diff --git a/clients/web/src/App.tsx b/clients/web/src/App.tsx
index 2e61e1125..8faaebfdd 100644
--- a/clients/web/src/App.tsx
+++ b/clients/web/src/App.tsx
@@ -107,9 +107,7 @@ import { useResourceSubscriptions } from "@inspector/core/react/useResourceSubsc
 import { useMessageLog } from "@inspector/core/react/useMessageLog.js";
 import { useFetchRequestLog } from "@inspector/core/react/useFetchRequestLog.js";
 import { useStderrLog } from "@inspector/core/react/useStderrLog.js";
-import { useSandboxUrl } from "@inspector/core/react/useSandboxUrl.js";
-import { useServerListWritable } from "@inspector/core/react/useServerListWritable.js";
-import { useInspectorVersion } from "@inspector/core/react/useInspectorVersion.js";
+import { useInitialConfig } from "@inspector/core/react/useInitialConfig.js";
 import { usePendingClientRequests } from "@inspector/core/react/usePendingClientRequests.js";
 import { InspectorView } from "./components/views/InspectorView/InspectorView";
 import type {
@@ -697,19 +695,16 @@ function App() {
   const appRendererRef = useRef<AppRendererHandle>(null);
   const configBaseUrl =
     typeof window !== "undefined" ? window.location.origin : "http://localhost";
-  const { sandboxUrl } = useSandboxUrl({
-    baseUrl: configBaseUrl,
-    authToken: getAuthToken(),
-  });
-  // Read-only sessions (launched with `--config` or an ad-hoc server) hide
-  // catalog CRUD; the default catalog and `--catalog` stay writable.
-  const { writable: serverListWritable } = useServerListWritable({
-    baseUrl: configBaseUrl,
-    authToken: getAuthToken(),
-  });
-  // The Inspector version (root package.json), shown in the lower-right corner.
-  // The browser can't read it off disk, so the backend sends it via /api/config.
-  const { version: inspectorVersion } = useInspectorVersion({
+  // One `GET /api/config` fetch recovers every static payload field the app
+  // reads: the MCP Apps `sandboxUrl`, the session's `writable` flag (read-only
+  // `--config` / ad-hoc sessions hide catalog CRUD; the default catalog and
+  // `--catalog` stay writable), and the Inspector `version` shown in the
+  // lower-right corner (the browser can't read it off disk).
+  const {
+    sandboxUrl,
+    writable: serverListWritable,
+    version: inspectorVersion,
+  } = useInitialConfig({
     baseUrl: configBaseUrl,
     authToken: getAuthToken(),
   });
diff --git a/clients/web/src/test/core/react/useSandboxUrl.test.tsx b/clients/web/src/test/core/react/useInitialConfig.test.tsx
similarity index 52%
rename from clients/web/src/test/core/react/useSandboxUrl.test.tsx
rename to clients/web/src/test/core/react/useInitialConfig.test.tsx
index 152a5f3e1..3d246e881 100644
--- a/clients/web/src/test/core/react/useSandboxUrl.test.tsx
+++ b/clients/web/src/test/core/react/useInitialConfig.test.tsx
@@ -1,12 +1,15 @@
 /**
- * Tests for useSandboxUrl — runs in happy-dom under the unit project. Uses a
+ * Tests for useInitialConfig — runs in happy-dom under the unit project. Uses a
  * controlled fake `fetch` so each branch (present / absent / non-string / HTTP
- * error / network throw) and the auth header are asserted directly.
+ * error / network throw / post-unmount guards) and the auth header are asserted
+ * directly. This is the single hook that replaced useSandboxUrl /
+ * useServerListWritable / useInspectorVersion (#1643), so it covers each field's
+ * branch matrix in one place.
  */
 
 import { describe, it, expect, vi } from "vitest";
 import { renderHook, waitFor } from "@testing-library/react";
-import { useSandboxUrl } from "@inspector/core/react/useSandboxUrl";
+import { useInitialConfig } from "@inspector/core/react/useInitialConfig";
 
 function jsonResponse(body: unknown, ok = true): Response {
   return {
@@ -16,30 +19,40 @@ function jsonResponse(body: unknown, ok = true): Response {
   } as unknown as Response;
 }
 
-describe("useSandboxUrl", () => {
-  it("starts loading, then resolves the sandboxUrl from the config payload", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(
-        jsonResponse({ sandboxUrl: "http://localhost:6299/sandbox" }),
-      );
+describe("useInitialConfig", () => {
+  it("starts loading, then resolves all three fields from one config payload", async () => {
+    const fetchFn = vi.fn().mockResolvedValue(
+      jsonResponse({
+        version: "2.0.0",
+        sandboxUrl: "http://localhost:6299/sandbox",
+        writable: false,
+      }),
+    );
 
     const { result } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
 
+    // Initial (pre-fetch) state: version/sandboxUrl undefined, writable defaults
+    // true, loading true.
     expect(result.current.loading).toBe(true);
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
+    expect(result.current.writable).toBe(true);
 
