kernel(rite-ef): apply RG16(a) -- a Feast of the Lord leaves the impeded Sunday uncommemorated

Caput III "De Dominicis", RG 16(a): a Feast of the Lord, I or II class,
occurring on a II-class Sunday takes the Sunday's own place with all its
rights and privileges -- of the Sunday, therefore, no commemoration is
made. band's entry 14 already ranked such a feast above the Sunday
correctly; disposition had no exception for the collision, so the impeded
Sunday fell through to the ordinary RG 95/109(a) commemorate-or-omit
catch-all and was wrongly admitted as a privileged commemoration.

Adds a branch to Rite_ef.Precedence_ef.disposition, gated on all four of:
loser is temporal-origin, loser rank Class2, loser carries the Sunday slug
marker, winner rank Class1-or-2 with subject Lord. No signature change --
disposition already receives the winner (RG 33's own vigil-omission branch
already reads it); each conjunct is proved independently load-bearing by
a dedicated disposition_cases row, including one real-data case each for
the winner's subject and rank conjuncts, and a defensive synthetic case
for the winner rank conjunct's currently-unreachable Class3 shape. A new
end-to-end resolve-level test (2028-08-06, the Transfiguration) proves the
real band/disposition pipeline together, checking the Omit reason string
distinguishes this from admit's own admission-limit cut.

2 files changed, 208 insertions, 8 deletions

diff --git a/lib/rites/rite_ef/precedence_ef.ml b/lib/rites/rite_ef/precedence_ef.ml
index db7e708..179fa13 100644
--- a/lib/rites/rite_ef/precedence_ef.ml
+++ b/lib/rites/rite_ef/precedence_ef.ml
@@ -244,13 +244,14 @@ let band (ctx : Vocab_ef.season Precedence.context) (c : Vocab_ef.rank Precedenc
 
 (* Task 8: what happens to the day's LOSING candidate (docs/research/
    rules-register.md §4, "Occurrence" RG 92-95 and "Vigils" RG 33, plus RG
-   94). [band] above decides who wins; this decides the loser's fate, which
-   turns on the LOSER's own rank and status (RG 95), except RG 33's vigil
-   omission, which also has to read the winner. Nothing here ever returns
-   [Precedence.Repose]: that disposition denotes RG 100-102's *repositio*
-   (perpetual impediment from a proper/diocesan calendar), out of this
-   plan's scope -- see calendar.mli's own note that nothing in the EF
-   ruleset currently emits it. *)
+   94; also §6.0/Caput III "De Dominicis" RG 16(a), below). [band] above
+   decides who wins; this decides the loser's fate, which turns on the
+   LOSER's own rank and status (RG 95), except RG 33's vigil omission and RG
+   16(a)'s Sunday-suppression, which also have to read the winner. Nothing
+   here ever returns [Precedence.Repose]: that disposition denotes RG
+   100-102's *repositio* (perpetual impediment from a proper/diocesan
+   calendar), out of this plan's scope -- see calendar.mli's own note that
+   nothing in the EF ruleset currently emits it. *)
 
 (* RG 33 -- CORRECTED 2026-08-12 (Task 16, primary-source-verified against
    docs/research/1962-06-23,_SS_Ioannes_XXIII,_Missale_Romanum,_LT.pdf, the
@@ -605,6 +606,70 @@ let disposition ~(winner : Vocab_ef.rank Precedence.candidate)
        register's own §4 "Vigils" entry states RG 32 only as "same pattern
        [as RG 31]", not verbatim -- now closed here). *)
     Precedence.Omit
+  else if
+    is_temporal
+    && cel.Celebration.rank = Class2
+    && is_sunday_slug (Slug.to_string cel.Celebration.slug)
+    && (let wcel = winner.Precedence.cel in
+        (wcel.Celebration.rank = Class1 || wcel.Celebration.rank = Class2)
+        && wcel.Celebration.subject = Subject.Lord)
+  then
+    (* RG 16(a) (docs/research/rules-register.md §6.0, Caput III "De
+       Dominicis", primary text): "Dominica II classis, in occurrentia,
