feat(ef): the Creed, RG 475-476

Whether the Creed is said at Mass. New Rubrics_ef.creed, reached through
a new Rite.t.creed field and a new Liturgical_day.t.creed bool (false,
not an option, for a rite that has not implemented the rule); colitur
rubrics gains a fourth TAB-separated column.

475(a) reads the TEMPORAL cycle's own weekday, not the observed day: a
Sunday impeded by a Feast of the Lord (RG 16a) still says the Creed.
475(d)'s three octaves (Nativity, Easter, Pentecost) are pure date/
Easter-offset windows, checked first, since a saint's feast winning the
day inside one of them still says the Creed ("etiam in festis
occurrentibus") -- St Stephen, 26 December, is the live witness.

RG 23 classifies Ash Wednesday and every feria of Holy Week (including
the Sacred Triduum) as feriae, not festa, however high their rank, so
475(b)/(c)'s "in festis" never reaches them; this single check subsumes
476(a)'s own naming of the Chrism/Lord's-Supper Mass and the Easter
Vigil. RG 28-34 vigils are a third liturgical-day category, also
excluded from "in festis" regardless of rank -- reuses the already-
exported Precedence_ef.is_vigil rather than a new list.

475(e)'s Apostle/Evangelist natalicia list (creed_apostle_slugs) was
derived by grepping data/ef/sanctoral.sexp directly and checking each
candidate's own date against whether it is that saint's dies natalis --
not copied from any list supplied with the task. The Conversion of St
Paul and the 30 June Commemoration of St Paul are excluded (neither is
a natalicium); the Chair of St Peter and St Barnabas are included only
because the clause names them explicitly, which is exactly why it has
to: neither is a natalicium either.

475(c)'s BVM half reuses Precedence_ef.marian_slugs (newly exported)
rather than the subject field alone: checked against the shipped data,
almost every Marian sanctoral entry ships subject=Saint, not Bvm.

man/colitur.1's rubrics section is updated to match the new column;
test/cli.t repinned via dune promote for the same reason. Verified
day/readings output byte-identical to v0.10.1 across the whole
1583-9999 domain (both binaries' concatenated day+readings output,
6,148,492 lines each, zero diff). Domain-wide: 882,996 days say the
Creed, 2,191,250 do not; every one of the domain's 439,178 Sundays says
it, zero exceptions.

5 files changed, 25 insertions, 0 deletions

diff --git a/lib/kernel/calendar.ml b/lib/kernel/calendar.ml
index 7fe9f67..d55e38d 100644
--- a/lib/kernel/calendar.ml
+++ b/lib/kernel/calendar.ml
@@ -547,6 +547,9 @@ let build_day (rite : ('s, 'r) Rite.t) (idx : 'r Layer.index)
     rite.Rite.readings ~observed:resolution.Precedence.observed.Precedence.cel ~temporal ~date
       ~temporal_at:rite.Rite.temporal
   in
+  let creed =
+    rite.Rite.creed ~temporal ~observed:resolution.Precedence.observed.Precedence.cel ~date
+  in
   {
     Liturgical_day.date;
     rite = rite.Rite.id;
@@ -559,6 +562,7 @@ let build_day (rite : ('s, 'r) Rite.t) (idx : 'r Layer.index)
     omitted;
     citations;
     formulary;
+    creed;
   }
 
 let year (rite : ('s, 'r) Rite.t) (layer : 'r Layer.t) (y : int) :
diff --git a/lib/kernel/liturgical_day.ml b/lib/kernel/liturgical_day.ml
index 709f878..09ac0a1 100644
--- a/lib/kernel/liturgical_day.ml
+++ b/lib/kernel/liturgical_day.ml
@@ -26,5 +26,6 @@ type ('s, 'r) t = {
   formulary : Mass_formulary.t option;
       (** which Mass the day says, and how that was decided; [None] only for
           a rite with no lectionary -- see {!Mass_formulary} *)
+  creed : bool;  (** whether the Creed is said at this day's Mass; see {!Rite.t.creed} *)
 }
 [@@deriving sexp]
diff --git a/lib/kernel/liturgical_day.mli b/lib/kernel/liturgical_day.mli
index 4a71d6d..eb45e61 100644
--- a/lib/kernel/liturgical_day.mli
+++ b/lib/kernel/liturgical_day.mli
@@ -33,5 +33,9 @@ type ('s, 'r) t = {
           {!Mass_formulary}. [None] only for a rite with no lectionary; for
           EF it is [Some] on every day of every year 1583..9999, asserted by
           {!Validate}. *)
+  creed : bool;
+      (** Whether the Creed is said at this day's Mass -- {!Rite.t.creed},
+          EF: RG 475-476. A decision, not an [option]: [false] for a rite
+          that has not implemented the rule, same as [creed] itself. *)
 }
 [@@deriving sexp]
diff --git a/lib/kernel/rite.ml b/lib/kernel/rite.ml
index a7d21d3..4999fc2 100644
--- a/lib/kernel/rite.ml
+++ b/lib/kernel/rite.ml
@@ -18,4 +18,5 @@ type ('s, 'r) t = {
     date:Date.t ->
     temporal_at:(Date.t -> ('s, 'r) Temporal.t) ->
     Mass_formulary.t option * Citation.t list;
+  creed : temporal:('s, 'r) Temporal.t -> observed:'r Celebration.t -> date:Date.t -> bool;
 }
diff --git a/lib/kernel/rite.mli b/lib/kernel/rite.mli
index 45f3ed6..39538d0 100644
--- a/lib/kernel/rite.mli
+++ b/lib/kernel/rite.mli
@@ -92,4 +92,19 @@ type ('s, 'r) t = {
           temporal identity (the preceding Sunday's, for the ferial rule)
           without re-implementing the temporal cycle -- the same shape
           [transfer_target]'s own [occupant] callback established. *)
+  creed : temporal:('s, 'r) Temporal.t -> observed:'r Celebration.t -> date:Date.t -> bool;
+      (** Whether the Creed is said, post-Gospel/homily, at this day's Mass
+          (EF: RG 475-476). A [bool], not an [option]: this is a decision,
+          and a rite that has not implemented the rule returns [false]
+          explicitly rather than leaving the question unanswered.
+
+          [temporal] and [observed] are supplied for the same reason
+          [readings] gets both: a rubric like this one can turn on either
+          the day's TEMPORAL-cycle identity (e.g. "is this a Sunday, even
+          one a feast has displaced") or on the celebration actually
+          observed, and only the rite knows which. [date] is supplied for
+          the same reason [readings] gets it too -- a rubric keyed to an
+          Easter-relative window (e.g. "within the octave of Easter") needs
+          the civil date and the rite's own Easter to test it, and neither
+          [temporal] nor [observed] alone carries that arithmetic. *)
 }