     await waitFor(() => expect(result.current.loading).toBe(false));
+    expect(result.current.version).toBe("2.0.0");
     expect(result.current.sandboxUrl).toBe("http://localhost:6299/sandbox");
+    expect(result.current.writable).toBe(false);
+    // One static payload, one request.
+    expect(fetchFn).toHaveBeenCalledTimes(1);
   });
 
   it("sends the bearer auth header when a token is provided", async () => {
     const fetchFn = vi.fn().mockResolvedValue(jsonResponse({}));
 
     renderHook(() =>
-      useSandboxUrl({
+      useInitialConfig({
         baseUrl: "http://test.local/",
         authToken: "secret-token",
         fetchFn,
@@ -57,77 +70,119 @@ describe("useSandboxUrl", () => {
   it("omits the auth header when no token is provided", async () => {
     const fetchFn = vi.fn().mockResolvedValue(jsonResponse({}));
 
-    renderHook(() => useSandboxUrl({ baseUrl: "http://test.local", fetchFn }));
+    renderHook(() =>
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
+    );
 
     await waitFor(() => expect(fetchFn).toHaveBeenCalled());
     const [, init] = fetchFn.mock.calls[0];
     expect(init.headers["x-mcp-remote-auth"]).toBeUndefined();
   });
 
-  it("leaves sandboxUrl undefined when the payload omits it", async () => {
+  it("applies each field's default when the payload omits it", async () => {
     const fetchFn = vi
       .fn()
       .mockResolvedValue(jsonResponse({ defaultEnvironment: {} }));
 
     const { result } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
 
     await waitFor(() => expect(result.current.loading).toBe(false));
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
+    // Missing writable (legacy backend) stays writable.
+    expect(result.current.writable).toBe(true);
   });
 
-  it("leaves sandboxUrl undefined when the field is not a usable string", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({ sandboxUrl: "" }));
+  it("leaves version/sandboxUrl undefined when the fields are not usable strings", async () => {
+    const fetchFn = vi
+      .fn()
+      .mockResolvedValue(jsonResponse({ version: "", sandboxUrl: "" }));
 
     const { result } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
 
     await waitFor(() => expect(result.current.loading).toBe(false));
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
   });
 
-  it("leaves sandboxUrl undefined on a non-ok response", async () => {
+  // Only an explicit `false` flips the list read-only. A nonconforming backend
+  // could send a falsy-but-not-false value (null / 0 / a string); each is
+  // `!== false`, so each must leave the list writable.
+  it.each([null, 0, "no"])(
+    "keeps writable true for writable=%j (falsy but not false)",
+    async (value) => {
+      const fetchFn = vi
+        .fn()
+        .mockResolvedValue(jsonResponse({ writable: value }));
+
+      const { result } = renderHook(() =>
+        useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
+      );
+
+      await waitFor(() => expect(result.current.loading).toBe(false));
+      expect(result.current.writable).toBe(true);
+    },
+  );
+
+  it("applies defaults on a non-ok response", async () => {
     const fetchFn = vi
       .fn()
-      .mockResolvedValue(jsonResponse({ sandboxUrl: "x" }, false));
+      .mockResolvedValue(
+        jsonResponse(
+          { version: "9.9.9", sandboxUrl: "http://x/sb", writable: false },
+          false,
+        ),
+      );
 
     const { result } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
 
     await waitFor(() => expect(result.current.loading).toBe(false));
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
+    expect(result.current.writable).toBe(true);
   });
 
-  it("leaves sandboxUrl undefined when the fetch throws", async () => {
+  it("applies defaults when the fetch throws", async () => {
     const fetchFn = vi.fn().mockRejectedValue(new Error("network down"));
 
     const { result } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
 
     await waitFor(() => expect(result.current.loading).toBe(false));
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
+    expect(result.current.writable).toBe(true);
   });
 
   it("falls back to globalThis.fetch when no fetchFn is provided", async () => {
-    const globalFetch = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ sandboxUrl: "http://global/sb" }));
+    const globalFetch = vi.fn().mockResolvedValue(
+      jsonResponse({
+        version: "3.1.4",
+        sandboxUrl: "http://global/sb",
+        writable: false,
+      }),
+    );
     const original = globalThis.fetch;
     globalThis.fetch = globalFetch as unknown as typeof fetch;
     try {
       const { result } = renderHook(() =>
-        useSandboxUrl({ baseUrl: "http://test.local" }),
+        useInitialConfig({ baseUrl: "http://test.local" }),
       );
       await waitFor(() => expect(result.current.loading).toBe(false));
       expect(globalFetch).toHaveBeenCalledWith(
         "http://test.local/api/config",
         expect.objectContaining({ method: "GET" }),
       );
+      expect(result.current.version).toBe("3.1.4");
       expect(result.current.sandboxUrl).toBe("http://global/sb");
+      expect(result.current.writable).toBe(false);
     } finally {
       globalThis.fetch = original;
     }
@@ -145,19 +200,25 @@ describe("useSandboxUrl", () => {
     );
 
