kernel(temporal): Holy Thursday is white, per RG128(b)'s named exception

RG 128(b) excepts "Missa sive Chrismatis sive in Cena Domini feria V
Hebdomadae sanctae" from the Septuagesima-to-Easter-Vigil violet span
as a whole-Mass exception (unlike Palm Sunday's blessing/procession,
which the same sentence carves out as only part of that day) -- so
Holy Thursday's Mass is white, not violet. temporal_ef.ml fell through
to the generic Passiontide ferial path (season_colour Passiontide =
violet) for this date, since [named] has no entry for the Triduum at
all (rank was already correct via [privileged_feria]; only colour was
wrong).

Found via Task 16's missalemeum oracle comparison: every other Triduum
day's oracle colour set includes violet as an option (Good Friday
"bv", Holy Saturday "vw" -- already-flagged, deliberately deferred
per-action gaps, register §3b), but Holy Thursday's is white alone.

This is a genuine NEW divergence from lectio too (lectio has no such
exception and still prints violet for Holy Thursday) -- added as
Layer C11 to the differential harness and data/ef/expected-divergences
.sexp, 46 rows (2005-2050), rather than silently changing what that
harness accepts.

Also corrected a stale comment on season_colour claiming white's RG
paragraph was never pinned -- RG 119 was found and cited in the
register on 2026-08-11 but the correction was never copied into this
file's own comment.

1 files changed, 9 insertions, 7 deletions

diff --git a/test/test_differential.ml b/test/test_differential.ml
index dd601a1..a9bdb91 100644
--- a/test/test_differential.ml
+++ b/test/test_differential.ml
@@ -76,13 +76,14 @@
      family would still be caught by everything except the digit itself.
 
    - Layer C (data/ef/expected-divergences.sexp, matched by
-     [layer_c_reason] below): the CITED allow-list. Ten genuine liturgical
-     disagreements, each citing its RG paragraph and stating which engine is
-     right (always colitur, verified against the Missal/register, never
-     against lectio's own behaviour -- "lectio does it differently" is not
-     itself a justification anywhere in this file). This is the ONLY layer
-     that may cover a difference in rank, colour, or which celebration is
-     observed; A and B never do (enforced structurally below: A/B only ever
+     [layer_c_reason] below): the CITED allow-list. Eleven genuine liturgical
+     disagreements (C11 added by Task 16's oracle work, below), each citing
+     its RG paragraph and stating which engine is right (always colitur,
+     verified against the Missal/register, never against lectio's own
+     behaviour -- "lectio does it differently" is not itself a justification
+     anywhere in this file). This is the ONLY layer that may cover a
+     difference in rank, colour, or which celebration is observed; A and B
+     never do (enforced structurally below: A/B only ever
      touch the season/slug fields, and Layer C's predicates each require an
      exact, narrow field-diff SET, not "anything goes").
 
@@ -448,6 +449,7 @@ let layer_c_reason (l : row) (c : row) diffs =
     (String.equal l.date "2011-07-02" || String.equal l.date "2011-07-04")
     && subset diffs [ Slug_f; Rank; Colour_f ]
   then Some "C10"
+  else if String.equal c.slug "ef-passiontide-2-thursday" && diffs = [ Colour_f ] then Some "C11"
   else None
 
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