diff --git a/apps/desktop/scripts/dev.mjs b/apps/desktop/scripts/dev.mjs
index 56e7ec7e31..b58be3e5ba 100644
--- a/apps/desktop/scripts/dev.mjs
+++ b/apps/desktop/scripts/dev.mjs
@@ -160,6 +160,20 @@ if (!devUrl) {
   process.exit(1);
 }
 
+// Let Vite finish the initial dependency crawl + optimizer commit before the
+// window loads (issue #4775). `warmupRequest` on the renderer entry kicks the
+// recursive pre-transform of the static import graph (which registers every
+// reachable dep with the optimizer), and `waitForRequestsIdle` resolves at
+// crawl end — the same signal the dep optimizer waits on before committing
+// node_modules/.vite/deps. Loading Electron before that commit let the page
+// execute chunks from a previous optimizer generation alongside fresh ones —
+// two React instances, a null hook dispatcher, and a renderer crash on the
+// first lazy component. warmupRequest swallows transform errors itself, so
+// this can never abort the launch; it only reorders the startup race away.
+log('vite', 'warming renderer entry and waiting for the dep crawl to settle...');
+await server.environments.client.warmupRequest('/main.tsx');
+await server.environments.client.waitForRequestsIdle();
+
 log('electron', `launching against ${devUrl} (renderer HMR live)`);
 
 // Created before launch so signals during codesign/preparation are durable.
diff --git a/apps/desktop/src/main/__tests__/main-renderer-dev-cache.test.ts b/apps/desktop/src/main/__tests__/main-renderer-dev-cache.test.ts
new file mode 100644
index 0000000000..ee97638993
--- /dev/null
+++ b/apps/desktop/src/main/__tests__/main-renderer-dev-cache.test.ts
@@ -0,0 +1,48 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { clearDevRendererHttpCache } from '../main-renderer-dev-cache.js';
+
+describe('dev renderer HTTP cache hygiene (issue #4775)', () => {
+  it('clears the session HTTP cache before loading a Vite dev server', async () => {
+    let cleared = 0;
+    const session = { async clearCache() { cleared += 1; } };
+    const didClear = await clearDevRendererHttpCache(session, { useDevServer: true });
+    assert.equal(didClear, true);
+    assert.equal(cleared, 1);
+  });
+
+  it('leaves the cache alone for packaged file:// builds', async () => {
+    let cleared = 0;
+    const session = { async clearCache() { cleared += 1; } };
+    const didClear = await clearDevRendererHttpCache(session, { useDevServer: false });
+    assert.equal(didClear, false);
+    assert.equal(cleared, 0);
+  });
+
+  it('downgrades a clearCache failure to a warning instead of blocking load', async () => {
+    const session = {
+      async clearCache(): Promise<void> { throw new Error('cache locked'); },
+    };
+    const didClear = await clearDevRendererHttpCache(session, { useDevServer: true });
+    assert.equal(didClear, false);
+  });
+});
diff --git a/apps/desktop/src/main/main-renderer-dev-cache.ts b/apps/desktop/src/main/main-renderer-dev-cache.ts
new file mode 100644
index 0000000000..adeb1071f5
--- /dev/null
+++ b/apps/desktop/src/main/main-renderer-dev-cache.ts
@@ -0,0 +1,68 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+/**
+ * Dev-server cache hygiene (issue #4775).
+ *
+ * Vite serves optimized deps as `Cache-Control: immutable` keyed by per-dep
+ * `?v=` browserHash labels, and the optimizer preserves a dep's label across
+ * re-optimization commits — including ones where the dep's bundle bytes
+ * changed (Vite upgrade, patch re-application, interrupted commit). The
+ * persistent session cache then resurrects a previous generation's
+ * react/react-dom chunk graph next to freshly transformed sources that import
+ * today's react copy: two React instances in one page, a null hook
+ * dispatcher, and `Cannot read properties of null (reading 'useRef')`
+ * killing the renderer on the first lazily loaded component.
+ *
+ * Clearing the HTTP cache before loading the dev server keeps every dev
+ * session on exactly one optimizer generation. Packaged builds load file://
+ * and never touch this path; localStorage/cookies are not part of the HTTP
+ * cache and survive.
+ *
+ * Structural interfaces instead of `electron` imports: the module stays
+ * loadable in plain node tests (same pattern as main-renderer-loader.ts).
+ */
+export interface DevRendererCacheSession {
+  clearCache(): Promise<void>;
+}
+
+export interface DevRendererCacheEntry {
+  readonly useDevServer: boolean;
+}
+
+/**
+ * Clears the renderer session's HTTP cache when — and only when — the window
+ * is about to load a Vite dev server. Returns whether the cache was cleared.
+ * A clearCache failure downgrades to a warning: the duplicate-React crash it
+ * guards against is recoverable by reload, but a window that never opens is
+ * not.
+ */
+export async function clearDevRendererHttpCache(
+  session: DevRendererCacheSession,
+  rendererEntry: DevRendererCacheEntry,
+): Promise<boolean> {
+  if (!rendererEntry.useDevServer) return false;
+  try {
+    await session.clearCache();
+    return true;
+  } catch (error) {
+    console.warn('[main] failed to clear dev renderer HTTP cache:', error);
+    return false;
+  }
+}
diff --git a/apps/desktop/src/main/main-window.ts b/apps/desktop/src/main/main-window.ts
index 9f8fbc1e84..9709e0eb02 100644
--- a/apps/desktop/src/main/main-window.ts
+++ b/apps/desktop/src/main/main-window.ts
@@ -29,6 +29,7 @@ import { BrowserViewManager } from './browser/view-manager.js';
 import type { E2eFixture } from './e2e-fixture.js';
 import { installMainWindowPermissionPolicy } from './main-window-permission-policy.js';
 import { loadMainRenderer, resolveMainRendererEntry } from './main-renderer-loader.js';
+import { clearDevRendererHttpCache } from './main-renderer-dev-cache.js';
 import {
   type MainRendererFrameIdentity,
   observeMainRendererProcessGone,
@@ -522,6 +523,11 @@ export function createMainWindowController(deps: MainWindowControllerDeps): Main
       void writeSavedBounds(workspaceRoot, final);
     });
 
+    // Dev-server cache hygiene (issue #4775) — see main-renderer-dev-cache.ts
+    // for why a stale immutable dep-chunk graph must never survive into a new
+    // dev session (duplicate React instances → null hook dispatcher crash).
+    await clearDevRendererHttpCache(mainWindow.webContents.session, rendererEntry);
+
     await loadMainRenderer(mainWindow, rendererEntry);
 
     // PR-SHOW-AFTER-FIRST-COMMIT: reveal fallback. Start this budget only once