fix(gtm): invoke onBeforeGtmStart callback when ID is in config

.claude/plans/543-plausible-broken.md

@@ -0,0 +1,61 @@
+## DONE
+
+# Fix: Plausible Analytics new script not working (#543)
+
+## Problem
+Users report that the new Plausible script format (with `scriptId`) loads correctly in DOM but no events are sent.
+
+## Analysis
+
+### Root Cause
+The `clientInit` stub uses bare `plausible` identifier inconsistently with `window.plausible`:
+
+```js
+// Current code (plausible-analytics.ts:187)
+window.plausible = window.plausible || function () { (plausible.q = plausible.q || []).push(arguments) }, plausible.init = plausible.init || function (i) { plausible.o = i || {} }
+```
+
+Issues:
+1. **Inconsistent window reference**: First part uses `window.plausible`, second part uses bare `plausible`
+2. **Module scope**: In ES modules (strict mode), bare identifier resolution differs from non-module scripts
+3. **Compare to GA**: Google Analytics uses `w` (window) consistently throughout its clientInit
+
+### How Plausible's new script works
+The `pa-{scriptId}.js` script:
+1. Checks `plausible.o && S(plausible.o)` on load to pick up pre-init options
+2. The stub's `plausible.init()` stores options in `plausible.o`
+3. Script has domain hardcoded, doesn't need `data-domain` attribute
+
+### Verification
+Plausible script expected stub format:
+```js
+window.plausible = window.plausible || {}
+plausible.o && S(plausible.o)  // If .o exists, initialize with those options
+```
+
+Our stub needs to set `plausible.o` before script loads, which it does via:
+```js
+plausible.init = function(i) { plausible.o = i || {} }
+window.plausible.init(initOptions)
+```
+
+## Fix
+
+Update `clientInit` to use `window.plausible` consistently (like GA does):
+
+```ts
+clientInit() {
+  const w = window as any
+  w.plausible = w.plausible || function () { (w.plausible.q = w.plausible.q || []).push(arguments) }
+  w.plausible.init = w.plausible.init || function (i: PlausibleInitOptions) { w.plausible.o = i || {} }
+  w.plausible.init(initOptions)
+}
+```
+
+## Files to modify
+- `src/runtime/registry/plausible-analytics.ts`: Fix clientInit stub pattern
+
+## Test plan
+1. Run existing tests
+2. Test playground with plausible-analytics-v2.vue
+3. Verify script loads and init options are picked up

src/runtime/registry/google-tag-manager.ts

@@ -125,7 +125,7 @@ export function useScriptGoogleTagManager<T extends GoogleTagManagerApi>(
     onBeforeGtmStart?: (gtag: DataLayerPush) => void
   },
 ): UseScriptContext<UseFunctionType<NuxtUseScriptOptions<T>, T>> {
-  return useRegistryScript<T, typeof GoogleTagManagerOptions>(
+  const instance = useRegistryScript<T, typeof GoogleTagManagerOptions>(
     options?.key || 'googleTagManager',
     (opts) => {
       const dataLayerName = opts?.l ?? opts?.dataLayer ?? 'dataLayer'
@@ -183,4 +183,17 @@ export function useScriptGoogleTagManager<T extends GoogleTagManagerApi>(
     },
     options,
   )
+
+  // Handle callback for cached/pre-initialized scripts (e.g., when ID is in nuxt.config)
+  // If script was already initialized by the plugin, clientInit already ran without this callback
+  if (import.meta.client && options?.onBeforeGtmStart) {
+    const dataLayerName = options?.l ?? options?.dataLayer ?? 'dataLayer'
+    const gtag = (window as any).gtag
+    // If gtag exists, script was already initialized - invoke callback immediately
+    if (gtag) {
+      options.onBeforeGtmStart(gtag)
+    }
+  }
+
+  return instance
 }