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>

selfhost/frontend/component_gen2.ludic

@@ -62,7 +62,12 @@ function cm_set(c: int, ty: pointer, k: pointer, x: pointer, head: Node) -> poin
   if (ty == "[]float") { return `  value_set_floats(o, "{k}", {x})\n` }
   if (ty == "[]string") { return `  value_set_strs(o, "{k}", {x})\n` }
   if (ty == "[]bool") { return `  value_set_bools(o, "{k}", {x})\n` }
-  return `  value_put(o, "{k}", {cm_to(c, ty, x, head)})\n`
+  let line = vw_set(0, ty, "o", k, x, head)       # a record or a list of them: filled in place (view_fill)
+  if line == null {
+    cm_err(c, `a {ty} is something a template cannot read`)
+    return ""
+  }
+  return line
 }
 function cm_to(c: int, ty: pointer, x: pointer, head: Node) -> pointer {
   if (ty == "Val") { return x }