sqlmc_list_coverage: What a finding may and may not claim

The most important section in this document.

• Every finding carries how many databases were actually read. drift.scanned is the denominator, and no count means anything without it. "Missing from 3" is a mistake at 5 and a half-done rollout at 40.
• A database that could not be read is in failed and absent from the findings. It is not counted as an object missing. "Not there" and "not looked at" are different answers, and this design exists to keep them apart.
• Empty findings means nothing was seen to differ across the databases that were read. It is not a claim that the group is consistent. No partial scan can establish that, and an agent that reports "the estate is consistent" from an empty array has said something the data does not support.

If you are summarizing a scan for a human, carry the denominator into the summary. "No differences across the 12 databases read" is true; "no differences" is not.