Currently, compaction.setupInputs() and its helpers (compaction.grow, compaction.expandInputs) does not consider FileMetadata.Compacting. That is, we set up the inputs for a compaction, and expand them with various heuristics, completing ignoring concurrent compactions. There is a final step where we check for a conflict via inputAlreadyCompacting(). But this seems wasteful. We might have been able to pick a compaction if we had respected FileMetadata.Compacting rather than blindly expanding the compaction inputs.