As per the docs, "the sharding policy defines if and how Extents (data shards) in the Azure Data Explorer cluster should be sealed."
What does it mean for an extent to be "sealed"? Does it mean that once an extent is sealed, it won't be considered for future merge/rebuild operations?
Once an extent is sealed, its data is queryable (meaning, queries will scan data in this extent).
All extents are subject to data-grooming operations like partitioning, merge, rebuild, compaction...
We'll update the documentation to make it clearer. Thanks for your feedback.