some renaming of variables

docs/s18-validation.md

@@ -17,7 +17,7 @@ Validated on 2026-11-03 against the confirmed S18 specification.
 Focused solver tests cover showcase bookends (including extra showcases), single
 and absent showcases, changing gaps, coach exemptions, infeasibility, the strict
 priority of showcase attendance over balance, and style/age scores. Lifecycle
-and HTTP tests cover skipped empty groups, first-show-date ages, retained x after
+and HTTP tests cover skipped empty groups, first-show-date ages, retained preferredDayParts after
 daypart removal, atomic structural validation, invalid drafts, final status
 invalidation, stale solver results, timeout preservation, coach identity links,
 and ordered JSON round trips including version-2 migration.
@@ -36,7 +36,7 @@ assessed against `CODING_STANDARDS.md` and `docs/backend-review.md`:
 - `ScheduleRules` has cyclomatic signals for independent configuration checks
   and showcase cases. Each rule family is isolated in a short method and shared
   between finalization and solver-result validation.
-- `ShowSchedules` retains branching for nullable initial settings, retained x,
+- `ShowSchedules` retains branching for nullable initial settings, retained preferredDayParts,
   and structural draft validation. It stages complete replacement lists before
   mutation and uses the existing aggregate lock. It separates schedule lifecycle
   from the already broad `SchoolManagementService` aggregate owner.