Track a transferred saint's origin date on DayWinner and Commemoration

Adds transferredFrom to both DayWinner's sanctoral variant and
Commemoration's sanctoral variant, set in calendar/index.ts's
applyIncomingTransfer whenever a transferred-in candidate actually lands
(wins outright) or ends up merely commemorated (lost a collision, or fell
below the landing day's own threshold) — previously this signal was
discarded after resolveDay used it once to decide the winner, so nothing
downstream could tell a transferred feast apart from a native one.

Also adds transferredAway to LiturgicalDay, set from a date's own native
occurrence when its candidate couldn't be kept there at all, so a UI can
note "this office moved elsewhere" without asserting a specific landing
date (which a later, unmodeled multi-hop chain — e.g. into Holy Week —
could get wrong).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013g7AsSvMD9oazR17f3BxLz

src/calendar/index.ts

@@ -56,6 +56,7 @@ function applyIncomingTransfer(
   temporalCategory: TemporalCategory,
   winner: DayWinner,
   commemorations: Commemoration[],
+  fromDate: string,
 ): DayWinner {
   if (temporalCategory === 'privileged-feria-major') {
     // Deferred: a transfer landing on one of these (the concrete case is
@@ -67,6 +68,18 @@ function applyIncomingTransfer(
     // ordinary-sunday landing.
     return winner;
   }
+  // Tags the returned winner with where it transferred from, but only when
+  // the candidate actually ended up winning here — a collision loss (the
+  // candidate merely commemorated, incumbent keeps the day) isn't a landing.
+  const tagIfLanded = (result: DayWinner): DayWinner =>
+    result.kind === 'sanctoral' && result.id === candidate.id ? { ...result, transferredFrom: fromDate } : result;
+  // Same tagging, but for the candidate's own *commemoration* — it still
+  // needs marking as arrived-via-transfer even when it lost the landing
+  // day outright (a collision loss, or falling below the landing day's own
+  // threshold in decideOccurrence) rather than merely being naturally due
+  // for commemoration here.
+  const tagCommemorations = (result: Commemoration[]): Commemoration[] =>
+    result.map((c) => (c.kind === 'sanctoral' && c.id === candidate.id ? { ...c, transferredFrom: fromDate } : c));
   if (winner.kind === 'temporal') {
     // Found via real data: a transferred-in Simplex saint was blindly
     // winning outright even when it landed on a privileged Sunday (Trinity
@@ -74,15 +87,15 @@ function applyIncomingTransfer(
     // the *same* precedence rules a native occurrence would have used,
     // not just take over because nothing else was assigned here.
     const decided = decideOccurrence(temporalCategory, winner.id, candidate);
-    commemorations.push(...decided.commemorations);
+    commemorations.push(...tagCommemorations(decided.commemorations));
     // If the candidate fails here too (decided.transfer set), that's a
     // transfer chain — not modeled, same "not delivered rather than
     // guessed at" stance as the privileged-feria-major case above.
-    return decided.winner;
+    return tagIfLanded(decided.winner);
   }
   const collision = resolveCollision(candidate, winner);
-  commemorations.push(...collision.commemorations);
+  commemorations.push(...tagCommemorations(collision.commemorations));
-  return collision.winner;
+  return tagIfLanded(collision.winner);
 }
 
 /**
@@ -99,13 +112,15 @@ export function resolveDay(isoDate: string): LiturgicalDay {
   let winner = result.winner;
   const commemorations = [...result.commemorations];
 
-  const yesterday = resolveNativeOccurrence(addDays(isoDate, -1));
+  const yesterdayIso = addDays(isoDate, -1);
+  const yesterday = resolveNativeOccurrence(yesterdayIso);
   if (yesterday.result.transfer?.direction === 'forward') {
-    winner = applyIncomingTransfer(yesterday.result.transfer.candidate, temporalCategory, winner, commemorations);
+    winner = applyIncomingTransfer(yesterday.result.transfer.candidate, temporalCategory, winner, commemorations, yesterdayIso);
   }
-  const tomorrow = resolveNativeOccurrence(addDays(isoDate, 1));
+  const tomorrowIso = addDays(isoDate, 1);
+  const tomorrow = resolveNativeOccurrence(tomorrowIso);
   if (tomorrow.result.transfer?.direction === 'backward') {
-    winner = applyIncomingTransfer(tomorrow.result.transfer.candidate, temporalCategory, winner, commemorations);
+    winner = applyIncomingTransfer(tomorrow.result.transfer.candidate, temporalCategory, winner, commemorations, tomorrowIso);
   }
 
   winner = applyOctaves(isoDate, winner, commemorations);
@@ -116,7 +131,13 @@ export function resolveDay(isoDate: string): LiturgicalDay {
   applyEpiphany6Commemoration(isoDate, commemorations);
   applyAdventFourVigilCommemoration(isoDate, weekday, commemorations);
 
-  return { date: isoDate, weekday, season, temporalCategory, winner, commemorations };
+  // This date's own native candidate (if any) couldn't be kept here and
+  // moved on instead — see calendar/types.ts's `transferredAway` doc
+  // comment for why this is tracked separately from `Commemoration`, and
+  // why no landing date is recorded.
+  const transferredAway = result.transfer ? { candidate: result.transfer.candidate } : undefined;
+
+  return { date: isoDate, weekday, season, temporalCategory, winner, commemorations, transferredAway };
 }
 
