calendar/readings: report Sunday as its own display rank, not solemnity

The Ordinary Form's Table of Liturgical Days treats Sunday as its own
category, never a solemnity. temporal.go's sundayDay() already marks these
days distinctly from named solemnities (Class stays unset, unlike solemn()'s
ClassLord); internal/readings/offline.go now reads that existing signal to
relabel the REPORTED rank to "sunday" for ordinary and privileged-season
Sundays alike, leaving Celebration.Rank, ofRankOrder and all precedence
untouched. Named solemnities landing on a Sunday (Easter, Pentecost, ...)
and feasts of the Lord (Holy Family) keep reporting their own rank. The 1962
form is untouched.

Added calendar.RankSunday (display-only, deliberately excluded from
ofRankOrder), the i18n Sunday/niedziela words, and a test pinning the exact
dates from the original bug report.

1 files changed, 47 insertions, 1 deletions

diff --git a/internal/readings/offline.go b/internal/readings/offline.go
index be7c430..b2c16df 100644
--- a/internal/readings/offline.go
+++ b/internal/readings/offline.go
@@ -162,10 +162,56 @@ func dayInfo(cfg config.Config, day calendar.LiturgicalDay) liturgy.DayInfo {
 	return liturgy.DayInfo{
 		Name:   celebrationName(cfg, day.Observed),
 		Colour: string(day.Colour),
-		Rank:   string(day.Observed.Rank),
+		Rank:   displayRank(cfg, day),
 	}
 }
 
+// displayRank is the Ordinary Form's REPORTED rank for the observed
+// celebration -- it never changes calendar.Celebration.Rank (the engine's own
+// field, which drives precedence via ofRankOrder); it only relabels what is
+// handed to a caller here, after the engine has already finished computing.
+//
+// In the 1969 Universal Norms' Table of Liturgical Days, Sunday is its own
+// category, not a solemnity. The calendar engine's temporal.go builds every
+// "Nth Sunday of <season>" day (Ordinary Time, Advent, Lent, the Easter
+// season, Christmas time, and Palm Sunday) with sundayDay(), which sets
+// Rank=solemnity but leaves Class at its zero value (calendar.ClassNone) --
+// solemnity is a placeholder there, not a real classification. A genuinely
+// NAMED solemnity of the Lord that happens to fall on a Sunday (Easter Sunday
+// itself, Pentecost, Ascension/Corpus Christi when transferred, Trinity,
+// Christ the King, Christmas, Epiphany) is built by solemn(), which does set
+// Class=ClassLord, and must keep reporting "solemnity"; a feast of the Lord
+// (Holy Family, Baptism of the Lord) is Rank=feast already and is untouched.
+//
+// Investigated first: temporal.go's own Sunday bool (sundayDay's
+// `Sunday: !priv`) looked like the natural signal, but it does not reach
+// calendar.LiturgicalDay at all (LiturgicalDay carries no such field, only
+// the aggregate ObservedBand), and even if plumbed through it would be the
+// wrong signal here -- by its own doc comment it marks only the band-6
+// Christmas-time/Ordinary-time Sundays, not the band-2 Advent/Lent/Easter
+// Sundays this change must ALSO relabel (the 1st Sunday of Advent from the
+// original bug report is band 2, Privileged=true, Sunday=false). Using
+// Celebration.Class instead of that flag, or of temporalDay.Privileged,
+// covers exactly the sundayDay()-built set in both bands without adding any
+// new field: RankSolemnity + Layer=="temporal" + Class!=ClassLord occurs only
+// from sundayDay(), and (checked against every call site in temporal.go) only
+// ever on an actual Sunday, so the weekday check below is defensive, not
+// load-bearing.
+//
+// The Extraordinary Form (1962) has no such category and is untouched: this
+// only ever fires when the modern form is selected.
+func displayRank(cfg config.Config, day calendar.LiturgicalDay) string {
+	obs := day.Observed
+	if cfg.Selection().Form != "old" &&
+		day.Weekday == time.Sunday &&
+		obs.Layer == "temporal" &&
+		obs.Rank == calendar.RankSolemnity &&
+		obs.Class != calendar.ClassLord {
+		return string(calendar.RankSunday)
+	}
+	return string(obs.Rank)
+}
+
 // celebrationName is the observed celebration's name in the UI language,
 // resolved by naming.CelebrationName (name.<lang> -> English -> Latin ->
 // humanized slug). An empty result (unnamed feria) omits the header line.