     const { result, unmount } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
     expect(result.current.loading).toBe(true);
 
     unmount();
     // Resolve after unmount — the post-fetch isCancelled() guard returns early.
-    resolveFetch?.(jsonResponse({ sandboxUrl: "http://late/sb" }));
+    resolveFetch?.(
+      jsonResponse({ version: "2.0.0", sandboxUrl: "http://late/sb" }),
+    );
     // Let the microtask queue drain so the continuation runs.
     await Promise.resolve();
     await Promise.resolve();
-    // No assertion error / React warning means the guards held; the last
-    // observed value stayed at its initial undefined.
+    // This test exists to exercise the post-unmount `isCancelled()` guard
+    // branches; it can't detect their removal (React 18 dropped the
+    // setState-after-unmount warning, and `result.current` is frozen at the last
+    // render), so it only asserts the fields stayed at their initial values.
+    expect(result.current.version).toBeUndefined();
     expect(result.current.sandboxUrl).toBeUndefined();
+    expect(result.current.writable).toBe(true);
   });
 
   it("drops a response whose json resolves after unmount", async () => {
@@ -175,16 +236,17 @@ describe("useSandboxUrl", () => {
     const fetchFn = vi.fn().mockResolvedValue(res);
 
     const { result, unmount } = renderHook(() =>
-      useSandboxUrl({ baseUrl: "http://test.local", fetchFn }),
+      useInitialConfig({ baseUrl: "http://test.local", fetchFn }),
     );
     // Let the fetch resolve so we're parked awaiting json().
     await waitFor(() => expect(fetchFn).toHaveBeenCalled());
     await Promise.resolve();
 
