mara chose to accept extra queued sweep passes over adding a new
hive-jobq primitive (or a hive-c0re one-off) for "don't queue another
of this kind". Every sweep caller now plain-inserts its node; the
capacity-1 Dep::Resource per sweep kind (MatrixSweep/KnowledgeTree)
still keeps two passes of the same kind from running concurrently, it
just no longer collapses a tick that lands while one is live or queued
into the existing one.
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