refactor(#730): restate the checkpoint submitter as an xstate statechart

.oxlintrc.json

@@ -185,6 +185,9 @@
           // a response resolver's request context: wraps the live fetch Request; no readonly form
           { "from": "package", "name": "ResponseResolverInfo", "package": "msw" },
           { "from": "package", "name": "Collection", "package": "@msw/data" },
+          // a live actor handle: subscription and mailbox state xstate mutates internally, no
+          // readonly form
+          { "from": "package", "name": "AnyActorRef", "package": "xstate" },
           {
             "from": "package",
             "name": ["CryptoKey", "Request", "Response", "AbortSignal"],

libs/game/idle-client/package.json

@@ -22,9 +22,9 @@
     "@vers/styled-system": "workspace:*",
     "@vers/trace": "workspace:*",
     "idb": "catalog:",
-    "p-retry": "catalog:",
     "react": "catalog:",
     "tiny-invariant": "catalog:",
+    "xstate": "catalog:",
     "zod": "catalog:",
     "zustand": "catalog:"
   },

libs/game/idle-client/src/submission/build-machine-types.ts

@@ -0,0 +1,10 @@
+/**
+ * xstate's `setup()` consumes its `types` property at the type level only — the runtime value is
+ * never read — so an empty object can stand in for any machine's context/events/input shape. This
+ * owns the one assertion that requires, keeping machine definitions free of `{} as` casts.
+ */
+// oxlint-disable-next-line typescript/no-unnecessary-type-parameters -- T exists purely so callers can name the phantom shape
+export function buildMachineTypes<T>(): T {
+  // oxlint-disable-next-line typescript/no-unsafe-type-assertion -- compile-time phantom; xstate never reads the value
+  return {} as T;
+}