     unmount();
-    resolveJson?.({ sandboxUrl: "http://late/sb" });
+    resolveJson?.({ version: "2.0.0", writable: false });
     await Promise.resolve();
     await Promise.resolve();
-    expect(result.current.sandboxUrl).toBeUndefined();
+    expect(result.current.version).toBeUndefined();
+    expect(result.current.writable).toBe(true);
   });
 });
diff --git a/clients/web/src/test/core/react/useInspectorVersion.test.tsx b/clients/web/src/test/core/react/useInspectorVersion.test.tsx
deleted file mode 100644
index 4d1f84927..000000000
--- a/clients/web/src/test/core/react/useInspectorVersion.test.tsx
+++ /dev/null
@@ -1,181 +0,0 @@
-/**
- * Tests for useInspectorVersion — runs in happy-dom under the unit project. Uses
- * a controlled fake `fetch` so each branch (present / absent / non-string / HTTP
- * error / network throw / post-unmount guards) and the auth header are asserted
- * directly. Mirrors useSandboxUrl's test (same `/api/config` fetch shape).
- */
-
-import { describe, it, expect, vi } from "vitest";
-import { renderHook, waitFor } from "@testing-library/react";
-import { useInspectorVersion } from "@inspector/core/react/useInspectorVersion";
-
-function jsonResponse(body: unknown, ok = true): Response {
-  return {
-    ok,
-    status: ok ? 200 : 401,
-    json: async () => body,
-  } as unknown as Response;
-}
-
-describe("useInspectorVersion", () => {
-  it("starts loading, then resolves the version from the config payload", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ version: "2.0.0" }));
-
-    const { result } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    expect(result.current.loading).toBe(true);
-    expect(result.current.version).toBeUndefined();
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.version).toBe("2.0.0");
-  });
-
-  it("sends the bearer auth header when a token is provided", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({}));
-
-    renderHook(() =>
-      useInspectorVersion({
-        baseUrl: "http://test.local/",
-        authToken: "secret-token",
-        fetchFn,
-      }),
-    );
-
-    await waitFor(() => expect(fetchFn).toHaveBeenCalled());
-    const [url, init] = fetchFn.mock.calls[0];
-    // Trailing slash on baseUrl is normalized away.
-    expect(url).toBe("http://test.local/api/config");
-    expect(init.method).toBe("GET");
-    expect(init.headers["x-mcp-remote-auth"]).toBe("Bearer secret-token");
-  });
-
-  it("omits the auth header when no token is provided", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({}));
-
-    renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(fetchFn).toHaveBeenCalled());
-    const [, init] = fetchFn.mock.calls[0];
-    expect(init.headers["x-mcp-remote-auth"]).toBeUndefined();
-  });
-
-  it("leaves version undefined when the payload omits it", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ defaultEnvironment: {} }));
-
-    const { result } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.version).toBeUndefined();
-  });
-
-  it("leaves version undefined when the field is not a usable string", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({ version: "" }));
-
-    const { result } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.version).toBeUndefined();
-  });
-
-  it("leaves version undefined on a non-ok response", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ version: "9.9.9" }, false));
-
-    const { result } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.version).toBeUndefined();
-  });
-
-  it("leaves version undefined when the fetch throws", async () => {
-    const fetchFn = vi.fn().mockRejectedValue(new Error("network down"));
-
-    const { result } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.version).toBeUndefined();
-  });
-
-  it("falls back to globalThis.fetch when no fetchFn is provided", async () => {
-    const globalFetch = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ version: "3.1.4" }));
-    const original = globalThis.fetch;
-    globalThis.fetch = globalFetch as unknown as typeof fetch;
-    try {
-      const { result } = renderHook(() =>
-        useInspectorVersion({ baseUrl: "http://test.local" }),
-      );
-      await waitFor(() => expect(result.current.loading).toBe(false));
-      expect(globalFetch).toHaveBeenCalledWith(
-        "http://test.local/api/config",
-        expect.objectContaining({ method: "GET" }),
-      );
-      expect(result.current.version).toBe("3.1.4");
-    } finally {
-      globalThis.fetch = original;
-    }
-  });
-
-  it("drops a response that resolves after unmount (no state update)", async () => {
-    let resolveFetch: ((r: Response) => void) | undefined;
-    const fetchFn = vi.fn().mockReturnValue(
-      new Promise<Response>((r) => {
-        resolveFetch = r;
-      }),
-    );
-
-    const { result, unmount } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-    expect(result.current.loading).toBe(true);
-
-    unmount();
-    resolveFetch?.(jsonResponse({ version: "2.0.0" }));
-    await Promise.resolve();
-    await Promise.resolve();
-    expect(result.current.version).toBeUndefined();
-  });
-
-  it("drops a response whose json resolves after unmount", async () => {
-    let resolveJson: ((v: unknown) => void) | undefined;
-    const res = {
-      ok: true,
-      status: 200,
-      json: () =>
-        new Promise((r) => {
-          resolveJson = r;
-        }),
-    } as unknown as Response;
-    const fetchFn = vi.fn().mockResolvedValue(res);
-
-    const { result, unmount } = renderHook(() =>
-      useInspectorVersion({ baseUrl: "http://test.local", fetchFn }),
-    );
-    await waitFor(() => expect(fetchFn).toHaveBeenCalled());
-    await Promise.resolve();
-
-    unmount();
-    resolveJson?.({ version: "2.0.0" });
-    await Promise.resolve();
-    await Promise.resolve();
-    expect(result.current.version).toBeUndefined();
-  });
-});
diff --git a/clients/web/src/test/core/react/useServerListWritable.test.tsx b/clients/web/src/test/core/react/useServerListWritable.test.tsx
