fix: land #33992 from @darkamenosa

Co-authored-by: Tom <hxtxmu@gmail.com>

extensions/test-utils/plugin-runtime-mock.ts

@@ -123,6 +123,17 @@ export function createPluginRuntimeMock(overrides: DeepPartial<PluginRuntime> =
         })) as unknown as PluginRuntime["channel"]["reply"]["resolveEnvelopeFormatOptions"],
       },
       routing: {
+        buildAgentSessionKey: vi.fn(
+          ({
+            agentId,
+            channel,
+            peer,
+          }: {
+            agentId: string;
+            channel: string;
+            peer?: { kind?: string; id?: string };
+          }) => `agent:${agentId}:${channel}:${peer?.kind ?? "direct"}:${peer?.id ?? "peer"}`,
+        ) as unknown as PluginRuntime["channel"]["routing"]["buildAgentSessionKey"],
         resolveAgentRoute: vi.fn(() => ({
           agentId: "main",
           accountId: "default",