chore(template): clean-slate template snapshot from bb4a0c7

Curated, product-agnostic snapshot of the post-story-04 tree: demo
content deleted, auth-only reference feature, web-next shell, all gates
green. Product-specific docs, ADRs 027-029, PRDs/epics/archive, editor
library traces, and product naming are curated out; generic template
repairs (coverage provider devDeps, root test:coverage script, live
lint fixes, root-only release-please) are kept. See TEMPLATE.md for
provenance, curation list, and usage.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/core-eslint/rules/component-must-have-test.test.js

@@ -0,0 +1,59 @@
+import { describe, it } from "vitest";
+import { RuleTester } from "eslint";
+import path from "node:path";
+import os from "node:os";
+import fs from "node:fs";
+import rule from "./component-must-have-test.js";
+
+function makeFixture({ withTest }) {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), "cmht-"));
+  const dir = path.join(root, "packages", "core-ui", "src", "atoms", "Button");
+  fs.mkdirSync(dir, { recursive: true });
+  const component = path.join(dir, "Button.tsx");
+  fs.writeFileSync(
+    component,
+    `export const Button = () => <button>x</button>;`,
+  );
+  if (withTest) {
+    fs.writeFileSync(
+      path.join(dir, "Button.test.tsx"),
+      `import { it } from "vitest"; it("works", () => {});`,
+    );
+  }
+  return { component };
+}
+
+const tester = new RuleTester({
+  languageOptions: {
+    parser: await import("@typescript-eslint/parser"),
+    ecmaVersion: "latest",
+    sourceType: "module",
+    parserOptions: { ecmaFeatures: { jsx: true } },
+  },
+});
+
+describe("component-must-have-test", () => {
+  it("passes when sibling .test.tsx exists", () => {
+    const { component } = makeFixture({ withTest: true });
+    tester.run("component-must-have-test", rule, {
+      valid: [
+        { filename: component, code: fs.readFileSync(component, "utf8") },
+      ],
+      invalid: [],
+    });
+  });
+
+  it("fires when no sibling .test.tsx exists", () => {
+    const { component } = makeFixture({ withTest: false });
+    tester.run("component-must-have-test", rule, {
+      valid: [],
+      invalid: [
+        {
+          filename: component,
+          code: fs.readFileSync(component, "utf8"),
+          errors: [{ messageId: "missingTest" }],
+        },
+      ],
+    });
+  });
+});