Add the O Antiphons (Dec 17-23) as an unconditional Vespers Magnificat override

advent-4's own remaining Magnificat-antiphon gap turned out to be a
mechanism problem, not missing content: Dec 17-23 always carries one of
the seven "O Antiphons" at Vespers, keyed to the calendar date itself,
not to whichever Advent week (advent-3 or advent-4, varies by year)
happens to govern that date -- a single per-week file was structurally
the wrong shape.

Added vespers-o-antiphons.yml (MM-DD keyed) and a new lookup tier in
getMagnificatAntiphon, checked unconditionally ahead of both the
per-week temporal file and a real sanctoral winner's own antiphon --
direct instruction: the O Antiphon wins this one text slot on these
seven dates regardless of who otherwise wins the day (e.g. St. Thomas,
Dec 21, still keeps every other part of his own office). Two of the
seven (O Clavis David/O Oriens, Dec 20-21) couldn't be live-verified --
every reference-engine track routes those two dates through St.
Thomas's Vigil/feast instead, which this app's own vigil-of-st-thomas.yml
already documents diverging from -- so they're marked draft rather than
verified.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ME8QNPdEmHSbSx1r6VmDRG

src/hours/resolve-common.ts

@@ -9,6 +9,7 @@ import { isInTriduum } from '../calendar/temporal';
 import { splitAntiphon, isDoubleOrHigher } from './antiphon';
 import { getLaudsSaintOverride } from './lauds-psalmody-overrides';
 import vespersMagnificatAntiphonsData from '../data/hours/vespers-magnificat-antiphons.yml';
+import vespersOAntiphonsData from '../data/hours/vespers-o-antiphons.yml';
 
 type BilingualText = Partial<Record<string, string>>;
 type TranslationStatus = 'verified' | 'draft' | 'missing';
@@ -21,6 +22,10 @@ interface MagnificatWeekdayDefault {
 const vespersMagnificatAntiphons = vespersMagnificatAntiphonsData as Partial<
   Record<Weekday, MagnificatWeekdayDefault>
 >;
+// Keyed by "MM-DD" (Dec 17-23) — see the data file's own header for why
+// these seven can't live in a per-Advent-week temporal-proper file the
+// way every other week's Magnificat antiphon does.
+const vespersOAntiphons = vespersOAntiphonsData as Partial<Record<string, MagnificatWeekdayDefault>>;
 
 function toResolvedText(proper: ProperText): ResolvedText {
   return { text: proper.text, status: proper.status, citation: proper.citation };
@@ -817,15 +822,43 @@ export function getBenedictusAntiphon(day: LiturgicalDay): ResolvedText {
  * order exactly (temporal id, then a saint's own `${propers}-magnificat-
  * antiphon`, then their Common category's `magnificat-antiphon-${common}`
  * — none of that content authored yet, a separate future pass the same
- * shape as the Benedictus one was), but with one real difference: a bare
+ * shape as the Benedictus one was), but with two real differences: a bare
  * ferial weekday (Mon-Sat) has actual content to fall back to —
  * data/hours/vespers-magnificat-antiphons.yml's classic "quote the
  * Magnificat's own text in sequence" set — which Benedictus has no
- * equivalent of. `withPaschaltideAlleluia` applied to that fallback too,
- * by analogy with the Common-category treatment above; not independently
+ * equivalent of; and the O Antiphons below, checked before either the
+ * temporal or sanctoral branch even runs.
+ *
+ * `withPaschaltideAlleluia` applied to the weekday fallback too, by
+ * analogy with the Common-category treatment above; not independently
  * confirmed for this specific case.
+ *
+ * The O Antiphons (Dec 17-23) are checked first, unconditionally —
+ * ahead of *both* the per-week `${winner.id}-magnificat-antiphon` file
+ * and a real sanctoral winner's own antiphon, deliberately: this is the
+ * app's own design choice (2026-08-30 user instruction), not a
+ * reconstruction of any single historical rite's rubric — the reference
+ * engine itself doesn't do this uniformly (its own Dec 20/21 live query
+ * shows St. Thomas's own antiphon instead, see vespers-o-antiphons.yml's
+ * header), but this app deliberately gives the O Antiphon absolute
+ * priority for this one specific text slot on these seven dates,
+ * regardless of who otherwise wins the day. Every other part of the
+ * office (chapter/responsory/hymn/versicle/collect, Lauds' own Benedictus
+ * antiphon) is untouched by this — a saint who wins Dec 17-23 (St.
+ * Thomas, Dec 21) still gets everything else that comes with winning,
+ * just not this one slot. This also means a saint's own real Magnificat
+ * antiphon, once authored, is permanently unreachable on one of these
+ * seven dates under *this* calendar's own construction — deliberately
+ * accepted, since a saint's real antiphon is still worth having on file
+ * for a differently-constructed calendar (e.g. a future user-editable
+ * one) even where the shipped calendar's own precedence never surfaces
+ * it here.
  */
 export function getMagnificatAntiphon(day: LiturgicalDay): ResolvedText {
+  const oAntiphon = vespersOAntiphons[day.date.slice(5)];
+  if (oAntiphon) {
+    return oAntiphon.status ? { text: oAntiphon.antiphon, status: oAntiphon.status } : verifiedText(oAntiphon.antiphon);
+  }
   const winner = resolveOfficeWinner(day);
   if (winner.kind === 'temporal') {
     const named = toResolvedText(getTemporalProper(`${winner.id}-magnificat-antiphon`));