tweaking building logic

microservices/LocationsApi/README.md

@@ -43,7 +43,8 @@ unclaimed visible location consumes one completed Scout.
 Buildings are stored on location records. The first building type is `LogCamp`,
 which can be built on controlled Forest territory, takes 60 seconds to build,
 and adds 5 wood per minute to the owning player's resource generation after it
-finishes.
+finishes. Each location has one building slot; a building under construction
+occupies that slot.
 
 Timer settings are stored in the MongoDB `GameSettings` collection and are
 seeded on first read:

microservices/LocationsApi/Services/LocationService.cs

@@ -137,7 +137,7 @@ public class LocationService
 
         if (!string.IsNullOrWhiteSpace(location.BuildingType))
         {
-            throw new InvalidOperationException("This location already has a building.");
+            throw new InvalidOperationException("This location already has a building or construction in progress.");
         }
 
         if (!string.Equals(location.Terrain, "Forest", StringComparison.OrdinalIgnoreCase))
@@ -166,7 +166,7 @@ public class LocationService
 
         if (updated is null)
         {
-            throw new InvalidOperationException("This location already has a building.");
+            throw new InvalidOperationException("This location already has a building or construction in progress.");
         }
 
         return updated;