path: root/test/test_differential.ml

(* Task 15: differential harness vs lectio (sibling project, Go), EF only,
   2005-2050 -- validation layer 3 of the design spec's five (colitur CLAUDE.md
   "Validation" section; layers 1-2, Types and Property, are already built and
   green). lectio's own EF stream is committed as a fixture
   (test/fixtures/lectio-ef-2005-2050.txt, provenance -- including the
   SHA-256 this file's own [test_fixture_checksum] asserts, so a hand-edit or
   partial re-copy of the fixture fails loudly rather than silently becoming
   an unlabelled snapshot -- in the sibling .provenance file next to it);
   colitur's side is recomputed fresh from this library on every run, through
   the SAME pipeline `colitur day` uses (Colitur_kernel.Calendar over the
   real data/ef/sanctoral.sexp + adjustments.sexp), not the compiled binary.

   *** THREE STATED LIMITS THIS COMPARATOR DOES NOT PRETEND TO EXCEED ***

   1. Commemorations are NOT compared. lectio's trailing "+other-slug" tokens
      are the LOSING sanctoral candidates for the day (its own dumper's doc
      comment says so), not an RG 111 admitted set -- lectio has no RG 111
      admission logic at all. Comparing that column would compare colitur's
      real admitted commemorations against lectio's rejects, which proves
      nothing. Of the eleven fixed columns the fixture's own dumper now
      prints, nine are read from either stream: the original seven (date
      weekday season week slug rank colour) plus, since Task 8, the two
      reading-citation columns (first, gospel) -- name_en/name_pl (the
      remaining two) are parsed and immediately discarded, never compared
      (this file's own [row_of_line] comment says why).

   2. lectio's own EF oracle test (~/git/projects/lectio,
      internal/calendar/oracle_ef_test.go) asserts ONLY season, strictly,
      against missalemeum, and ONLY for 2025-2026. Rank and colour are logged
      there, never asserted. So lectio's advertised "0-error vs references
      2005-2050" covers season-exactness for the EF, not full-row-exactness.
      A rank or colour difference below is therefore NOT presumptive evidence
      that colitur is wrong -- every one is adjudicated against the Missal/RG
      register directly (data/ef/expected-divergences.sexp), never against
      lectio's say-so. (Layer 4, the oracle differential against missalemeum
      itself, is what actually validates rank and colour; that is a later
      task.)

   3. The WEEK column is not compared, at all, on either side. Two reasons,
      both confirmed by reading lectio's own source
      (cmd/lectio-ef-dump/main.go's doc comment): first, lectio prints week
      "0" (rendered "-") "where no season week applies, e.g. named I class
      feasts and per annum green-season ferias" -- an internal DISPLAY
      convention of lectio's, not a liturgical fact, so there is nothing to
      cross-check it against. Second, even where both sides print a real
      number, the two engines anchor Time-after-Epiphany week numbering
      differently (colitur: the first Sunday on/after Epiphany; lectio: a
      fixed offset from 6 January -- register §3c item 5) and the offset
      between them is NOT constant (it depends on which weekday 6 January
      falls on, and re-synchronises mid-season), so no clean formula-based
      check is possible without reimplementing lectio's own algorithm here.
      Slug identity, rank and colour -- where the real liturgical substance
      lives -- remain fully and separately compared; only the bare integer
      is out of scope. See the report for the concrete rows this weakens.

   *** THE THREE-LAYER DESIGN (controller ruling, Task 15 dispatch) ***

   REFRESHED (2026-08-12, task 2026-08-12-colitur-rg16a, branch ef-rebootstrap):
   the fixture was regenerated from lectio's CURRENT HEAD (3b32c00), which has
   fixed seven EF calendar defects since the fixture was first pinned (commit
   2386a45) -- see the fixture's own provenance note for the exact commits and
   defect list. Of 16801 day-pairs (2005-2050), 11826 now already match on the
   raw seven columns (up from roughly 11201 against the stale fixture); of the
   4975 that don't, only 10 distinct RAW (field-diff, including the
   never-compared week column) signatures cover all of them, independently
   recomputed against this fixture and colitur's current output, not copied
   from the original task-15-class-summary.txt (which described the OLD
   fixture and is stale). After Layers A and B below strip the week column and
   the vocabulary/numbering artifacts, only 540 of those 4975 remain genuine
   differences -- all 540 explained by Layer C (368 + 138 + 31 + 3, see each
   entry's own citation), 0 unexplained. They resolve into three strictly
   separate layers:

   - Layer A (this file's [norm_season]/[norm_slug]): vocabulary. A
     declarative, explicit, closed table of naming synonyms that carry no
     liturgical substance -- lectio's "easter"/"christmas" ARE colitur's
     "paschaltide"/"christmastide"; a handful of slugs are two different
     engines' names for the identical office (Christmas Vigil, Holy Name
     Sunday, the Pentecost-octave Ember days, the two Passiontide weeks).
     Every entry is a literal string pair, never a pattern -- widening this
     to a wildcard is exactly how a real bug would get hidden, so it is not
     done even where it would shorten the table.

   - Layer B ([strip_epiphany_index]): numbering. The ONE case in the whole
     4975 where a slug's embedded index genuinely cannot be reconciled by a
     literal table (Time-after-Epiphany's non-constant offset, limit 3
     above) -- both sides' embedded week digit is stripped to a common
     family+weekday form before comparing, while rank and colour (which
     carry no week-index information for an ordinary green-season
     feria/Sunday) remain fully compared, so a genuine identity bug in this
     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. Each entry cites its RG
     paragraph and states 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").

   REFRESHED (2026-08-12, ef-rebootstrap fixture regeneration): lectio's own
   fix wave (2386a45 -> 3b32c00, provenance note has the full commit list)
   independently fixed the exact defects nine of the thirteen entries this
   file used to carry were about -- C2, C3, C4, C5, C7, C10, C11, C12 and C13
   all now match ZERO rows against the refreshed fixture and were CLOSED
   (removed from data/ef/expected-divergences.sexp and from
   [layer_c_reason] below), each with its citation preserved and the closure
   recorded in docs/research/rules-register.md, not silently deleted -- see
   the report for the full before/after account. C9's old shape ("St Joseph
   observed ON a Lent Sunday", lectio's own defect 4) also closed the same
   way, but a NARROWER, different divergence involving the same saint
   survived the refresh and was re-cited as a new entry, C14 (below), not
   folded back into the old C9 id (the two are different rules; conflating
   them would be exactly the "count proving cardinality where identity was
   required" vacuity flavour this project's harnesses are specifically
   checked against). Three entries survive unchanged in kind: C1 (368 rows,
   up from 361 -- the 7 rows C13 used to carve out fold back into C1's own
   shape now that lectio's slug matches there too, see C1's own note), C6
   (138 rows, unchanged count but a narrower shape -- lectio fixed the RANK
   this entry used to also cover, leaving only the SLUG naming difference,
   see C6's own note) and C8 (31 rows, wholly unchanged -- lectio still
   computes no Rogation days at all).

