merge: RG 33's third omission trigger

The last unbuilt clause in the EF module. A II/III-class vigil is omitted
entirely when the feast it precedes fails to keep its own day -- 1 744 days
across 1583-9999, three verified shapes, zero unexplained.

Rule and vigil inventory independently confirmed by O'Connell 1964, outside
the Divinum Officium -> missalemeum -> lectio lineage. The 10 affected days
in 2005-2050 are allow-listed as C39; no external day-level witness exists,
which the note states rather than glosses.

1 files changed, 55 insertions, 0 deletions

diff --git a/lib/rites/rite_ef/precedence_ef.ml b/lib/rites/rite_ef/precedence_ef.ml
index b69ee52..36aea83 100644
--- a/lib/rites/rite_ef/precedence_ef.ml
+++ b/lib/rites/rite_ef/precedence_ef.ml
@@ -600,6 +600,61 @@ let is_bvm_office (c : Vocab_ef.rank Precedence.candidate) =
    (§6) rather than guessed. *)
 let is_omissible_vigil (rank : Vocab_ef.rank) = rank = Vocab_ef.Class2 || rank = Vocab_ef.Class3
 
+(* RG 33's THIRD omission trigger, the clause [is_omissible_vigil]'s own
+   comment above records as unimplemented: "vel si festum cui praemittitur in
+   alium diem transferri aut ad commemorationem reduci contingat" -- "or if
+   the feast it precedes happens to be transferred to another day or reduced
+   to a commemoration".
+
+   Each pair is (vigil slug, the slug of the feast it precedes). RG 34 fixes
+   the feast on the day AFTER the vigil ("Vigiliae... celebrantur die
+   praecedenti festum"), so the kernel needs no date here, only the identity
+   -- and it must be given the identity rather than deriving it, because
+   these slugs do not derive from one another: two of the five share a stem
+   with their feast and three do not (see {!Precedence.rules.vigil_feast}).
+
+   The five are exhaustive for the 1962 universal calendar. The four
+   sanctoral ones are the only entries in data/ef/sanctoral.sexp matching
+   [is_vigil]; the fifth is temporal_ef's own Ascension vigil. The two
+   I-class vigils (Nativity Eve, Pentecost Vigil) are deliberately ABSENT:
+   RG 33 governs only "Vigilia II aut III classis", and RG 30 puts a I-class
+   vigil beyond losing in the first place -- the same argument
+   [is_omissible_vigil] already makes for the other two triggers.
+
+   A user overlay adding a diocesan vigil is NOT covered by this table and
+   its vigil will not be omitted. That is a data limit, not an architectural
+   one -- the kernel hook takes any candidate -- and it is stated here rather
+   than papered over with a slug-shape heuristic that would be wrong for
+   three of the five universal cases it can already be checked against. *)
+(* Built with [Slug.of_string_exn], deliberately, and at module initialisation
+   rather than per call. A malformed literal here is a PROGRAMMING error in a
+   static table, not untrusted input, and the alternative found by mutation
+   testing is worse than a crash: with [Slug.of_string] and [Result.to_option]
+   a typo (an uppercase letter is enough -- slugs are lowercase-only) collapses
+   to [None], which this function's own contract reads as "not a vigil", and
+   the whole rule switches itself off for that entry in silence. That failure
+   was reproduced: mutating "lawrence" to "lawrence-WRONG" reddened FOUR tests,
+   all of them the ones that notice the rule missing, and none that notice it
+   pointing at the wrong feast -- indistinguishable from deleting the row.
+   The same mutation with a well-formed "lawrence-wrong" reddens eighteen.
+   Raising at startup keeps a typo loud; [Rite_ef]'s own bundle is constructed
+   at initialisation too, so the failure surfaces before any calendar is
+   resolved. *)
+let vigil_feast_table =
+  List.map
+    (fun (vigil, feast) -> (vigil, Slug.of_string_exn feast))
+    [ ("ef-ascension-vigil", "ef-ascension");
+      ("vigil-of-the-nativity-of-st-john-the-baptist", "nativity-of-st-john-the-baptist");
+      ("vigil-of-sts-peter-paul", "sts-peter-paul");
+      ("vigil-of-st-lawrence", "lawrence");
+      ("vigil-of-the-assumption", "assumption-of-the-blessed-virgin-mary") ]
+
+let vigil_feast (c : Vocab_ef.rank Precedence.candidate) : Slug.t option =
+  let cel = c.Precedence.cel in
+  if not (is_omissible_vigil cel.Celebration.rank) then None
+  else List.assoc_opt (Slug.to_string cel.Celebration.slug) vigil_feast_table
+
+
 (* Every Sunday slug this rite's temporal cycle produces -- named
    (temporal_ef.ml's [named], e.g. "ef-easter-sunday") or the generic
    "ef-<season>-sunday-<n>" fallback ([sunday_slug]) -- contains this