frame keeps: a model's records filled in place, kept event numbers, list spares, Json.read_file

From the fence's kept frames in 22 minutes of play:

- A component field that is a record or a list of records was `value_put(o, k, view_val_T(x))`,
  a whole new tree every frame (HudPrompt's notifications). view_fill.ludic generates view_set_T /
  view_set_list_T / view_fill_T that fill the object and list under the key in place.
- value_list_fit dropped the items it cut off and value_item made new ones as the list grew back,
  a Value per item per regrowth (value_item / value_set_strs); the cut-off items are now the
  list's spares (Val.spare), and an item of another kind is turned rather than replaced.
- ludic.ui: a scroll box's "scroll" and a slider's "change" fired a fresh Value.float a frame
  (sc_walk, scroll.ludic:36); ui_fire_float takes one from a ring kept with the state (fired.ludic).
  ui_object_fit_into is exported, for a draw that keeps its list.
- Json.read_file(path): read, parsed, and the file's text given back - Json.parse(Fs.read_text())
  kept the whole file on every read (Maroon Lake's settings peeks).

Golden value_list_regrow: a list alternating 6 and 2 items every frame keeps nothing (the toolchain
before this fails it: +128 B new Val from value_item). Game compiles; ludic.i18n/settings/hints/
base tests pass (ludic.ui has none); arena and fence goldens unchanged.

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

examples/lang/value_list_regrow.ludic

@@ -0,0 +1,16 @@
+# value_list_regrow.ludic - a model's list filled in place that shrinks and grows back, frame after
+# frame, makes nothing: the items cut off are the list's spares, handed out again as it grows (each
+# regrowth once made a new Value per item, and the failing fence stopped it at the warm-up's cap):
+#   bad 0 xs 2
+program ValueListRegrow {
+  entry {
+    let o = Value.object()
+    let long = ["a", "b", "c", "d", "e", "f"]
+    let short = ["x", "y"]
+    for f in 0 .. 3500 {
+      if f % 2 == 0 { value_set_strs(o, "xs", long) } else { value_set_strs(o, "xs", short) }
+      Mem.frame()
+    }
+    print(`bad {Mem.bad_frames()} xs {Value.count(Value.get(o, "xs"))}`)
+  }
+}