   13 January (register §6's long-open "Baptism of the Lord" item) is
   EMPIRICALLY CONFIRMED FIXED, not separately allow-listed, in ALL 46 years
   again as of this refresh: lectio's own fix wave independently fixed its
   equivalent of the same RG16(a) defect the now-closed C13 used to allow-
   list (its slug now matches colitur's `commemoration-of-the-baptism-of-
   the-lord` on all 7 of the Sunday years too, not only the 39 non-Sunday
   ones), so the residual difference on every one of the 46 rows is season
   alone -- covered by C1, the Jan 6-13 boundary, with no separate entry
   needed any more. *)

module Cal = Colitur_kernel.Calendar
module Layer = Colitur_kernel.Layer
module Overlay = Colitur_kernel.Overlay
module LD = Colitur_kernel.Liturgical_day
module Slug = Colitur_kernel.Slug
module Date = Colitur_kernel.Date
module Cel = Colitur_kernel.Celebration
module Colour = Colitur_kernel.Colour
module Subject = Colitur_kernel.Subject
module Citation = Colitur_kernel.Citation
module V = Rite_ef.Vocab_ef

(* Same relative paths test_rite_ef.ml/test_sanctoral_ef.ml use: dune test
   runs from _build/default/test/. *)
let sanctoral_path = "../data/ef/sanctoral.sexp"
let adjustments_path = "../data/ef/adjustments.sexp"
let fixture_path = "fixtures/lectio-ef-2005-2050.txt"
let allow_list_path = "../data/ef/expected-divergences.sexp"

(* The fixture's own provenance note (test/fixtures/lectio-ef-2005-2050.provenance)
   records this same digest, so it is discoverable by a reader who never runs
   the suite. Recorded here too, and ASSERTED (fix round 1, finding 4): a
   provenance note is enough to REGENERATE the fixture but says nothing about
   whether the committed bytes still match the commit they claim to come
   from -- an unnoticed hand-edit or partial re-copy would silently turn the
   whole oracle into an unlabelled snapshot of whatever someone last ran.
   Regenerate this constant (and the provenance note's copy) together,
   deliberately, after re-running the exact command the provenance note
   names -- never by copying the actual value back in to make a mismatch
   pass, which would defeat the point of pinning it at all. *)
let fixture_sha256 = "8c0b9d9fc284138e69dbbbd87e9153a17f1abb69a39928464d83d248a819f376"

(* Same technique tools/bootstrap_sanctoral.ml already uses for this exact
   purpose (that file's own comment: shelling out to the system's
   [sha256sum], not an OCaml crypto library -- Task 15's deps are frozen).
   Unlike that tool, this avoids even the (already-permitted, per that
   file's own comment, "already in the switch") [unix] library: [Sys.command]
   plus a redirected-to-file capture needs nothing beyond the Stdlib every
   dune executable already links. Depends on [sha256sum] being on PATH,
   which every environment this suite has actually run in (Debian, per
   CLAUDE.md) provides via coreutils; a machine without it fails this check
   with a command-not-found exit code rather than silently skipping it. *)
let sha256_of_file path =
  let tmp = Filename.temp_file "colitur_differential_sha256" ".txt" in
  Fun.protect
    ~finally:(fun () -> try Sys.remove tmp with Sys_error _ -> ())
    (fun () ->
      let cmd = Printf.sprintf "sha256sum %s > %s" (Filename.quote path) (Filename.quote tmp) in
      let rc = Sys.command cmd in
      if rc <> 0 then Alcotest.failf "sha256sum exited %d for %s (is it on PATH?)" rc path;
      let ic = open_in tmp in
      let line =
        try input_line ic
        with End_of_file ->
          close_in ic;
          Alcotest.failf "sha256sum produced no output for %s" path
      in
      close_in ic;
      match String.index_opt line ' ' with
      | Some i -> String.sub line 0 i
      | None -> Alcotest.failf "unexpected sha256sum output for %s: %S" path line)

let real_layer () =
  let layer =
    match Layer.load V.rank_of_sexp sanctoral_path with
    | Ok l -> l
    | Error e -> Alcotest.failf "%s: failed to load: %s" sanctoral_path e
  in
  let overlay =
    match Overlay.load V.rank_of_sexp adjustments_path with
    | Ok o -> o
    | Error e -> Alcotest.failf "%s: failed to load: %s" adjustments_path e
  in
  let layer, diagnostics = Overlay.apply layer overlay in
  Alcotest.(check (list string)) "the committed overlay applies cleanly, no diagnostics" []
    (List.map Overlay.diagnostic_to_string diagnostics);
  layer

(* [Rite_ef.context] takes [~lectionary] (fix round 1, coordinator review) --
   caller-supplied, same as [real_layer] above. *)
let real_lectionary () =
  match Colitur_kernel.Lectionary.load "../data/ef/lectionary.sexp" with
  | Ok l -> l
  | Error e -> Alcotest.failf "../data/ef/lectionary.sexp: failed to load: %s" e

(* The Commons (data/ef/commons.sexp) travel the same caller-supplied seam
   as the lectionary above, and [~commons] is required rather than defaulted
   so that no caller can silently run with none -- nothing in layers 3-5
   compares reading citations, so a rite quietly missing its Commons would
   be invisible. Loaded here even where this file asserts nothing about
   readings, so that the rite under test is the same one bin/main.ml
   assembles. *)
let real_commons () =
  match Rite_ef.Lectionary_ef.Commons.load "../data/ef/commons.sexp" with
  | Ok c -> c
  | Error e -> Alcotest.failf "../data/ef/commons.sexp: failed to load: %s" e

(* --- The seven-column row both streams share (commemorations excluded, --- *)
(* limit 1 above). *)
type row = {
  date : string;
  weekday : string;
  season : string;
  week : string;
  slug : string;
  rank : string;
  colour : string;
  (* Fix round 1 (coordinator finding F3): ONLY ever populated for colitur's
     own row (see [colitur_rows_2005_2050] below) -- lectio's own fixture
     format has no subject column at all, so [row_of_line] (the lectio-side
     parser) sets this to "-", a placeholder never read on that side. Every
     Layer C predicate that reads [subject] must therefore read it off the
     COLITUR row [c], never [l] -- the same asymmetry [row]'s other fields
     do not have, called out here rather than left implicit. *)
  subject : string;
  (* Task 8: the day's resolved Epistle/Lesson and Gospel citations, ALREADY
     DECODED (lectio's own "_"-for-space convention reversed at parse time,
     [decode_field] below; colitur's own [Citation.reference] never contains
     an underscore in the first place, so decoding it is a no-op) -- both
     sides therefore carry the same "-" sentinel for "no reading resolved"
     that the fixture's own name/week columns already use, so a plain
     [String.equal] is the whole comparison, matching every other field in
     this record. *)
  first : string;
  gospel : string;
}

let read_lines path =
  let ic = open_in path in
  let rec loop acc =
    match input_line ic with
    | line -> loop (line :: acc)
    | exception End_of_file ->
        close_in ic;
        List.rev acc
  in
  loop []

(* Reverses the fixture's own "_" -for-space, "-" -for-absent encoding
   (shared by the name_en/name_pl columns and, since Task 7's
   lectio-ef-dump refresh, by first/gospel too -- see the fixture's own
   .provenance note). Verified against the real file, not assumed: a
   citation like ["Rom_13:11-14"] round-trips to ["Rom 13:11-14"], and the
   literal sentinel ["-"] (no underscore in it) passes through unchanged,
   so one function serves both the "real value" and the "absent" case
   without a special-cased branch. *)
let decode_field s = String.map (fun c -> if c = '_' then ' ' else c) s

let row_of_line line =
  match String.split_on_char ' ' line with
  | date :: weekday :: season :: week :: slug :: rank :: colour :: _name_en :: _name_pl :: first
    :: gospel :: _others ->
      { date;
        weekday;
        season;
        week;
        slug;
        rank;
        colour;
        subject = "-";
        first = decode_field first;
        gospel = decode_field gospel
      }
  | _ -> Alcotest.failf "malformed fixture line (fewer than 11 fields): %S" line

let lectio_rows () = List.map row_of_line (read_lines fixture_path)

