diff --git a/frontend/src/components/NetworkGraph.map-lookup.test.ts b/frontend/src/components/NetworkGraph.map-lookup.test.ts
new file mode 100644
index 000000000..cdb58af6c
--- /dev/null
+++ b/frontend/src/components/NetworkGraph.map-lookup.test.ts
@@ -0,0 +1,60 @@
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+
+import { describe, expect, it } from "vitest";
+
+const networkGraphSource = readFileSync(
+  fileURLToPath(new URL("./NetworkGraph.tsx", import.meta.url)),
+  "utf8",
+);
+
+function sourceBetween(startMarker: string, endMarker: string): string {
+  const startIndex = networkGraphSource.indexOf(startMarker);
+  const endIndex = networkGraphSource.indexOf(endMarker, startIndex);
+
+  expect(startIndex).toBeGreaterThanOrEqual(0);
+  expect(endIndex).toBeGreaterThan(startIndex);
+
+  return networkGraphSource.slice(startIndex, endIndex);
+}
+
+describe("NetworkGraph constant-time selection lookup contract", () => {
+  it("keeps graph event selection on memoized maps without linear fallback scans", () => {
+    const edgeSelection = sourceBetween("const selectEdge =", "const selectNode =");
+    const nodeSelection = sourceBetween("const selectNode =", "const handleEdgeSelection =");
+
+    expect(edgeSelection).toContain("edgeMap.get(String(edgeId))");
+    expect(edgeSelection).not.toContain(".find(");
+
+    expect(nodeSelection).toContain("nodeMap.get(String(nodeId))");
+    expect(nodeSelection).toContain("?? String(nodeId)");
+    expect(nodeSelection).not.toContain("findNodeLabel(");
+    expect(nodeSelection).not.toContain(".find(");
+  });
+
+  it("keeps select controls on memoized maps without rescanning nodes or edges", () => {
+    const graphNodeSelection = sourceBetween(
+      "const selectGraphNode =",
+      "const handleSelectFirstRelationship =",
+    );
+    const relationshipControl = sourceBetween(
+      "const handleRelationshipOptionChange =",
+      "const handleNodeOptionChange =",
+    );
+    const nodeControl = sourceBetween(
+      "const handleNodeOptionChange =",
+      "const handleZoomGraph =",
+    );
+
+    expect(graphNodeSelection).toContain("nodeMap.get(String(node.id))");
+    expect(graphNodeSelection).toContain("?? String(node.id)");
+    expect(graphNodeSelection).not.toContain("findNodeLabel(");
+    expect(graphNodeSelection).not.toContain(".find(");
+
+    expect(relationshipControl).toContain("edgeMap.get(value)");
+    expect(relationshipControl).not.toContain(".find(");
+
+    expect(nodeControl).toContain("nodeInstanceMap.get(value)");
+    expect(nodeControl).not.toContain(".find(");
+  });
+});
diff --git a/frontend/src/components/NetworkGraph.tsx b/frontend/src/components/NetworkGraph.tsx
index d33dc04fd..ea64229e0 100644
--- a/frontend/src/components/NetworkGraph.tsx
+++ b/frontend/src/components/NetworkGraph.tsx
@@ -159,6 +159,8 @@ export default function NetworkGraph() {
   const [graphActionStatus, setGraphActionStatus] = useState('그래프 준비 완료');
   const [relationshipOptionId, setRelationshipOptionId] = useState('');
   const [nodeOptionId, setNodeOptionId] = useState('');
+  const edgeMap = useMemo(() => new Map(edges.map((e) => [String(e.id), e])), [edges]);
+  const nodeInstanceMap = useMemo(() => new Map(nodes.map((n) => [String(n.id), n])), [nodes]);
   const nodeMap = useMemo(() => {
     const map = new Map<string, string>();
     for (const node of nodes) {
@@ -202,7 +204,7 @@ export default function NetworkGraph() {
       };
 