+       festis II classis praefertur. Attamen: a) festum Domini I aut II
+       classis, in dominica II classis occurrens, locum tenet ipsius
+       dominicae cum omnibus iuribus et privilegiis: de dominica, proinde,
+       NULLA FIT COMMEMORATIO" -- a Feast of the Lord, I or II class,
+       occurring on a II-class Sunday, takes the Sunday's own place with all
+       its rights and privileges: OF THE SUNDAY, THEREFORE, NO
+       COMMEMORATION IS MADE. {!band} entry 14 already ranks such a feast
+       above the Sunday (RG 91 entry 14 < entry 15), so the feast is
+       correctly [observed]; this is [disposition]'s own answer for what
+       becomes of the SUNDAY once it has lost -- [Omit], not the [Commemorate]
+       every other impeded II-class Sunday gets via RG 109(a)/RG 111(b)
+       below. This is the ONE place in this function that needs the WINNER's
+       [subject], not only the loser's own fields -- like RG 33's vigil
+       omission above, not a new kind of signature: [Precedence.rules.disposition]
+       already takes [~winner], this is simply its first other reader.
+
+       Both winner-side conjuncts are load-bearing, proved by
+       [test_precedence_ef.ml]'s own paired rows (the brief's "one without
+       the other proves nothing"):
+       - [rank = Class1 || rank = Class2]: {!band} entries 11-13 admit ANY
+         I-class feast -- Lord or Saint alike, no subject test at all (entry
+         14's own comment: unlike entry 16, entries 11-13 draw no such
+         line) -- ahead of a II-class Sunday. REACHABLE at Class1 on real
+         data: e.g. the Nativity of St John the Baptist (24 June, I class,
+         Saint) landing on a Time-after-Pentecost Sunday already wins the
+         day under {!band} alone; without this conjunct RG 16(a) would
+         wrongly fire for it too. (At Class2 this conjunct adds no further
+         cases beyond what the [subject = Lord] conjunct below already
+         requires -- entry 16's ordinary II-class feasts never outrank a
+         Sunday in {!band} in the first place, 16 > 15 -- so it is only
+         independently reachable at Class1.)
+       - [subject = Lord]: at Class2 this is what {!band} entry 14 already
+         requires of its own winners, so it adds no further restriction
+         there; at Class1 it is independently reachable and necessary, per
+         the St John Baptist example above -- dropping it would fire RG
+         16(a) for any winning I-class feast at all, exactly the
+         over-wide branch the task brief warns against.
+
+       The SUNDAY-side conjuncts: [rank = Class2] excludes a I-class Sunday
+       (Advent/Lent/Passiontide, Low Sunday, {!band} entry 6) -- RG 16(a)'s
+       own text says "Dominica II classis", not "any Sunday", and a I-class
+       Sunday can never actually reach here as a [loser] against a
+       Class1-or-2 Lord winner in the first place: entry 6's own band value
+       (6) is lower than every entry a Lord feast of Class1 or Class2 could
+       occupy (3, 11-14), so a I-class Sunday always wins outright -- this
+       is exactly why the rubric restricts itself to II class. [is_sunday_slug]
+       (the same marker RG 33's [impedes_vigil] and RG 109(a)'s
+       [privilege_of] already use, with no [is_temporal] guard there either
+       -- no sanctoral slug this codebase's data produces contains
+       {!sunday_marker}) is the "Dominica" half; [is_temporal] is kept
+       alongside it anyway, the same explicit-but-not-load-bearing defence
+       the RG26 branch above gives its own [not is_vigil] guard, rather than
+       relying on that absence silently. *)
+    Precedence.Omit
   else
     (* RG 95's other branch: "aut commemorantur aut penitus omittuntur" --