deleted file mode 100644
index 68eb5aebd..000000000
--- a/clients/web/src/test/core/react/useServerListWritable.test.tsx
+++ /dev/null
@@ -1,177 +0,0 @@
-/**
- * Tests for useServerListWritable — runs in happy-dom under the unit project.
- * Uses a controlled fake `fetch` so each branch (writable / read-only / absent
- * field / HTTP error / network throw) and the auth header are asserted directly.
- */
-
-import { describe, it, expect, vi } from "vitest";
-import { renderHook, waitFor } from "@testing-library/react";
-import { useServerListWritable } from "@inspector/core/react/useServerListWritable";
-
-function jsonResponse(body: unknown, ok = true): Response {
-  return {
-    ok,
-    status: ok ? 200 : 401,
-    json: async () => body,
-  } as unknown as Response;
-}
-
-describe("useServerListWritable", () => {
-  it("defaults to writable while loading, then keeps true for a writable session", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({ writable: true }));
-
-    const { result } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    expect(result.current.loading).toBe(true);
-    expect(result.current.writable).toBe(true);
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.writable).toBe(true);
-  });
-
-  it("resolves writable:false for a read-only session", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ writable: false }));
-
-    const { result } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.writable).toBe(false);
-  });
-
-  it("stays writable when the field is absent (legacy backend)", async () => {
-    const fetchFn = vi.fn().mockResolvedValue(jsonResponse({}));
-
-    const { result } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.writable).toBe(true);
-  });
-
-  it("sends the bearer auth header when a token is provided", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ writable: false }));
-
-    renderHook(() =>
-      useServerListWritable({
-        baseUrl: "http://test.local/",
-        authToken: "secret-token",
-        fetchFn,
-      }),
-    );
-
-    await waitFor(() => expect(fetchFn).toHaveBeenCalled());
-    const [url, init] = fetchFn.mock.calls[0] as [string, RequestInit];
-    // Trailing slash on baseUrl is trimmed.
-    expect(url).toBe("http://test.local/api/config");
-    expect((init.headers as Record<string, string>)["x-mcp-remote-auth"]).toBe(
-      "Bearer secret-token",
-    );
-  });
-
-  it("stays writable on an HTTP error", async () => {
-    const fetchFn = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ writable: false }, false));
-
-    const { result } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    // An !ok response is ignored (the body is never read), so the writable
-    // default survives even though loading still settles via `finally`.
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.writable).toBe(true);
-  });
-
-  it("stays writable when fetch throws", async () => {
-    const fetchFn = vi.fn().mockRejectedValue(new Error("network down"));
-
-    const { result } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-
-    await waitFor(() => expect(result.current.loading).toBe(false));
-    expect(result.current.writable).toBe(true);
-  });
-
-  it("falls back to globalThis.fetch when no fetchFn is provided", async () => {
-    const globalFetch = vi
-      .fn()
-      .mockResolvedValue(jsonResponse({ writable: false }));
-    const original = globalThis.fetch;
-    globalThis.fetch = globalFetch as unknown as typeof fetch;
-    try {
-      const { result } = renderHook(() =>
-        useServerListWritable({ baseUrl: "http://test.local" }),
-      );
-      await waitFor(() => expect(result.current.loading).toBe(false));
-      expect(globalFetch).toHaveBeenCalledWith(
-        "http://test.local/api/config",
-        expect.objectContaining({ method: "GET" }),
-      );
-      expect(result.current.writable).toBe(false);
-    } finally {
-      globalThis.fetch = original;
-    }
-  });
-
-  it("drops a response that resolves after unmount (no state update)", async () => {
-    // Gate the fetch so it is still in flight at unmount; the isCancelled()
-    // guards (after fetch and in finally) short-circuit so no setState runs on
-    // the dead component and `loading` is never flipped.
-    let resolveFetch: ((r: Response) => void) | undefined;
-    const fetchFn = vi.fn().mockReturnValue(
-      new Promise<Response>((r) => {
-        resolveFetch = r;
-      }),
-    );
-
-    const { result, unmount } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-    expect(result.current.loading).toBe(true);
-
-    unmount();
-    resolveFetch?.(jsonResponse({ writable: false }));
-    await Promise.resolve();
-    await Promise.resolve();
-    // Guards held: the post-unmount value stayed at the writable default.
-    expect(result.current.writable).toBe(true);
-  });
-
-  it("drops a response whose json resolves after unmount", async () => {
-    // Fetch resolves before unmount but json() resolves after, exercising the
-    // second isCancelled() guard (post-json).
-    let resolveJson: ((v: unknown) => void) | undefined;
-    const res = {
-      ok: true,
-      status: 200,
-      json: () =>
-        new Promise((r) => {
-          resolveJson = r;
-        }),
-    } as unknown as Response;
-    const fetchFn = vi.fn().mockResolvedValue(res);
-
-    const { result, unmount } = renderHook(() =>
-      useServerListWritable({ baseUrl: "http://test.local", fetchFn }),
-    );
-    await waitFor(() => expect(fetchFn).toHaveBeenCalled());
-    await Promise.resolve();
-
-    unmount();
-    resolveJson?.({ writable: false });
-    await Promise.resolve();
-    await Promise.resolve();
-    expect(result.current.writable).toBe(true);
-  });
-});
diff --git a/clients/web/src/test/setup.ts b/clients/web/src/test/setup.ts
index 871993ff1..25a226a4e 100644
--- a/clients/web/src/test/setup.ts
+++ b/clients/web/src/test/setup.ts
@@ -34,7 +34,7 @@ Object.defineProperty(window, "localStorage", {
 });
 
