feat(of): Lectionary_of -- reading-cycle arithmetic and the lectionary chain

Task 4 of Phases 3-5: the last Rite.t field OF still needed, `readings`.

The cycle rules are CODE, cited to OLM (Ordo Lectionum Missae) 1981
Praenotanda -- verified against the real page image
(docs/research/of/olm-1981.pdf pp.32-33/"XXXII-XXXIII"), not the
document's own unreliable OCR text layer, per the design spec's own
caveat. n. 66 (with its footnote 102's worked example, 1980=C/1981=A/
1982=B/1983=C) gives the three-year Sunday cycle; n. 69 point 4 gives
the two-year weekday cycle, Year I in odd label years, Year II in
even. Both derive the "label year" the same way: one more than the
civil year Advent I opened in, per n. 66's footnote 102 itself
("nempe a prima hebdomada Adventus, quae cadit in anno civili
praecedente") -- so the cycle turns at Advent I, not 1 January, exactly
where the task brief said to get it right. The design spec's own
citation for the weekday rule, "Praenotanda n. 649", does not survive
a direct check against the primary source (search finds "649" only in
unrelated index/page-number entries); corrected here to n. 69, the
paragraph the rule's own Latin text actually sits under, confirmed by
the page image's own printed margin number.

The data is bootstrapped from lectio's of-lectionary.ini (988 keys,
niedziela.pl, harvest 2020-2025) by tools/bootstrap_lectionary_of.ml
-- OCaml, not the brief's own suggested .py: tools/bootstrap_lectionary
.ml already established this exact shape for EF, including a real
safety net ([assert_reachable], sweeping Rite_of.Temporal_of.temporal
AND the real merged sanctoral layer directly) that a second-language
reimplementation would either duplicate or lose. Handles two real
data anomalies found while building it: one malformed ini line (a
Polish Septuagint-numbering annotation for Sirach 3, "Syr 3,2-6.12-14"
against OLM/CEI/USA's shared Nova Vulgata, matching the design spec's
own sec5 finding); and two Sunday-cycle-labelled bases (Annunciation,
Immaculate Conception) where a scraping-year artifact left one of
three cycle letters carrying a different day's Mass entirely --
resolved by a general, mechanical 2-of-3 majority rule, not a
per-saint hand edit, and logged.

Coverage measured in both directions, per the brief's own Step 1:
- 1 of 365 days in civil year 2026 (25 December, the Christmas DAY
  Mass) has no Temporal_of-slug match anywhere in lectio's 988 keys --
  only the Vigil is present. Named in the data file's own header.
- 0 of 438 distinct lectio bases map to no colitur slug, after 19 are
  deliberately excluded (late-Advent/Christmas-season DATE-keyed
  duplicates lectio also carries in a WEEKDAY-keyed form colitur's own
  slugs actually match -- Lectionary.t has no date-keyed lookup at
  all, so the date-keyed family is transcription-inert, not silently
  dropped: named explicitly, not a residual).

Lectionary_of.readings is three steps (no Commons indirection, unlike
EF -- out of this task's scope): the observed celebration's own
embedded citations; else, for a real sanctoral winner, its own slug
looked up directly (flat, then both cycle letters); else the day's
own temporal slug, same lookup. No preceding-Sunday fallback: OF's own
two-year cycle assigns every Ordinary Time weekday its own reading by
design, and no OF norm was found instructing otherwise.

Tests (test/test_lectionary_of.ml, 12 cases): a cycle-arithmetic table
straddling Advent 1980/1981/1982/2025 inside single civil years,
reproducing OLM n.66's own worked example directly; SHA-256 pins on
both the emitted file and lectio's own source (embedded in the
provenance header); a pinned, NAMED 2026 coverage result (364 resolve,
exactly {25 December} does not -- never a bare count); two resolution-
chain spot checks (a plain ferial, and a saint's day beating the
ferial it would otherwise fall on); and a real subprocess test that a
missing lectio source file fails the generator loudly, non-zero exit,
no output written -- the exact bug Task 1's own generator shipped and
needed a review round to fix.

dune test: exit 0, 856 tests. make check (COLITUR_EXHAUSTIVE_SWEEP=1,
full 1583-9999 sweep): exit 0, 862 tests, ~342s, both run unpiped in
the foreground. git diff --stat v1.0.0..HEAD -- lib/rites/rite_ef/
lib/kernel/ data/ef/ still empty.

