Function scanCandidatesForHighlight

scanCandidatesForHighlight(
    runDir: string,
    candidates: readonly string[],
    articleType: string,
    date: string,
): { headline: string; summary: string }
Walk a list of candidate artefact paths and return the first non-generic headline + summary pair, plus the first usable lede summary seen along the way.
Parameters
- runDir: string
  Absolute run directory path
- candidates: readonly string[]
  Run-relative candidate filenames to probe
- articleType: string
  Article-type slug (used by isGenericHeading)
- date: string
  ISO run date (used by isGenericHeading)
Returns { headline: string; summary: string }
{headline, summary} where either field may be empty
- Defined in aggregator/metadata/artifact-walker.ts:198