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, 6 insertions, 0 deletions

diff --git a/lib/kernel/rite.ml b/lib/kernel/rite.ml
index 89fceb6..91326a6 100644
--- a/lib/kernel/rite.ml
+++ b/lib/kernel/rite.ml
@@ -11,4 +11,10 @@ type ('s, 'r) t = {
   season_runs : 's list;
   transfer_target :
     'r Precedence.candidate -> Date.t -> (Date.t -> 'r Celebration.t) -> Date.t;
+  readings :
+    observed:'r Celebration.t ->
+    temporal:('s, 'r) Temporal.t ->
+    date:Date.t ->
+    temporal_at:(Date.t -> ('s, 'r) Temporal.t) ->
+    Citation.t list;
 }