data(ef): close and derive the RG 91 entry 27 allow-list rows

The BVM Saturday office is now genuinely correct, so both comparators'
allow-lists move -- every count derived from the harnesses' own failure
output, never transcribed or guessed.

lectio differential (data/ef/expected-divergences.sexp, C17, new,
colitur): lectio builds no equivalent office at all, so it keeps
showing the plain season colour on every otherwise-unoccupied Class4
Saturday where colitur now shows white. Season, slug and rank all still
agree (the office deliberately reuses the ordinary ferial slug), so
Colour_f alone is the complete diff set -- gated on colitur's own
rank/weekday/colour rather than a date list, the same shape M2 used, at
416 rows over 2005-2050.

missalemeum oracle (data/ef/expected-divergences-missalemeum.sexp): M2
is CLOSED, REMOVED, the same shape as this file's own M4/M6/M7/M9/M12/
M14/M17 precedents -- not re-adjudicated to a different verdict, gone
because the colour divergence it named no longer occurs on any of its
former 22 dates. What is left on all 22 is Observed_identity_unresolved
alone (colitur's BVM-Saturday candidate is temporal-origin and
deliberately carries no English name) -- exactly M18's own shape, not a
distinct citation any more. Keeping M2 as a separate id would have kept
silently absorbing these rows under a stale "colour differs" citation
whose own reason had stopped firing (subset's own diff-set test admits
a SMALLER set than the one named) -- the same "count proving cardinality
where identity was required" trap this project's review process
watches for. M18's own expected_rows moves 373 -> 395 accordingly.

1 files changed, 23 insertions, 0 deletions

diff --git a/test/test_differential.ml b/test/test_differential.ml
index bea1bf4..3f416fd 100644
--- a/test/test_differential.ml
+++ b/test/test_differential.ml
@@ -516,6 +516,28 @@ let holy_name_fallback_dates_2005_2050 =
     "2034-01-02"; "2035-01-02"; "2036-01-02"; "2040-01-02"; "2041-01-02"; "2045-01-02";
     "2046-01-02"; "2047-01-02" ]
 
+(* C17 -- ef-bvm-saturday task: RG 91 entry 27 ("Officium sanctae Mariae in
+   sabbato" -- see data/ef/expected-divergences.sexp's own C17 note for the
+   full RG 78/RG 120(b) citation). lectio builds no equivalent office at all
+   (checked directly against its own tridentine-calendar.ini/generator, the
+   same "genuine upstream gap, not a colitur bootstrap miss" shape C15/C16
+   already document for their own gaps) -- it shows the ordinary season
+   colour on every otherwise-unoccupied Class4 Saturday where colitur's own
+   RG 78 fix now shows white. Season, slug and rank all still agree --
+   temporal_ef.ml's own [bvm_saturday_names] citation ("Slug" paragraph)
+   deliberately REUSES the ordinary ferial slug rather than minting a new
+   one, precisely so this predicate's diff set stays [Colour_f] alone, never
+   [Slug_f] too. Gated on colitur's own [rank]/[weekday]/[colour] rather
+   than a date list, the same shape M2 (data/ef/expected-divergences-
+   missalemeum.sexp) already uses for the identical reason: this
+   population is large (a large fraction of all Saturdays domain-wide) and
+   entirely formulaic (RG 78's own condition, "otherwise unoccupied
+   IV-class Saturday", reduces exactly to this triple), not a short,
+   individually-interesting list of dates the way C14/C15/C16 above are. *)
+let is_bvm_saturday_row (c : row) diffs =
+  diffs = [ Colour_f ] && String.equal c.weekday "saturday" && String.equal c.rank "class-4"
+  && String.equal c.colour "white"
+
 (* [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). *)
@@ -571,6 +593,7 @@ let layer_c_reason (l : row) (c : row) diffs =
     && subset diffs [ Slug_f; Rank ]
     && String.equal c.slug "ef-holy-name"
   then Some "C16"
+  else if is_bvm_saturday_row c diffs then Some "C17"
   else None
 
 (* ---------------------------------------------------------------------- *)