kernel+ef: resolve readings, chain steps 1 and 2

Liturgical_day.citations has read "always empty until Plan 4" since Plan 3;
it is now filled. Rite.t gains a readings function, rite-supplied for the
same reason transfer_target is: what a day with no proper falls back to is a
rubric, not a universal. Calendar calls it and passes its own temporal
function as the callback the rite needs to reach another date.

Steps 1 and 2 only: the observed celebration's own proper, else the day's own
temporal slug. Nothing encodes "Lent has daily propers" -- the presence of an
entry is the discriminator.

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/rites/rite_ef/lectionary_ef.mli b/lib/rites/rite_ef/lectionary_ef.mli
new file mode 100644
index 0000000..fe9359e
--- /dev/null
+++ b/lib/rites/rite_ef/lectionary_ef.mli
@@ -0,0 +1,15 @@
+open Colitur_kernel
+
+(** The EF lectionary resolution chain. All rubric knowledge about what a day
+    with no proper falls back to lives here, not in the kernel.
+
+    Steps 1 and 2 only (Task 4): the observed celebration's own proper, else
+    the day's own temporal slug in the lectionary. A day matching neither
+    gets [] for now -- the ferial fallback to the preceding Sunday (Task 5)
+    and the Commons (Task 6) are not built here. *)
+val readings :
+  observed:Vocab_ef.rank Celebration.t ->
+  temporal:(Vocab_ef.season, Vocab_ef.rank) Temporal.t ->
+  date:Date.t ->
+  temporal_at:(Date.t -> (Vocab_ef.season, Vocab_ef.rank) Temporal.t) ->
+  Citation.t list