Its not supported, however, we have aggregated ports from multiple switches/ports (physical switch stack) and it seems to work (in production enviornment), we have been using this configuration for almost a year without issue. The switchs (stacked) will use spanning tree to block one of the aggregated ports. We have tested by unplugging one of the aggregate ports from the switch side, traffic flows across the 2nd aggregated switch port almost instantaneously. I'm not suggested you try it but just replying with my experience.
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