Derive the "subfolder path" relative to analysis/daily/<date>/ for a given brief filepath. Returns null when the brief is not inside the canonical analysis/daily/<YYYY-MM-DD>/<subfolder...>/executive-brief.md layout.
analysis/daily/<date>/
null
analysis/daily/<YYYY-MM-DD>/<subfolder...>/executive-brief.md
Example: analysis/daily/2026-05-08/election-cycle/current/executive-brief.md → election-cycle/current.
analysis/daily/2026-05-08/election-cycle/current/executive-brief.md
election-cycle/current
Derive the "subfolder path" relative to
analysis/daily/<date>/for a given brief filepath. Returnsnullwhen the brief is not inside the canonicalanalysis/daily/<YYYY-MM-DD>/<subfolder...>/executive-brief.mdlayout.Example:
analysis/daily/2026-05-08/election-cycle/current/executive-brief.md→election-cycle/current.