(* Recomputes colitur's day-by-day output straight from the library --
   exactly [Colitur_kernel.Calendar.year] + [Rite_ef.context] over the real
   committed data, the same pipeline bin/main.ml's `colitur day` runs (that
   file's own [day_report]/[day_line] comments explain the two-liturgical-
   year-per-civil-year indexing this mirrors). Duplicated here rather than
   shared with bin/main.ml (an executable, not a library) -- the same choice
   test_rite_ef.ml already made for [real_layer] above. *)
let colitur_rows_2005_2050 () =
  let layer = real_layer () in
  let rite = Rite_ef.context ~lectionary:(real_lectionary ()) ~commons:(real_commons ()) in
  let by_rata : (int, (V.season, V.rank) LD.t) Hashtbl.t = Hashtbl.create 20000 in
  for y = 2004 to 2050 do
    let days = Cal.year rite layer y in
    Array.iter (fun (d : (V.season, V.rank) LD.t) -> Hashtbl.replace by_rata (Date.to_rata d.LD.date) d) days
  done;
  let mk y m d = match Date.make ~year:y ~month:m ~day:d with Ok t -> t | Error e -> failwith e in
  let rows = ref [] in
  for y = 2005 to 2050 do
    let d = ref (mk y 1 1) in
    let stop = mk y 12 31 in
    while Date.compare !d stop <= 0 do
      (match Hashtbl.find_opt by_rata (Date.to_rata !d) with
      | Some day ->
          let t = day.LD.temporal in
          let cel = day.LD.observed in
          let week =
            match t.Colitur_kernel.Temporal.week with Some n -> string_of_int n | None -> "-"
          in
          (* [Rite.readings] already resolved the day's citations (calendar.ml's
             own [build_day]); this just projects the ONE reading of each
             PART lectio's own dumper prints ("first"/"gospel" -- neither
             engine's EF stream carries Psalm/Second/Tract/etc, task-7-report.md's
             own note on why). "-" for a part with no resolved reading, the
             same sentinel [row_of_line]'s [decode_field] leaves an absent
             lectio field as, so the two sides compare with a plain
             [String.equal] like every other field here. *)
          let citation_ref part =
            match List.find_opt (fun (c : Citation.t) -> c.Citation.part = part) day.LD.citations with
            | Some c -> c.Citation.reference
            | None -> "-"
          in
          rows :=
            { date = Date.to_iso8601 day.LD.date;
              weekday = Date.weekday_to_string t.Colitur_kernel.Temporal.weekday;
              season = V.season_to_string t.Colitur_kernel.Temporal.season;
              week;
              slug = Slug.to_string cel.Cel.slug;
              rank = V.rank_to_string cel.Cel.rank;
              colour = Colour.to_string cel.Cel.colour;
              subject = Subject.to_string cel.Cel.subject;
              first = citation_ref Citation.First;
              gospel = citation_ref Citation.Gospel
            }
            :: !rows
      | None -> Alcotest.failf "internal error: no resolved day for %s" (Date.to_iso8601 !d));
      d := Date.add_days !d 1
    done
  done;
  List.rev !rows

(* ---------------------------------------------------------------------- *)
(* Layer A: vocabulary. Explicit, closed tables; no wildcards, no pattern  *)
(* matching against arbitrary content -- every case below is a literal    *)
(* string compared against a literal string.                             *)
(* ---------------------------------------------------------------------- *)

(* lectio's season word -> colitur's season word. The ONLY two seasons that
   are spelled differently; every other season word is shared verbatim
   (both call Advent "advent", Lent "lent", etc.). *)
let norm_season = function
  | "easter" -> "paschaltide"
  | "christmas" -> "christmastide"
  | s -> s

let weekdays = [ "monday"; "tuesday"; "wednesday"; "thursday"; "friday"; "saturday" ]

(* lectio's slug -> the colitur slug for the SAME office, where the two
   projects simply chose different names. [month]/[lectio_rank] disambiguate
   the two cases where lectio reuses one slug for what colitur names two
   different ways (see each branch's own comment). *)
let rec norm_slug ~month ~lectio_rank slug =
  if String.equal slug "vigil-of-christmas" then "ef-nativity-vigil"
    (* register §6: lectio names its vigils "vigil-of-X" (prefix); colitur's
       own convention is "X-vigil" (suffix). Same celebration -- confirmed a
       genuine duplicate in Task 11, where colitur's overlay suppresses
       lectio's key entirely from the sanctoral layer. *)
  else if
    (* "ef-christmas-sunday-0"/"ef-christmas-0-<weekday>" mean TWO different
       things in lectio depending on which window they fall in: the Sunday
       within Holy Name week (2-5 January, colitur's own named feast) or an
       ordinary day within the Nativity Octave (26-31 December, where colitur
       uses its own ef-nativity-octave-day-N naming instead, Layer C's C6 --
       that window keeps a genuine RANK difference too, so it must not be
       absorbed here). Gating on [month = 1] keeps this table from ever
       touching the December occurrence. *)
    month = 1
  then
    if String.equal slug "ef-christmas-sunday-0" then "ef-holy-name-sunday"
    else
      match List.find_opt (fun wd -> String.equal slug ("ef-christmas-0-" ^ wd)) weekdays with
      | Some wd -> "ef-christmas-1-" ^ wd
      | None -> norm_slug_rest ~lectio_rank slug
  else norm_slug_rest ~lectio_rank slug

and norm_slug_rest ~lectio_rank slug =
  (* Passiontide: lectio never distinguishes Passion week (colitur's week 1,
     class-3 ferias) from Holy week (colitur's week 2, class-1 ferias) in the
     slug -- both print "ef-passiontide-0-<weekday>". Rank, independently and
     strictly compared elsewhere, is what actually tells the two weeks apart
     (RG 91 entries 22 vs 2/7), so using it here to pick the expected colitur
     digit does not launder away a genuine identity bug: a colitur bug that
     mixed up the two weeks would, on the evidence available in this stream,
     also very likely show up as a rank mismatch of its own. *)
  match List.find_opt (fun wd -> String.equal slug ("ef-passiontide-0-" ^ wd)) weekdays with
  | Some wd -> (
      match lectio_rank with
      | "class-3" -> "ef-passiontide-1-" ^ wd
      | "class-1" -> "ef-passiontide-2-" ^ wd
      | _ -> slug)
  | None -> (
      match slug with
      | "ef-easter-8-wednesday" -> "ef-pentecost-ember-wed"
      | "ef-easter-8-friday" -> "ef-pentecost-ember-fri"
      | "ef-easter-8-saturday" -> "ef-pentecost-ember-sat"
      | s -> s)

