Lean build: always ship core (manifest-less) frontends

scripts/stage-frontend.mjs

@@ -5,7 +5,9 @@
 // plugins' frontend dirs into frontend/src/.plugins-staged/<name>/ and codegens
 // frontend/src/router/routes.gen.js, which the router imports. A per-site build
 // selects plugins via the SITE_PLUGINS env (comma-separated); with none set,
-// every plugin that has a frontend/ is staged (the default full build).
+// every plugin that has a frontend/ is staged (the default full build). A
+// frontend dir with no manifest.json is a CORE feature and is ALWAYS staged
+// regardless of SITE_PLUGINS.
 //
 // Both outputs are generated (gitignored). Run by npm predev/prebuild.
 
@@ -26,9 +28,18 @@ const withFrontend = readdirSync(pluginsDir, { withFileTypes: true })
     && existsSync(join(pluginsDir, entry.name, 'frontend', 'routes.js')))
   .map(entry => entry.name)
 
-const chosen = requested.length
-  ? withFrontend.filter(name => requested.includes(name))
-  : withFrontend
+// A frontend dir with no manifest.json is a CORE feature (e.g. applications),
+// not a per-site plugin - it MUST always ship, or a lean build loses a core
+// page (its nav is advertised by the core, so the route would 404 to a blank
+// screen). SITE_PLUGINS selection applies only to real plugins (those with a
+// manifest).
+const isPlugin = name => existsSync(join(pluginsDir, name, 'manifest.json'))
+const coreFrontend = withFrontend.filter(name => !isPlugin(name))
+const pluginFrontend = withFrontend.filter(isPlugin)
+const chosenPlugins = requested.length
+  ? pluginFrontend.filter(name => requested.includes(name))
+  : pluginFrontend
+const chosen = [...coreFrontend, ...chosenPlugins]
 
 // Copy each chosen plugin's frontend dir into the staging area (clean first so
 // a removed plugin does not linger).