Stop pooling the governing Sunday's own Matins content on a weekday

nocturnReadingIds pooled the governing Sunday's own nocturn-readings
id (temporalId) and its month-week-N sibling whenever any temporal
commemoration survived on a 3-nocturn day, with no weekday check --
so a Duplex+ saint winning outright on a plain weekday that also
carried a temporal commemoration pulled in a whole second homily's
worth of unrelated Sunday content. Live-verified against the
reference engine (Tridentine 1906, St. Joseph of Cupertino's day):
real Nocturn III there is just the winning saint's own Common homily
plus a single "Commemoratio Feriae" lesson -- no Sunday content at
all. Gates temporalKept to day.weekday === 'sunday'.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AGjUyhUZJaSjiniEmnLdak

TODO.md

@@ -5282,3 +5282,25 @@ on every split lesson, and does so consistently across the *entire* nocturn-read
 just Ember days — flagged for the user as a real presentational rough edge, not fixed yet pending
 their call on scope (a corpus-wide UI/authoring change, not a narrow one-file fix).
 
+**Third follow-on, same session**: user then asked why a Sunday's own patristic homily was
+showing up on a Friday at all. Pulled the live reference engine's own Matins page for St. Joseph
+of Cupertino's day (Tridentine 1906) to check, rather than reasoning from vu's data alone: real
+Nocturn III there is exactly 3 lessons — 2 from the winning Duplex saint's own Common homily, plus
+a single "**Commemoratio Feriæ**" lesson for the displaced Ember day. No Sunday content
+whatsoever. `hours/matins.ts`'s `nocturnReadingIds` had a `temporalKept` block that pooled the
+governing Sunday's own id (`temporalId`) *and* its `month-week-N` sibling whenever any temporal
+commemoration survived on a 3-nocturn day, with no weekday check at all — so a Duplex+ saint
+winning outright on a plain weekday (not a Sunday) that also happened to carry a temporal
+commemoration pulled in a whole second homily's worth of unrelated content (here: St. Ambrose's
+homily + its own Gospel from `post-pentecost-16`, and St. Leo's September-fast sermon from
+`month-week-093` — two different reference-engine representations of the *same* underlying
+Sunday, both wrongly pooled at once). Fixed by gating `temporalKept` to `day.weekday === 'sunday'`
+— the governing Sunday's own content only belongs in the pool when that Sunday is the day actually
+being celebrated. Live-verified by reloading `/vu/2026-09-18/matins`: both spurious readings are
+gone. `npm test` (2025 passed) and `tsc --noEmit` both pass.
+
+Still open, by the user's own explicit request to land this first: Ember Friday's own homily
+still surfaces as all 3 of its lessons even when merely commemorated, where the live engine caps
+a commemorated feria at exactly one lesson (its own Lectio 1 only) — same shape of fix as this
+one, not yet done.
+

src/hours/matins.ts

@@ -654,20 +654,37 @@ function nocturnReadingIds(day: LiturgicalDay, temporalId: string, date: string,
   }
   // The plain temporalId/month-week content is the *governing Sunday's own*
   // Nocturn 2/3 patristic material, real content for that Sunday itself —
-  // only pooled on a real 3-nocturn day, and (as before) only when the
-  // day's own occurrence decision (calendar/commemorations.ts's
-  // decideOccurrence) actually retained the temporal identity in some form:
-  // the temporal cycle won outright (day.winner.kind === 'temporal' -- a
-  // plain Sunday, or a named temporal override like Christ the King), or it
-  // survives as a commemoration alongside a sanctoral winner. Excluded:
-  // decideOccurrence's `ordinary-feria` branch, where a real feast --
-  // however low-ranked -- wins with zero commemorations, correctly
-  // suppressing the temporal identity entirely (e.g. St. Bartholomew,
-  // duplex-2-classis, 2026-08-24 -- his own proper reading has no Nocturn
-  // 3 content, and without this gate the leftover 13th-Sunday-after-
-  // Pentecost/month-week content wrongly filled Nocturn 3 instead).
+  // only pooled on a real 3-nocturn day, only on the Sunday itself (see
+  // below), and (as before) only when the day's own occurrence decision
+  // (calendar/commemorations.ts's decideOccurrence) actually retained the
+  // temporal identity in some form: the temporal cycle won outright
+  // (day.winner.kind === 'temporal' -- a plain Sunday, or a named temporal
+  // override like Christ the King), or it survives as a commemoration
+  // alongside a sanctoral winner. Excluded: decideOccurrence's
+  // `ordinary-feria` branch, where a real feast -- however low-ranked --
+  // wins with zero commemorations, correctly suppressing the temporal
+  // identity entirely (e.g. St. Bartholomew, duplex-2-classis, 2026-08-24
+  // -- his own proper reading has no Nocturn 3 content, and without this
+  // gate the leftover 13th-Sunday-after-Pentecost/month-week content
+  // wrongly filled Nocturn 3 instead).
+  //
+  // `day.weekday === 'sunday'` gate added 2026-09-03: live-verified
+  // (Tridentine 1906) that a Duplex+ saint winning outright on a *weekday*
+  // that also happens to carry a temporal commemoration (e.g. St. Joseph
+  // of Cupertino, Duplex, Friday Sept 18) gets no Sunday content at all --
+  // the reference engine's own Nocturn III there is just the saint's own
+  // Common homily (2 lessons) plus a single "Commemoratio Feriæ" lesson
+  // for the displaced feria, never the week's separate governing-Sunday
+  // homily (Ambrose's/Leo's, in that live case). This mechanism previously
+  // fired on *any* 3-nocturn day with a surviving temporal commemoration,
+  // regardless of weekday, wrongly pooling in a whole extra Sunday's worth
+  // of unrelated patristic content on top of the day's own two real
+  // sources. The governing Sunday's own content only belongs in the pool
+  // when that Sunday *is* the day being celebrated.
   const temporalKept =
-    threeNocturns && (day.winner.kind === 'temporal' || day.commemorations.some((c) => c.kind === 'temporal'));
+    threeNocturns &&
+    day.weekday === 'sunday' &&
+    (day.winner.kind === 'temporal' || day.commemorations.some((c) => c.kind === 'temporal'));
   if (temporalKept) {
     ids.add(temporalId);
     const monthWeek = monthWeekId(date);