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, 37 insertions, 0 deletions

diff --git a/internal/readings/readings_test.go b/internal/readings/readings_test.go
index 143b43e..1674d85 100644
--- a/internal/readings/readings_test.go
+++ b/internal/readings/readings_test.go
@@ -99,6 +99,43 @@ func TestLoadModern(t *testing.T) {
 	}
 }
 
+// TestSundayRankIsDisplayOnly guards the Ordinary Form's Sunday display rank.
+// Sunday is its own category in the 1969 Universal Norms' Table of Liturgical
+// Days -- never a solemnity -- so an ordinary "Nth Sunday of <season>" temporal
+// day (Ordinary Time, Advent, Lent, the Easter season, Christmas time; this
+// also covers Palm Sunday) must report "sunday". A NAMED solemnity of the Lord
+// that happens to fall on a Sunday (Easter Sunday itself, Pentecost) is a
+// genuine solemnity and must keep reporting "solemnity"; a feast of the Lord
+// (Holy Family) must keep reporting "feast". This is display-only: it must
+// never touch the engine's internal precedence, so the 1962 form (which has no
+// such Sunday category -- Sundays report their class exactly as before) is
+// asserted unchanged too. Dates are the ones from the original bug report,
+// plus the Easter/Pentecost/Holy Family dates they imply for the same
+// liturgical year.
+func TestSundayRankIsDisplayOnly(t *testing.T) {
+	cases := []struct {
+		date, lect, wantRank, why string
+	}{
+		{"2026-08-09", "new", "sunday", "19th Sunday in Ordinary Time"},
+		{"2026-11-29", "new", "sunday", "1st Sunday of Advent"},
+		{"2027-03-28", "new", "solemnity", "Easter Sunday itself"},
+		{"2027-05-16", "new", "solemnity", "Pentecost"},
+		{"2026-12-27", "new", "feast", "Holy Family"},
+		{"2026-08-09", "traditional", "class-2", "1962 Sunday after Pentecost"},
+		{"2026-11-29", "traditional", "class-1", "1962 1st Sunday of Advent"},
+	}
+	for _, c := range cases {
+		cfg := config.Config{Lectionary: c.lect}
+		_, info, err := Load(cfg, Options{Date: c.date, All: true})
+		if err != nil {
+			t.Fatalf("%s (%s, %s): Load: %v", c.date, c.lect, c.why, err)
+		}
+		if info.Rank != c.wantRank {
+			t.Errorf("%s (%s, %s): Rank = %q, want %q (name=%q)", c.date, c.lect, c.why, info.Rank, c.wantRank, info.Name)
+		}
+	}
+}
+
 // TestLoadTraditional computes the Extraordinary Form day offline: it never
 // needs the network, and yields the EF epistle+gospel with a header name.
 func TestLoadTraditional(t *testing.T) {