fix: honest installer success (gate license/next-steps on child install)

The package postflight showed the "License Key Required" / next-steps
message even when a bundled child extension failed to sub-install
(Joomla only logs those failures). Add a fail-open manifest verifier
(missingChildExtensions) that confirms every declared child landed in
#__extensions and enqueues an error + returns before the license path
when any are missing. Fails open so a transient glitch never fakes a
failure.

Claude-Session: https://claude.ai/code/session_01B9aZHSWbiiZykJD88pYx8R

source/script.php

@@ -16,9 +16,104 @@ class Pkg_MokoSuiteFieldInstallerScript
 {
 	public function postflight(string $type, InstallerAdapter $adapter): void
 	{
+		// Be honest about success. Joomla's package installer only LOGS a failed child
+		// sub-install but still runs this postflight, so don't show the license /
+		// next-steps message if a bundled extension is actually missing. Fails open
+		// (see missingChildExtensions) so a query/IO glitch never fakes a failure.
+		$missing = $this->missingChildExtensions($adapter);
+
+		if (!empty($missing))
+		{
+			Factory::getApplication()->enqueueMessage(
+				'<h4>MokoSuiteField did not install correctly.</h4>'
+				. '<p>The following bundled extensions are missing: '
+				. htmlspecialchars(implode(', ', $missing), ENT_QUOTES) . '</p>'
+				. '<p>Please uninstall MokoSuiteField and reinstall the full package.</p>',
+				'error'
+			);
+
+			return;
+		}
+
 		$this->warnMissingLicenseKey();
 	}
 
+	/**
+	 * Verify every child extension declared in the package manifest actually landed in
+	 * #__extensions. Returns readable labels of any that are missing.
+	 *
+	 * Matching per Joomla's #__extensions uniqueness: type = <file> "type"; element =
+	 * <file> "id" (for plugins, strip a leading plg_<group>_); plugins also match
+	 * folder = <file> "group".
+	 *
+	 * FAILS OPEN: any error returns [] so a transient glitch never fakes a failure.
+	 */
+	private function missingChildExtensions($adapter): array
+	{
+		try
+		{
+			$manifest = $adapter->getParent()->getManifest();
+
+			if (!$manifest || !isset($manifest->files) || !isset($manifest->files->file))
+			{
+				return [];
+			}
+
+			$db      = Factory::getDbo();
+			$missing = [];
+
+			foreach ($manifest->files->file as $file)
+			{
+				$attrs  = $file->attributes();
+				$id     = isset($attrs['id']) ? (string) $attrs['id'] : '';
+				$exType = isset($attrs['type']) ? (string) $attrs['type'] : '';
+
+				if ($id === '' || $exType === '')
+				{
+					continue;
+				}
+
+				$group   = isset($attrs['group']) ? (string) $attrs['group'] : '';
+				$element = $id;
+
+				// Plugin element in #__extensions is the id minus any leading plg_<group>_.
+				if ($exType === 'plugin' && $group !== '')
+				{
+					$prefix = 'plg_' . $group . '_';
+
+					if (strpos($element, $prefix) === 0)
+					{
+						$element = substr($element, \strlen($prefix));
+					}
+				}
+
+				$query = $db->getQuery(true)
+					->select('COUNT(*)')
+					->from($db->quoteName('#__extensions'))
+					->where($db->quoteName('element') . ' = ' . $db->quote($element))
+					->where($db->quoteName('type') . ' = ' . $db->quote($exType));
+
+				if ($exType === 'plugin' && $group !== '')
+				{
+					$query->where($db->quoteName('folder') . ' = ' . $db->quote($group));
+				}
+
+				if ((int) $db->setQuery($query)->loadResult() === 0)
+				{
+					$label     = trim((string) $file);
+					$missing[] = $label !== '' ? preg_replace('/\.zip$/i', '', $label) : $id;
+				}
+			}
+
+			return $missing;
+		}
+		catch (\Throwable $e)
+		{
+			// Fail open — never fake a failure on a glitch.
+			return [];
+		}
+	}
+
 	private function warnMissingLicenseKey(): void
 	{
 		try