Make the ResizeObserver test mock constructible under any vitest

web/.eslintrc.cjs

@@ -7,7 +7,7 @@ module.exports = {
     'plugin:react/jsx-runtime',
     'plugin:react-hooks/recommended',
   ],
-  ignorePatterns: ['dist', '.eslintrc.cjs'],
+  ignorePatterns: ['dist', 'coverage', '.eslintrc.cjs'],
   parserOptions: { ecmaVersion: 'latest', sourceType: 'module' },
   settings: { react: { version: '18.2' } },
   plugins: ['react-refresh'],

web/.gitignore

@@ -10,6 +10,7 @@ lerna-debug.log*
 node_modules
 dist
 dist-ssr
+coverage
 *.local
 
 # Editor directories and files

web/src/test/setup.js

@@ -16,12 +16,15 @@ if (globalThis.__VITEST_SETUP_LOADED__) {
   // Extend Vitest's expect with accessibility matchers
   expect.extend({ toHaveNoViolations });
 
-  // Mock ResizeObserver (needed for Recharts)
-  globalThis.ResizeObserver = vi.fn().mockImplementation(() => ({
-    observe: vi.fn(),
-    unobserve: vi.fn(),
-    disconnect: vi.fn(),
-  }));
+  // Mock ResizeObserver (needed for Recharts). A plain class rather than
+  // vi.fn().mockImplementation(): Recharts calls `new ResizeObserver(...)`,
+  // and whether a mock function is constructible is a vitest implementation
+  // detail that changed in v5.
+  globalThis.ResizeObserver = class ResizeObserver {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+  };
 
   // Mock scrollIntoView (needed for Logs component)
   Element.prototype.scrollIntoView = vi.fn();