temporal(ef): Holy Name of Jesus, RG 17(a) -- fallback + Lord subject

RG 17(a): "festum Ss.mi Nominis Iesu, celebrandum dominica quae occurrit
a die 2 ad 5 ianuarii (secus die 2 ianuarii)" -- both photographic scans,
confirmed on the calendarium's own January table and the Mass propers'
own heading. Two defects closed together, since they interact through
RG 91 entry 14/RG 16(a):

1. The Sunday shape (2-5 January) now tags subject = Lord, matching
   RG 91 entry 14 ("Festa Domini II classis") -- previously subject =
   Temporal, the same defect shape Holy Family had before it.
2. The fallback (RG 17(a)'s own "secus die 2 ianuarii", the calendarium's
   "vel, ea deficiente, die 2 ianuarii") is now built: 2 January carries
   the feast whenever no Sunday falls 2-5 January that year. Before this
   fix colitur emitted no Holy Name office at all in such a year -- a
   real II-class feast simply missing, on 3,619 of 8,417 years in the
   domain (43%; 20 of the 46 years 2005-2050, independently re-derived
   against `date -d`).

Both shapes band identically at RG 91 entry 14's MOVABLE half
(Precedence_ef.entry_14_movable_band) -- one feast, not two differently
classified ones, per the Mass propers' own single heading covering both
dates. No live collision exists in the current sanctoral data (nothing
fixed-date falls 2-5 January besides a Commemoration_only entry on 5
Jan), so the RG 16(a)/RG 112(a) interaction is proved with synthetic
precedence-level fixtures mirroring Holy Family's own precedent, not a
live-data regression. One asymmetry the synthetic tests found and kept
honest rather than forced: a losing Holy-Name-Sunday is privileged
(RG 109(a), "of a Sunday") and survives RG 111(a)'s cap; a losing
Holy-Name-fallback is not (2 January is not a Sunday, and no other
RG 109(a)-(f) category applies to it), so it gets no commemoration at
all if ever outranked -- both individually correct readings of RG 109/111's
closed lists.

Golden pins follow the brief's own vacuity warning: the Sunday shape
already emitted the right slug/rank/colour before this fix (an ordinary
Sunday and Holy Name coincide on those fields), so its pin asserts
subject explicitly rather than pinning the whole line uncritically; the
fallback pin (2029-01-02) is the one with teeth against the larger
defect, reddening on slug/rank/subject together if reverted.

Mutation-tested: each half of the fix reverted separately reddens
exactly its own tests (Sunday subject: the dedicated unit test, the
golden pin's subject field, one precedence end-to-end test; fallback:
the fallback unit/anchor/golden tests, the new C16 differential count,
and both shapes of the precedence end-to-end tests) and nothing else.

Adds data/ef/expected-divergences.sexp's C16 (lectio has no fallback for
this window at all) -- the lectio differential's own count, independently
re-derived against `date -d` for the fixture's 2005-2050 span, not
transcribed from the domain-wide figure. The missalemeum oracle window
(2026-2027) exercises only the Sunday shape and needed no new entry:
subject is not one of its compared fields, and both years' rows already
corroborate the Sunday-shape ranking (missalemeum's own 2026-01-04 and
2027-01-03 rows: rank 2, white, title "Holy Name of Jesus").

1 files changed, 21 insertions, 0 deletions

diff --git a/test/test_differential.ml b/test/test_differential.ml
index 94adb2c..bea1bf4 100644
--- a/test/test_differential.ml
+++ b/test/test_differential.ml
@@ -500,6 +500,22 @@ let joseph_annunciation_collision_dates_2005_2050 = [ "2008-04-01"; "2035-04-03"
 let holy_family_baptism_collision_dates_2005_2050 =
   [ "2008-01-13"; "2013-01-13"; "2019-01-13"; "2030-01-13"; "2036-01-13"; "2041-01-13"; "2047-01-13" ]
 
+(* C16 -- ef-holyname-rg110 task: RG 17(a)'s own fallback (2 January, "secus
+   die 2 ianuarii"), for every civil year 2005-2050 with no Sunday 2-5
+   January -- independently re-derived against `date -d <year>-01-0{2..5}
+   +%u`, not transcribed from the register's domain-wide figure (see
+   data/ef/expected-divergences.sexp's own C16 note for the full citation
+   and the derivation). lectio has no equivalent fallback at all (checked
+   directly against tridentine-calendar.ini, which carries no 01-02 entry),
+   so it shows the plain Christmastide ferial slug on every one of these
+   dates, class-4 -- colitur's own `ef-holy-name`, class-2, is a genuine
+   [Slug_f; Rank] divergence, not a naming synonym Layer A could absorb. *)
+let holy_name_fallback_dates_2005_2050 =
+  [ "2006-01-02"; "2007-01-02"; "2008-01-02"; "2012-01-02"; "2013-01-02"; "2017-01-02";
+    "2018-01-02"; "2019-01-02"; "2023-01-02"; "2024-01-02"; "2029-01-02"; "2030-01-02";
+    "2034-01-02"; "2035-01-02"; "2036-01-02"; "2040-01-02"; "2041-01-02"; "2045-01-02";
+    "2046-01-02"; "2047-01-02" ]
+
 (* [layer_c_reason l c diffs] returns the [data/ef/expected-divergences.sexp]
    [id] this row-pair's remaining (post Layer A/B) diff set belongs to, or
    [None] if nothing here explains it (a genuine, uncovered failure). *)
@@ -550,6 +566,11 @@ let layer_c_reason (l : row) (c : row) diffs =
     && subset diffs [ Season; Slug_f ]
     && String.equal c.slug "ef-time-after-epiphany-sunday-1"
   then Some "C15"
+  else if
+    List.mem l.date holy_name_fallback_dates_2005_2050
+    && subset diffs [ Slug_f; Rank ]
+    && String.equal c.slug "ef-holy-name"
+  then Some "C16"
   else None
 
 (* ---------------------------------------------------------------------- *)