fix(scripts): exempt Storybook stories from coverage:diff gate

Story files are excluded from vitest by design (they run in Storybook
runner, not vitest). Add *.stories.{ts,tsx} to ALLOWED_GLOBS so the
L1 diff gate doesn't flag them as "new untested file".

Also add error-handling test for useOptionalConsent rethrow path
(cookie-consent-banner lines 52-53) achieving 100% statement coverage.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

coverage/summary.json

@@ -1,16 +1,16 @@
 {
-  "generatedAt": "2026-05-19T21:20:25.856Z",
-  "commit": "de17803",
+  "generatedAt": "2026-05-19T21:23:46.645Z",
+  "commit": "1b6f2d1",
   "repo": {
-    "statements": 97.34,
-    "branches": 91.98,
+    "statements": 97.38,
+    "branches": 92.08,
     "functions": 97.09,
-    "lines": 97.34,
+    "lines": 97.38,
     "counts": {
-      "lf": 5742,
-      "lh": 5589,
-      "brf": 1147,
-      "brh": 1055,
+      "lf": 5758,
+      "lh": 5607,
+      "brf": 1149,
+      "brh": 1058,
       "fnf": 344,
       "fnh": 334
     }
@@ -115,15 +115,15 @@
       }
     },
     "@repo/core-ui": {
-      "statements": 99.49,
-      "branches": 90.2,
+      "statements": 100,
+      "branches": 91.35,
       "functions": 100,
-      "lines": 99.49,
+      "lines": 100,
       "counts": {
-        "lf": 396,
-        "lh": 394,
-        "brf": 102,
-        "brh": 92,
+        "lf": 412,
+        "lh": 412,
+        "brf": 104,
+        "brh": 95,
         "fnf": 18,
         "fnh": 18
       }

packages/core-ui/src/cookie-consent-banner/cookie-consent-banner-unexpected-error.test.tsx

@@ -0,0 +1,61 @@
+/**
+ * Isolated test file for the error-re-throw path in useOptionalConsent.
+ * Uses vi.mock to make useConsent throw a non-ConsentContextError so that
+ * lines 52-53 (the `throw e` branch) are exercised.
+ */
+import { describe, it, expect, vi } from "vitest";
+import { Component, type ReactNode } from "react";
+import { render, screen } from "@testing-library/react";
+
+vi.mock("@repo/core-consent/react", () => ({
+  useConsent: vi.fn(() => {
+    throw new Error("unexpected-non-consent-error");
+  }),
+  ConsentContextError: class ConsentContextError extends Error {
+    constructor() {
+      super("no provider");
+      this.name = "ConsentContextError";
+    }
+  },
+}));
+
+import { CookieConsentBanner } from "./cookie-consent-banner";
+
+class ErrorBoundary extends Component<
+  { children: ReactNode },
+  { caught: string | null }
+> {
+  constructor(props: { children: ReactNode }) {
+    super(props);
+    this.state = { caught: null };
+  }
+
+  static getDerivedStateFromError(error: Error) {
+    return { caught: error.message };
+  }
+
+  render() {
+    if (this.state.caught) {
+      return <div data-testid="caught">{this.state.caught}</div>;
+    }
+    return this.props.children;
+  }
+}
+
+describe("CookieConsentBanner — useOptionalConsent rethrows non-ConsentContextError", () => {
+  it("surfaces unexpected render errors through an error boundary", () => {
+    const consoleSpy = vi.spyOn(console, "error").mockImplementation(() => {});
+
+    render(
+      <ErrorBoundary>
+        <CookieConsentBanner variant="modal" />
+      </ErrorBoundary>,
+    );
+
+    expect(screen.getByTestId("caught")).toHaveTextContent(
+      "unexpected-non-consent-error",
+    );
+
+    consoleSpy.mockRestore();
+  });
+});

scripts/coverage/diff.mjs

@@ -32,6 +32,8 @@ import { execSync } from "node:child_process";
 const ALLOWED_GLOBS = [
   // Test artifacts
   /\.test\.(ts|tsx|js|mjs)$/,
+  // Storybook story files — excluded from vitest by design; tested in Storybook runner
+  /\.stories\.(ts|tsx)$/,
   /\/__factories__\//,
   /\/__contracts__\//,
   /\/__fixtures__\//,

scripts/coverage/diff.test.mjs

@@ -210,6 +210,21 @@ describe("computeDiffCoverage", () => {
     assert.equal(result.summary.filesChanged, 3);
   });
 
+  test("skips Storybook story files (.stories.ts/.stories.tsx — excluded from vitest coverage)", () => {
+    const lcov = parseLcov(lcovText);
+    const diff = new Map([
+      [
+        "packages/core-ui/src/cookie-consent-banner/cookie-consent-banner.stories.tsx",
+        new Set([1, 2, 3, 4, 5]),
+      ],
+      ["packages/core-ui/src/atoms/button/button.stories.ts", new Set([1, 2])],
+    ]);
+    const result = computeDiffCoverage(diff, lcov);
+    assert.equal(result.status, "pass");
+    assert.equal(result.summary.filesGated, 0);
+    assert.equal(result.summary.filesChanged, 2);
+  });
+
   test("skips packages/core-testing/ (tooling package, no lcov generated)", () => {
     const lcov = parseLcov(lcovText);
     const diff = new Map([