Produce a coverage & quality profile of a Narrative dataset (or access
rule): row count, per-column null/fill rate, cardinality, ranges,
top-values, inferred column shape, and quality flags. Reads bundled
stats + sample first, recovers missing/stale stats by configuring and
recalculating them, and escalates to a cheap `/write-nql` query only
for a measure no stat can provide. Descriptive, not prescriptive.
Use when: "profile dataset N", "what does dataset N look like",
"coverage and quality of <dataset>", "what id types does N emit",
"null rates / cardinality for <dataset>", "is this dataset's stats
fresh".
(narrative-common)
