feat: adopt strict TDD framework and add adversarial test suite

- Update AGENTS.md and .agents/rules/blog-system.md with strict TDD mandate
- Extract Eleventy custom filters into modular src/_filters/index.js for unit testing
- Add npm test script using Node.js native test runner (node:test)
- Create test/site-config.test.js for environment validation and fatal error assertions
- Create test/filters.test.js for adversarial filter edge cases (dates, limits, reading time, headings)
- Create test/frontmatter-schema.test.js enforcing post metadata contracts
- Create test/design-rules.test.js enforcing strict anti-patterns (no glassmorphism, no shadows, max 4px radius)
- Create test/build-integrity.test.js checking static output, zero 404 links, and TOC anchor targets

src/_data/site.js

@@ -1,24 +1,26 @@
 import fs from "node:fs";
 import path from "node:path";
 
-// Load .env variables into process.env if present
-try {
-  const envPath = path.resolve(process.cwd(), ".env");
-  if (fs.existsSync(envPath)) {
-    const envContent = fs.readFileSync(envPath, "utf-8");
-    for (const line of envContent.split("\n")) {
-      const trimmed = line.trim();
-      if (trimmed && !trimmed.startsWith("#") && trimmed.includes("=")) {
-        const [key, ...vals] = trimmed.split("=");
-        const value = vals.join("=").trim().replace(/^["']|["']$/g, "");
-        if (!process.env[key.trim()]) {
-          process.env[key.trim()] = value;
+// Load .env variables into process.env if SITE_DOMAIN is not already defined
+if (!process.env.SITE_DOMAIN) {
+  try {
+    const envPath = path.resolve(process.cwd(), ".env");
+    if (fs.existsSync(envPath)) {
+      const envContent = fs.readFileSync(envPath, "utf-8");
+      for (const line of envContent.split("\n")) {
+        const trimmed = line.trim();
+        if (trimmed && !trimmed.startsWith("#") && trimmed.includes("=")) {
+          const [key, ...vals] = trimmed.split("=");
+          const value = vals.join("=").trim().replace(/^["']|["']$/g, "");
+          if (!process.env[key.trim()]) {
+            process.env[key.trim()] = value;
+          }
         }
       }
     }
+  } catch (e) {
+    // Silent fallback
   }
-} catch (e) {
-  // Silent fallback
 }
 
 const siteDomain = process.env.SITE_DOMAIN;

src/_filters/index.js

@@ -0,0 +1,74 @@
+import { DateTime } from "luxon";
+
+/**
+ * Custom Eleventy Filters for River Rooks Blog
+ */
+
+export const postDate = (dateObj) => {
+  if (!dateObj) return "";
+  const date = typeof dateObj === "string" ? new Date(dateObj) : dateObj;
+  const dt = DateTime.fromJSDate(date, { zone: "utc" });
+  if (!dt.isValid) return "";
+  return dt.toFormat("LLL dd, yyyy").toUpperCase();
+};
+
+export const isoDate = (dateObj) => {
+  if (!dateObj) return "";
+  const date = typeof dateObj === "string" ? new Date(dateObj) : dateObj;
+  const dt = DateTime.fromJSDate(date, { zone: "utc" });
+  if (!dt.isValid) return "";
+  return dt.toISODate() || "";
+};
+
+export const limit = (arr, count) => {
+  if (!Array.isArray(arr)) return [];
+  if (count <= 0) return [];
+  return arr.slice(0, count);
+};
+
+export const filterTagList = (tags) => {
+  const internalTags = ["all", "nav", "post", "posts"];
+  if (!tags) return [];
+  const tagArray = Array.isArray(tags) ? tags : [tags];
+  return tagArray.filter((tag) => {
+    if (typeof tag !== "string") return false;
+    const clean = tag.replace(/^#/, "").toLowerCase();
+    return !internalTags.includes(clean);
+  });
+};
+
+export const readingTime = (text, frontmatterTime) => {
+  if (frontmatterTime) return frontmatterTime;
+  if (!text || typeof text !== "string") return "1 MIN READ";
+  const clean = text.replace(/<[^>]+>/g, "").trim();
+  if (!clean) return "1 MIN READ";
+  const words = clean.split(/\s+/).filter(Boolean).length;
+  const minutes = Math.max(1, Math.ceil(words / 200));
+  return `${minutes} MIN READ`;
+};
+
+export const extractHeadings = (htmlContent) => {
+  if (!htmlContent || typeof htmlContent !== "string") return [];
+  const headingRegex = /<h([23])\s+id="([^"]+)"[^>]*>(.*?)<\/h\1>/gis;
+  const headings = [];
+  let match;
+  while ((match = headingRegex.exec(htmlContent)) !== null) {
+    headings.push({
+      level: parseInt(match[1], 10),
+      id: match[2],
+      title: match[3].replace(/<[^>]+>/g, "").trim()
+    });
+  }
+  return headings;
+};
+
+export const filters = {
+  postDate,
+  isoDate,
+  limit,
+  filterTagList,
+  readingTime,
+  extractHeadings
+};
+
+export default filters;