fix(of): Nativity Vigil no longer suppresses a Sunday of Advent

Temporal_of.named claimed 24 December unconditionally as
of-nativity-vigil (Sollemnitas), and temporal's dispatch matched named
before sunday_slug. On a Sunday 24 December, the Fourth Sunday of
Advent -- Tabula I.2, Normae n. 5's own privileged Sundays of Advent,
Lent and Easter -- was silently replaced by the Vigil.

named now returns None for 24 December when that date is itself a
Sunday, so temporal's dispatch falls through to sunday_slug and the
day resolves as of-advent-sunday-4. The Vigil Mass is an evening Mass
of the following solemnity, not an office belonging to 24 December's
own civil day -- the same civil-day-granularity reasoning already
applied to Holy Thursday (Precedence_of.band's entry-1 comment) and to
expected-divergences-litcal.sexp's L1 entry. Every non-Sunday
24 December is unaffected.

Audited every other named entry for the same latent shape (see
.superpowers/sdd/of-r8-advent-iv-report.md): none of them has it,
either because the date can never fall on a Sunday, or because the
date IS the definition of that Sunday (Palm Sunday, Easter, Pentecost,
Trinity, Christ the King), or because the competing movable-Sunday
windows are constructed to exclude that date.

Added test_nativity_vigil_yields_to_advent_sunday, covering
2028-12-24 and 2034-12-24 (both inside the litcal fixture window) and
the 2026-12-24 non-Sunday control. Re-ran the litcal layer: no
allow-list counts moved, since it compares only season and
Ordinary-Time week, and both readings of 24 December are "advent"
either way. Updated test_precedence_of.ml's "entry 3, not 9" comment,
which had carried this as a known, unfixed defect, to describe the
fix; its own pinned assertion (a hand-built Thursday candidate) needed
no change.

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/rites/rite_of/temporal_of.mli b/lib/rites/rite_of/temporal_of.mli
index 982ff05..d2acadd 100644
--- a/lib/rites/rite_of/temporal_of.mli
+++ b/lib/rites/rite_of/temporal_of.mli
@@ -103,7 +103,16 @@ val christ_the_king : int -> Date.t
     threading extra state through every other branch too -- the exact
     reason EF's own [named] excludes its structurally identical Holy
     Family/Holy Name. {!temporal} applies all three as its own targeted
-    dispatch instead. *)
+    dispatch instead.
+
+    24 December is ALSO conditional, not unconditional like the rest of this
+    function's fixed dates: it yields [of-nativity-vigil] only when that date
+    is not itself a Sunday. On a Sunday, [None] is returned so {!temporal}'s
+    dispatch falls through to {!sunday_slug}'s own [of-advent-sunday-4] --
+    Tabula I.2/Normae n. 5's Sundays of Advent outrank the Vigil (Tabula
+    I.3), the same evening-Mass-inside-the-civil-day reasoning already
+    applied to Holy Thursday (see [named]'s own implementation comment for
+    the full argument). *)
 val named : Date.t -> (Vocab_of.season * string * Colour.t * Vocab_of.rank) option
 
 (** Week within the season, 1-indexed, Sunday-aligned (constant across a