOAuthPersistBlob,
+  type OAuthPersistBackend,
+} from "../oauth-persist.js";
+
+export interface FileOAuthPersistBackendOptions {
+  filePath: string;
+}
+
+export function createFileOAuthPersistBackend(
+  options: FileOAuthPersistBackendOptions,
+): OAuthPersistBackend {
+  return {
+    async read() {
+      const raw = await readStoreFile(options.filePath);
+      return parseOAuthPersistBlob(raw);
+    },
+    async write(snapshot) {
+      await writeStoreFile(
+        options.filePath,
+        serializeOAuthPersistBlob(snapshot),
+      );
+    },
+    async remove() {
+      await deleteStoreFile(options.filePath);
+    },
+  };
+}
diff --git a/core/auth/node/storage-node.ts b/core/auth/node/storage-node.ts
index 49bb1f34..e46e20a2 100644
--- a/core/auth/node/storage-node.ts
+++ b/core/auth/node/storage-node.ts
@@ -1,6 +1,6 @@
 import { OAuthStorageBase } from "../oauth-storage.js";
 import { OAuthMemoryStore } from "../store.js";
-import { createFileOAuthPersistBackend } from "../oauth-persist.js";
+import { createFileOAuthPersistBackend } from "./oauth-persist-file.js";
 import {
   getDefaultStorageDir,
   getStoreFilePath,
diff --git a/core/auth/oauth-persist.ts b/core/auth/oauth-persist.ts
index 66d36c7d..133dc419 100644
--- a/core/auth/oauth-persist.ts
+++ b/core/auth/oauth-persist.ts
@@ -1,17 +1,15 @@
 /**
- * OAuth persistence format and backends (file, remote HTTP, sessionStorage).
- * Writes plain JSON `{ servers, idpSessions }`. On read, accepts legacy
- * persist envelopes `{ state: { servers, idpSessions }, version }` and
- * promotes the inner payload.
+ * OAuth persistence format and isomorphic backends (remote HTTP,
+ * sessionStorage). Writes plain JSON `{ servers, idpSessions }`. On read,
+ * accepts legacy persist envelopes `{ state: { servers, idpSessions },
+ * version }` and promotes the inner payload.
+ *
+ * This module must stay browser-safe: it imports only the Node-free
+ * `store-serialize` helpers, never `store-io` (which pulls `node:fs`). The
+ * Node-only file backend lives in `./node/oauth-persist-file.ts`.
  */
 
-import {
-  readStoreFile,
-  writeStoreFile,
-  deleteStoreFile,
-  serializeStore,
-  parseStore,
-} from "../storage/store-io.js";
+import { serializeStore, parseStore } from "../storage/store-serialize.js";
 import type { IdpSessionState } from "./storage.js";
 import type { ServerOAuthState } from "./store.js";
 
@@ -76,30 +74,6 @@ export interface OAuthPersistBackend {
   remove?(): Promise<void>;
 }
 
-export interface FileOAuthPersistBackendOptions {
-  filePath: string;
-}
-
-export function createFileOAuthPersistBackend(
-  options: FileOAuthPersistBackendOptions,
-): OAuthPersistBackend {
-  return {
-    async read() {
-      const raw = await readStoreFile(options.filePath);
-      return parseOAuthPersistBlob(raw);
-    },
-    async write(snapshot) {
-      await writeStoreFile(
-        options.filePath,
-        serializeOAuthPersistBlob(snapshot),
-      );
-    },
-    async remove() {
-      await deleteStoreFile(options.filePath);
-    },
-  };
-}
-
 export interface RemoteOAuthPersistBackendOptions {
   baseUrl: string;
   storeId: string;
diff --git a/core/storage/store-io.ts b/core/storage/store-io.ts
index 5e0273b4..db04fe2e 100644
--- a/core/storage/store-io.ts
+++ b/core/storage/store-io.ts
@@ -12,6 +12,10 @@ import { readFile, writeFile } from "atomically";
 // isomorphic code can reuse it without pulling Node deps into the browser.
 export { validateStoreId } from "./store-id.js";
 
+// Likewise re-export the pure JSON (de)serializers from the Node-free
+// `store-serialize` module so existing `store-io` importers are unaffected.
+export { serializeStore, parseStore } from "./store-serialize.js";
+
 /**
  * Default storage directory (~/.mcp-inspector/storage or %USERPROFILE%\.mcp-inspector\storage on Windows).
  */
@@ -120,17 +124,3 @@ export async function deleteStoreFile(filePath: string): Promise<void> {
     }
   }
 }
-
-/**
- * Serialize store data to JSON string (consistent format for server writes).
- */
-export function serializeStore(data: unknown): string {
-  return JSON.stringify(data, null, 2);
-}
-
-/**
- * Parse store JSON string. Use after readStoreFile when returning parsed object.
- */
-export function parseStore(raw: string): unknown {
-  return JSON.parse(raw);
-}
diff --git a/core/storage/store-serialize.ts b/core/storage/store-serialize.ts
new file mode 100644
index 00000000..83c435be
--- /dev/null
+++ b/core/storage/store-serialize.ts
@@ -0,0 +1,16 @@
+/**
+ * Pure, Node-free JSON (de)serialization for store files. Split from
+ * `store-io.ts` (which imports `node:fs`/`node:path`/`atomically`) so
+ * isomorphic code — e.g. the browser OAuth persistence flow in
+ * `core/auth/oauth-persist.ts` — can (de)serialize store blobs without
+ * pulling Node deps into the browser bundle. `store-io.ts` re-exports these
+ * so existing importers are unaffected.
+ */
+
+export function serializeStore(data: unknown): string {
+  return JSON.stringify(data, null, 2);
+}
+
+export function parseStore(raw: string): unknown {
+  return JSON.parse(raw);
+}