diff --git a/src/kernbench/policy/routing/router.py b/src/kernbench/policy/routing/router.py
index 0869079..d4ec39b 100644
--- a/src/kernbench/policy/routing/router.py
+++ b/src/kernbench/policy/routing/router.py
@@ -111,6 +111,13 @@ class PathRouter:
         self._adj_all: dict[str, list[tuple[str, float]]] = defaultdict(list)
         self._adj_mcpu_dma: dict[str, list[tuple[str, float]]] = defaultdict(list)
         self._adj_local: dict[str, list[tuple[str, float]]] = defaultdict(list)
+        # Memoize path lookups: adj dicts are built once here and never
+        # mutated (topology is static per ADR-0006 / SPEC §0.1), so
+        # (id(adj), start, goal) is a stable cache key for the router's
+        # lifetime. Callers use the returned path list read-only.
+        self._path_cache: dict[
+            tuple[int, str, str], tuple[list[str], float]
+        ] = {}
         for e in graph.edges:
             w = e.routing_weight_mm if e.routing_weight_mm is not None else e.distance_mm
             self._adj_all[e.src].append((e.dst, w))
@@ -185,8 +192,14 @@ class PathRouter:
         start: str,
         goal: str,
     ) -> tuple[list[str], float]:
+        cache_key = (id(adj), start, goal)
+        cached = self._path_cache.get(cache_key)
+        if cached is not None:
+            return cached
         if start == goal:
-            return [start], 0.0
+            result = ([start], 0.0)
+            self._path_cache[cache_key] = result
+            return result
         best: dict[str, float] = {start: 0.0}
         prev: dict[str, str] = {}
         heap: list[tuple[float, str]] = [(0.0, start)]
@@ -200,7 +213,9 @@ class PathRouter:
                     cur = prev[cur]
                 path.append(start)
                 path.reverse()
-                return path, d
+                result = (path, d)
+                self._path_cache[cache_key] = result
+                return result
             if d > best.get(node, float("inf")):
                 continue
             for neighbor, edge_dist in adj[node]: