fix: resume campaign progress safely

scripts/verify-battle-save-normalization.mjs

@@ -90,6 +90,38 @@ try {
     isValidBattleSaveState(legacyStateWithoutSortieOrder, options),
     'Expected legacy battle saves without a sortie order to remain valid.'
   );
+  const generatedBattleSave = {
+    ...validState,
+    battleResumeGeneration: 7
+  };
+  assert(
+    isValidBattleSaveState(
+      generatedBattleSave,
+      options
+    ) &&
+      parseBattleSaveState(
+        JSON.stringify(generatedBattleSave),
+        options
+      )?.battleResumeGeneration === 7,
+    'Expected a non-negative battle-resume generation to round-trip.'
+  );
+  assert(
+    !isValidBattleSaveState(
+      {
+        ...validState,
+        battleResumeGeneration: -1
+      },
+      options
+    ) &&
+      !isValidBattleSaveState(
+        {
+          ...validState,
+          battleResumeGeneration: 1.5
+        },
+        options
+      ),
+    'Expected invalid battle-resume generations to be rejected.'
+  );
   const validPendingBattleEventState = {
     ...validState,
     pendingBattleEvents: [