 /**

src/calendar/types.ts

@@ -161,6 +161,12 @@ export type DayWinner =
       // First Vespers is being anticipated this evening (i.e. this feast
       // belongs to *tomorrow*, but is winning tonight's Vespers/Compline).
       vespersFrom?: 'firstVespersOfTomorrow';
+      // Set by calendar/index.ts's resolveDay/applyIncomingTransfer when
+      // this winner is only here because its own native date (an adjacent
+      // ISO date) couldn't hold it (calendar/commemorations.ts's
+      // `decideOccurrence` `transfer` signal) — the ISO date it transferred
+      // *from*. Absent for a feast winning on its own native date.
+      transferredFrom?: string;
     } & SanctoralIdentity);
 
 /**
@@ -184,6 +190,14 @@ export type Commemoration =
       // commemoration (a real collision, an octave day, etc.), which
       // carries no such qualifier.
       vespersNote?: 'today' | 'tomorrow';
+      // Set by calendar/index.ts's applyIncomingTransfer, same meaning as
+      // `DayWinner`'s own `transferredFrom` — this saint is only
+      // commemorated here (rather than absent) because a transfer landed
+      // on this date and lost a collision, or fell below the landing
+      // day's own outright-winning threshold, not because it's natively
+      // due for commemoration here. Absent for an ordinary same-day
+      // commemoration.
+      transferredFrom?: string;
     } & SanctoralIdentity)
   | { kind: 'octave'; id: string; name: string; nameLa?: string };
 
@@ -199,4 +213,16 @@ export interface LiturgicalDay {
   winner: DayWinner;
   /** Everything else commemorated alongside the winner — see the doc comment on Commemoration. */
   commemorations: Commemoration[];
+  /** Set when this date's own native sanctoral candidate couldn't be kept
+   * here at all (calendar/commemorations.ts's `decideOccurrence` `transfer`
+   * signal) and moved to a later/earlier date instead. No landing date is
+   * recorded here — `resolveDay` only ever checks the immediate adjacent
+   * date, but a real landing can chain further than that (an unmodeled
+   * case noted in `applyIncomingTransfer`, e.g. a transfer running into
+   * Holy Week), so naming a specific "to" date risked asserting a wrong
+   * one; this exists purely so the display can say "not an omission, this
+   * office moved elsewhere" without claiming to know where. Distinct from
+   * — and not implied by — `Commemoration`, since a transferred-away
+   * candidate gets no commemoration on its own native date at all. */
+  transferredAway?: { candidate: SanctoralIdentity };
 }

tests/calendar/april-sanctoral.test.ts

@@ -45,7 +45,14 @@ describe('April sanctoral pull (first pass)', () => {
     ]);
 
     const monday = resolveDay('2029-04-30');
-    expect(monday.winner).toEqual({ kind: 'sanctoral', id: 'st-robert', name: 'St. Robert, Abbot', nameLa: 'Sanctus Robertus, Abbas', rank: 'duplex' });
+    expect(monday.winner).toEqual({
+      kind: 'sanctoral',
+      id: 'st-robert',
+      name: 'St. Robert, Abbot',
+      nameLa: 'Sanctus Robertus, Abbas',
+      rank: 'duplex',
+      transferredFrom: '2029-04-29',
+    });
     expect(monday.commemorations).toEqual([
       { kind: 'sanctoral', id: 'st-peter-martyr', name: 'St. Peter Martyr, Martyr', nameLa: 'Sanctus Petrus Martyr, Martyr', rank: 'semiduplex' },
     ]);

tests/calendar/november-sanctoral.test.ts

@@ -85,6 +85,7 @@ describe('November sanctoral pull (first pass)', () => {
       name: 'St. Clement I, Pope and Martyr',
       nameLa: 'Sanctus Clemens I, Papa et Martyr',
       rank: 'semiduplex',
+      transferredFrom: '2025-11-23',
     });
     expect(followingDay.commemorations).toEqual([
       { kind: 'sanctoral', id: 'st-chrysogonus', name: 'St. Chrysogonus, Martyr', nameLa: 'Sanctus Chrysogonus, Martyr', rank: 'simplex' },

tests/calendar/september-sanctoral.test.ts

@@ -28,6 +28,7 @@ describe('September sanctoral pull (first pass)', () => {
       name: 'St. Raymond Nonnatus, Confessor',
       nameLa: 'Sanctus Raymundus Nonnatus, Confessor',
       rank: 'semiduplex',
+      transferredFrom: '2025-08-31',
     });
     expect(day.commemorations).toEqual([
       { kind: 'sanctoral', id: 'ss-twelve-brothers', name: 'Ss. Twelve Brothers, Martyrs', nameLa: 'Duodecim Fratres, Martyres', rank: 'simplex' },

tests/calendar/transfer.test.ts

@@ -28,7 +28,14 @@ describe('transfer mechanism (resolveDay integration)', () => {
       rank: 'semiduplex',
     });
     expect(saturday.commemorations).toEqual([
-      { kind: 'sanctoral', id: 'vigil-of-st-lawrence', name: 'Vigil of St. Lawrence', nameLa: 'Vigilia Sancti Laurentii', rank: 'vigil' },
+      {
+        kind: 'sanctoral',
+        id: 'vigil-of-st-lawrence',
+        name: 'Vigil of St. Lawrence',
+        nameLa: 'Vigilia Sancti Laurentii',
+        rank: 'vigil',
+        transferredFrom: '2026-08-09',
+      },
     ]);
 
     // The Sunday's own winner is unaffected by the vigil, but St. Romanus