Both library layouts load nested bundles through the shared embedScript, which fixes VerticalTabsLayout on the dev server

VerticalTabsLayout kept a private script loader without the dev-server ES-module
rule, so a bundle nested through it under bun run dev loaded as a classic script,
reported success, and never defined its tag. It and StackLayout now call
library/utils/embedScript.js loadScriptOnce; StackLayout keeps its own
resolveBundleSrc step first. loadScriptOnce gains an empty-url no-op (a
<script src=""> re-fetched the page) and carries StackLayout's stack-demo
measurement beside the gallery's. One copy of the pattern and one cache.

library/layouts/StackLayout.vue

@@ -80,10 +80,8 @@
 import { defineComponent } from 'vue'
 import { useShadowStyles } from '@map/composables/useShadowStyles.js'
 import { bundleTreeRoot } from '@map/utils/embedBase.js'
+import { loadScriptOnce } from '@map/utils/embedScript.js'
 
-// Inject a bundle script exactly once per URL (deduped across all layout instances). Same helper the
-// tabs layout + the SPA use — resolves after the IIFE's customElements.define has run.
-const _stlLoaded = {}
 // ★ ANCHOR A SIBLING-BUNDLE src TO THE TREE ROOT, NOT TO A GUESSED DEPTH.
 // THE BUG (Driver-reported 2026-09-23, verbatim console text):
 //     Could not load <doxa-research-map> from ../../doxa-research-map/doxa-research-map.js
@@ -134,30 +132,11 @@ function resolveBundleSrc(url) {
   return url
 }
 
+// Inject a bundle script exactly once per URL, through the ONE shared loader (library/utils/embedScript.js:
+// the dedupe cache, the dev-server ES-module rule, the empty-url no-op). Only the src resolution is this
+// layout's own: a sibling-bundle src is anchored to the tree root first (resolveBundleSrc above).
 function injectScriptOnce(rawUrl) {
-  const url = resolveBundleSrc(rawUrl)
-  if (!url) return Promise.resolve()
-  if (_stlLoaded[url]) return _stlLoaded[url]
-  _stlLoaded[url] = new Promise((ok, fail) => {
-    const s = document.createElement('script')
-    s.src = url
-    // ★ A DEV ENTRY IS AN ES MODULE, AND A CLASSIC <script> LIES ABOUT LOADING IT.
-    // Pointing a classic script at /plugin-designs/<bundle>/index.js fires onload SUCCESSFULLY and
-    // only THEN throws "Cannot use import statement outside a module", asynchronously. So this
-    // promise resolved, waitForDefine() below timed out, the tag never registered, and the section
-    // rendered empty — with NO failed request and NO console error at the injection site. onload is
-    // structurally incapable of detecting this.
-    // MEASURED on stack-demo's dev leaf 2026-09-22: 0 failed requests, and yet
-    // customElements.get('research-dashboard-map') === false with 0 rows rendered.
-    // Same rule as plugin-studio.vue:255, which hit this first. It belongs HERE because StackLayout
-    // is the SHARED layout — dashboard-plus-grid and research-map-plus-grid inject through this same
-    // function, so one fix covers all three consumers instead of becoming a fourth private copy.
-    if (/^\/plugin-designs\//.test(url) || /\/index\.js(\?|$)/.test(url)) s.type = 'module'
-    s.onload = () => ok()
-    s.onerror = () => { delete _stlLoaded[url]; fail(new Error('failed to load ' + url)) }
-    document.head.appendChild(s)
-  })
-  return _stlLoaded[url]
+  return loadScriptOnce(resolveBundleSrc(rawUrl))
 }
 
 function waitForDefine(tag, timeoutMs = 5000) {

library/layouts/VerticalTabsLayout.vue

@@ -246,22 +246,12 @@ import { tStatic } from '../i18n/index.js'
 const tr = (key, en) => tStatic(key) || en
 import { useShadowStyles } from '@map/composables/useShadowStyles.js'
 import { icon as localIcon } from '@map/layouts/app-wrapper-material/icons.js'
+import { loadScriptOnce } from '@map/utils/embedScript.js'
 
-// Inject a bundle script exactly once per URL (deduped across all layout instances). Resolves after
-// the IIFE has executed (so its customElements.define has run). Mirrors the SPA/studio's once().
-const _vtlLoaded = {}
-function injectScriptOnce(url) {
-  if (!url) return Promise.resolve()
-  if (_vtlLoaded[url]) return _vtlLoaded[url]
-  _vtlLoaded[url] = new Promise((ok, fail) => {
-    const s = document.createElement('script')
-    s.src = url
-    s.onload = () => ok()
-    s.onerror = () => { delete _vtlLoaded[url]; fail(new Error('failed to load ' + url)) }
-    document.head.appendChild(s)
-  })
-  return _vtlLoaded[url]
-}
+// Inject a bundle script exactly once per URL, through the ONE shared loader (library/utils/embedScript.js).
+// This layout's private copy lacked the dev-server ES-module rule, so a bundle nested through it under
+// bun run dev loaded as a classic script, reported success, and never defined its tag.
+const injectScriptOnce = (url) => loadScriptOnce(url)
 
 // Wait until a custom element tag is defined (up to ~5s). If a src bundle was injected, its
 // define() has already run by onload; this covers elements registered async after script exec.

library/utils/embedScript.js

@@ -29,11 +29,18 @@
  *   The built tree ships IIFEs, where a classic tag is correct, so this only ever bites under the dev
  *   server — exactly the surface a developer works on. Rule: a rooted /plugin-designs/ entry (or any
  *   .../index.js) is a dev ES module; everything else is a built IIFE.
+ *   MEASURED a second time, independently, on stack-demo's dev leaf 2026-09-22 (StackLayout, before it
+ *   used this file): 0 failed requests, and yet customElements.get('research-dashboard-map') === false
+ *   with 0 rows rendered. VerticalTabsLayout's private copy LACKED this rule until it moved here, so a
+ *   bundle nested through it on the dev server never defined its tag.
+ *
+ * An empty url is a no-op: a <script src=""> would re-fetch the page itself.
  *
  * SRI is optional (attrs.integrity).
  */
 const _loaded = {}
 export function loadScriptOnce(url, attrs) {
+  if (!url) return Promise.resolve()
   if (_loaded[url]) return _loaded[url]
   _loaded[url] = new Promise((ok, fail) => {
     const s = document.createElement('script')