fix(sidebar): match the collapse cookie value strictly (not a substring)

A substring search for 'sidebar_collapsed=1' also matched 'sidebar_collapsed=10',
desyncing the pre-paint sidebar rail and client store from the strict server read.
Parse the cookie value and compare it to '1' exactly, in both the pre-paint inline
script and readCollapsedCookie. Added a store test.

Author: waleedlatif1

apps/sim/app/layout.tsx

@@ -79,9 +79,11 @@ export default function RootLayout({ children }: { children: React.ReactNode })
                 var defaultSidebarWidth = 248;
                 try {
                   // Collapse comes from the cookie (independent of localStorage
-                  // parsing); the persisted width is read defensively below.
-                  var hasCookie = document.cookie.indexOf('sidebar_collapsed=') !== -1;
-                  var collapsed = document.cookie.indexOf('sidebar_collapsed=1') !== -1;
+                  // parsing); the persisted width is read defensively below. Match the
+                  // value strictly so 'sidebar_collapsed=10' isn't read as collapsed.
+                  var cookieMatch = document.cookie.match(/(?:^|;\s*)sidebar_collapsed=([^;]*)/);
+                  var hasCookie = cookieMatch !== null;
+                  var collapsed = cookieMatch !== null && cookieMatch[1] === '1';
 
                   var state = null;
                   try {

apps/sim/stores/sidebar/store.test.ts

@@ -0,0 +1,34 @@
+/**
+ * @vitest-environment jsdom
+ */
+import { afterEach, describe, expect, it } from 'vitest'
+import { readCollapsedCookie } from './store'
+
+function setCookie(value: string) {
+  document.cookie = `sidebar_collapsed=${value}; path=/`
+}
+
+afterEach(() => {
+  document.cookie = 'sidebar_collapsed=; path=/; max-age=0'
+})
+
+describe('readCollapsedCookie', () => {
+  it('is true only for an exact value of 1', () => {
+    setCookie('1')
+    expect(readCollapsedCookie()).toBe(true)
+  })
+
+  it('is false for 0', () => {
+    setCookie('0')
+    expect(readCollapsedCookie()).toBe(false)
+  })
+
+  it('does not treat a substring value like 10 as collapsed', () => {
+    setCookie('10')
+    expect(readCollapsedCookie()).toBe(false)
+  })
+
+  it('is false when the cookie is absent', () => {
+    expect(readCollapsedCookie()).toBe(false)
+  })
+})

apps/sim/stores/sidebar/store.ts

@@ -35,10 +35,11 @@ function applyCollapsedCookie(collapsed: boolean) {
   document.cookie = `sidebar_collapsed=${collapsed ? '1' : '0'}; path=/; max-age=31536000; samesite=lax`
 }
 
-/** Reads the collapse state the server saw, so the client store seeds identically. */
-function readCollapsedCookie(): boolean {
+/** Reads the collapse state the server saw, so the client store seeds identically. Matches the
+ * cookie value strictly (`=1`) so `sidebar_collapsed=10` and the like aren't read as collapsed. */
+export function readCollapsedCookie(): boolean {
   if (typeof document === 'undefined') return false
-  return document.cookie.includes('sidebar_collapsed=1')
+  return document.cookie.match(/(?:^|;\s*)sidebar_collapsed=([^;]*)/)?.[1] === '1'
 }
 
 export const useSidebarStore = create<SidebarState>()(