feat: ant path rendering on cahnges

frontend/src/lib/graphPath.ts

@@ -0,0 +1,67 @@
+/**
+ * Graph path utilities: compute which nodes/edges are "on the path" of an update.
+ * Used to show connection ant trail only along the full chain (upstream → updating → downstream).
+ * Works with any node types; any node can signal it is updating via startConnectionPathUpdate(id).
+ */
+
+export type GraphEdge = { source: string; target: string }
+
+/** Nodes reachable from seedIds by following edges forward (source → target). */
+export function getDownstreamNodeIds(edges: GraphEdge[], seedIds: string[]): Set<string> {
+  const out = new Set<string>(seedIds)
+  let added = true
+  while (added) {
+    added = false
+    for (const e of edges) {
+      if (out.has(e.source) && !out.has(e.target)) {
+        out.add(e.target)
+        added = true
+      }
+    }
+  }
+  return out
+}
+
+/** Nodes that can reach any seed by following edges backward (target → source). */
+export function getUpstreamNodeIds(edges: GraphEdge[], seedIds: string[]): Set<string> {
+  const out = new Set<string>(seedIds)
+  let added = true
+  while (added) {
+    added = false
+    for (const e of edges) {
+      if (out.has(e.target) && !out.has(e.source)) {
+        out.add(e.source)
+        added = true
+      }
+    }
+  }
+  return out
+}
+
+/**
+ * All node ids that lie on the path of an update.
+ * - If triggerNodeIds is non-empty: path = nodes that are both downstream of a trigger and
+ *   upstream of an updating node (only the chain that actually triggered the update).
+ * - Otherwise: path = upstream ∪ updating ∪ downstream of updating (legacy full upstream/downstream).
+ * An edge should show the update animation iff both its source and target are in this set.
+ */
+export function getPathNodeIds(
+  edges: GraphEdge[],
+  updatingNodeIds: string[],
+  triggerNodeIds?: string[]
+): Set<string> {
+  if (updatingNodeIds.length === 0) return new Set()
+  const upstream = getUpstreamNodeIds(edges, updatingNodeIds)
+  if (triggerNodeIds != null && triggerNodeIds.length > 0) {
+    const downstreamOfTrigger = getDownstreamNodeIds(edges, triggerNodeIds)
+    const path = new Set<string>()
+    upstream.forEach((id) => {
+      if (downstreamOfTrigger.has(id)) path.add(id)
+    })
+    return path
+  }
+  const downstream = getDownstreamNodeIds(edges, updatingNodeIds)
+  const path = new Set<string>(upstream)
+  downstream.forEach((id) => path.add(id))
+  return path
+}