Label Matins nocturns and the Invitatory in the rendered ordo

Adds a section-heading ResolvedPart kind and emits "Invitatory" and
"Nocturn I/II/III" headings in matins.ts, so the hour's structural
boundaries are visible instead of rendering as one undifferentiated
stream of parts. Ferial (1-nocturn) days get no Nocturn heading, matching
their existing single-unnumbered-nocturn design.

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

src/hours/matins.ts

@@ -105,6 +105,8 @@ interface MatinsSundayAntiphons {
 }
 const sundayAntiphons = matinsSundayAntiphonsData as unknown as MatinsSundayAntiphons;
 
+const NOCTURN_NUMERAL = ['I', 'II', 'III'] as const;
+
 type PsalmPart = Extract<ResolvedPart, { kind: 'psalm' }>;
 
 function plainPsalm(number: number): PsalmPart {
@@ -302,15 +304,19 @@ export function resolveOrdo(date: string): ResolvedOrdo {
   const parts: ResolvedPart[] = [
     { kind: 'versicle', text: resolveCommon(getOpeningVersicleId(day.season, day.winner)) },
     plainPsalm(3),
+    { kind: 'section-heading', label: 'Invitatory' },
     ...invitatoryParts(day),
     { kind: 'hymn', text: resolveCommon('matins-hymn-ferial') },
   ];
 
   if (threeNocturns && day.weekday === 'sunday') {
+    parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[0]}` });
     parts.push(...sundayPsalmNocturn(sundayAntiphons.nocturn1, day));
     parts.push(...(nocturn1Readings ?? []));
+    parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[1]}` });
     parts.push(...sundayPsalmNocturn(sundayAntiphons.nocturn2, day));
     parts.push(...(nocturn2Readings ?? []));
+    parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[2]}` });
     parts.push(...sundayCanticleNocturn(sundayAntiphons.nocturn3, day));
     parts.push(...(nocturn3Readings ?? []));
     parts.push({ kind: 'te-deum', text: resolveCommon('te-deum') });
@@ -324,18 +330,24 @@ export function resolveOrdo(date: string): ResolvedOrdo {
     // three-tier picture).
     const override = winner.kind === 'sanctoral' ? getMatinsPsalmodyOverride(winner.id) : undefined;
     if (override) {
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[0]}` });
       parts.push(...sundayPsalmNocturn(override.nocturn1, day));
       parts.push(...(nocturn1Readings ?? []));
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[1]}` });
       parts.push(...sundayPsalmNocturn(override.nocturn2, day));
       parts.push(...(nocturn2Readings ?? []));
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[2]}` });
       parts.push(...sundayCanticleNocturn(override.nocturn3, day));
       parts.push(...(nocturn3Readings ?? []));
     } else {
       const [n1, n2, n3] = ferialPsalmodyThreeNocturns(day);
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[0]}` });
       parts.push(...n1);
       parts.push(...(nocturn1Readings ?? []));
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[1]}` });
       parts.push(...n2);
       parts.push(...(nocturn2Readings ?? []));
+      parts.push({ kind: 'section-heading', label: `Nocturn ${NOCTURN_NUMERAL[2]}` });
       parts.push(...n3);
       parts.push(...(nocturn3Readings ?? []));
     }

src/hours/types.ts

@@ -210,6 +210,11 @@ export type ResolvedPart =
   // have a single unnumbered nocturn and don't use this wrapper at all —
   // see hours/matins.ts). `nocturn` is 1-3.
   | { kind: 'nocturn-psalmody'; nocturn: number; psalms: ResolvedPart[] }
+  // A standalone structural heading with no content of its own — marks the
+  // start of a larger named section that doesn't correspond to one specific
+  // part kind (Matins' "Invitatory", "Nocturn I/II/III"). Distinct from the
+  // per-part `<h3 class="ordo-part-label">` every other kind already uses.
+  | { kind: 'section-heading'; label: string }
   // Matins only. Sung after the last lesson on a 3-nocturn day (Sunday or
   // a Duplex+ sanctoral winner) — see hours/matins.ts. Never present on a
   // plain ferial (1-nocturn) day.

src/ui/hour-view.ts

@@ -122,6 +122,8 @@ function renderPart(part: ResolvedPart, languages: readonly string[]): string {
           ${part.psalms.map((p) => renderPart(p, languages)).join('')}
         </section>
       `;
+    case 'section-heading':
+      return `<h2 class="section-heading">${escapeHtml(part.label)}</h2>`;
     case 'te-deum':
       return `
         <section class="ordo-part ordo-part-te-deum">

src/ui/styles.css

@@ -275,6 +275,15 @@ button:focus-visible {
   margin: 0 0 var(--space-1);
 }
 
+.section-heading {
+  font-size: 1.2rem;
+  text-transform: uppercase;
+  letter-spacing: 0.06em;
+  color: var(--color-brass);
+  font-family: var(--font-ui);
+  margin: var(--space-4) 0 var(--space-2);
+}
+
 .ordo-part-citation {
   font-family: var(--font-ui);
   font-size: 0.85em;