diff --git a/.github/workflows/update.yml b/.github/workflows/update.yml
index 89477f16..613c4309 100644
--- a/.github/workflows/update.yml
+++ b/.github/workflows/update.yml
@@ -53,8 +53,8 @@ jobs:
           # Overlay only what the rclone sync (prepare) placed:
           # app/routes/**/*.mdx and public images from Google Drive.
           # Code merges from main are handled by the promote workflow.
-          rsync -a --delete ../app/routes/ ./app/routes/
-          rsync -a --delete ../public/ ./public/
+          rsync -a ../app/routes/ ./app/routes/
+          rsync -a ../public/ ./public/
 
           # Force-add the content files. They are intentionally gitignored on main
           # (to avoid committing dev fixture copies), but we explicitly want them
@@ -83,7 +83,7 @@ jobs:
       - name: Install Playwright browsers
         run: npx playwright install chromium
       - name: Run readability test on built site
-        run: npm run test:reading || echo "Skipped failing tests"
+        run: npm run test:reading
       - if: failure()
         uses: ./.github/actions/notify-failure
         with:
diff --git a/.gitignore b/.gitignore
index d59f107e..ece35473 100644
--- a/.gitignore
+++ b/.gitignore
@@ -13,7 +13,7 @@ dist
 
 # MDX files copied from app/fixtures to app/routes during `npm run dev`
 app/routes/**/*.mdx
-
+!app/routes/essays/programming/functional/andthen-and-then-monad.mdx
 # Change them to your taste:
 wrangler.toml
 # package-lock.json
diff --git a/.nvmrc b/.nvmrc
index 6f4247a6..a45fd52c 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-26
+24
diff --git a/app/routes/essays/programming/functional/andthen-and-then-monad.mdx b/app/routes/essays/programming/functional/andthen-and-then-monad.mdx
new file mode 100644
index 00000000..73bd8eac
--- /dev/null
+++ b/app/routes/essays/programming/functional/andthen-and-then-monad.mdx
@@ -0,0 +1,28 @@
+---
+title: "andThen and then Monad"
+date: 2026-08-23
+---
+
+<article>
+
+# andThen and then Monad
+
+このエッセイでは、関数型プログラミングにおける `andThen` と `then` のモナド的な使い方について解説します。
+
+## 背景
+
+モナドは、`bind`（`>>=`）として知られる操作で、計算を連結します。`andThen` は JavaScript の `Promise` で同様の役割を果たします。
+
+## 実例
+
+```js
+Promise.resolve(5)
+  .andThen(x => Promise.resolve(x * 2))
+  .then(y => console.log(y)); // 10
+```
+
+## まとめ
+
+`andThen` と `then` は、モナドの法則を満たすように設計できます。
+
+</article>
diff --git a/package.json b/package.json
index df5b39fe..4404c2b7 100644
--- a/package.json
+++ b/package.json
@@ -43,7 +43,8 @@
     "vitest": "^4.1.11"
   },
   "engines": {
-    "node": "26.x"
+    "node": ">=24"
+
   },
   "overrides": {
     "@hono/node-server": "1.19.17"