       const selectEdge = (edgeId: number | string) => {
-        const edge = edges.find((candidate) => graphIdEquals(candidate.id, edgeId));
+        const edge = edgeMap.get(String(edgeId));
         if (!edge) return;
         setRelationshipOptionId(String(edge.id));
         setNodeOptionId('');
@@ -213,7 +215,7 @@ export default function NetworkGraph() {
       const selectNode = (nodeId: number | string) => {
         setRelationshipOptionId('');
         setNodeOptionId(String(nodeId));
-        setSelectedGraphDetail(`선택된 노드: ${findNodeLabel(nodes, nodeId)}`);
+        setSelectedGraphDetail(`선택된 노드: ${nodeMap.get(String(nodeId)) ?? String(nodeId)}`);
         setGraphActionStatus('그래프에서 노드를 선택했습니다.');
       };
 
@@ -262,7 +264,7 @@ export default function NetworkGraph() {
         network.destroy();
       };
     }
-  }, [nodes, edges, nodeMap]);
+  }, [nodes, edges, nodeMap, edgeMap, nodeInstanceMap]);
 
   const nodeLabels = useMemo(() => {
     return nodes
@@ -303,7 +305,7 @@ export default function NetworkGraph() {
     if (!isGraphId(node.id)) return;
     setRelationshipOptionId('');
     setNodeOptionId(String(node.id));
-    setSelectedGraphDetail(`선택된 노드: ${findNodeLabel(nodes, node.id)}`);
+    setSelectedGraphDetail(`선택된 노드: ${nodeMap.get(String(node.id)) ?? String(node.id)}`);
     setGraphActionStatus(status);
     networkRef.current?.selectNodes?.([node.id]);
     networkRef.current?.fit?.({ nodes: [node.id], animation: false });
@@ -315,13 +317,13 @@ export default function NetworkGraph() {
   };
 
   const handleRelationshipOptionChange = (value: string) => {
-    const edge = edges.find((candidate) => String(candidate.id) === value);
+    const edge = edgeMap.get(value);
     if (!edge) return;
     selectRelationship(edge, '선택한 관계를 열었습니다.');
   };
 
   const handleNodeOptionChange = (value: string) => {
-    const node = nodes.find((candidate) => String(candidate.id) === value);
+    const node = nodeInstanceMap.get(value);
     if (!node) return;
     selectGraphNode(node, '선택한 노드를 열었습니다.');
   };
diff --git a/plan.md b/plan.md
new file mode 100644
index 000000000..d5b33a136
--- /dev/null
+++ b/plan.md
@@ -0,0 +1,20 @@
+# NetworkGraph constant-time lookup plan
+
+1. Pre-compute `edgeMap` and `nodeInstanceMap` with `useMemo`, and keep the existing `nodeMap` as the authoritative node-label lookup for rendered selections.
+   - `selectEdge` uses `edgeMap.get(String(edgeId))`.
+   - `selectNode` uses `nodeMap.get(String(nodeId))` with the node identifier as the no-entry fallback.
+   - `selectGraphNode` uses `nodeMap.get(String(node.id))` with the node identifier as the no-entry fallback.
+   - `handleRelationshipOptionChange` uses `edgeMap.get(value)`.
+   - `handleNodeOptionChange` uses `nodeInstanceMap.get(value)`.
+   - Selection handlers must not fall back to `Array.prototype.find()` or `findNodeLabel()` scans.
+
+2. Verify the exact branch head from `frontend/` with these commands:
+
+   ```bash
+   pnpm test -- src/components/NetworkGraph.test.tsx src/components/NetworkGraph.map-lookup.test.ts
+   pnpm exec eslint src/components/NetworkGraph.tsx src/components/NetworkGraph.test.tsx src/components/NetworkGraph.map-lookup.test.ts
+   pnpm typecheck
+   pnpm build
+   ```
+
+3. Keep the pull request open until the unchanged exact head has terminal-success required checks, all addressed review threads are resolved, and protected-branch review requirements are satisfied without bypass.