        commemorated or wholly omitted. Reached by every SANCTORAL loser
diff --git a/test/test_precedence_ef.ml b/test/test_precedence_ef.ml
index a0e1db1..facf3eb 100644
--- a/test/test_precedence_ef.ml
+++ b/test/test_precedence_ef.ml
@@ -540,7 +540,100 @@ let disposition_cases =
        Omit under the refuted privilege_of=Ordinary gate",
       an_ordinary_sunday,
       cand ~rank:V.Class3 "ef-synthetic-ordinary-class3-feria",
-      "Commemorate(Ordinary)" )
+      "Commemorate(Ordinary)" );
+    (* RG 16(a) (register §6.0, Caput III "De Dominicis"): "festum Domini I
+       aut II classis, in dominica II classis occurrens, ... de dominica,
+       proinde, nulla fit commemoratio" -- a Feast of the Lord, I or II
+       class, impeding a II-class Sunday, leaves the Sunday with NO
+       commemoration at all, unlike every other impeded II-class Sunday
+       (contrast the very first row of this table, and [privilege_cases]'s
+       own (a): both plain [Class1]/other-sanctoral winners still admit the
+       Sunday, [Commemorate(Privileged)]). Two positive rows, I and II
+       class, both real slugs/ranks/subjects this project's own audit
+       confirmed against the calendarium (this task's own report): the
+       Transfiguration (6 Aug, II class, "IN TRANSFIGURATIONE D. N. I. C.")
+       and the Precious Blood (1 Jul, I class, "PRETIOSISSIMI SANGUINIS
+       D. N. I. C."). *)
+    ( "RG16(a): a Feast of the Lord, II class, impedes a II-class Sunday -> \
+       Omit, no commemoration at all",
+      cand ~origin:P.Sanctoral ~rank:V.Class2 ~subject:Sub.Lord ~layer:PE.universal_layer
+        "transfiguration-of-our-lord",
+      an_ordinary_sunday,
+      "Omit" );
+    ( "RG16(a): a Feast of the Lord, I class, impedes a II-class Sunday -> \
+       Omit, no commemoration at all",
+      cand ~origin:P.Sanctoral ~rank:V.Class1 ~subject:Sub.Lord ~layer:PE.universal_layer
+        "precious-blood-of-our-lord-jesus-christ",
+      an_ordinary_sunday,
+      "Omit" );
+    (* Conjunct 1/4, WINNER subject: RG 16(a) names a feast "Domini", not any
+       I-class feast. {!band} entries 11-13 admit any I-class feast ahead of
+       a II-class Sunday with no subject test (unlike entry 14, see that
+       entry's own comment) -- so a real I-class SAINT feast can win the day
+       exactly as a Lord feast would, and must NOT trigger RG 16(a). Real
+       slug/rank/subject from data/ef/sanctoral.sexp (24 June, I class,
+       "NATIVITAS S. IOANNIS BAPTISTAE", subject Saint): 24 June falls on a
+       Time-after-Pentecost Sunday in real years (e.g. 2029), so this is a
+       live, not merely synthetic, shape -- {!band} entries 11-13 rank it
+       ahead of the ordinary Sunday's own entry 15 regardless of subject.
+       Dropping the [subject = Lord] conjunct would wrongly Omit the Sunday
+       here too. *)
+    ( "RG16(a) does NOT fire for a I-class feast of a SAINT (not the Lord) \
+       impeding a II-class Sunday -- stays Commemorate(Privileged)",
+      cand ~origin:P.Sanctoral ~rank:V.Class1 ~subject:Sub.Saint ~layer:PE.universal_layer
+        "nativity-of-st-john-the-baptist",
+      an_ordinary_sunday,
+      "Commemorate(Privileged)" );
+    (* Conjunct 2/4, LOSER rank: RG 16(a) names "Dominica II classis", not
+       any Sunday. A I-class Sunday (Advent/Lent/Passiontide, Low Sunday,
+       {!band} entry 6) can never actually reach here as a loser against a
+       Class1-or-2 Lord winner in real banding (entry 6's own band value, 6,
+       beats every entry such a winner could occupy, 3/11-14), which is
+       exactly why the primary text restricts itself to II class -- but
+       [disposition] takes no [context] and cannot itself re-derive that
+       band fact, so the rank check is what actually enforces it here.
