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

turbo/generators/lib/anchor-validate.ts

@@ -0,0 +1,26 @@
+import { existsSync, readFileSync } from "node:fs";
+import { join } from "node:path";
+
+/**
+ * Throws with a clear message if any required anchor is missing from the target
+ * file. Generator actions call this in their prompt validator so the run aborts
+ * cleanly before any partial output lands on disk.
+ */
+export function assertAnchors(
+  repoRoot: string,
+  relativePath: string,
+  anchors: string[],
+): void {
+  const path = join(repoRoot, relativePath);
+  if (!existsSync(path)) {
+    throw new Error(`Required file does not exist: ${relativePath}`);
+  }
+  const content = readFileSync(path, "utf8");
+  for (const anchor of anchors) {
+    if (!content.includes(anchor)) {
+      throw new Error(
+        `Missing anchor "${anchor}" in ${relativePath}. Add it before running this generator.`,
+      );
+    }
+  }
+}