merge: celebrant Mass rubrics, and four rubrical corrections

colitur now prints what a real ordo prints for the Mass: which formulary is
said and how it was reached, the Gloria, the Creed, the preface, and the
commemorations with their Low-Mass/sung distinction. colitur rubrics joins
day and readings.

Four defects were found and fixed on the way, each by an external witness
rather than by inspection: the Creed said at Requiem Masses (RG 476(f)),
the missing bissextile shift of St Matthias and St Gabriel (2 041 leap
years), Rogation Monday and Tuesday coloured violet in Paschaltide (RG
119(b)), and the ferias after the Ascension resuming the wrong Sunday's
Mass rather than the Ascension's.

Validation gained a sixth layer and then some: the preface is checked
against three independent publishers over seven witness-years (FIUV, three
LMS editions, three extraordinaryform.org editions), none of which shares
the Divinum Officium -> missalemeum -> lectio lineage the older layers all
descend from.

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/kernel/date.mli b/lib/kernel/date.mli
index 2f632c8..0e86d54 100644
--- a/lib/kernel/date.mli
+++ b/lib/kernel/date.mli
@@ -14,6 +14,13 @@ val month : t -> int
 val day : t -> int
 val weekday : t -> weekday
 
+(** Proleptic Gregorian leap-year test: divisible by 4, except a century year
+    not divisible by 400. The same rule {!make}/{!days_in_month} already use
+    internally to admit 29 February -- exposed so a rite can key its own
+    calendar-reckoning rules (e.g. a kalends-doubling convention) off the
+    identical, single-sourced definition rather than re-deriving it. *)
+val is_leap : int -> bool
+
 (** [to_rata]/[of_rata] expose the underlying day-count (days since 1970-01-01);
     [of_rata] and [add_days] are unbounded total arithmetic (they may denote a
     year outside 1583..9999 — only [make] enforces the domain). *)