1 files changed, 107 insertions, 0 deletions

diff --git a/lib/rites/rite_of/lectionary_of.ml b/lib/rites/rite_of/lectionary_of.ml
new file mode 100644
index 0000000..1664fad
--- /dev/null
+++ b/lib/rites/rite_of/lectionary_of.ml
@@ -0,0 +1,107 @@
+(* See lectionary_of.mli for the full citations and design argument. *)
+open Colitur_kernel
+
+type sunday_cycle = Year_a | Year_b | Year_c
+type weekday_cycle = Year_i | Year_ii
+
+let sunday_cycle_letter = function Year_a -> "a" | Year_b -> "b" | Year_c -> "c"
+let weekday_cycle_letter = function Year_i -> "i" | Year_ii -> "ii"
+
+(* The civil year in which the liturgical year CONTAINING [date] opened --
+   i.e. the year y such that [year_start y <= date < year_start (y + 1)].
+   This is the one piece of arithmetic both cycle rules share, and it is
+   exactly the "get the boundary right" the task brief names: a date in,
+   say, early December belongs to the liturgical year that opened THAT
+   same Advent only once Advent has actually started that year (compared
+   by real date, not by month) -- a month-based shortcut ("December always
+   means the new liturgical year") is wrong in the (real, if rare) case of
+   a December date still ahead of that year's own Advent I. *)
+let liturgical_year_open_year ~year_start date =
+  let y = Date.year date in
+  if Date.compare date (year_start y) >= 0 then y else y - 1
+
+(* OLM n.66 + footnote 102 (mli's own citation): the LABEL year is the one
+   most of the liturgical year falls in, i.e. one more than the year
+   Advent opened in ("a prima hebdomada Adventus, quae cadit in anno
+   civili praecedente" -- the first week of Advent falls in the PRECEDING
+   civil year relative to the label). Divisible by 3 -> C, then A, then B,
+   worked example 1980=C/1981=A/1982=B/1983=C verified against the real
+   page image. *)
+let sunday_cycle ~year_start date =
+  let label = liturgical_year_open_year ~year_start date + 1 in
+  match label mod 3 with 0 -> Year_c | 1 -> Year_a | _ -> Year_b
+
+(* OLM n.69 point 4 (mli's own citation): "Annus primus adhibetur annis
+   imparibus, annus secundus vero annis paribus" -- Year I in odd label
+   years, Year II in even. Same label-year computation as [sunday_cycle]
+   above, for the identical reason: this is a two-year cycle, not a
+   three-year one, but the label-year definition itself does not depend on
+   which modulus governs it. *)
+let weekday_cycle ~year_start date =
+  let label = liturgical_year_open_year ~year_start date + 1 in
+  if label mod 2 = 1 then Year_i else Year_ii
+
+(* Tries [base] flat, then [base]-<sunday letter>, then [base]-<weekday
+   letter>, in that order. Safe unconditionally: tools/
+   bootstrap_lectionary_of.ml emits a given base under AT MOST ONE of
+   these three forms (a flat entry when the two/three cycle years were
+   byte-identical, a cycle-lettered family otherwise -- never both), so at
+   most one of the three lookups below can ever hit, and trying the two
+   irrelevant forms for a family of the other kind or a flat family is
+   simply two wasted, harmless misses. This is what lets [readings] below
+   stay ignorant of which of the two cycle systems (or neither) a given
+   slug's own family actually uses. *)
+let lookup_any lectionary ~year_start base date =
+  match Lectionary.find lectionary base with
+  | Some cs -> Some cs
+  | None -> (
+      let with_suffix suffix = Slug.of_string_exn (Slug.to_string base ^ "-" ^ suffix) in
+      match Lectionary.find lectionary (with_suffix (sunday_cycle_letter (sunday_cycle ~year_start date))) with
+      | Some cs -> Some cs
+      | None -> Lectionary.find lectionary (with_suffix (weekday_cycle_letter (weekday_cycle ~year_start date))))
+
+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
+  | _ :: _ as cs ->
+      (Some { Mass_formulary.said = Some observed.Celebration.slug; via = Mass_formulary.Proper }, cs)
+  | [] -> (
+      (* Step 2: a sanctoral entity actually won the day -- i.e. the
+         observed celebration is not itself the day's own temporal office.
+         Same guard shape as Rite_ef.Lectionary_ef.readings' own step 4
+         (see that module's implementation comment for the full argument
+         for why this comparison, not a [subject]/[status] test, is the
+         right one): comparing SLUGS is exact whenever the temporal and
+         sanctoral streams cannot collide, which holds here for the
+         identical reason it holds for EF -- every Temporal_of slug this
+         module ever constructs carries the "of-" prefix (temporal_of.ml's
+         own [temporal], every branch), and 0 of the 222 shipped
+         data/of/calendar-2002.sexp + amendments sanctoral slugs do. *)
+      let sanctoral_office =
+        not (Slug.equal observed.Celebration.slug temporal.Temporal.office.Celebration.slug)
+      in
+      match
+        if sanctoral_office then lookup_any lectionary ~year_start observed.Celebration.slug date else None
+      with
+      | Some cs ->
+          (* Mass_formulary.Proper, not .Common -- see lectionary_of.mli's
+             own doc comment on this branch for the full argument. In
+             short: EF's [Common] constructor names a SPECIFIC mechanism
+             (several saints sharing one formulary via an explicit
+             assignment table, data/ef/commons.sexp) that OF's own data has
+             no counterpart for -- every sanctoral slug this step resolves
+             carries its OWN dedicated lectio entry, not a shared one, so
+             relabelling it [Common] would claim a mechanism that is not
+             actually present. [Proper] is the honest fit: "the observed
+             celebration's own proper Mass", true regardless of whether the
+             citations are embedded on Celebration.t (step 1) or held
+             externally in [lectionary] (this step) -- a storage detail
+             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
+          | Some cs ->
+              ( Some { Mass_formulary.said = Some temporal.Temporal.office.Celebration.slug;
+                       via = Mass_formulary.Own_slug },
+                cs )
+          | None -> (None, [])))