feat(ef): implement RG 33's third omission trigger

RG 33 omits a II/III-class vigil in three cases: it falls on a Sunday, it
falls on a I-class feast, "vel si festum cui praemittitur in alium diem
transferri aut ad commemorationem reduci contingat". Only the first two
were built; the third was recorded in precedence_ef.ml as unimplemented on
the grounds that no witness existed in the shipped data. That reasoning was
wrong, and the rule fires on 1 744 days across 1583-9999.

Both halves of the clause reduce to one observable question -- is the feast
the OBSERVED office on the following day (RG 34 puts it there) -- so the
kernel asks it once per candidate, after place_transfers has settled the
year. No fixed point is needed: a vigil is a candidate only on its own day,
never on its feast's, so suppressing it cannot change what the next day
observes. Precedence.rules gains vigil_feast, which returns the slug of the
feast a vigil precedes; the kernel cannot infer that itself, because only
two of the five vigil/feast pairs share a slug stem.

Blast radius, measured pre-change binary vs HEAD over the whole domain and
classified: 1 744 days, three shapes, zero unexplained. 1 199 are the feast
reduced to a commemoration (10 August on a Sunday, St Lawrence); 478 and 67
are the feast transferred under RG 96 after the Sacred Heart or Corpus
Christi takes its day. The Assumption's and the Ascension's vigils never
qualify -- their I-class feasts always keep their own day.

Independently witnessed, which is unusual here. The published Ordo -- the
only witness outside the Divinum Officium -> missalemeum -> lectio lineage
-- omits St Lawrence's vigil on 2025-08-09, agreeing with colitur against
both engines. That date had been read earlier as an Ordo gap; the Ordo was
right, and correcting the misreading is what surfaced this clause. On
2027-08-09 the feast does keep its day and the Ordo omits a vigil colitur
correctly keeps, which is a genuine Ordo gap.

Allow-lists: C39 (lectio, 10 rows) and a 2038 oracle class citing the
register, the 2026-2027 window having no instance. The golden pin asserting
St Lawrence's vigil is violet moved 2025 -> 2027; its own comment had
reasoned about the vigil's weekday and missed that RG 33 also looks at the
feast's. Two new pins cover both shapes of the clause.

The vigil/feast table is built with Slug.of_string_exn: mutation testing
showed that of_string plus Result.to_option turns a typo into None, which
this hook's contract reads as "not a vigil", switching the rule off in
silence. Two tests assert the table against the shipped data in both
directions.

1 files changed, 35 insertions, 0 deletions

diff --git a/lib/rites/rite_ef/precedence_ef.mli b/lib/rites/rite_ef/precedence_ef.mli
index 419613a..4c2523a 100644
--- a/lib/rites/rite_ef/precedence_ef.mli
+++ b/lib/rites/rite_ef/precedence_ef.mli
@@ -217,6 +217,41 @@ val disposition :
   loser:Vocab_ef.rank Precedence.candidate ->
   Precedence.disposition
 
+(** RG 33's third omission trigger. Given a candidate, the feast it is a
+    VIGIL of, when that vigil is one this rule can omit; [None] otherwise --
+    which is every candidate that is not one of the five II/III-class vigils
+    in the 1962 universal calendar.
+
+    Answers only the identity question. Whether the feast actually kept its
+    own day is {!Colitur_kernel.Calendar}'s to determine, because only the
+    kernel holds the settled post-transfer placement of the whole year; see
+    {!Colitur_kernel.Precedence.rules.vigil_feast} for the division of labour
+    and for why the feast is NAMED here rather than inferred there.
+
+    The I-class vigils (Nativity Eve, Pentecost Vigil) are outside this rule
+    by RG 33's own wording and outside losing at all by RG 30, so they are
+    absent from the table and this returns [None] for them -- the same
+    argument {!is_omissible_vigil} already makes for the rule's other two
+    triggers. *)
+val vigil_feast : Vocab_ef.rank Precedence.candidate -> Slug.t option
+
+(** The (vigil slug, feast slug) pairs {!vigil_feast} answers from, exposed so
+    the test suite can assert both directions against the shipped sanctoral
+    data: that every slug named here exists, and that no II/III-class vigil in
+    the data is missing from it. Neither is checkable by a type, and both fail
+    SILENTLY -- an unmatched slug simply makes RG 33 inert for that entry. *)
+val vigil_feast_table : (string * Slug.t) list
+
+(** Whether a slug names a vigil, by either of the two conventions this
+    calendar's data uses (a "-vigil" suffix from the temporal cycle, a
+    "vigil-of-" prefix from the sanctoral bootstrap). Exposed for the same
+    table-drift assertions as {!vigil_feast_table}. *)
+val is_vigil : string -> bool
+
+(** Whether a rank is one RG 33 can omit -- II or III class. I-class vigils are
+    outside the rule (RG 30). Exposed alongside {!is_vigil}. *)
+val is_omissible_vigil : Vocab_ef.rank -> bool
+
 (** Slug prefix marking a celebration as one of RG 91 entry 17's days within
     the Octave of the Nativity (29-31 Dec -- 26-28 Dec are Stephen, John, the
     Innocents, sanctoral, never this prefix). Also colitur's own convention