kernel(calendar): place transferred celebrations (RG 96-98)

Calendar.year now runs a placement pass after resolving every day: each
deferred candidate (RG 95's I-class-only right of translation, via
Precedence's Transfer disposition) is placed on the next day the rite's
new Rite.t.transfer_target names as admissible, transferred_in/out are
set on the two ends of the move, and the whole year is re-resolved to a
fixed point, bounded by a hard max_transfer_rounds = 64 guard.

transfer_target is rite-supplied rather than a generic search Calendar
drives itself: RG 96's 'not I or II class' is not derivable from band or
disposition alone (RG 91's own table lets a universal I-class feast
outrank an ordinary Sunday in a raw contest, yet RG 96 forbids landing a
translation there regardless), and the search's starting point is
rite-specific too (the Annunciation exception). It takes an occupant
callback exposing what Calendar currently resolves as observed on any
date, so the rite never has to re-implement occurrence resolution.

Two correctness properties drove most of the design:

- A candidate's permanent natural loss at its own origin (the layer entry
  never moves) is rediscovered every round; left unfiltered this
  oscillates a placed candidate between two dates forever, since its own
  rank makes it look 'occupied' to a fresh search from its origin. Both
  the round loop's gather and the final per-day omitted accounting filter
  this out, keeping only sightings that are either brand new or losing at
  a candidate's *current* target (a fresh RG 97-98 bump).

- RG 97-98's sort has to actually decide something, not just happen to
  agree with Precedence.resolve's own tie-break next round: a
  claimed-this-round overlay lets earlier-processed candidates in one
  round block later ones in the same pass, so two coinciding I-class
  feasts land on consecutive admissible days in the one round they
  collide, in band order.

Also folds in Task 5's review finding: year_bounds clamps y to [1582,
9999] once, up front, rather than guarding start and stop independently
(each guard only ever covered one of the two rite.year_start calls,
leaving year 999 and year 100000 each able to call it out of domain
through the other branch).

1 files changed, 24 insertions, 0 deletions

diff --git a/lib/kernel/rite.mli b/lib/kernel/rite.mli
index db8e86f..6d12dd4 100644
--- a/lib/kernel/rite.mli
+++ b/lib/kernel/rite.mli
@@ -15,4 +15,28 @@ type ('s, 'r) t = {
       (** the expected run-length-compressed season sequence over one liturgical
           year. NOT necessarily [vocab.seasons]: a rite may have one season
           appear in two separate runs (the modern form's Ordinary Time does). *)
+  transfer_target :
+    'r Precedence.candidate -> Date.t -> (Date.t -> 'r Celebration.t) -> Date.t;
+      (** RG 96: where an impeded I-class feast goes. Given the deferred
+          candidate, the date it was impeded on, and [occupant] -- a callback
+          exposing what {!Calendar} currently resolves as observed on any
+          given date -- returns the date to place it on.
+
+          Deliberately one rite-supplied function, not a generic search Calendar
+          drives itself: "not I or II class" is not derivable from [band] or
+          [disposition] alone. RG 91's own table would let a universal I-class
+          feast (entry 11) numerically outrank an ordinary Sunday (entry 15,
+          II class) in a raw occurrence contest -- entry 11 comes before entry
+          15, and lower wins -- so testing "would the translated feast win
+          here" is not the same question as "is this day free to receive a
+          translation": RG 96 forbids landing on the Sunday regardless of
+          which one would structurally win. Only the rite knows which of its
+          own ranks are exempt from translation onto them. The rite also
+          owns the search's starting point, because RG 96's exception is
+          rite-specific too: the Annunciation does not search forward from
+          its own impeded date at all, it goes straight to the Monday after
+          Low Sunday (searching onward from there only if that day is itself
+          blocked). [occupant] is supplied rather than a raw layer/temporal
+          pair so the rite never has to re-implement occurrence resolution
+          just to answer "what sits here". *)
 }