feat(ludic.update): a Velopack game updating itself, a frame at a time

latest.json asked once and polled (the newest version and its notes, in
a language or English); then Velopack's releases.<os>.json, the plan (the
delta chain when the installed full package is on disk, no delta is
missing and the chain weighs less than the full one; the newest full
package otherwise, named as the feed names it), each package streamed to
the packages folder with its bytes on a bar and an eased pace, its
SHA-256 by Get-FileHash or shasum in a child, Update patch per delta and
Update apply --waitPid. macOS keeps its packages outside the bundle and
names --rootDir and --packageDir; a translocated app is not installed.

Ports with the runtime as every default: UpdateWorld (platform, exe, pid,
now_ms), UpdateNet (get, download, poll, text, received, free),
UpdateProc (spawn, poll, free). Config: feed, app_id, version, root,
packages, mac_packages, scratch. It words nothing: states, UPDATE_ERR_*
codes and numbers, and UPDATE_STARTED / _STOPPED / _APPLYING facts - the
game exits on the last.

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

packages/ludic.update/latest.ludic

@@ -0,0 +1,73 @@
+# latest.ludic - "a new version is out": latest.json asked once, polled a frame at a time, so a
+# slow or absent network costs the frame nothing - it simply never says there is one.
+# latest.json is {"version": "0.5.1", "notes": {"en": ["...", ...], "tr": [...]}}
+var update__ask: int = 0
+var update__ask_h: int = -1
+var update__latest: string = ""
+var update__notes: Val = null
+
+# once a frame on the screen that shows it; with show_current, the notes of the version being
+# played are kept too (a launcher shows them)
+export function update_check_tick(show_current: bool) -> void {
+  if update__ask == UPDATE_ASK_IDLE {
+    update__ask_h = UpdateNet.get(update__conf().feed + "/" + update__conf().latest)
+    update__ask = UPDATE_ASKING
+    if update__ask_h < 0 { update__ask = UPDATE_NONE }
+    return
+  }
+  if update__ask != UPDATE_ASKING { return }
+  let st = UpdateNet.poll(update__ask_h)
+  if st < 0 { return }
+  update__ask = UPDATE_NONE
+  if st > 0 { update__latest_read(Json.parse(UpdateNet.text(update__ask_h)), show_current) }
+  UpdateNet.free(update__ask_h)
+  update__ask_h = -1
+}
+
+function update__latest_read(v: Val, show_current: bool) -> void {
+  if v == null or Value.kind(v) != 6 or Value.has(v, "version") == 0 { return }
+  let ver = Value.as_str(Value.get(v, "version"))
+  let mine = update__conf().version
+  if update_newer(ver, mine) { update__ask = UPDATE_NEWER }
+  else if ver == mine and show_current { update__ask = UPDATE_CURRENT }
+  else { return }
+  update__latest = ver
+  if Value.has(v, "notes") != 0 { update__notes = Value.get(v, "notes") }
+}
+
+export function update_ask_state() -> int { return update__ask }
+export function update_latest() -> string { return update__latest }
+export function update_shown() -> bool { return update__ask == UPDATE_NEWER or update__ask == UPDATE_CURRENT }
+export function update_fresh() -> bool { return update__ask == UPDATE_NEWER }
+
+# the notes in this language, else English, else none
+export function update_notes(lang: string) -> []string {
+  let out = new []string
+  if update__notes == null or Value.kind(update__notes) != 6 { return out }
+  var key = lang
+  if Value.has(update__notes, key) == 0 { key = "en" }
+  if Value.has(update__notes, key) == 0 { return out }
+  let l = Value.get(update__notes, key)
+  for i in 0 .. Value.count(l) { push(out, Value.as_str(Value.at(l, i))) }
+  return out
+}
+
+# back to before anything was asked or installed (tests)
+export function update_reset() -> void {
+  if update__ask_h >= 0 { UpdateNet.free(update__ask_h) }
+  update__ask_h = -1
+  update__ask = UPDATE_ASK_IDLE
+  update__latest = ""
+  update__notes = null
+  update__release()
+  update__state = UPDATE_IDLE
+  update__err = UPDATE_ERR_NONE
+  update__target = ""
+  update__files = null
+  update__total_bytes = 0
+  update__done_bytes = 0
+  update__i = 0
+  update__rate = 0
+  update__rate_t = -1
+  q_clear(update_facts())
+}