 // Benign default `fetch`. Several components hit the backend on mount — e.g.
-// the app reads `GET /api/config` via `useSandboxUrl` / `useServerListWritable`.
+// the app reads `GET /api/config` via `useInitialConfig`.
 // Under happy-dom (no server) those real requests 404 and log alarming
 // `GET .../api/config 404 (Not Found)` lines that make a green run look broken.
 // Returning an empty 200 keeps such *incidental* calls quiet. Tests that care
diff --git a/core/react/useInitialConfig.ts b/core/react/useInitialConfig.ts
new file mode 100644
index 000000000..884b23705
--- /dev/null
+++ b/core/react/useInitialConfig.ts
@@ -0,0 +1,122 @@
+/**
+ * React hook over the `GET /api/config` endpoint — the single fetch of the
+ * static `InitialConfigPayload` the dev/prod web backends serve alongside the
+ * SPA (see `core/mcp/remote/node/server.ts`). It exposes the three fields the
+ * web app reads off that payload:
+ *
+ * - `sandboxUrl` — the MCP Apps sandbox proxy URL. The backend mounts
+ *   `sandbox_proxy.html` on a separate controller port and advertises the URL
+ *   here; the Apps screen embeds it as the trusted outer iframe. `undefined`
+ *   until the fetch resolves, and whenever the backend omits it (legacy backend,
+ *   or a build without the sandbox controller) — callers treat that as "Apps
+ *   unavailable" rather than a blank iframe.
+ * - `writable` — whether the session's server list is a writable catalog or a
+ *   read-only session (`--config` / ad-hoc `--server-url`). Defaults to `true`
+ *   until the fetch resolves and whenever the field is absent (a legacy backend
+ *   predating the flag), so the default catalog keeps full CRUD.
+ * - `version` — the Inspector version the backend reads from the root
+ *   `package.json` (the browser can't read it off disk). `undefined` until the
+ *   fetch resolves, and whenever the backend omits it (legacy backend) — the UI
+ *   renders nothing then.
+ *
+ * This consolidates the three former single-field hooks (`useSandboxUrl`,
+ * `useServerListWritable`, `useInspectorVersion`), each of which fetched the
+ * same static payload separately, into one request (#1643).
+ *
+ * Fetches on mount, and re-fetches if `baseUrl` or `authToken` changes (rare —
+ * effectively a full reload; the GET is idempotent). A response that resolves
+ * after unmount or a re-fetch is dropped rather than overwriting current state.
+ */
+
+import { useCallback, useEffect, useState } from "react";
+
+export interface UseInitialConfigOptions {
+  /** Base URL of the remote server (typically `window.location.origin`). */
+  baseUrl: string;
+  /** Optional auth token for the `x-mcp-remote-auth` header. */
+  authToken?: string;
+  /** Fetch function to use (default: globalThis.fetch). Useful in tests. */
+  fetchFn?: typeof fetch;
+}
+
+export interface UseInitialConfigResult {
+  /** The Inspector version, or undefined when unavailable / not yet loaded. */
+  version: string | undefined;
+  /** The sandbox proxy URL, or undefined when unavailable / not yet loaded. */
+  sandboxUrl: string | undefined;
+  /** Whether the server list is writable (catalog) or read-only (session). */
+  writable: boolean;
+  /** True while the initial fetch is in flight. */
+  loading: boolean;
+}
+
+/** Minimal shape we read from the `/api/config` payload. */
+interface ConfigPayload {
+  version?: unknown;
+  sandboxUrl?: unknown;
+  writable?: unknown;
+}
+
+/** Coerce a payload field to a usable non-empty string, else undefined. */
+function usableString(value: unknown): string | undefined {
+  return typeof value === "string" && value ? value : undefined;
+}
+
+export function useInitialConfig(
+  opts: UseInitialConfigOptions,
+): UseInitialConfigResult {
+  const { baseUrl, authToken, fetchFn } = opts;
+  const doFetch = fetchFn ?? globalThis.fetch;
+  const base = baseUrl.replace(/\/$/, "");
+
+  const [version, setVersion] = useState<string | undefined>(undefined);
+  const [sandboxUrl, setSandboxUrl] = useState<string | undefined>(undefined);
+  // Default writable so the common (catalog) case shows CRUD immediately and a
+  // legacy backend that omits the field keeps working.
+  const [writable, setWritable] = useState<boolean>(true);
+  const [loading, setLoading] = useState<boolean>(true);
+
+  // `isCancelled` lets the effect drop a response that resolves after unmount or
+  // after a re-run (baseUrl/authToken change), so a stale payload can't overwrite
+  // current state. React 18 no longer warns on setState-after-unmount — it's a
+  // silent no-op — so the guard is about correctness, not the warning.
+  const load = useCallback(
+    async (isCancelled: () => boolean): Promise<void> => {
+      const headers: Record<string, string> = {};
+      if (authToken) headers["x-mcp-remote-auth"] = `Bearer ${authToken}`;
+      try {
+        const res = await doFetch(`${base}/api/config`, {
+          method: "GET",
+          headers,
+        });
+        if (isCancelled() || !res.ok) return;
+        const body = (await res.json()) as ConfigPayload;
+        if (isCancelled()) return;
+        // Tolerate missing/non-usable fields — a legacy backend that omits any
+        // of them leaves that value at its "unavailable" default rather than
+        // showing a bogus value.
+        setVersion(usableString(body.version));
+        setSandboxUrl(usableString(body.sandboxUrl));
