fix: avoid inserting scripts when manual mode and not used

Fixes #56

.playground/pages/manual-off.vue

@@ -0,0 +1,15 @@
+<script lang="ts" setup>
+import { defineRouteRules } from '#imports'
+
+defineRouteRules({
+  delayHydration: 'manual',
+})
+</script>
+
+<template>
+  <div>
+    <div>
+      <HydrationStatus />
+    </div>
+  </div>
+</template>

src/runtime/components/DelayHydration.mjs

@@ -1,11 +1,13 @@
-import { defineAsyncComponent } from 'vue'
+import { Comment, Fragment, defineAsyncComponent, h } from 'vue'
 
 export default defineAsyncComponent({
   loader() {
     const hydrationApi = import.meta.client ? window._$delayHydration || Promise.resolve() : Promise.resolve()
     return new Promise((resolve) => {
       hydrationApi.then(() => {
-        resolve((props, { slots }) => slots.default?.(props))
+        resolve((props, { slots }) => {
+          return h(Fragment, [h(Comment, 'nuxt-delay-hydration-component'), slots.default?.(props)])
+        })
       })
     })
   },

src/runtime/nitro-plugin.ts

@@ -23,6 +23,13 @@ export default defineNitroPlugin((nitro) => {
     if (!currentMode)
       return
 
+    if (currentMode === 'manual') {
+      // we only insert the script if the page is using it
+      if (!htmlContext.body.some(h => h.includes('<!--[--><!--nuxt-delay-hydration-component--><!--[-->'))) {
+        return
+      }
+    }
+
     let extraScripts = ''
     if (currentMode === 'init') {
       const ASSET_RE = new RegExp(`<script[^>]*src="${config.app.buildAssetsDir}[^>]+><\\/script>`)