ef(lectionary): a feria says the preceding Sunday's Mass

Chain step 3. Guarded on weekday <> Sun: a Sunday reaching this branch
would look up its own slug via days_since_sunday Sun = 0 and loop --
every other chain step consults data, this one consults a strictly
earlier date, so that guard is the whole chain's termination argument.
Reaches the Sunday by Date.add_days plus a fresh temporal_at call, never
by string surgery on the day's own slug -- the slug shapes are genuinely
inconsistent across seasons (ef-advent-sunday-1 vs ef-advent-1-monday,
week number on opposite sides of the season name).

Uses the preceding Sunday's TEMPORAL slug, never its observed one: the
rubric is the preceding Sunday's Mass even in a year a feast displaced
that Sunday from being observed (pinned: 2028-12-26, the Monday after a
Vigil-displaced Advent IV Sunday, still takes Advent IV's Mass).

Measured over the full 1583-9999 domain (temporal cycle only, no
sanctoral contest): of 412 distinct temporal slugs, 305 carry no
lectionary entry of their own; of the 304 that are feria (non-Sunday)
slugs, step 3 alone resolves 297 of them via their preceding Sunday.
The 7 that remain, plus the 1 uncovered Sunday slug itself
(ef-holy-name-sunday), all trace to the same two missing lectionary
entries (Holy Name Sunday and 30 December), not to eight independent
gaps or a step-3 defect -- traced date-by-date, not merely counted.
Day-level effect, 2005-2050 (full Precedence+Calendar pipeline,
matching this project's existing differential window): 16807 days,
16531 resolved (98.36%), 276 still empty; step 3 alone accounts for
4503 of the resolved days, more than either step 1 or step 2.

Warrant is the same class as step 2's, not a confirmed Missal
citation: lectio hard-codes this shape as literal duplicated data on
the four Advent ferias (Advent I's own readings copied onto the
following Monday-Thursday) and leaves the rest of that same shape
simply absent; step 3 turns the duplication into a rule.

dune test --force: 344 tests, all green (was 340).

1 files changed, 3 insertions, 2 deletions

diff --git a/lib/rites/rite_ef/rite_ef.mli b/lib/rites/rite_ef/rite_ef.mli
index 1a4c715..12f5609 100644
--- a/lib/rites/rite_ef/rite_ef.mli
+++ b/lib/rites/rite_ef/rite_ef.mli
@@ -27,8 +27,9 @@ module Lectionary_ef = Lectionary_ef
       argument {!Colitur_kernel.Rite.t.transfer_target}'s contract requires).
     - [readings]: {!Lectionary_ef.readings} partially applied to the caller's
       own [~lectionary] -- the observed celebration's own proper, else the
-      day's own temporal slug in data/ef/lectionary.sexp (chain steps 1-2;
-      the ferial fallback and the Commons are later work).
+      day's own temporal slug, else (a weekday with no entry of its own) the
+      preceding Sunday's temporal slug, in data/ef/lectionary.sexp (chain
+      steps 1-3; the Commons are later work).
 
     Deliberately carries no [sanctoral]/[lectionary] fields the way the
     original design-doc sketch of [RITE] does: {!Colitur_kernel.Rite.t} (the