fix(of-lectionary): stop serving drifting readings for O-Antiphon and Christmas-season dates

The bootstrap excluded 19 lectio bases as "date-keyed duplicates", but
17 of them were not duplicates at all: the 8 O-Antiphon days
(17-24 December) and 8 further Christmas-season dates (29-31 December,
2-5 and 7 January) each carry unique per-date content found nowhere else
among the emitted entries, verified against lectio's own ini directly.
17 December is Gen 49:2,8-10 / Matthew 1:1-17, but colitur was falling
through to that year's unrelated weekday-keyed "advent-3-mon" content
instead.

OLM n. 69.3 explains why: those ferias are fixed by civil date, unlike
every other Advent/Christmastide/Paschaltide feria, which is merely
non-alternating within a weekday slot. Temporal_of's own ferial slugs
for these dates are weekday-keyed, so looking one of those up served
whichever OTHER date happened to share that year's weekday alignment --
a citation that silently drifted year to year on ~16 real civil dates
(6 January stays excluded: Temporal_of fixes Epiphany there
unconditionally, so that date can never reach the ferial path at all;
two more, easter-6-thu and advent-4-sat, stay excluded for their own,
different structural reasons).

Fixed with a date-keyed lookup route (Lectionary_of.date_keyed_slug),
tried before the weekday-keyed one in readings' own step 3.
Temporal_of's slugs are unchanged -- only which lectionary key resolves
a day's citations. tools/bootstrap_lectionary_of.ml now maps the 17
bases to synthetic date-keyed slugs instead of excluding them, and its
own reachability sweep calls date_keyed_slug directly so the two can
never drift apart. Re-emitted data/of/lectionary.sexp (754 -> 770
entries) and corrected its provenance header, which previously
described these dates as excluded duplicates.

Also states, for the first time, a Minor finding from the same review:
190 of 222 shipped sanctoral slugs have no dedicated lectionary entry
and correctly fall through to the ferial per OLM norms -- expected
behaviour, not a gap, but never said in the coverage report before.

New tests pin 17 December (Gen 49:2,8-10 / Matthew 1:1-17) and 2 January
(1 John 2:22-28 / John 1:19-28) in two years with different weekday
alignments, proving neither reading drifts, plus direct boundary
coverage of date_keyed_slug itself (both windows, the 6 January
exclusion, and the Sunday guard).

1 files changed, 34 insertions, 2 deletions

diff --git a/lib/rites/rite_of/lectionary_of.ml b/lib/rites/rite_of/lectionary_of.ml
index 1664fad..eb3e4e0 100644
--- a/lib/rites/rite_of/lectionary_of.ml
+++ b/lib/rites/rite_of/lectionary_of.ml
@@ -60,6 +60,24 @@ let lookup_any lectionary ~year_start base date =
       | Some cs -> Some cs
       | None -> Lectionary.find lectionary (with_suffix (weekday_cycle_letter (weekday_cycle ~year_start date))))
 
+(* See lectionary_of.mli's own doc comment for the full citation (OLM n.
+   69.3) and argument. Kept as ordinary [Printf.sprintf] string
+   construction, not a lookup table, so tools/bootstrap_lectionary_of.ml's
+   own reachability sweep (which calls this function directly, not a
+   hand-copied re-implementation) and this module's own runtime lookup can
+   never drift apart -- the single failure mode a hand-duplicated version
+   in each place would invite. *)
+let date_keyed_slug date =
+  if Date.weekday date = Date.Sun then None
+  else
+    let m = Date.month date and dd = Date.day date in
+    if m = 12 && dd >= 17 && dd <= 24 then Some (Slug.of_string_exn (Printf.sprintf "of-advent-dec-%d" dd))
+    else if m = 12 && dd >= 29 && dd <= 31 then
+      Some (Slug.of_string_exn (Printf.sprintf "of-christmas-dec-%d" dd))
+    else if m = 1 && ((dd >= 2 && dd <= 5) || dd = 7) then
+      Some (Slug.of_string_exn (Printf.sprintf "of-christmas-jan-%d" dd))
+    else None
+
 let readings ~lectionary ~year_start ~(observed : Vocab_of.rank Celebration.t)
     ~(temporal : (Vocab_of.season, Vocab_of.rank) Temporal.t) ~date ~temporal_at:_ =
   match observed.Celebration.citations with
@@ -99,9 +117,23 @@ let readings ~lectionary ~year_start ~(observed : Vocab_of.rank Celebration.t)
              Mass_formulary.source was never built to carry. *)
           (Some { Mass_formulary.said = Some observed.Celebration.slug; via = Mass_formulary.Proper }, cs)
       | None -> (
-          match lookup_any lectionary ~year_start temporal.Temporal.office.Celebration.slug date with
+          (* OLM n. 69.3's own date-fixed windows (see date_keyed_slug's
+             own doc comment): tried BEFORE the ordinary weekday-keyed
+             slug lookup, not instead of it, so every other temporal day
+             is unaffected -- this branch only ever hits inside the two
+             named civil-date windows, and [date_keyed_slug] itself
+             already refuses a Sunday, where a NAMED Sunday office (never
+             one of these weekday-keyed ferial slugs) is what temporal.
+             office actually names. *)
+          match (match date_keyed_slug date with Some s -> Lectionary.find lectionary s | None -> None) with
           | Some cs ->
               ( Some { Mass_formulary.said = Some temporal.Temporal.office.Celebration.slug;
                        via = Mass_formulary.Own_slug },
                 cs )
-          | None -> (None, [])))
+          | None -> (
+              match lookup_any lectionary ~year_start temporal.Temporal.office.Celebration.slug date with
+              | Some cs ->
+                  ( Some { Mass_formulary.said = Some temporal.Temporal.office.Celebration.slug;
+                           via = Mass_formulary.Own_slug },
+                    cs )
+              | None -> (None, []))))