+       Sourced from [Temporal_ef.temporal]'s own real output (Advent I
+       Sunday 2026, Class1, "ef-advent-sunday-1"), the same row
+       [disposition_cases]'s own RG95/RG109(a) entry above already uses.
+       Dropping the [rank = Class2] conjunct on the loser would wrongly Omit
+       this Sunday's commemoration too. *)
+    ( "RG16(a) does NOT fire for a I-class Sunday, even losing to a Feast of \
+       the Lord -- stays Commemorate(Privileged)",
+      cand ~origin:P.Sanctoral ~rank:V.Class2 ~subject:Sub.Lord ~layer:PE.universal_layer
+        "transfiguration-of-our-lord",
+      of_temporal (T.advent_start 2026),
+      "Commemorate(Privileged)" );
+    (* Conjunct 3/4, LOSER is a Sunday at all: RG 16(a) protects "de
+       dominica" specifically, not every ordinary office a Feast of the Lord
+       happens to impede. An ordinary sanctoral SAINT losing to the same
+       Lord-subject Class2 winner as the row above must still reach the
+       ordinary RG 95/111(c) commemorate-or-omit flow, not RG 16(a)'s
+       special no-commemoration rule. Dropping [is_sunday_slug] (or its
+       [is_temporal] companion) here would wrongly Omit this ordinary
+       saint's commemoration too. *)
+    ( "RG16(a) does NOT fire for an ordinary (non-Sunday) SAINT losing to a \
+       Feast of the Lord -- stays Commemorate(Ordinary)",
+      cand ~origin:P.Sanctoral ~rank:V.Class2 ~subject:Sub.Lord ~layer:PE.universal_layer
+        "transfiguration-of-our-lord",
+      cand ~origin:P.Sanctoral ~rank:V.Class2 ~layer:PE.universal_layer "ef-some-other-saint",
+      "Commemorate(Ordinary)" );
+    (* Conjunct 4/4, WINNER rank: RG 16(a) says "I aut II classis", not any
+       class. Every real [subject = Lord] entry this project's own sanctoral
+       audit found is Class1 or Class2 (this task's own report), so this
+       conjunct is not independently reachable on real data -- SYNTHETIC,
+       the same defensive-but-not-load-bearing status this file already
+       gives the RG26 branch's own [not is_vigil] guard above. Without the
+       rank conjunct, [subject = Lord] alone would wrongly Omit this
+       Sunday's commemoration under a hypothetical Class3 "feast of the
+       Lord" too, which RG 16(a)'s own "I aut II classis" text does not
+       cover. *)
+    ( "SYNTHETIC: RG16(a) does NOT fire for a Class3 feast of the Lord \
+       (outside \"I aut II classis\") impeding a II-class Sunday -- stays \
+       Commemorate(Privileged)",
+      cand ~origin:P.Sanctoral ~rank:V.Class3 ~subject:Sub.Lord ~layer:PE.universal_layer
+        "ef-synthetic-class3-lord-feast",
+      an_ordinary_sunday,
+      "Commemorate(Privileged)" )
   ]
 
 (* Task 9: [privilege_of]'s RG 109 categories (§4, "Commemorations"),
@@ -929,6 +1022,44 @@ let test_ii_class_sunday_privileged_witness_admitted_end_to_end () =
     [ ("ef-some-saint", "omitted: admission limit reached") ]
     (List.map (fun (c, reason) -> (S.to_string c.P.cel.Cel.slug, reason)) resolution.P.omitted)
 
+(* RG 16(a) (register §6.0) reached end-to-end through the REAL pipeline
+   ([PE.band] AND [PE.disposition] together, not [disposition] in
+   isolation as [disposition_cases]'s own rows above test it): a real civil
+   date this task's own blast-radius measurement names as a live instance
+   of the bug this branch fixes -- 6 August 2028 is a Sunday (independently
+   checked with `date -d 2028-08-06 +%A`, the same cross-check discipline
+   [test_golden.ml]'s own header requires), Time after Pentecost week 9, and
+   the Transfiguration (6 Aug, II class, "IN TRANSFIGURATIONE D. N. I. C.")
