fix: correct tenant key reference and update health check logic for empty collections

Author: lohanidamodar

src/Usage/Adapter/ClickHouse.php

@@ -1317,7 +1317,7 @@ private function validateMetricsBatch(array $metrics): void
 
             // Validate tenant when provided (metric-level tenant overrides adapter tenant)
             if (array_key_exists('tenant', $metricData)) {
-                $tenantValue = $metricData['$tenant'];
+                $tenantValue = $metricData['tenant'];
 
                 if ($tenantValue !== null) {
                     if (is_int($tenantValue)) {
@@ -1753,6 +1753,7 @@ private function parseQueries(array $queries): array
                     $this->validateAttributeName($attribute);
                     $escapedAttr = $this->escapeIdentifier($attribute);
                     $paramName = 'param_' . $paramCounter++;
+                    $singleValue = null;
                     if ($attribute === 'time') {
                         if (is_array($values)) {
                             /** @var \DateTime|string|null $singleValue */
@@ -1774,6 +1775,7 @@ private function parseQueries(array $queries): array
                     $this->validateAttributeName($attribute);
                     $escapedAttr = $this->escapeIdentifier($attribute);
                     $paramName = 'param_' . $paramCounter++;
+                    $singleValue = null;
                     if ($attribute === 'time') {
                         if (is_array($values)) {
                             /** @var \DateTime|string|null $singleValue */

src/Usage/Adapter/Database.php

@@ -45,11 +45,12 @@ public function healthCheck(): array
 
             // Check if collection exists
             $collectionName = $this->collection ?? 'usage';
-            if (!$this->db->getCollection($collectionName)->isEmpty()) {
+            if ($this->db->getCollection($collectionName)->isEmpty()) {
                 return [
-                    'healthy' => true,
+                    'healthy' => false,
                     'database' => $databaseName,
-                    'collection' => $collectionName
+                    'collection' => $collectionName,
+                    'error' => "Collection '{$collectionName}' is missing or empty in database '{$databaseName}'"
                 ];
             }