precedence_ef: a II-class privileged feria yields to a feast (defect 2)

precedenceEF's equal-class tie-break only distinguished "ordinary
III/IV-class feria yields" from "everything else wins" -- Sundays,
named feasts, Lent/Passiontide ferias, AND II-class privileged ferias
(the Ember days, the late-Advent 17-23 Dec ferias) were all bucketed
into the same "wins its tie" branch. RG 91 disagrees at class 2:
entry 15 (Sundays) sits ABOVE entry 16 (II-class feasts of the
universal Church), so a Sunday wins -- but entry 16 sits ABOVE entry
18 (II-class ferias, including the Ember days), so those FERIAS
yield instead, the opposite direction from a Sunday. St Matthew (21
September, II class) was losing to the September Ember Wednesday
every time the two coincided; St Thomas (21 December, II class) was
losing to an ordinary late-Advent feria the same way once the
previous commit correctly promoted those ferias to II class.

The fix distinguishes a II-class Sunday from a II-class feria using a
Sunday flag that already existed on `candidate` (used by the OF path)
but was never wired up for EF: temporal_ef.go's efCel always set
Sunday: false, even on an actual Sunday. A new efSunday helper (efCel
plus the flag) replaces the three efCel calls inside temporalEF's
Sunday branch, and computeEF now propagates td.Sunday into the day's
temporal candidate.

precedence_ef_test.go's own pre-existing witness ("at equal class, the
temporal office wins") encoded exactly the bug: a bare class-2
temporal candidate with no Sunday/season information, standing in for
"the temporal office" in general. It is rewritten into two explicit
cases (Sunday wins its tie; a privileged feria yields) plus the
existing Lent/Passiontide-vs-ordinary III/IV-class case restated
explicitly rather than left implicit.

Witness (precedence_ef_repro_test.go): TestMatthewBeatsSeptemberEmberWednesday.
Fails before this commit with:
  2016-09-21 observed = "ef-september-ember-wed" want matthew (RG 91
    entry 16 beats entry 18)
  2022-09-21 observed = "ef-september-ember-wed" want matthew (RG 91
    entry 16 beats entry 18)

With this commit, all seven named defects are fixed:
LECTIO_EF_ORACLE_STRICT=1 go test ./internal/calendar/... -run TestOracleEF
passes (0 unallow-listed rank/colour mismatches over 730 days). The
gate stays in place for this commit; a following commit removes it.

1 files changed, 36 insertions, 13 deletions

diff --git a/internal/calendar/precedence_ef.go b/internal/calendar/precedence_ef.go
index 4fda626..a1788be 100644
--- a/internal/calendar/precedence_ef.go
+++ b/internal/calendar/precedence_ef.go
@@ -22,24 +22,47 @@ func efRankOrder(r Rank) int {
 }
 
 // precedenceEF ranks an EF candidate for occurrence (lower = higher precedence):
-// by class first, then a tie-break at equal class (1960 occurrence table).
+// by class first, then a tie-break at equal class (RG 91's Table of
+// Precedence, read entry-by-entry within each class).
 //
-// The tie-break is asymmetric by season. An ORDINARY feria (per annum, Advent,
-// Septuagesima) yields to an equal-class feast — the feast is celebrated and the
-// feria commemorated (e.g. St Francis Xavier, Dec 3, on an Advent feria). The
-// ferias of Lent and Passiontide are privileged: they outrank an equal-class
-// feast, which is only commemorated. Sundays and named temporal feasts likewise
-// win their ties. The *2 class spacing means the ±1 tie-break never crosses a
-// class boundary.
+// The tie-break is asymmetric by season AND, at class 2, by whether the
+// temporal day is a Sunday or a privileged FERIA:
+//   - III/IV class: an ORDINARY feria (per annum, Advent to 16 Dec,
+//     Septuagesima) yields to an equal-class feast (entries 24/25 above the
+//     feria) -- the feast is celebrated, the feria commemorated (e.g. St
+//     Francis Xavier, Dec 3). The ferias of Lent and Passiontide are
+//     privileged (entry 22, ABOVE entry 24): they outrank an equal-class
+//     feast, which is only commemorated.
+//   - II class: an ordinary SUNDAY wins its tie (entry 15, above entry 16's
+//     feasts) -- but a II-class privileged FERIA (the Ember days, the
+//     late-Advent 17-23 Dec ferias, entry 18) sits BELOW entry 16 and yields
+//     to an equal-class feast, the opposite of a Sunday's own tie. This is
+//     the same table shape as III class's Advent/per-annum ferias, just
+//     inverted for which II-class temporal days count as "privileged".
+//   - I class: Sundays (entry 6) and I-class ferias (entry 7, Ash
+//     Wednesday/Holy Week) both sit above entry 11's feasts, so they always
+//     win -- there is no I-class "ordinary feria yields" case at all.
+//
+// The *2 class spacing means the ±1 tie-break never crosses a class boundary.
 func precedenceEF(c candidate) int {
 	p := (6 - efRankOrder(c.Cel.Rank)) * 2 // class-1 -> 2, ferial -> 12
 	if c.Temporal {
-		ordinaryFeria := (c.Cel.Rank == RankClass3 || c.Cel.Rank == RankClass4) &&
-			c.Season != Lent && c.Season != Passiontide
-		if ordinaryFeria {
-			p++ // an ordinary feria yields to an equal-class feast
+		yieldsToFeast := false
+		switch c.Cel.Rank {
+		case RankClass3, RankClass4:
+			yieldsToFeast = c.Season != Lent && c.Season != Passiontide
+		case RankClass2:
+			// A II-class Sunday (entry 15) wins; a II-class privileged feria --
+			// Ember days, the late-Advent 17-23 Dec ferias (entry 18) -- yields
+			// to an equal-class feast (entry 16), e.g. St Matthew (21 Sep)
+			// beating the September Ember Wednesday, or St Thomas (21 Dec)
+			// beating an Advent late feria.
+			yieldsToFeast = !c.Sunday
+		}
+		if yieldsToFeast {
+			p++
 		} else {
-			p-- // Sundays, named feasts, and penitential ferias win their ties
+			p-- // Sundays, I-class ferias, and penitential (Lent/Passiontide) ferias win their ties
 		}
 	} else if c.Cel.Class == ClassLord && c.Cel.Rank == RankClass2 {
 		// A II class feast of the Lord takes the place of a II class Sunday it