refactor(javascript): own application node merging in the graph domain

src/domain/javascript/javascriptApplicationGraph.ts

@@ -502,6 +502,51 @@ export const createJavaScriptApplicationNode = (
   });
 };
 
+/** Merge authenticated entities, retaining every distinct observation. */
+export const mergeJavaScriptApplicationNodes = (
+  nodes: readonly ApplicationNode[],
+): ApplicationNode[] => {
+  const groups = new Map<
+    string,
+    {
+      node: ApplicationNode;
+      observations: Map<string, ApplicationNode["observations"][number]>;
+    }
+  >();
+  for (const node of nodes) {
+    const group = groups.get(node.node_id);
+    if (group === undefined) {
+      groups.set(node.node_id, {
+        node,
+        observations: new Map(
+          node.observations.map((observation) => [
+            observation.observation_id,
+            observation,
+          ]),
+        ),
+      });
+      continue;
+    }
+    if (
+      node.kind !== group.node.kind ||
+      canonicalJson(node.identity) !== canonicalJson(group.node.identity)
+    )
+      throw new TypeError("Colliding JAG node identifiers disagree");
+    for (const observation of node.observations)
+      group.observations.set(observation.observation_id, observation);
+  }
+  return [...groups.values()].map(({ node, observations }) =>
+    createJavaScriptApplicationNode({
+      kind: node.kind,
+      identity: node.identity,
+      observations: [...observations.values()].map(
+        ({ observation_id: _id, identifier_strategy: _strategy, ...value }) =>
+          value,
+      ),
+    }),
+  );
+};
+
 /** Build one normalized directed relationship and derive its semantic ID. */
 export const createJavaScriptApplicationEdge = (
   input: unknown,