Throwdowns: the throwdown kit, so a mode is a plugin and the SDK knows no particular mode

Plugins register modes (card, replaces, order, flag, players) and publish documents through
reskate.throwdowns.ui: the setup page, the waiting card, HUD slots themed on the game's HUD_<theme>_*
widgets, the match panel, flags and match restrictions. SmokeyDawg58's native plumbing
(throwdown_menu.cpp and its .inl files) renders them and posts throwdown_ui events back. kit::flag
is the one native flag registration. General services added for it: reskate.files, reskate.ui.dialog,
reskate.skater push/hold/bone_cam, reskate.camera.pad_flight, reskate.physics competition,
reskate.session.world, reskate.tricks feed/gesture, and world entities.

His ten modes are now Lua in his plugin: the rules, referee and wire (td/rules, referee, wire), and
every page and HUD document (td/ui*.lua). Extension/Modes and reskate.modes are gone, along with
every race and 1-UP branch in the SDK. The plugin test drives each mode through kit events.

A native setup page is never written to while it closes into flag placement: its rows are not
republished, the stock page is put back once the exit is over, and the stock Players slider is left
alone while a plugin flag is out. This fixes the crashes on the Deathrace button and on 1-UP's
Confirm.

Extension/Plugins/plugin_api.cpp

@@ -17,14 +17,15 @@ namespace {
 struct Event {
     std::string_view name, permission;
 };
-constexpr std::array<Event, 25> events{{
+constexpr std::array<Event, 26> events{{
     {"load", {}}, {"unload", {}}, {"tick", {}}, {"level_loaded", {}}, {"level_unloading", {}},
     {"trick_started", "events.tricks"}, {"trick_landed", "events.tricks"}, {"line_broken", "events.tricks"},
     {"draw", "overlay"}, {"player_joined", "session.read"}, {"player_left", "session.read"}, {"message", "net.session"},
     {"skater_state", "events.skater"}, {"bail", "events.skater"}, {"chat", "chat.read"}, {"track_changed", "music"},
     {"throwdown", "throwdowns"}, {"action", "input"}, {"screen_closed", "ui.screen"},
     {"board_landed", "events.skater"}, {"body_hit", "events.skater"}, {"bail_end", "events.skater"},
-    {"physics_step", "events.physics"}, {"grind_exit", "events.skater"}, {"throwdown_mode", "throwdowns"},
+    {"physics_step", "events.physics"}, {"grind_exit", "events.skater"}, {"trick_notes", "events.tricks"},
+    {"throwdown_ui", "throwdowns"},
 }};
 constexpr std::size_t maximum_key = 128;
 constexpr std::size_t maximum_command = 48;
@@ -82,6 +83,12 @@ Json to_json(lua_State* L, int index, int depth, Budget& budget) {
         budget.spend(0, length);
         return std::string(text, length);
     }
+    case LUA_TVECTOR: { // a position: [x, y, z]
+        const float* v = lua_tovector(L, index);
+        if (!std::isfinite(v[0]) || !std::isfinite(v[1]) || !std::isfinite(v[2])) throw std::runtime_error("JSON has no NaN or infinity");
+        budget.spend(3, 0);
+        return Json::array({static_cast<double>(v[0]), static_cast<double>(v[1]), static_cast<double>(v[2])});
+    }
     case LUA_TTABLE: {
         luaL_checkstack(L, 4, "tables nested too deep");
         const int length = lua_objlen(L, index);
@@ -676,6 +683,8 @@ void Api::install(Plugin& plugin, lua_State* L) {
     install_ui_api(plugin, L);
     install_more_api(plugin, L);
     install_world_api(plugin, L);
+    install_services_api(plugin, L);
+    install_kit_api(plugin, L);
     readonly();
     lua_setglobal(L, "reskate");
     lua_pushcfunction(L, ApiFunctions::print, "print");