A new run replaces the saved run only once it has staged; a failed start says why and leaves the saved run

Launch cleared the run store before generating, and a generation or staging failure only reached the log: the
Generating Galaxy dialog stayed up, StartGame threw, and the saved run was already gone.

RunSave.Replace runs a start with the saved run still stored: when it returns a staged run the saved run's records go,
and when it returns null or throws, only the records it wrote (the arena's orbits and bodies) go. StartGame's
new-run branch is StartScenario, chosen by PendingScenario rather than by the absence of a SavedGame; it mints into an
empty ledger, and a failed start clears CurrentGalaxy (so quitting saves nothing) and refuses on the main menu with
every failure. Launch no longer clears; a galaxy that throws is refused on the title menu. The menu offers Continue
whenever no run is live, which replaces MainMenu.InGame (cut, with its prefab value and scene override), so a
failed start can resume the saved run in place.

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

Assets/Scripts/ServerShared/SavedGame.cs

@@ -155,17 +155,37 @@ public static class RunSave
     }
 
     // Removes every run record (SavedGame, SavedZone, OrbitData, BodyData, ProvenanceLedger) in one Commit.
-    public static void Clear(CultCache cache)
+    public static void Clear(CultCache cache) => Remove(cache, Records(cache));
+
+    // A new run replaces the saved one only once it has started: start runs with the saved run still in the store.
+    // When it returns a value, the saved run's records go. When it returns null or throws, the records it wrote go and
+    // the saved run stays as it was.
+    public static T Replace<T>(CultCache cache, Func<T> start) where T : class
     {
-        var run = cache.AllStoredDocuments
+        var saved = Records(cache);
+        T started = null;
+        try
+        {
+            started = start();
+        }
+        finally
+        {
+            Remove(cache, started != null ? saved : Records(cache).Except(saved).ToArray());
+        }
+        return started;
+    }
+
+    private static CultRecordKey[] Records(CultCache cache) =>
+        cache.AllStoredDocuments
             .Where(stored => IsRunRecord(stored.Descriptor.DocumentType))
             .Select(stored => stored.Key)
             .ToArray();
+
+    private static void Remove(CultCache cache, CultRecordKey[] records) =>
         cache.Commit(batch =>
         {
-            foreach (var key in run) batch.Remove(key);
+            foreach (var key in records) batch.Remove(key);
         });
-    }
 
     public static bool IsRunRecord(Type documentType) =>
         AetheriaStores.RunTypes.Any(home => home.IsAssignableFrom(documentType));