(* ---------------------------------------------------------------------- *)
(* Layer B: numbering (register §3c item 5). The Time-after-Epiphany       *)
(* week-index embedded in a slug is stripped to a common form on BOTH     *)
(* sides before comparing -- see limit 3 in this file's header comment    *)
(* for why a table (Layer A's tool) cannot do this instead.               *)
(* ---------------------------------------------------------------------- *)

let starts_with ~prefix s =
  let lp = String.length prefix in
  String.length s >= lp && String.equal (String.sub s 0 lp) prefix

let is_digit_string s = s <> "" && String.for_all (fun c -> c >= '0' && c <= '9') s

let strip_epiphany_index slug =
  let prefix = "ef-time-after-epiphany-" in
  if not (starts_with ~prefix slug) then slug
  else
    let rest = String.sub slug (String.length prefix) (String.length slug - String.length prefix) in
    match String.index_opt rest '-' with
    | None -> slug
    | Some i ->
        let left = String.sub rest 0 i in
        let right = String.sub rest (i + 1) (String.length rest - i - 1) in
        if is_digit_string left && List.mem right weekdays then prefix ^ right
        else if String.equal left "sunday" && is_digit_string right then prefix ^ "sunday"
        else slug

(* ---------------------------------------------------------------------- *)
(* Field-diff computation: applies Layers A and B, then reports exactly   *)
(* which of the SEVEN substantive columns still differ (week is never     *)
(* inspected at all -- limit 3). weekday is included defensively: dates   *)
(* are checked 1:1 aligned before this runs, so it should never fire, and *)
(* if it ever does that is real signal, not noise to normalise away.      *)
(*                                                                        *)
(* Task 8: First_f/Gospel_f join the SAME diff set the other five fields  *)
(* share -- deliberately, not a separate pass gated on "only when the day *)
(* otherwise matches". A citation difference on a day whose identity      *)
(* ALSO differs is not a second, independent fact needing its own         *)
(* citation -- it is the same divergence Layer C already explains         *)
(* (different office observed, therefore a different Mass read); each     *)
(* Layer C predicate below is widened to accept First_f/Gospel_f          *)
(* alongside its own existing field set wherever that is what the real    *)
(* fixture data shows, never blanket-permitted. *)
(* ---------------------------------------------------------------------- *)

type field = Weekday | Season | Slug_f | Rank | Colour_f | First_f | Gospel_f

let field_name = function
  | Weekday -> "weekday"
  | Season -> "season"
  | Slug_f -> "slug"
  | Rank -> "rank"
  | Colour_f -> "colour"
  | First_f -> "first"
  | Gospel_f -> "gospel"

let month_of_date date = int_of_string (String.sub date 5 2)

let diff_fields (l : row) (c : row) =
  let m = month_of_date l.date in
  let l_season = norm_season l.season in
  let l_slug = strip_epiphany_index (norm_slug ~month:m ~lectio_rank:l.rank l.slug) in
  let c_slug = strip_epiphany_index c.slug in
  List.filter_map
    (fun x -> x)
    [ (if String.equal l.weekday c.weekday then None else Some Weekday);
      (if String.equal l_season c.season then None else Some Season);
      (if String.equal l_slug c_slug then None else Some Slug_f);
      (if String.equal l.rank c.rank then None else Some Rank);
      (if String.equal l.first c.first then None else Some First_f);
      (if String.equal l.gospel c.gospel then None else Some Gospel_f);
      (if String.equal l.colour c.colour then None else Some Colour_f)
    ]

(* ---------------------------------------------------------------------- *)
(* Layer C: the cited allow-list (data/ef/expected-divergences.sexp).     *)
(* Each predicate below names the [id] it matches; the sexp file carries  *)
(* that id's citation, verdict and expected row count. A predicate fires  *)
(* only on an EXACT, narrow field-diff set -- never "any difference at    *)
(* all" -- so it cannot silently absorb a difference outside what its own *)
(* citation actually explains.                                            *)
(* ---------------------------------------------------------------------- *)

let subset xs ys = List.for_all (fun x -> List.mem x ys) xs
let day_of_date date = int_of_string (String.sub date 8 2)

(* ef-rebootstrap fixture refresh (2026-08-12): C2, C3, C4, C5, C7, C10, C11,
   C12 and C13's own predicates/helper bindings (sunday_iclass_slugs,
   rose_sunday_slugs, advent_feria_slug, fixed_iii_class_reclassified_slugs,
   jan13_lord_sunday_dates_2005_2050, and the inline C7/C10/C11 date/slug
   checks) are REMOVED here, not left dead -- each matched zero rows against
   the refreshed fixture (lectio's own fix wave, 2386a45 -> 3b32c00,
   independently fixed the exact defects these entries were about), so their
   citations moved to docs/research/rules-register.md (closure record, with
   the RG paragraph preserved) and their sexp rows to nothing --
   data/ef/expected-divergences.sexp no longer declares those ids at all.
   Removing a predicate strengthens this harness the same way removing its
   sexp row does: if any of these nine shapes ever reappears (a regression in
   colitur, or lectio moving again), it now surfaces as UNEXPLAINED instead
   of being silently re-absorbed by a citation whose own divergence no
   longer exists. *)

(* Fix round 1, finding 1: C1 and C6 (below) originally gated on calendar
   date alone, with no slug/slug-family check -- unlike every other entry
   here. The reviewer constructed the failure this leaves open: if a future
   sanctoral regeneration made some OTHER 29-31 December celebration win the
   day (colliding coincidentally with C6's own [Slug_f; Rank] diff shape),
   it would be silently absorbed under "RG 91 entry 17, Nativity Octave" --
   a citation that has nothing to do with the real cause. [subset diffs
   [...]] alone was never enough; the SLUG that actually won must also be
   the one each citation is about. Both lists below are exact literals (the
   Nativity Octave's three colitur-only day slugs; the closed set of
   offices that can legitimately observe C1's Jan 6-13 window), not
   patterns -- a slug outside them fails through to [None] instead of being
   absorbed. *)
let jan_6_13_slug slug =
  String.equal slug "ef-epiphany"
  || String.equal slug "commemoration-of-the-baptism-of-the-lord"
  || List.exists (fun wd -> String.equal slug ("ef-christmas-2-" ^ wd)) weekdays

let nativity_octave_day_slugs =
  [ "ef-nativity-octave-day-5"; "ef-nativity-octave-day-6"; "ef-nativity-octave-day-7" ]

(* C18 (ef-sanctoral-audit, 2026-08-14): the closed set of colitur
   [status = Feast] sanctoral slugs whose bootstrapped [colour] was
   corrected against RG 124 (data/ef/adjustments.sexp's own audit-block
   comment has the full citation and per-slug reasoning); every one of
   these still carries lectio's OLD, uncorrected colour, so a row where
   this is the ONLY colitur candidate observed for its own date diffs on
   [Colour_f] alone whenever it wins the day (most years -- these are all
   ordinary universal feasts, rarely impeded). Deliberately a literal list,
   not a shape predicate, the same discipline C6/C14/C15/C16 already use:
   a colour diff on any OTHER slug must still surface as unexplained. Eight
   further audit corrections (prisca/peter/vitus/margaret/agapitus/liborii/
   mark-i, all Commemoration_only, plus the new `barbara` Add) are NOT
   listed here and need no predicate: [colitur_rows_2005_2050] emits only
   the OBSERVED day's own record, and a [Commemoration_only] candidate can
   never be observed (Precedence.resolve's own design), so their corrected
   colours have no row in this comparison to explain. *)
let audit_colour_corrected_slugs =
  [ "conversion-of-st-paul"; "chair-of-st-peter"; "john-of-san-fecundo"; "ephrem-of-syria";
    "julia-of-falconieri"; "john-gualbert"; "camillus-de-lellis"; "jerome-emiliani"; "apollinaris";
    "martha"; "alphonsus-liguori"; "augustine"; "rose-of-lima"; "josaphat" ]

