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, 16 insertions, 0 deletions

diff --git a/internal/calendar/precedence_ef_repro_test.go b/internal/calendar/precedence_ef_repro_test.go
index 1f38996..77919d9 100644
--- a/internal/calendar/precedence_ef_repro_test.go
+++ b/internal/calendar/precedence_ef_repro_test.go
@@ -65,3 +65,19 @@ func TestTransferSkipsBothIAndIIClass(t *testing.T) {
 		t.Errorf("2011-07-04 observed = %q want precious-blood-of-our-lord-jesus-christ (RG 96: first day that is neither I nor II class)", got)
 	}
 }
+
+// TestMatthewBeatsSeptemberEmberWednesday: RG 91 -- St Matthew (21 September,
+// II class) and the September Ember Wednesday are both II class; the table
+// decides the tie. Entry 16 (II-class feasts of the universal Church) sits
+// ABOVE entry 18 (II-class ferias, including the Ember days) -- the feast
+// wins, the Ember feria is only commemorated.
+func TestMatthewBeatsSeptemberEmberWednesday(t *testing.T) {
+	// 21 September falls on the September Ember Wednesday whenever the third
+	// Sunday of September is the 18th -- 2016 and 2022 both qualify.
+	for _, date := range []string{"2016-09-21", "2022-09-21"} {
+		day := efCompute(date)
+		if day.Observed.Slug != "matthew" {
+			t.Errorf("%s observed = %q want matthew (RG 91 entry 16 beats entry 18)", date, day.Observed.Slug)
+		}
+	}
+}