+        // Only an explicit `false` makes the list read-only; a missing field
+        // (legacy backend) stays writable.
+        setWritable(body.writable !== false);
+      } catch {
+        // Network error / aborted fetch: leave every field at its default
+        // (version/sandboxUrl undefined, writable true).
+      } finally {
+        if (!isCancelled()) setLoading(false);
+      }
+    },
+    [base, authToken, doFetch],
+  );
+
+  useEffect(() => {
+    let cancelled = false;
+    void load(() => cancelled);
+    return () => {
+      cancelled = true;
+    };
+  }, [load]);
+
+  return { version, sandboxUrl, writable, loading };
+}
diff --git a/core/react/useInspectorVersion.ts b/core/react/useInspectorVersion.ts
deleted file mode 100644
index 81300bfc6..000000000
--- a/core/react/useInspectorVersion.ts
+++ /dev/null
@@ -1,83 +0,0 @@
-/**
- * React hook over the `GET /api/config` endpoint that recovers the Inspector
- * `version` the backend reads from the root `package.json`. The browser can't
- * read the filesystem the way the CLI/TUI do, so the version is delivered on the
- * config payload (see `webServerConfigToInitialPayload`) and surfaced here.
- *
- * Mirrors {@link useSandboxUrl} / {@link useServerListWritable} (same
- * `/api/config` source, same fetch shape). `version` is `undefined` until the
- * fetch resolves, and stays `undefined` if the backend omits it (a legacy
- * backend that predates the field) — the UI simply renders nothing then.
- */
-
-import { useCallback, useEffect, useState } from "react";
-
-export interface UseInspectorVersionOptions {
-  /** Base URL of the remote server (typically `window.location.origin`). */
-  baseUrl: string;
-  /** Optional auth token for the `x-mcp-remote-auth` header. */
-  authToken?: string;
-  /** Fetch function to use (default: globalThis.fetch). Useful in tests. */
-  fetchFn?: typeof fetch;
-}
-
-export interface UseInspectorVersionResult {
-  /** The Inspector version, or undefined when unavailable / not yet loaded. */
-  version: string | undefined;
-  /** True while the initial fetch is in flight. */
-  loading: boolean;
-}
-
-/** Minimal shape we read from the `/api/config` payload. */
-interface ConfigPayload {
-  version?: unknown;
-}
-
-export function useInspectorVersion(
-  opts: UseInspectorVersionOptions,
-): UseInspectorVersionResult {
-  const { baseUrl, authToken, fetchFn } = opts;
-  const doFetch = fetchFn ?? globalThis.fetch;
-  const base = baseUrl.replace(/\/$/, "");
-
-  const [version, setVersion] = useState<string | undefined>(undefined);
-  const [loading, setLoading] = useState<boolean>(true);
-
-  const load = useCallback(
-    async (isCancelled: () => boolean): Promise<void> => {
-      const headers: Record<string, string> = {};
-      if (authToken) headers["x-mcp-remote-auth"] = `Bearer ${authToken}`;
-      try {
-        const res = await doFetch(`${base}/api/config`, {
-          method: "GET",
-          headers,
-        });
-        if (isCancelled() || !res.ok) return;
-        const body = (await res.json()) as ConfigPayload;
-        if (isCancelled()) return;
-        // Tolerate a missing/non-string field — a legacy backend that omits it
-        // leaves the version hidden rather than showing a bogus value.
-        setVersion(
-          typeof body.version === "string" && body.version
-            ? body.version
-            : undefined,
-        );
-      } catch {
-        // Network error / aborted fetch: leave version undefined (hidden).
-      } finally {
-        if (!isCancelled()) setLoading(false);
-      }
-    },
-    [base, authToken, doFetch],
-  );
-
-  useEffect(() => {
-    let cancelled = false;
-    void load(() => cancelled);
-    return () => {
-      cancelled = true;
-    };
-  }, [load]);
-
-  return { version, loading };
-}
diff --git a/core/react/useSandboxUrl.ts b/core/react/useSandboxUrl.ts
deleted file mode 100644
index 95d06807b..000000000
--- a/core/react/useSandboxUrl.ts
+++ /dev/null
@@ -1,88 +0,0 @@
-/**
- * React hook over the `GET /api/config` endpoint, used to recover the MCP Apps
- * sandbox URL the backend serves alongside the SPA. The dev/prod web backends
- * mount `sandbox_proxy.html` on a separate controller port and advertise the
- * resulting URL as `sandboxUrl` on the config payload (see
- * `clients/web/server/vite-hono-plugin.ts`). The Apps screen embeds that URL as
- * the trusted outer iframe of the double-iframe sandbox; without it MCP Apps
- * cannot run, so the screen renders an unavailable state instead.
- *
- * Fetches on mount, and re-fetches if `baseUrl` or `authToken` changes (rare —
- * effectively a full reload; the GET is idempotent). `sandboxUrl` is `undefined`
- * until the fetch resolves and stays `undefined` if the backend omits it (legacy
- * backend, or a build without the sandbox controller) — callers should treat
- * that as "Apps unavailable" rather than falling back to a blank iframe.
- */
-
-import { useCallback, useEffect, useState } from "react";
-
-export interface UseSandboxUrlOptions {
-  /** Base URL of the remote server (typically `window.location.origin`). */
-  baseUrl: string;
-  /** Optional auth token for the `x-mcp-remote-auth` header. */
-  authToken?: string;
-  /** Fetch function to use (default: globalThis.fetch). Useful in tests. */
-  fetchFn?: typeof fetch;
-}
-
-export interface UseSandboxUrlResult {
