feat: expose stable overworld checkpoints to mods

src/mods/Loader.lua

@@ -571,6 +571,7 @@ function Loader:_api(mod)
   local modId = mod.manifest.id
   local Storage = engineRequire("src.mods.Storage")
   local storage = Storage and Storage.new(modId, loader.fs)
+  local Checkpoint = engineRequire("src.core.Checkpoint")
   local api = {
     id = modId,
     version = mod.manifest.version,
@@ -670,6 +671,15 @@ function Loader:_api(mod)
       list = function(_, game, prefix) return storage:list(game, prefix) end,
       delete = function(_, game, key) return storage:delete(game, key) end,
     },
+    -- Runtime safety and reconstruction stay engine-owned. Checkpoints contain
+    -- data only; no controller, stack, coroutine or renderer object crosses out.
+    checkpoints = {
+      inspect = function(_, game) return Checkpoint.inspect(game) end,
+      capture = function(_, game) return Checkpoint.capture(game) end,
+      restore = function(_, game, checkpoint)
+        return Checkpoint.restore(game, checkpoint)
+      end,
+    },
     options = {
       define = function(_, schema)
         assert(type(schema) == "table", "options schema must be a table of rows")