full-junit-result is required parameter to have smart sharding. Flank/flank#902 is reported on flank side. And according to flank source code

https://github.com/Flank/flank/blob/master/test_runner/src/main/kotlin/ftl/reports/util/ReportManager.kt#L133
will call
https://github.com/Flank/flank/blob/master/test_runner/src/main/kotlin/ftl/gc/GcStorage.kt#L62
for uplading the file. Without full-junit-result or legacy-junit-result, I failed to configure smart sharding. New logic and keyword is introduced in Flank/flank#798.