docs(bigquery): document location resolution fallback in ArrowQueryPageFetcher

Author: jinseopkim0

java-bigquery/google-cloud-bigquery/src/main/java/com/google/cloud/bigquery/BigQueryImpl.java

@@ -359,6 +359,13 @@ public Page<FieldValueList> getNextPage() {
       List<FieldValueList> rowBatch = new ArrayList<>((int) Math.min(pageSize, 10000L));
 
       try {
+        // Resolve job location in order: JobId location -> BigQueryOptions location -> "global"
+        // default.
+        // The Storage Read API stream resource name requires a location component (e.g.
+        // projects/{project}/locations/{location}/jobs/{job}/streams/_default). If no specific
+        // location
+        // was provided on the job or service options, defaulting to "global" allows queries created
+        // without an explicit location to still stream results without failing.
         String location = jobId.getLocation();
         if (location == null) {
           location = serviceOptions.getLocation();