play 2's frame keeps and a dropped file: a var() join made at once, the hint rail emptied in place, save_read gives its text back

- ludic.ui cv_join (units_pieces.ludic:93): a var() value's pieces were joined by +, a text left
  behind per piece on every memo miss; it is written at its length at once (units_join.ludic), and
  the miss is its own declared function (cs_vars_miss), bounded by the memo.
- ludic.hints hn_slots (rail.ludic:41): hints_reset made a new rail every time; the rail is
  emptied in place, made again only for another count (rail_slots.ludic).
- value_spare_put (value.ludic:138): a list's spares grow only past the most it has ever cut off;
  declared as such.
- ludic.save: save_read reads, parses and frees the file's text - the tree's strings are the
  parser's own - and says whether the text was whole (SaveRead.intact) for the words of a refusal.
  Maroon Lake's trip and home reads kept the whole file on every load and every menu card read.

Tests: ludic.save (10), ludic.hints (8); the 36 ui examples; value_list_regrow, json_saves and
alloc_fence_declared unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.hints/rail.ludic

@@ -35,12 +35,6 @@ export function hints_config(hints_st: mut HintsState, shown: int, every: float)
   hints_st.hn_every = every
   hints_st.hn_top = hn_slots(shown)
 }
-# a rail of n empty places
-function hn_slots(n: int) -> []int {
-  let out = new []int
-  for i in 0 .. n { push(out, -1) }
-  return out
-}
 
 # the next pass comes on the next tick rather than in a second
 export function hints_refresh(hints_st: mut HintsState) -> void { hints_st.hn_t = 0.0 }
@@ -96,7 +90,7 @@ export function hints_pick(hints_st: HintsState) -> int { return hints_st.hn_pic
 export function hints_hot(hints_st: HintsState, k: int) -> bool { return k == hints_st.hn_pick }
 
 export function hints_reset(hints_st: mut HintsState) -> void {
-  hints_st.hn_top = hn_slots(hints_st.hn_shown)
+  hn_empty(hints_st)
   hints_st.hn_n = 0
   hints_st.hn_t = 0.0
   hints_st.hn_pick = 0