(* C14 (ef-rebootstrap fixture refresh, 2026-08-12; replaces the closed C9,
   see data/ef/expected-divergences.sexp's own C14 note for the full RG
   citation): the exact 3 civil days, across the whole 2005-2050 window,
   where St Joseph's (19 March, I class) RG 96 transfer walk is congested
   enough by Passiontide/Holy Week/the Easter octave to cross Easter AND
   collide with the Annunciation's own transferred "sedes propria" (RG 96
   Attamen (a), Monday after Low Sunday) -- independently re-derived from
   this fixture and colitur's own output (`grep joseph-spouse` both sides,
   filtered to rows with a real post-Layer-A/B diff), not copied from the
   register's prior "2008, 2035, 2046" prose. A LITERAL date list, not a
   slug predicate, per the SAME discipline C12/C13 already used (a plain
   "involves this slug" predicate is exactly what let the old C9 silently
   cover two textually-unrelated divergences at once -- see C14's own sexp
   note for the full account of why that was wrong). *)
let joseph_annunciation_collision_dates_2005_2050 = [ "2008-04-01"; "2035-04-03"; "2046-04-03" ]

(* C15 -- ef-rg112-rg110 task: SPLIT OUT of C1's own blanket 6-13 January
   window, not a new kind of divergence -- the same discipline C13 (now
   closed, see the header above) already established for this exact date,
   and the SAME check the task brief asked for explicitly ("if C1 now
   absorbs a different observed celebration, split it out"). Before this
   task, colitur had no Holy Family office at all: on these seven dates (13
   January, the one civil day it falls on a Sunday in the 2005-2050 window
   -- 2008, 2013, 2019, 2030, 2036, 2041, 2047), colitur's own generic
   Sunday fallback happened to lose outright to the fixed Commemoration of
   the Baptism of the Lord (RG16(a)'s existing "festum Domini beats an
   ordinary Sunday" mechanism, subject Lord already present in the
   REBOOTSTRAPPED data), producing the SAME slug lectio's own tridentine-
   calendar.ini shows for that date ("commemoration-of-the-baptism-of-the-
   lord") -- only [Season] differed (RG 72-73 vs lectio's own 6 January
   boundary), squarely inside C1's own shape. Now that Holy Family is built
   (RG 17(b)) and correctly outranks the fixed Baptism (RG 91 entry 14,
   "primum mobilia, deinde fixa"; RG 112(a) excludes the Baptism as a
   commemoration too, both this task's own precedence_ef.ml changes),
   colitur's own slug on these seven dates changes to
   "ef-time-after-epiphany-sunday-1" (Holy Family's own, unchanged from the
   ordinary-Sunday key it always carried, temporal_ef.ml's own comment on
   why) -- a GENUINE identity divergence against lectio, which has no Holy
   Family at all and still shows the fixed Baptism observed there. Gated on
   the literal 7-date list AND colitur's own slug (the same guard C1/C6/C8/
   C14 already apply, fix round 1's own finding 1: a predicate must pin
   WHICH celebration it is about, not only the date). *)
let holy_family_baptism_collision_dates_2005_2050 =
  [ "2008-01-13"; "2013-01-13"; "2019-01-13"; "2030-01-13"; "2036-01-13"; "2041-01-13"; "2047-01-13" ]

(* C16 -- ef-holyname-rg110 task: RG 17(a)'s own fallback (2 January, "secus
   die 2 ianuarii"), for every civil year 2005-2050 with no Sunday 2-5
   January -- independently re-derived against `date -d <year>-01-0{2..5}
   +%u`, not transcribed from the register's domain-wide figure (see
   data/ef/expected-divergences.sexp's own C16 note for the full citation
   and the derivation). lectio has no equivalent fallback at all (checked
   directly against tridentine-calendar.ini, which carries no 01-02 entry),
   so it shows the plain Christmastide ferial slug on every one of these
   dates, class-4 -- colitur's own `ef-holy-name`, class-2, is a genuine
   [Slug_f; Rank] divergence, not a naming synonym Layer A could absorb. *)
let holy_name_fallback_dates_2005_2050 =
  [ "2006-01-02"; "2007-01-02"; "2008-01-02"; "2012-01-02"; "2013-01-02"; "2017-01-02";
    "2018-01-02"; "2019-01-02"; "2023-01-02"; "2024-01-02"; "2029-01-02"; "2030-01-02";
    "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 =
  (* Fix round 1 (coordinator finding F3): [c.subject] added -- the ONLY
     field in this predicate that pins WHICH celebration is observed, not
     merely its shape. Every other Layer C entry pins a colitur slug (C1's
     own [jan_6_13_slug], C6's [nativity_octave_day_slugs], C8/C14/C15/C16's
     own literal slug checks); this entry could not, because the office
     deliberately REUSES the ordinary ferial slug (Rite_ef.Temporal_ef's own
     [bvm_saturday_names] citation, "Slug" paragraph) -- there is no fixed
     slug string to pin. [subject = "bvm"] is the field that DOES uniquely
     identify the office (set nowhere else the differential's own
     [colitur_rows_2005_2050] can produce a Saturday/Class4/white
     combination for), closing the gap a shape-only predicate left open:
     without this conjunct, a FUTURE bug that made some OTHER white,
     Class4, Saturday candidate exist (Christmastide/Paschaltide, where
     [season_colour] is already white, so a real bug there could slip
     through unnoticed by colour alone) would be silently absorbed here
     too. *)
  diffs = [ Colour_f ] && String.equal c.weekday "saturday" && String.equal c.rank "class-4"
  && String.equal c.colour "white" && String.equal c.subject "bvm"

(* C19 (task 8, branch ef-lectionary): the Time-after-Epiphany WEEK-INDEX
   offset (limit 3 in this file's own header comment, [strip_epiphany_index]
   above) is not merely a slug-digit cosmetic difference -- it is a real
   week-COUNT divergence between the two engines for the REST of the season
   whenever Holy Family (RG 17(b)) has just displaced the fixed Baptism
   commemoration (the same 7 years C15 above names): colitur's own week
   numbering runs one week "behind" lectio's until Time after Epiphany ends
   at Septuagesima (which re-synchronises both engines' counts from zero),
   so the SAME calendar day's Sunday-derived reading (whichever Sunday's
   Mass a feria repeats, or a Sunday's own Mass) is drawn from two
   adjacent-but-different weeks on each side -- a citation divergence with
   NO slug divergence at all (Layer B's own [strip_epiphany_index] already
   normalises the embedded digit away, correctly: the office FAMILY is the
   same, only which week's content is read differs). Confirmed empirically,
   not assumed: every occurrence across the whole 2005-2050 fixture falls in
   exactly these 7 years, and only on a [c.slug] in the
   [ef-time-after-epiphany-] family -- checked, not merely gated, so a real
   bug on an unrelated slug in one of these years still surfaces as
   unexplained. [Colour_f] joins the accepted set for the Saturdays that
   ALSO happen to carry C17's own BVM-Saturday office that week -- a second,
   independent, already-cited cause layering onto the SAME row, not
   something this predicate explains on its own; C17's own 416-row count is
   untouched, since its own guard still requires diffs = EXACTLY
   [Colour_f], which these rows (carrying [First_f]/[Gospel_f] too) never
   satisfy. *)
let epiphany_week_shift_years_2005_2050 = [ 2008; 2013; 2019; 2030; 2036; 2041; 2047 ]

let year_of_date date = int_of_string (String.sub date 0 4)