-  /** The sandbox proxy URL, or undefined when unavailable / not yet loaded. */
-  sandboxUrl: string | undefined;
-  /** True while the initial fetch is in flight. */
-  loading: boolean;
-}
-
-/** Minimal shape we read from the `/api/config` payload. */
-interface ConfigPayload {
-  sandboxUrl?: unknown;
-}
-
-export function useSandboxUrl(opts: UseSandboxUrlOptions): UseSandboxUrlResult {
-  const { baseUrl, authToken, fetchFn } = opts;
-  const doFetch = fetchFn ?? globalThis.fetch;
-  const base = baseUrl.replace(/\/$/, "");
-
-  const [sandboxUrl, setSandboxUrl] = useState<string | undefined>(undefined);
-  const [loading, setLoading] = useState<boolean>(true);
-
-  // `isCancelled` lets the effect drop a response that resolves after unmount,
-  // avoiding a setState on a dead component (React 18 warns, doesn't throw).
-  const load = useCallback(
-    async (isCancelled: () => boolean): Promise<void> => {
-      const headers: Record<string, string> = {};
-      if (authToken) headers["x-mcp-remote-auth"] = `Bearer ${authToken}`;
-      try {
-        const res = await doFetch(`${base}/api/config`, {
-          method: "GET",
-          headers,
-        });
-        if (isCancelled() || !res.ok) return;
-        const body = (await res.json()) as ConfigPayload;
-        if (isCancelled()) return;
-        // Tolerate a missing/non-string field — anything but a usable URL means
-        // "unavailable", which the Apps screen surfaces as its own empty state.
-        setSandboxUrl(
-          typeof body.sandboxUrl === "string" && body.sandboxUrl
-            ? body.sandboxUrl
-            : undefined,
-        );
-      } catch {
-        // Network error / aborted fetch: leave sandboxUrl undefined. The Apps
-        // screen degrades to its unavailable state rather than a blank iframe.
-      } finally {
-        if (!isCancelled()) setLoading(false);
-      }
-    },
-    [base, authToken, doFetch],
-  );
-
-  useEffect(() => {
-    let cancelled = false;
-    void load(() => cancelled);
-    return () => {
-      cancelled = true;
-    };
-  }, [load]);
-
-  return { sandboxUrl, loading };
-}
diff --git a/core/react/useServerListWritable.ts b/core/react/useServerListWritable.ts
deleted file mode 100644
index 949430b21..000000000
--- a/core/react/useServerListWritable.ts
+++ /dev/null
@@ -1,82 +0,0 @@
-/**
- * React hook over the `GET /api/config` endpoint that recovers the session's
- * `writable` flag. The backend sets `writable: false` when the web UI was
- * launched against a read-only server list — a `--config` session file or an
- * ad-hoc `--server-url` / command target — so the UI can hide catalog CRUD
- * (add / edit / remove / reorder / settings-save) it would only get a 403 for.
- *
- * Mirrors {@link useSandboxUrl} (same `/api/config` source, same fetch shape).
- * Defaults to `true` until the fetch resolves and whenever the field is absent
- * (a legacy backend that predates the flag), so the default catalog and
- * `--catalog` keep full CRUD without any UI change.
- */
-
-import { useCallback, useEffect, useState } from "react";
-
-export interface UseServerListWritableOptions {
-  /** Base URL of the remote server (typically `window.location.origin`). */
-  baseUrl: string;
-  /** Optional auth token for the `x-mcp-remote-auth` header. */
-  authToken?: string;
-  /** Fetch function to use (default: globalThis.fetch). Useful in tests. */
-  fetchFn?: typeof fetch;
-}
-
-export interface UseServerListWritableResult {
-  /** Whether the server list is writable (catalog) or read-only (session). */
-  writable: boolean;
-  /** True while the initial fetch is in flight. */
-  loading: boolean;
-}
-
-/** Minimal shape we read from the `/api/config` payload. */
-interface ConfigPayload {
-  writable?: unknown;
-}
-
-export function useServerListWritable(
-  opts: UseServerListWritableOptions,
-): UseServerListWritableResult {
-  const { baseUrl, authToken, fetchFn } = opts;
-  const doFetch = fetchFn ?? globalThis.fetch;
-  const base = baseUrl.replace(/\/$/, "");
-
-  // Default writable so the common (catalog) case shows CRUD immediately and a
-  // legacy backend that omits the field keeps working.
-  const [writable, setWritable] = useState<boolean>(true);
-  const [loading, setLoading] = useState<boolean>(true);
-
-  const load = useCallback(
-    async (isCancelled: () => boolean): Promise<void> => {
-      const headers: Record<string, string> = {};
-      if (authToken) headers["x-mcp-remote-auth"] = `Bearer ${authToken}`;
-      try {
-        const res = await doFetch(`${base}/api/config`, {
-          method: "GET",
-          headers,
-        });
-        if (isCancelled() || !res.ok) return;
-        const body = (await res.json()) as ConfigPayload;
-        if (isCancelled()) return;
-        // Only an explicit `false` makes the list read-only; a missing field
-        // (legacy backend) stays writable.
-        setWritable(body.writable !== false);
-      } catch {
-        // Network error / aborted fetch: leave writable at its default (true).
-      } finally {
-        if (!isCancelled()) setLoading(false);
-      }
-    },
-    [base, authToken, doFetch],
-  );
-
-  useEffect(() => {
-    let cancelled = false;
-    void load(() => cancelled);
-    return () => {
-      cancelled = true;
-    };
-  }, [load]);
-
-  return { writable, loading };
-}