fix toShortSafely: yes we can safely convert -1 to short :)

core/src/main/scala/flatgraph/DiffGraphApplier.scala

@@ -74,10 +74,7 @@ private[flatgraph] class DiffGraphApplier(graph: Graph, diff: DiffGraphBuilder)
             already
           case None =>
             val nodeKind = detached.nodeKind
-            assert(
-              nodeKind < graph.schema.getNumberOfNodeKinds,
-              s"given nodeKind=$nodeKind does not fit into the graph schema, which only supports node kinds [0..${graph.schema.getNumberOfNodeKinds - 1}] (inclusive range)"
-            )
+            graph.schema.verifyNodeKindIsValid(nodeKind)
 
             val seqId = graph.nodeCountByKind(nodeKind) + Option(newNodes(nodeKind)).map { _.size }.getOrElse(0)
             val res   = graph.schema.makeNode(graph, nodeKind, seqId)

core/src/main/scala/flatgraph/Graph.scala

@@ -51,9 +51,10 @@ class Graph(val schema: Schema, val storagePathMaybe: Option[Path] = None) exten
   private[flatgraph] val neighbors: Array[AnyRef]        = makeNeighbors()
 
   /** Note: this included `deleted` nodes! You might want to use `livingNodeCountByKind` instead. */
-  private[flatgraph] def nodeCountByKind(kind: Int): Int =
-    if (nodesArray.length <= kind) 0
-    else nodesArray(kind).length
+  private[flatgraph] def nodeCountByKind(kind: Int): Int = {
+    schema.verifyNodeKindIsValid(kind)
+    nodesArray(kind).length
+  }
 
   def _nodes(nodeKind: Int): InitNodeIterator[GNode] = {
     if (nodeKind < 0 || schema.getNumberOfNodeKinds <= nodeKind) InitNodeIteratorArray(Array.empty[GNode])

core/src/main/scala/flatgraph/Schema.scala

@@ -133,6 +133,13 @@ abstract class Schema {
   def allocateEdgeProperty(nodeKind: Int, direction: Direction, edgeKind: Int, size: Int): Array[_]
   def getNodePropertyFormalType(nodeKind: Int, propertyKind: Int): FormalQtyType.FormalType
   def getNodePropertyFormalQuantity(nodeKind: Int, propertyKind: Int): FormalQtyType.FormalQuantity
+
+  def verifyNodeKindIsValid(kind: Int): Unit = {
+    assert(
+      0 <= kind && kind < getNumberOfNodeKinds,
+      s"given nodeKind=$kind does not belong to (this) graph schema, which only supports node kinds [0..${getNumberOfNodeKinds - 1}] (inclusive range)"
+    )
+  }
 }
 
 class FreeSchema(

core/src/main/scala/flatgraph/misc/Conversions.scala

@@ -3,8 +3,11 @@ package flatgraph.misc
 object Conversions {
   extension (i: Int) {
     def toShortSafely: Short = {
-      assert(0 <= i && i <= Short.MaxValue, throw new ConversionException(s"cannot safely downcast int with value=$i to short"))
-      i.toShort
+      val shortValue = i.toShort
+      if (shortValue.toInt == i)
+        shortValue
+      else
+        throw new ConversionException(s"cannot safely downcast int with value=$i to short")
     }
   }
 }