⚡ Bolt: [performance improvement] Avoid O(E) array allocation in calculateMetrics

.jules/bolt.md

@@ -2,3 +2,7 @@
 ## 2024-05-28 - PageRank Calculation Bottleneck on Massive Site Graphs
 **Learning:** During iterative algorithms like PageRank or HITS, accessing node data via `Map.get(url)` inside nested loops results in significant performance degradation for massive site graphs. `Map` lookups add unpredictable overhead to the inner computation cycle.
 **Action:** Always map generic unique identifiers (like `url`s) to zero-indexed integers (`urlToIndex`) before entering iterative hot loops. Use typed contiguous arrays (like `Float64Array`) and standard contiguous arrays (for adjacency lists) for purely O(1) buffer lookups during the computation, mapping results back to URLs only after convergence.
+
+## 2024-06-05 - Avoid .getEdges() Array Allocations in Hot Paths
+**Learning:** Generating the edge array via `graph.getEdges()` inside `calculateMetrics()` was resulting in excessive memory allocations (O(E) new objects per call) due to mapping over `graph.edges.entries()` and invoking `parseEdgeKey`. This caused unnecessary GC pressure for functions only needing edge connectivity info.
+**Action:** When only needing source/target relationships, iterate over `graph.edges.keys()` and inline the string splitting (`indexOf('\x00')`) to avoid intermediate object allocation entirely.

packages/core/src/graph/metrics.ts

@@ -23,23 +23,27 @@ export interface Metrics {
 
 export function calculateMetrics(graph: Graph, _maxDepth: number): Metrics {
   const nodes = graph.getNodes();
-  const edges = graph.getEdges();
 
   const totalPages = nodes.length;
-  const totalEdges = edges.length;
+  const totalEdges = graph.edges.size;
 
   // Identify broken nodes
   const brokenNodes = new Set(nodes.filter(n => n.status >= 400 || n.status === 0).map(n => n.url));
 
+  // ⚡ Bolt: Fast parsing of string edge keys instead of mapping over objects for O(1) string splits inside hot loop
   // Pre-compute outgoing edges per node for faster lookup
   const outgoingEdges = new Map<string, string[]>();
-  for (const edge of edges) {
-    let targets = outgoingEdges.get(edge.source);
+  for (const edgeKey of graph.edges.keys()) {
+    const splitIndex = edgeKey.indexOf('\x00');
+    const source = edgeKey.slice(0, splitIndex);
+    const target = edgeKey.slice(splitIndex + 1);
+
+    let targets = outgoingEdges.get(source);
     if (!targets) {
       targets = [];
-      outgoingEdges.set(edge.source, targets);
+      outgoingEdges.set(source, targets);
     }
-    targets.push(edge.target);
+    targets.push(target);
   }
 
   // Populate brokenLinks per node