+   falls on it. Before this fix `colitur day` emitted this Sunday as an
+   admitted [+ef-time-after-pentecost-sunday-9] commemoration on that date
+   (register §6.0's own reproduction); this proves the full pipeline now
+   agrees with the isolated [disposition] rows above: [observed] is the
+   Transfiguration ({!band} entry 14 already did this correctly before this
+   task), [commemorations] is EMPTY (not merely missing the Sunday from
+   [admit]'s cut -- RG 16(a) is a [disposition]-level Omit, before [admit]
+   ever runs), and the Sunday appears in [omitted] with
+   ["omitted: yielded to a higher day"] ({!Precedence.resolve}'s own Omit
+   reason), never ["omitted: admission limit reached"] (that reason would
+   mean the Sunday was tagged [Commemorate] and then cut by [admit] -- a
+   different, wrong mechanism for the same wrong end state). *)
+let test_rg16a_lord_feast_suppresses_sunday_end_to_end () =
+  let date = mk 2028 8 6 in
+  let day_ctx = ctx date in
+  let sunday = of_temporal date in
+  let transfiguration =
+    cand ~origin:P.Sanctoral ~rank:V.Class2 ~subject:Sub.Lord ~layer:PE.universal_layer
+      "transfiguration-of-our-lord"
+  in
+  let resolution = P.resolve real_rules day_ctx ~temporal:sunday ~sanctoral:[ transfiguration ] in
+  Alcotest.(check string) "the Transfiguration is observed, not the Sunday"
+    "transfiguration-of-our-lord" (S.to_string resolution.P.observed.P.cel.Cel.slug);
+  Alcotest.(check int) "no commemorations at all -- RG16(a)'s own \"nulla fit commemoratio\""
+    0 (List.length resolution.P.commemorations);
+  Alcotest.(check (list (pair string string)))
+    "the Sunday is omitted with RG16(a)'s own disposition-level reason, not admit's cut"
+    [ ("ef-time-after-pentecost-sunday-9", "omitted: yielded to a higher day") ]
+    (List.map (fun (c, reason) -> (S.to_string c.P.cel.Cel.slug, reason)) resolution.P.omitted)
+
 (* Completes Task 7's carried fix (RG 91 entry 8, §4): on a real Sunday
    landing on 2 November, All Souls does not merely lose (that was Task 7's
    [band] fix, proved by [test_all_souls_yields_to_sunday] above) -- it must
@@ -1166,6 +1297,10 @@ let suite =
         Alcotest.test_case
           "II-class Sunday override: RG109(b) witness admitted over an ordinary saint, end-to-end"
           `Quick test_ii_class_sunday_privileged_witness_admitted_end_to_end;
+        Alcotest.test_case
+          "RG16(a): a Feast of the Lord suppresses the Sunday's own commemoration entirely, \
+           end-to-end (2028-08-06)"
+          `Quick test_rg16a_lord_feast_suppresses_sunday_end_to_end;
         Alcotest.test_case "transfer_target: general RG96 search walks past more than one blocked day"
           `Quick test_transfer_target_general_multi_step_search;
         Alcotest.test_case "transfer_target: Annunciation exception starts at Monday after Low Sunday"