test(differential): fix round 1 (F2, F5) -- split 13-Jan-Sunday into C13

13 January retagged subject=Lord (previous commit's regeneration) makes
RG16(a) fire on the 7 years it falls on a Sunday within 2005-2050 (2008,
2013, 2019, 2030, 2036, 2041, 2047): colitur now observes the Baptism of
the Lord itself where it used to observe the generic Sunday slug. The diff
signature against lectio's fixture widens from {season;colour} to
{season;slug;colour} -- but jan_6_13_slug already pre-authorised this exact
slug across the whole 6-13 January window (correctly, for the other 39
non-Sunday years), so layer_c_reason routed the new, wider-shape rows into
C1 unchanged, and C1's own expected_rows (a pure row count) did not move.
A count proving cardinality where identity was required -- on the one day
this branch itself already flags as still wrong under RG 112.

Split into its own entry, C13, matched by an exact 7-date literal list
checked before C1 in the if/elif chain. C1's own expected_rows corrected
368 -> 361 (independently re-derived: a Python script reading
data/ef/sanctoral.sexp's regenerated output and the committed lectio
fixture directly, replicating diff_fields/layer_c_reason's own logic
outside the OCaml comparator -- not transcribed from the failing
comparator's own count).

C13's own citation records a refinement over the coordinator's framing,
checked directly rather than assumed: lectio's committed fixture is a
frozen snapshot that predates lectio's own equivalent fix to this entry's
class field (the same staleness shape as C12). Confirmed by building
lectio's own cmd/lectio-ef-dump from its current source tree (read-only)
and running it fresh for all 7 dates -- lectio's LIVE engine now agrees
with colitur's slug/rank/colour exactly, disagreeing only on season (the
already-understood C1 divergence). This is not evidence colitur's answer
is right against the Missal -- it is not (register's own RG112 item) --
only that this specific divergence from the fixture is a staleness
artifact, not a live disagreement between the two engines' current logic.

Also fixes F5: C12's own note said "5 of the 15 corrected slugs" while
listing and counting 7 -- corrected to 7.

Also corrects the module header's stale "13 January ... slug/rank/colour
already equal lectio's exactly, in all 46 years" claim (true only for the
39 non-Sunday years now).

1 files changed, 39 insertions, 5 deletions

diff --git a/test/test_differential.ml b/test/test_differential.ml
index cf5b95f..4d6aab0 100644
--- a/test/test_differential.ml
+++ b/test/test_differential.ml
@@ -88,11 +88,25 @@
      exact, narrow field-diff SET, not "anything goes").
 
    13 January (register §6's long-open "Baptism of the Lord" item) is
-   EMPIRICALLY CONFIRMED FIXED, not allow-listed: colitur's slug/rank/colour
-   for 13 January already equal lectio's exactly, in all 46 years (the
-   sanctoral wiring landed in Task 11's "13 Jan now resolves to the Baptism
-   of the Lord" review note). The only residual difference there is season
-   (covered by Layer C's C1, the Jan 6-13 boundary) -- see the report. *)
+   EMPIRICALLY CONFIRMED FIXED, not separately allow-listed, ONLY in the 39
+   of 46 years it is NOT a Sunday: colitur's slug/rank/colour equal
+   lectio's fixture exactly there (the sanctoral wiring landed in Task 11's
+   "13 Jan now resolves to the Baptism of the Lord" review note), and the
+   only residual difference on those 39 rows is season (covered by Layer
+   C's C1, the Jan 6-13 boundary).
+
+   CORRECTED (ef-rebootstrap fix round 1, F2): this note previously said
+   "in all 46 years" and "the only residual difference is season" without
+   qualification -- WRONG once `commemoration-of-the-baptism-of-the-lord`
+   became `subject = Lord` (ef-rebootstrap): on the remaining 7 years (13
+   January itself falls on a Sunday: 2008, 2013, 2019, 2030, 2036, 2041,
+   2047), RG16(a) now makes colitur observe the Baptism itself where it
+   used to observe the Sunday -- the OBSERVED SLUG differs from lectio's
+   fixture too, not merely colour. Allow-listed separately as C13
+   (`data/ef/expected-divergences.sexp`), whose own note has the full
+   account, including a live cross-check against lectio's CURRENT engine
+   (not the committed fixture, which predates lectio's own equivalent
+   fix) -- see the report. *)
 
 module Cal = Colitur_kernel.Calendar
 module Layer = Colitur_kernel.Layer
@@ -430,12 +444,32 @@ let fixed_iii_class_reclassified_slugs =
     "john-damascene"; "john-of-capistrano"; "john-of-god"; "patrick"; "sts-felicitas-perpetua";
     "thomas-aquinas"; "vincent-ferrer" ]
 
+(* C13 (ef-rebootstrap fix round 1, F2): the 7 years 13 January falls on a
+   Sunday within 2005-2050 -- independently re-derived, not copied from a
+   prior figure: `date -d <year>-01-13 +%A` = Sunday in exactly these 7
+   (2005-2050 is 46 years; 13 January cycles through the 7 weekdays with
+   the usual leap-year irregularity, landing on Sunday this many times).
+   A LITERAL list, not a predicate on [jan_6_13_slug] (which already, and
+   correctly, admits this exact slug for the other 39 non-Sunday years in
+   the window) -- checked BEFORE C1 below in the if/elif chain specifically
+   so it intercepts these 7 dates first; leaving C1's own guard as it was
+   would have let [jan_6_13_slug]'s pre-existing admission of this slug
+   silently absorb them into C1's count instead, the exact gap fix round 1
+   found: C1's own [expected_rows] is a bare row COUNT, blind to WHICH of
+   two different diff shapes produced it, so a real shape change here
+   (colitur's own OBSERVED CELEBRATION on these 7 dates, not merely its
+   colour) could move underneath the pin without the pin ever moving. *)
+let jan13_lord_sunday_dates_2005_2050 =
+  [ "2008-01-13"; "2013-01-13"; "2019-01-13"; "2030-01-13"; "2036-01-13"; "2041-01-13"; "2047-01-13" ]
+
 (* [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). *)
 let layer_c_reason (l : row) (c : row) diffs =
   let m = month_of_date l.date and d = day_of_date l.date in
   if diffs = [] then None
+  else if List.mem l.date jan13_lord_sunday_dates_2005_2050 && diffs = [ Season; Slug_f; Colour_f ] then
+    Some "C13"
   else if
     m = 1 && d >= 6 && d <= 13
     && subset diffs [ Season; Colour_f; Slug_f ]