diff --git a/apps/backend/src/lib/email-rendering.tsx b/apps/backend/src/lib/email-rendering.tsx
index 59e04640a..d79be5d55 100644
--- a/apps/backend/src/lib/email-rendering.tsx
+++ b/apps/backend/src/lib/email-rendering.tsx
@@ -56,6 +56,15 @@ const nodeModules = {
   "react": "19.1.1",
   "@react-email/components": "1.0.6",
   "arktype": "2.1.20",
+  // tailwindcss is a transitive dep (@react-email/tailwind wants "^4.1.18") that must be pinned
+  // exactly: executeJavascript runs this bundle on two engines (Freestyle and Vercel Sandbox) that
+  // install node_modules independently, so when a new matching tailwindcss version was published, one
+  // engine picked it up before the other and the rendered HTML differed byte-wise (4.3.3 emits
+  // "margin:0px" where 4.3.2 emitted "margin:0"), tripping the js-execution sanity test on
+  // essentially every run. Pinning it here dedupes the transitive dep onto one exact version on both
+  // engines. Other transitive deps still float via caret ranges; if the sanity test starts firing
+  // again with byte-different HTML, find the drifted package and pin it here the same way.
+  "tailwindcss": "4.3.3",
 };
 
 const entryJs = deindent`