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/entity-must-have-test.js

@@ -0,0 +1,55 @@
+import fs from "node:fs";
+import path from "node:path";
+
+/**
+ * Entity models (`entities/models/<x>.ts`) are pure domain logic — schemas,
+ * invariants, derivations. They are the cheapest layer to test and the most
+ * expensive to get wrong, so every model file must carry a sibling test.
+ *
+ * Scope is `entities/models/` only. Error classes (`entities/errors/`) are
+ * conventionally covered by a consolidated `errors.test.ts`, and barrels
+ * (`index.ts`) hold no logic — both are excluded.
+ */
+function isEntityModelFile(filename) {
+  const normalized = filename.replace(/\\/g, "/");
+  if (!normalized.includes("/entities/models/")) return false;
+  if (!normalized.endsWith(".ts")) return false;
+  if (normalized.endsWith(".test.ts")) return false;
+  if (normalized.endsWith(".d.ts")) return false;
+  if (normalized.endsWith("/index.ts")) return false;
+  return true;
+}
+
+/** @type {import("eslint").Rule.RuleModule} */
+export default {
+  meta: {
+    type: "problem",
+    docs: {
+      description:
+        "Every entity model file (entities/models/<x>.ts) must have a sibling <x>.test.ts.",
+    },
+    schema: [],
+    messages: {
+      missingTest:
+        "Entity model {{filename}} has no sibling test at {{expected}}. Entity models are pure domain logic — cover them with a unit test.",
+    },
+  },
+  create(context) {
+    return {
+      Program(node) {
+        const filename = context.filename;
+        if (!isEntityModelFile(filename)) return;
+        const expected = filename.replace(/\.ts$/, ".test.ts");
+        if (fs.existsSync(expected)) return;
+        context.report({
+          node,
+          messageId: "missingTest",
+          data: {
+            filename: path.basename(filename),
+            expected: path.basename(expected),
+          },
+        });
+      },
+    };
+  },
+};