(* C20 (task 8): lectio genuinely computes NO reading at all -- "-"/"-" on
   both parts -- for 14 civil days across 2005-2050, all seven of the
   readingless class-3 saints Task 6 gave a proper or a Common
   (data/ef/commons.sexp's own "OBSERVABILITY" note, task-6-report.md §1):
   colitur is MORE COMPLETE here, not wrong -- every one of these 14 answers
   is a direct Missal citation (data/ef/adjustments.sexp's own propers for
   thomas-aquinas/john-of-god/francis-of-paola, or data/ef/commons.sexp's
   own Common assignment for the other four), each read from three
   independent witnesses (task-6-report.md's own account of its own
   cross-check discipline), not invented. Gated on the literal 7-slug list
   (the same identity-pinning discipline every other entry here uses) AND
   on lectio's own field literally reading "-"/"-" -- never "any
   first/gospel mismatch on these slugs", which would also swallow a
   genuine future content disagreement on one of these same seven saints. *)
let lectio_no_reading_slugs =
  [ "vincent-ferrer"; "francis-of-paola"; "isidore-of-seville"; "thomas-aquinas"; "john-of-god";
    "sts-felicitas-perpetua"; "frances-rome" ]

(* C21 -- RETIRED, task 8 fix round 1 (coordinator review). Previously a
   [verdict open] entry (107 rows) for "colitur's step 3 cannot reach a
   correct answer for the fixed Christmastide slugs". That diagnosis has
   been SUPERSEDED, not merely fixed around: Important 3(a)'s own direct
   Missal formulary (tools/bootstrap_lectionary.ml's own
   [nativity_octave_entries]) gives [ef-nativity-octave-day-{5,6,7}] a
   real, correct answer via STEP 2, not step 3 at all, so "step 3 cannot
   reach it" is no longer even true. What C21 used to cover has split
   cleanly into two DIFFERENT, more precisely diagnosed populations:
   colitur's own [ef-nativity-octave-day-N] rows now fold into C6 above
   (widened, [verdict] re-opened -- see its own note); the
   [ef-christmas-1-<weekday>] rows that resume THAT slug's own (partly
   wrong, per RG 69) answer one hop later via step 3 are C25 below, a
   genuinely different id because the mechanism is now precisely RG 69
   propagating through step 3, not "step 3 has no answer". No predicate
   or helper of this file's own still names "C21" -- removing the code
   alongside the id is the same discipline this file's own header already
   applies to C2-C5/C7/C9-C13 (closed, cited, never left as dead code). *)

(* C22 (task 8, fix round 1, coordinator review, Critical 2): the Lenten
   Ember days (RG 91 entry 18, colitur's own ef-lent-ember-{wed,fri,sat})
   are reachable for the first time this fix round -- tools/
   bootstrap_lectionary.ml's own [colitur_keys] comment has the full
   account of the dead-key bug this closes. lectio's own SLUG for these
   three days already matched colitur's (both call it "ef-lent-ember-wed"
   etc, confirmed by this row's own [c.slug]/[l.slug] agreement -- no
   [Slug_f] in this entry's own diff set), but lectio's own READING
   resolution has the IDENTICAL internal mismatch colitur's used to have:
   its own ini keys this data under "ef-lent-1-<weekday>", and its own
   [caldata.Readings] never reaches it either, so it still falls back to
   Lent I Sunday's own Mass (e.g. "2 Cor. 6:1-10"/"Matt 4:1-11") on every
   one of these dates. That is a genuine LECTIO bug, reported here for
   upstream, NOT fixed in this task (the brief's own triage rule: record,
   do not patch the sibling project) -- and it is exactly the "Holy
   Thursday was violet in both" shape this project's own CLAUDE.md already
   names: layer 3 was STRUCTURALLY BLIND to this the whole time colitur
   also had the bug, because both engines independently produced the same
   wrong answer. Gated on colitur's own slug family (a literal 3-member
   list, not a pattern) and the diff set staying [First_f; Gospel_f]
   alone (slug/rank/colour already agree). Derived directly from the OCaml
   comparator's own failure output, not hand-counted first and cross-
   checked after: 128 (43 + 43 + 42 -- a few of the 46-year population are
   impeded by a competing sanctoral feast each year, so the Ember office
   itself is not always the observed day). *)
let lent_ember_slugs = [ "ef-lent-ember-wed"; "ef-lent-ember-fri"; "ef-lent-ember-sat" ]

(* C23/C24 (task 8, fix round 1, coordinator review, Critical 1): Holy
   Week's own citations (tools/bootstrap_lectionary.ml's own
   [holy_week_entries] comment has the full Missal citations and the two-
   scan corroboration for each). lectio has no Holy Week propers at all --
   every "ef-passiontide-0-<weekday>" ini section is Passion week's own
   Mass (or, for Tuesday specifically, Holy Tuesday's own Passion Gospel
   riding along on Passion week's own Epistle -- a genuine internal
   inconsistency in lectio's own source, not this project's to fix), so
   lectio shows THAT reused/conflated citation on every Holy Week weekday,
   every year, regardless of what the real Missal prints there.

   C23 covers the four days colitur now answers correctly and completely
   (Monday, Tuesday, Thursday, Saturday) -- verdict colitur, cited
   directly. C24 covers the two days colitur deliberately answers with []
   instead of a guess (Wednesday, Good Friday -- both genuinely
   multi-lesson liturgies with no single Epistle slot this schema could
   honestly fill; [holy_week_entries]'s own comment has the full argument
   for why forcing a pair would be an uncited editorial choice, not a
   Missal fact). Both entries: gated on colitur's own literal slug list
   and [diffs] staying exactly [First_f; Gospel_f] (identity already
   agrees on both). Every occurrence across the whole 2005-2050 fixture
   falls in all 46 years without exception, on every one of these six
   slugs -- Holy Week recurs every year by construction, so this is not a
   coincidental count the way a collision-driven entry's would be.
   Derived directly from the OCaml comparator's own failure output, not
   hand-counted first and cross-checked after: C23 184 (46 x 4), C24 92
   (46 x 2). *)
let holy_week_answered_slugs =
  [ "ef-passiontide-2-monday"; "ef-passiontide-2-tuesday"; "ef-passiontide-2-thursday";
    "ef-passiontide-2-saturday" ]

let holy_week_unanswered_slugs = [ "ef-passiontide-2-wednesday"; "ef-passiontide-2-friday" ]

