calendar: give Advent's ordinary ferias their own precedence tier

Found while starting the December sanctoral pull: Advent's plain
(non-Ember) weekday ferias have real standing in the live Monastic 1617
engine that the existing ordinary-feria category couldn't represent --
a Simplex saint (St. Bibiana, Dec 2) is merely commemorated there rather
than winning outright, while a Semiduplex+ saint (St. Nicholas, Dec 6)
wins with the feria itself commemorated back. Adds a third, weaker
privileged-feria-minor tier (Semiduplex+ threshold, vs. privileged-
feria's Duplex+) rather than reusing either existing tier, mirroring how
privileged-feria/privileged-feria-major were split in March. Lent's own
ordinary ferias likely share this property but are left as-is, unverified
this session.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/calendar/commemorations.ts

@@ -84,6 +84,18 @@ export function decideOccurrence(
       // feast, however low-ranked, is kept in its place.
       return { winner: sanctoralWinner(sanctoral), commemorations: [] };
 
+    case 'privileged-feria-minor':
+      // Advent's own ordinary ferias (verified: St. Bibiana, Simplex,
+      // merely commemorated under an Advent feria; St. Nicholas,
+      // Semiduplex, wins outright with the feria commemorated in return).
+      // Weaker than `privileged-feria`'s Duplex+ threshold — Semiduplex is
+      // already enough here — and unlike every other feria tier, nothing
+      // ever transfers: whichever side loses still gets a commemoration.
+      if (isAtLeast(sanctoral.rank, 'semiduplex')) {
+        return { winner: sanctoralWinner(sanctoral), commemorations: [{ kind: 'temporal', id: temporalId }] };
+      }
+      return { winner: temporalWinner, commemorations: [sanctoralCommemoration(sanctoral)] };
+
     case 'privileged-feria':
       // The lesser of the two privileged-feria tiers (Ember days outside
       // Holy Week/the Easter Octave, etc.) — behaves exactly like an

src/calendar/types.ts

@@ -82,8 +82,19 @@ export type FeastClass =
 // categories.yml for exactly which days fall in which tier — some of that
 // split (e.g. whether Pentecost's own Ember days share Lent's lesser tier
 // or Easter's major one) is still a reconstructed guess, not verified.
+// `privileged-feria-minor` is a third, weaker tier, added during the
+// December sanctoral pull after finding Advent's own ordinary (non-Ember)
+// ferias have real standing of their own in the live engine — a Simplex
+// saint (e.g. St. Bibiana, Dec 2) is merely commemorated there, while a
+// Semiduplex+ saint (e.g. St. Nicholas, Dec 6) wins outright with the
+// feria itself commemorated in return — neither of which the original
+// `ordinary-feria` fallback (any saint wins, nothing ever commemorated)
+// could represent. Lent's own ordinary ferias are documented as sharing
+// this same real-world property but are NOT switched to this tier yet —
+// unverified this session, left as `ordinary-feria` pending a future check.
 export type TemporalCategory =
   | 'ordinary-feria'
+  | 'privileged-feria-minor'
   | 'privileged-feria'
   | 'privileged-feria-major'
   | 'ordinary-sunday'

src/calendar/vespers.ts

@@ -44,6 +44,7 @@ function hasFirstVespers(day: LiturgicalDay): boolean {
 function keepsOwnSecondVespers(day: LiturgicalDay): boolean {
   if (
     day.weekday === 'sunday' ||
+    day.temporalCategory === 'privileged-feria-minor' ||
     day.temporalCategory === 'privileged-feria' ||
     day.temporalCategory === 'privileged-feria-major' ||
     isMajorFixedFeastOfTheLord(day.date)

src/data/calendar/temporal-categories.yml

@@ -34,7 +34,11 @@
 # Lent's and Pentecost's Ember days *are* modeled, since those are clean
 # Easter offsets.
 bySeason:
-  advent: { sunday: privileged-sunday, feria: ordinary-feria }
+  # Advent's ordinary ferias verified `privileged-feria-minor` during the
+  # December sanctoral pull (see calendar/types.ts's TemporalCategory doc
+  # comment) -- weaker than the Ember-day `privileged-feria` tier, but real
+  # standing nonetheless, unlike a plain `ordinary-feria`.
+  advent: { sunday: privileged-sunday, feria: privileged-feria-minor }
   # Christmastide's ferias are folded into the privileged-feria default for
   # the whole season as a simplification of "the Octave of Christmas (Dec
   # 25 - Jan 1) is privileged" — slightly overbroad into Jan 2-5, harmless.