Returns the aggregate verdict across every chain that has a recorded run, plus
the per-chain verdicts it is computed from.

One read serves both. Splitting the headline from its breakdown would put
them on two clocks, so a console could render "all chains sound" beside a row
saying otherwise with no way to tell which was stale.

Coverage is aggregated, never dropped. retentionTruncated is true when ANY
contributing chain's prefix was lawfully aged out under a valid SIGNED
watermark, and coverageFrom is the earliest instant from which EVERY
contributing chain is covered — the latest of the per-chain watermarks. Without
them a platform whose coverage had been truncated would read as plainly intact,
which is the false assurance this feature exists to remove.

Coverage is a MEASURE, and there is deliberately no completeness flag.
scopesTotal is how many chains this verdict speaks for, chainsKnown is how
many exist as counted over the last two enumeration traversals, and
chainsKnownAt is when that count was taken — read them together ("37 of 41,
measured 6 hours ago"). They are different populations measured at different
times: scopesTotal counts every chain with any recorded run and grows
continuously, so scopesTotal >= chainsKnown is satisfied by growth as readily
as by coverage and is NOT a completeness proof. A flag derived from that
comparison shipped once and failed open; it is gone rather than re-tuned.
chainsKnown is ABSENT — never 0 — when no trustworthy count is available:
nothing has enumerated the estate, the enumeration spans more passes than the
probe reads, or the run history this read reduced over no longer reaches back
across it. Absent means "no coverage claim is available".

everVerified: false is a first-class state and is NOT a pass. It is also the
only way a silently disabled scheduled job becomes visible.