(* C25 (task 8, fix round 1, coordinator review, Important 3(b)) --
   [verdict open], the SAME RG 69 gap C6 above re-opened, one hop removed.
   RG 69 (docs/research/scan1.txt:625-631, word for word: "De dominica
   infra octavam Nativitatis Domini... semper fit Officium cum
   commemoratione festi forte occurrentis... nisi dominica incidat in
   festum I classis") is unconditional: a Sunday landing 26-31 December
   should keep ITS OWN Office (with the day's feast merely commemorated),
   not the fixed weekday placeholder -- but colitur's [Temporal_ef] gives
   both the SAME slug, undifferentiated by weekday (C6's own note, and
   data/ef/expected-divergences.sexp's own C6 entry, have the full
   account). Confirmed, not merely inferred,
   that THIS entry is the direct, one-hop-removed consequence of that same
   gap: every single one of these rows' colitur-side citation is "Tit. 3,
   4-7" (the fixed weekday formulary), because [Lectionary_ef.readings]'
   step 3 resumes the SAME wrongly-undifferentiated Sunday C6 already
   names, not a second, independent cause. A genuine, precisely-diagnosed
   [Temporal_ef] defect -- out of this task's own scope (a behaviour
   change to a shared, multi-round-reviewed kernel-adjacent function) --
   recorded here per the coordinator's own instruction ("record it
   prominently... for a follow-up task"), not fixed and not left silently
   failing. Gated on the literal 4-slug family (the only members of
   [ef-christmas-1-<weekday>] this mechanism can ever reach -- Monday and
   Tuesday of that same week are always claimed first by the Circumcision
   or Holy Name's own DIRECT entries, so they can never fall through to
   this specific step-3 chain) and [diffs] staying exactly
   [First_f; Gospel_f] (identity already agrees -- this is a pure content
   consequence). Derived directly from the OCaml comparator's own failure
   output, not hand-counted first and cross-checked after: 57
   (19 + 19 + 13 + 6, Wednesday/Thursday/Friday/Saturday respectively). *)
let rg69_one_hop_slugs =
  [ "ef-christmas-1-wednesday"; "ef-christmas-1-thursday"; "ef-christmas-1-friday";
    "ef-christmas-1-saturday" ]

(* [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
    m = 1 && d >= 6 && d <= 13
    && subset diffs [ Season; Colour_f; Slug_f ]
    && (not (List.mem Slug_f diffs) || jan_6_13_slug c.slug)
  then Some "C1"
  else if
    m = 12
    && (d = 29 || d = 30 || d = 31)
    (* NARROWED, fixture-refresh review: this was [subset diffs [ Slug_f; Rank ]].
       Since lectio's own Christmas-octave rank was corrected (3b32c00) all 138
       rows diff on [Slug_f] ALONE, and the note below says so -- but leaving
       [Rank] in the accepted set did not merely over-permit, it made the entry
       BLIND: every row already carries a Slug_f diff, so an added Rank diff
       changed neither the diff-set membership nor the count. Demonstrated by
       the reviewer: dropping the RG 91 entry 17 elevation in temporal_ef
       (Class2 -> Class4 on octave days 5-7) left BOTH differential tests green
       with C6 still reporting 138. The slug guard below already pins identity;
       [Rank] only removed the ability to notice a rank regression.

       WIDENED, task 8 fix round 1 (coordinator review, Important 3(a)/(b)):
       [First_f; Gospel_f] joined the accepted set. Important 3(a)'s own fix
       (tools/bootstrap_lectionary.ml's [nativity_octave_entries]) gives
       these dates a real, Missal-verified citation for the first time --
       and it does NOT converge with lectio's own (differently incomplete)
       Sunday-walkback answer, so ALL 138 of this entry's rows now carry a
       citation diff too, not merely the slug one. See data/ef/expected-
       divergences.sexp's own C6 entry for why this entry's [verdict] is
       now [open], not [colitur] -- Important 3(b)'s own RG 69 finding. *)
    && subset diffs [ Slug_f; First_f; Gospel_f ]
    && List.mem c.slug nativity_octave_day_slugs
  then Some "C6"
  else if
    (String.equal c.slug "ef-rogation-monday" || String.equal c.slug "ef-rogation-tuesday")
    && subset diffs [ Season; Slug_f; Colour_f ]
  then Some "C8"
  else if
    List.mem l.date joseph_annunciation_collision_dates_2005_2050
    (* Task 8: [First_f; Gospel_f] joined the accepted set -- Joseph's own
       transferred office (Ecclus 45:1-6/Matt 1:18-21, his own proper) now
       genuinely differs from the plain feria lectio shows for the same
       civil date, exactly BECAUSE the identity already differs (this
       predicate's own pre-existing [Slug_f; Rank] pair); not a second,
       independent citation-only divergence. *)
    && subset diffs [ Slug_f; Rank; First_f; Gospel_f ]
    (* Colitur-slug guard, added by the fixture-refresh review. Fix round 1's
       own finding 1 established that a Layer C predicate must pin WHICH
       celebration the citation is about, not merely the date -- C1, C6 and C8
       all carry that guard; C14 was written after that ruling and omitted it.
       Demonstrated live: with [Calendar.compare_deferred] switched to RG 98
       origin order, the observed celebration on all three dates flips to the
       Annunciation, and C14 still matched exactly 3 rows with its count pin
       green. The suite only reddened because the SIBLING dates fell outside
       every predicate -- geometry, not this pin. *)
    && String.equal c.slug "joseph-spouse-of-the-bl-virgin-mary"
  then Some "C14"
  else if
    List.mem l.date holy_family_baptism_collision_dates_2005_2050
    (* Task 8: [First_f; Gospel_f] joined the accepted set for the same
       reason as C14 above -- Holy Family's own citations (Col 3:12-17/Luke
       2:42-52, its own proper) differ from the fixed Baptism's (which
       lectio still shows there) exactly BECAUSE the office identity
       already differs; the same single cause, not two. *)
    && subset diffs [ Season; Slug_f; First_f; Gospel_f ]
    && String.equal c.slug "ef-time-after-epiphany-sunday-1"
  then Some "C15"
  else if
    List.mem l.date holy_name_fallback_dates_2005_2050
    (* Task 8: [First_f; Gospel_f] joined the accepted set. Now that
       [ef-holy-name] carries its own citations (tools/bootstrap_lectionary.ml's
       own [derived_entries], sourced from RG 17(a)'s single Mass heading
       covering both shapes), most of these 20 rows already match lectio's
       own citation by coincidence -- lectio's OWN plain-ferial fallback,
       on years with no Sunday 2-5 January, usually lands on a December
       Sunday whose slug collapses to the SAME "ef-christmas-sunday-0" key
       this generator translated -- but on the 7 years where 1 January
       ITSELF is a Sunday, lectio's own fallback instead finds the
       Circumcision's own real Mass (Titus 2:11-15/Luke 2:21), a genuine
       divergence from colitur's RG 17(a) office, which reads the SAME
       Mass on 2 January regardless of what happened the day before. Both
       shapes are the identical underlying cause (colitur builds RG 17(a);
       lectio has no equivalent office at all), so both belong to this one
       id, not a split entry. *)
    && subset diffs [ Slug_f; Rank; First_f; Gospel_f ]
    && String.equal c.slug "ef-holy-name"
  then Some "C16"
  else if is_bvm_saturday_row c diffs then Some "C17"
  else if diffs = [ Colour_f ] && List.mem c.slug audit_colour_corrected_slugs then Some "C18"
  else if
    List.mem (year_of_date l.date) epiphany_week_shift_years_2005_2050
    && starts_with ~prefix:"ef-time-after-epiphany-" c.slug
    && subset diffs [ Colour_f; First_f; Gospel_f ]
  then Some "C19"
  else if
    diffs = [ First_f; Gospel_f ] && String.equal l.first "-" && String.equal l.gospel "-"
    && List.mem c.slug lectio_no_reading_slugs
  then Some "C20"
  else if List.mem c.slug rg69_one_hop_slugs && diffs = [ First_f; Gospel_f ] then Some "C25"
  else if List.mem c.slug lent_ember_slugs && diffs = [ First_f; Gospel_f ] then Some "C22"
  else if List.mem c.slug holy_week_answered_slugs && diffs = [ First_f; Gospel_f ] then Some "C23"
  else if List.mem c.slug holy_week_unanswered_slugs && diffs = [ First_f; Gospel_f ] then Some "C24"
  else None

