explore: batch callerTests' hop 2-3 caller lookups (#574)

getCallersMany fetches depth-1 callers for a whole frontier in one
incoming-edges query + one getNodesByIds instead of a getCallers
round-trip per node; the same 64-node budget bounds each hop.

Author: bompus

src/codegraph.ts

@@ -2823,6 +2823,14 @@ export class CodeGraph {
     return this.traverser.getCallers(nodeId, maxDepth);
   }
 
+  /**
+   * Depth-1 callers for many targets in two queries — the batch form of
+   * getCallers(id, 1), for bounded fan-in walks like callerTests.
+   */
+  getCallersMany(nodeIds: readonly string[]): Array<{ node: Node; edge: Edge }> {
+    return this.traverser.getCallersMany(nodeIds);
+  }
+
   /**
    * Get callees of a function/method
    *

src/graph/traversal.ts

@@ -294,6 +294,29 @@ export class GraphTraverser {
     return result;
   }
 
+  /**
+   * Depth-1 callers for MANY targets in two round-trips — one incoming-edges
+   * query + one getNodesByIds — instead of a getCallers(id, 1) pair per id.
+   * Same kind list as getCallersRecursive; a caller repeats once per target it
+   * calls, matching separate per-node calls, and once per target at most.
+   */
+  getCallersMany(nodeIds: readonly string[]): Array<{ node: Node; edge: Edge }> {
+    if (nodeIds.length === 0) return [];
+    const incoming = this.queries.getIncomingEdgesTo(nodeIds, ['calls', 'references', 'imports', 'instantiates', 'navigates']);
+    const nodes = this.queries.getNodesByIds(incoming.map((e) => e.source));
+    const reported = new Set<string>();
+    const out: Array<{ node: Node; edge: Edge }> = [];
+    for (const edge of incoming) {
+      const node = nodes.get(edge.source);
+      if (!node) continue;
+      const key = `${edge.target}${edge.source}`;
+      if (reported.has(key)) continue;
+      reported.add(key);
+      out.push({ node, edge });
+    }
+    return out;
+  }
+
   private getCallersRecursive(
     nodeId: string,
     maxDepth: number,

src/mcp/tools.ts

@@ -4559,17 +4559,18 @@ export class ToolHandler {
     for (let hop = 2; hop <= MAX_HOPS && frontier.length > 0 && budget > 0; hop++) {
       const next: Array<{ node: Node; edge: Edge }> = [];
       const found: Array<{ node: Node; edge: Edge }> = [];
-      for (const { node } of frontier) {
-        if (budget-- <= 0) break;
-        let callers: Array<{ node: Node; edge: Edge }> = [];
-        try { callers = cg.getCallers(node.id); } catch { continue; }
-        for (const c of callers) {
-          const n = c?.node;
-          if (!n || visited.has(n.id)) continue;
-          visited.add(n.id);
-          if (isTestPath(n.filePath)) found.push(c);
-          else next.push(c);
-        }
+      // One batched depth-1 callers query per hop instead of a getCallers
+      // round-trip per frontier node; the same 64-node budget bounds it.
+      const ids = frontier.slice(0, budget).map((f) => f.node.id);
+      budget -= ids.length;
+      let pairs: Array<{ node: Node; edge: Edge }> = [];
+      try { pairs = cg.getCallersMany(ids); } catch { pairs = []; }
+      for (const c of pairs) {
+        const n = c?.node;
+        if (!n || visited.has(n.id)) continue;
+        visited.add(n.id);
+        if (isTestPath(n.filePath)) found.push(c);
+        else next.push(c);
       }
       if (found.length > 0) return { callers: found, exhausted: budget <= 0 };
       frontier = next;