diff --git a/apps/web/src/components/AppSidebarLayout.tsx b/apps/web/src/components/AppSidebarLayout.tsx
index 3a70390d0c4..53a9ae48784 100644
--- a/apps/web/src/components/AppSidebarLayout.tsx
+++ b/apps/web/src/components/AppSidebarLayout.tsx
@@ -1,6 +1,12 @@
 import { useAtomValue } from "@effect/atom-react";
 import * as Schema from "effect/Schema";
-import { useEffect, useState, type CSSProperties, type ReactNode } from "react";
+import {
+  useEffect,
+  useState,
+  useSyncExternalStore,
+  type CSSProperties,
+  type ReactNode,
+} from "react";
 import { useLocation, useNavigate } from "@tanstack/react-router";
 
 import { isElectron } from "../env";
@@ -31,6 +37,15 @@ import { Tooltip, TooltipPopup, TooltipTrigger } from "./ui/tooltip";
 
 const MACOS_TRAFFIC_LIGHTS_LEFT_INSET = "90px";
 
+function subscribeToViewportWidth(onChange: () => void): () => void {
+  window.addEventListener("resize", onChange);
+  return () => window.removeEventListener("resize", onChange);
+}
+
+function readViewportWidth(): number {
+  return window.innerWidth;
+}
+
 function readInitialThreadSidebarWidth(): number {
   try {
     return resolveInitialThreadSidebarWidth(
@@ -109,7 +124,11 @@ export function AppSidebarLayout({ children }: { children: ReactNode }) {
   const useSidebarV2Theme = useSidebarV2 || isOnSettings;
   const isMacosDesktop = isElectron && isMacPlatform(navigator.platform);
   const [sidebarWidth, setSidebarWidth] = useState(readInitialThreadSidebarWidth);
-  const sidebarMaximumWidth = resolveThreadSidebarMaximumWidth(window.innerWidth);
+  // Subscribed rather than read once: the clamp must track live window size,
+  // and a clamped drag ends with an unchanged width, which skips the re-render
+  // that would otherwise refresh a render-time snapshot.
+  const viewportWidth = useSyncExternalStore(subscribeToViewportWidth, readViewportWidth);
+  const sidebarMaximumWidth = resolveThreadSidebarMaximumWidth(viewportWidth);
   const [isWindowFullscreen, setIsWindowFullscreen] = useState(() => {
     const getWindowFullscreenState = window.desktopBridge?.getWindowFullscreenState;
     return isMacosDesktop && typeof getWindowFullscreenState === "function"