(* ---------------------------------------------------------------------- *)
(* data/ef/expected-divergences.sexp loading -- a plain sequence of        *)
(* top-level records (not one wrapping list: see the file's own header). *)
(* ---------------------------------------------------------------------- *)

open Sexplib0.Sexp_conv

type allow_entry = { id : string; citation : string; verdict : string; note : string; expected_rows : int }
[@@deriving sexp]

let load_allow_list () =
  let sexps =
    try Sexplib.Sexp.load_sexps allow_list_path
    with e -> Alcotest.failf "%s: failed to load: %s" allow_list_path (Printexc.to_string e)
  in
  List.map allow_entry_of_sexp sexps

(* ---------------------------------------------------------------------- *)
(* The comparison itself, run once and shared by every test case below   *)
(* (Alcotest test cases are independent processes-in-a-list, not free to  *)
(* share mutable state across a suite, so this recomputes per call --     *)
(* acceptable: colitur's own 1583-9999 property sweep runs orders of      *)
(* magnitude more days in tens of seconds, and this is 16801 civil days,  *)
(* once per test case, twice total). *)
(* ---------------------------------------------------------------------- *)

type outcome = Matched | Explained of string | Unexplained of field list

let compare_streams () =
  let lectio = lectio_rows () in
  let colitur = colitur_rows_2005_2050 () in
  (lectio, colitur)

let classify lectio colitur =
  List.map2
    (fun (l : row) (c : row) ->
      if not (String.equal l.date c.date) then
        Alcotest.failf "streams misaligned: lectio %s vs colitur %s" l.date c.date;
      let diffs = diff_fields l c in
      if diffs = [] then (l, c, Matched)
      else
        match layer_c_reason l c diffs with
        | Some id -> (l, c, Explained id)
        | None -> (l, c, Unexplained diffs))
    lectio colitur

(* Task 8: [first]/[gospel] joined the row dump on both sides -- naming the
   date, the slug and the PART (via [diffs]' own field name, "first" or
   "gospel") and each side's reference is exactly what the task brief asks
   a citation mismatch to report, never a bare count. *)
let describe_unexplained (l : row) (c : row) diffs =
  Printf.sprintf
    "%s: %s differ -- lectio=(%s %s %s %s %s first=%s gospel=%s) colitur=(%s %s %s %s %s first=%s gospel=%s)"
    l.date
    (String.concat "," (List.map field_name diffs))
    l.weekday l.season l.slug l.rank l.colour l.first l.gospel c.weekday c.season c.slug c.rank c.colour
    c.first c.gospel

(* Fix round 1, finding 4: the fixture's own byte content must still match
   the SHA-256 its provenance note claims (lectio commit 2386a45, recorded
   both here and in test/fixtures/lectio-ef-2005-2050.provenance). Checked
   before anything else reads the fixture -- a drifted fixture makes every
   other assertion in this suite a statement about an unlabelled snapshot,
   not about the pinned lectio commit it claims to be. *)
let test_fixture_checksum () =
  Alcotest.(check string) "fixture SHA-256 matches its provenance note" fixture_sha256
    (sha256_of_file fixture_path)

(* Dates align 1:1 in the same order on both streams (both are one line per
   civil day, 2005-01-01..2050-12-31 -- see the fixture's own provenance
   note and [colitur_rows_2005_2050]'s construction). A silent misalignment
   would make every subsequent comparison meaningless -- checked first, on
   its own, rather than trusted. *)
let test_dates_align () =
  let lectio, colitur = compare_streams () in
  Alcotest.(check int) "both streams have 16801 rows (46*365 + 11 leap days)" 16801 (List.length lectio);
  Alcotest.(check int) "colitur recomputed the same number of rows" (List.length lectio) (List.length colitur);
  let mismatched =
    List.filter_map
      (fun (l, c) -> if String.equal l.date c.date then None else Some (l.date, c.date))
      (List.combine lectio colitur)
  in
  Alcotest.(check (list (pair string string))) "no misaligned dates" [] mismatched

(* The core assertion: every one of the 4975 raw differences is either
   normalised away (Layers A/B) or named in the cited allow-list (Layer C).
   Nothing else is permitted to pass silently. *)
let test_no_unexplained_differences () =
  let lectio, colitur = compare_streams () in
  let classified = classify lectio colitur in
  let unexplained =
    List.filter_map
      (fun (l, c, outcome) ->
        match outcome with Unexplained diffs -> Some (describe_unexplained l c diffs) | _ -> None)
      classified
  in
  Alcotest.(check (list string)) "no differences outside Layers A/B/C" [] unexplained

(* Teeth, not just green: EVERY Layer C entry's actual row count over this
   fixture must equal what data/ef/expected-divergences.sexp declares, in
   BOTH directions -- an id used by [layer_c_reason] that is missing from
   the sexp file, an id declared but never matched, or a count that has
   drifted either up or down, all fail loudly. A silent drift here is
   exactly the "allow-list absorbs a new bug" failure mode this task was
   warned about. *)
let test_layer_c_counts_match_citations () =
  let lectio, colitur = compare_streams () in
  let classified = classify lectio colitur in
  let actual_counts = Hashtbl.create 16 in
  List.iter
    (fun (_, _, outcome) ->
      match outcome with
      | Explained id ->
          Hashtbl.replace actual_counts id (1 + Option.value ~default:0 (Hashtbl.find_opt actual_counts id))
      | _ -> ())
    classified;
  let declared = load_allow_list () in
  let expected =
    List.sort compare (List.map (fun e -> (e.id, e.expected_rows)) declared)
  in
  let actual =
    List.sort compare
      (Hashtbl.fold (fun id n acc -> (id, n) :: acc) actual_counts [])
  in
  Alcotest.(check (list (pair string int)))
    "every allow-list id's actual row count matches its citation's expected_rows, and no id is unused or \
     undeclared"
    expected actual

let suite =
  ( "differential (lectio, EF, 2005-2050)",
    [ Alcotest.test_case "fixture SHA-256 matches its provenance note" `Quick test_fixture_checksum;
      Alcotest.test_case "streams are 16801 rows each, dates aligned 1:1" `Quick test_dates_align;
      Alcotest.test_case "every difference is normalised (A/B) or cited (C) -- none unexplained" `Quick
        test_no_unexplained_differences;
      Alcotest.test_case "Layer C counts match data/ef/expected-divergences.sexp exactly" `Quick
        test_layer_c_counts_match_citations
    ] )