rite(ef): an impeded I-class Sunday commemorates, not transfers

disposition's Class1 branch was unconditional on rank, so an impeded
I-class Sunday (Advent/Lent/Passiontide/Low Sunday) currently
transferred like a feast. RG 95 (register lines 323, 363) restricts the
right of translation to I-class FEASTS -- RG 91's own table lists
Sundays as a separate row (entry 6, line 332) from feasts (entries
11-13, lines 337-339) -- and RG 109(a) (line 374) lists "of a Sunday"
as a privileged commemoration category, which presupposes an impeded
Sunday stays put rather than moving to another day.

Excludes is_sunday_slug losers from the Transfer branch so they fall
through to the existing Commemorate (privilege_of loser) branch, which
already tags them Privileged via RG 109(a) with no further change.

Fires on real dates in the 2005-2050 differential window: 24 December
on Advent IV in 2023, 2028, 2034, 2045; 8 December on an Advent Sunday
in 2024, 2030, 2041.

Verified no previously-passing Transfer assertion used a Sunday-shaped
loser (grepped test_precedence_ef.ml, test_calendar.ml -- which uses
its own synthetic rite unrelated to Precedence_ef.disposition --
test_colitur.ml, test_validate.ml); confirmed by mutation-reverting the
fix and observing exactly the one new test fail, nothing else.

2 files changed, 42 insertions, 21 deletions

diff --git a/lib/rites/rite_ef/precedence_ef.ml b/lib/rites/rite_ef/precedence_ef.ml
index 06bbf7c..ff6f991 100644
--- a/lib/rites/rite_ef/precedence_ef.ml
+++ b/lib/rites/rite_ef/precedence_ef.ml
@@ -383,20 +383,34 @@ let disposition ~(winner : Vocab_ef.rank Precedence.candidate)
        I-class vigil (Nativity, Pentecost) impeded on its own Sunday/
        I-class-feast terms would wrongly transfer instead of vanishing. *)
     Precedence.Omit
-  else if cel.Celebration.rank = Class1 then
-    (* RG 95: only I-class feasts have the right of translation. This is the
+  else if
+    cel.Celebration.rank = Class1
+    && not (is_sunday_slug (Slug.to_string cel.Celebration.slug))
+  then
+    (* RG 95 (register lines 323, 363): only I-class FEASTS have the right
+       of translation -- RG 91's own table lists Sundays as a separate row
+       (entry 6, register line 332) from feasts (entries 11-13, register
+       lines 337-339), so a Sunday is never a "feast" in RG 95's sense, and
+       [is_sunday_slug] (the same marker RG 33's [impedes_vigil] and RG
+       109(a)'s [privilege_of] already use) excludes it here. This is the
        branch that completes Task 7's All Souls fix (register line 334, RG
-       91 entry 8): All Souls is I class and not a vigil, so once it loses
-       to an occurring Sunday it reaches here and transfers -- to 3
-       November per the register, but WHERE it lands is
-       Rite.transfer_target's job (RG 96), not this function's; disposition
-       only says THAT it moves. *)
+       91 entry 8): All Souls is I class, not a vigil, and not a Sunday
+       slug, so once it loses to an occurring Sunday it still reaches here
+       and transfers -- to 3 November per the register, but WHERE it lands
+       is Rite.transfer_target's job (RG 96), not this function's;
+       disposition only says THAT it moves. *)
     Precedence.Transfer
   else
-    (* RG 95's other branch, for everything below I class: "aut
-       commemorantur aut penitus omittuntur" -- commemorated or wholly
-       omitted. Which of the two survives is RG 108-111's admission count
-       ([admit], below), not this function's decision; this only opens the
+    (* RG 95's other branch: "aut commemorantur aut penitus omittuntur" --
+       commemorated or wholly omitted. Reached by everything below I class,
+       AND by an impeded I-class Sunday (excluded from the [Transfer] branch
+       above): RG 109(a) (register line 374) lists "of a Sunday" as a
+       privileged commemoration category, which presupposes an impeded
+       Sunday stays put rather than moving to another day the way a feast
+       does -- [privilege_of] tags it [Privileged] via the same
+       [is_sunday_slug] marker, with no further code needed here. Which of
+       commemorate/omit survives is RG 108-111's admission count ([admit],
+       below), not this function's decision; this only opens the
        commemoration, tagged with its real RG 109 privilege via
        [privilege_of].
 
diff --git a/lib/rites/rite_ef/precedence_ef.mli b/lib/rites/rite_ef/precedence_ef.mli
index 9c3af95..e1b3638 100644
--- a/lib/rites/rite_ef/precedence_ef.mli
+++ b/lib/rites/rite_ef/precedence_ef.mli
@@ -78,19 +78,26 @@ val sunday_marker : string
     - a [Class1] or [Class2] loser whose slug marks it a vigil ({!vigil_suffix})
       is [Omit] when the winner is any Sunday ({!sunday_marker}) or itself
       [Class1] (RG 33 -- entirely omitted, not merely commemorated);
-    - any other [Class1] loser is [Transfer] (RG 95 -- only I class has the
-      right of translation; this is also what moves All Souls, register
-      line 334, once it loses to an occurring Sunday -- WHERE it lands is
-      {!Rite.t.transfer_target}'s job, not this function's);
-    - everything else is [Commemorate], carrying its real RG 109 privilege
-      (see {!admit} below).
+    - any other [Class1] loser that is NOT a Sunday ({!sunday_marker}) is
+      [Transfer] (RG 95, register lines 323, 363 -- only I-class FEASTS have
+      the right of translation; RG 91's own table lists Sundays as a
+      separate row, entry 6, from feasts, entries 11-13, so a Sunday is
+      never a "feast" in RG 95's sense and does not transfer even when
+      impeded by a higher I-class day. This is also what moves All Souls,
+      register line 334, once it loses to an occurring Sunday -- WHERE it
+      lands is {!Rite.t.transfer_target}'s job, not this function's);
+    - everything else -- including an impeded I-class Sunday -- is
+      [Commemorate], carrying its real RG 109 privilege (see {!admit}
+      below); RG 109(a) (register line 374) lists "of a Sunday" as a
+      privileged commemoration category precisely because an impeded Sunday
+      stays put rather than moving to another day.
 
     Total over every winner/loser pair {!Precedence.resolve} or {!Calendar}
     can construct: [Vocab_ef.rank] (RG 8) and {!Celebration.status} are both
-    closed variants, so the four cases above exhaust every representable
-    shape -- there is no fifth, "unclassified" case the way {!band} needs
-    one, because this function's own return type has no such slot to fall
-    into by accident. *)
+    closed variants, so the cases above exhaust every representable shape --
+    there is no fifth, "unclassified" case the way {!band} needs one,
+    because this function's own return type has no such slot to fall into
+    by accident. *)
 val disposition :
   winner:Vocab_ef.rank Precedence.candidate ->
   loser:Vocab_ef.rank Precedence.candidate ->