diff --git a/apps/web/src/components/ChatView.browser.tsx b/apps/web/src/components/ChatView.browser.tsx
index 42658b0a..15cd06dd 100644
--- a/apps/web/src/components/ChatView.browser.tsx
+++ b/apps/web/src/components/ChatView.browser.tsx
@@ -30,6 +30,7 @@ import {
 import { scopedThreadKey, scopeThreadRef } from "@threadlines/client-runtime";
 import { createModelCapabilities, createModelSelection } from "@threadlines/shared/model";
 import { RouterProvider, createMemoryHistory } from "@tanstack/react-router";
+import { StrictMode } from "react";
 import * as Option from "effect/Option";
 import * as Schema from "effect/Schema";
 import { HttpResponse, http, ws } from "msw";
@@ -2376,6 +2377,8 @@ async function mountChatView(options: {
   resolveRpc?: (body: NormalizedWsRpcRequestBody) => unknown | undefined;
   initialPath?: string;
   waitForBootstrap?: boolean;
+  /** Mount under StrictMode, as main.tsx does, so mount-time effect cleanups run. */
+  strictMode?: boolean;
 }): Promise<MountedChatView> {
   fixture = buildFixture(options.snapshot);
   options.configureFixture?.(fixture);
@@ -2401,14 +2404,14 @@ async function mountChatView(options: {
     }),
   );
 
-  const screen = await render(
+  const app = (
     <AppAtomRegistryProvider>
       <RouterProvider router={router} />
-    </AppAtomRegistryProvider>,
-    {
-      container: host,
-    },
+    </AppAtomRegistryProvider>
   );
+  const screen = await render(options.strictMode ? <StrictMode>{app}</StrictMode> : app, {
+    container: host,
+  });
 
   await waitForWsClient();
   if (options.waitForBootstrap !== false) {
@@ -7835,6 +7838,31 @@ describe("ChatView timeline estimator parity (full app)", () => {
     }
   });
 
+  it("stays open under StrictMode", async () => {
+    // The app mounts under StrictMode, which runs every new effect's cleanup
+    // once right after mount. An unmount reset on the open dialog turned that
+    // into a palette that closed the instant it opened, in dev only.
+    const mounted = await mountChatView({
+      viewport: DEFAULT_VIEWPORT,
+      snapshot: createSnapshotForTargetUser({
+        targetMessageId: "msg-user-command-palette-strict-mode" as MessageId,
+        targetText: "command palette strict mode",
+      }),
+      strictMode: true,
+    });
+
+    try {
+      await openCommandPaletteFromTrigger();
+      await waitForLayout();
+      await waitForLayout();
+
+      expect(useCommandPaletteStore.getState().open).toBe(true);
+      await expect.element(page.getByTestId("command-palette")).toBeInTheDocument();
+    } finally {
+      await mounted.cleanup();
+    }
+  });
+
   it("filters command palette results as the user types", async () => {
     const mounted = await mountChatView({
       viewport: DEFAULT_VIEWPORT,
diff --git a/apps/web/src/components/CommandPalette.tsx b/apps/web/src/components/CommandPalette.tsx
index 7d91df36..66721a5b 100644
--- a/apps/web/src/components/CommandPalette.tsx
+++ b/apps/web/src/components/CommandPalette.tsx
@@ -450,6 +450,19 @@ export function CommandPalette({ children }: { children: ReactNode }) {
     return () => window.removeEventListener("keydown", onKeyDown);
   }, [keybindings, terminalOpen, toggleOpen]);
 
+  // The store outlives this tree, so a palette left open when the shell goes
+  // away (auth gate, pairing route, a test harness unmounting) must not greet
+  // the next mount already open. This wrapper mounts once with the shell, so
+  // its cleanup is the real teardown -- unlike the open dialog's, which
+  // StrictMode also runs right after mount.
+  useEffect(() => {
+    return () => {
+      if (useCommandPaletteStore.getState().open) {
+        setOpen(false);
+      }
+    };
+  }, [setOpen]);
+
   return (
     <ComposerHandleContext value={composerHandleRef}>
       <CommandDialog open={open} onOpenChange={setOpen}>
@@ -479,17 +492,12 @@ function OpenCommandPaletteDialog() {
   const composerHandleRef = useComposerHandleContext();
   // This component mounts once per palette session, so its mount-time
   // generation identifies the session every deferred close below belongs to.
-  // Async flows and the unmount reset close via `closeIfGeneration`: if the
-  // user closed or reopened the palette while a request was in flight (or
-  // React deferred the unmount cleanup past a new session), the stale close
-  // is a no-op instead of slamming a palette it does not own.
+  // Async flows close via `closeIfGeneration`: if the user closed or reopened
+  // the palette while a request was in flight, the stale close is a no-op
+  // instead of slamming a palette it does not own. There is deliberately no
+  // unmount cleanup here: React StrictMode runs a new effect's cleanup once
+  // right after mount, which closed the palette the instant it opened in dev.
   const [sessionGeneration] = useState(() => useCommandPaletteStore.getState().openGeneration);
-
-  useEffect(() => {
-    return () => {
-      closeIfGeneration(sessionGeneration);
-    };
-  }, [closeIfGeneration, sessionGeneration]);
   const [query, setQuery] = useState("");
   const deferredQuery = useDeferredValue(query);
   const isActionsOnly = deferredQuery.startsWith(">");