diff --git a/tests/integration/a2a/input_required/multi_hop_remote_agent_test.ts b/tests/integration/a2a/input_required/multi_hop_remote_agent_test.ts
new file mode 100644
index 000000000..24286b43f
--- /dev/null
+++ b/tests/integration/a2a/input_required/multi_hop_remote_agent_test.ts
@@ -0,0 +1,84 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import type {RemoteA2AAgentConfig} from '@google/adk';
+import {afterEach, beforeEach, describe, expect, it, vi} from 'vitest';
+
+const PORT_ENV_VAR = 'TEST_API_SERVER_PORT';
+
+const {agentConfigs} = vi.hoisted(() => ({
+  agentConfigs: [] as RemoteA2AAgentConfig[],
+}));
+
+// The agent card URL is not publicly readable off a constructed
+// RemoteA2AAgent, so record the config the agent module builds it with.
+vi.mock('@google/adk', async (importOriginal) => {
+  const actual = await importOriginal<typeof import('@google/adk')>();
+  return {
+    ...actual,
+    RemoteA2AAgent: class extends actual.RemoteA2AAgent {
+      constructor(config: RemoteA2AAgentConfig) {
+        super(config);
+        agentConfigs.push(config);
+      }
+    },
+  };
+});
+
+/**
+ * Re-evaluates the agent module against the currently stubbed environment.
+ *
+ * The port is read once at module evaluation time, so the module registry has
+ * to be reset before every import or later cases reuse the first evaluation.
+ */
+function importAgentModule() {
+  vi.resetModules();
+  return import('./test_agents/multi_hop_remote_agent.js');
+}
+
+describe('multi_hop_remote_agent', () => {
+  beforeEach(() => {
+    agentConfigs.length = 0;
+  });
+
+  afterEach(() => {
+    vi.unstubAllEnvs();
+  });
+
+  it('points the agent card at the port the harness supplied', async () => {
+    vi.stubEnv(PORT_ENV_VAR, '41234');
+
+    const {rootAgent} = await importAgentModule();
+
+    expect(rootAgent.name).toBe('multi_hop');
+    expect(agentConfigs).toHaveLength(1);
+    expect(agentConfigs[0].agentCard).toBe(
+      'http://localhost:41234/a2a/multi_hop/',
+    );
+  });
+
+  it.each([undefined, ''])(
+    'throws a "not set" error when the port is %j',
+    async (raw) => {
+      vi.stubEnv(PORT_ENV_VAR, raw);
+
+      await expect(importAgentModule()).rejects.toThrow(
+        `${PORT_ENV_VAR} is not set.`,
+      );
+    },
+  );
+
+  it.each(['abc', '41234abc', '0', '-1', '1.5', '   '])(
+    'throws a "positive integer" error when the port is %j',
+    async (raw) => {
+      vi.stubEnv(PORT_ENV_VAR, raw);
+
+      await expect(importAgentModule()).rejects.toThrow(
+        `${PORT_ENV_VAR} must be a positive integer, got "${raw}".`,
+      );
+    },
+  );
+});
diff --git a/tests/integration/a2a/input_required/test_agents/multi_hop_remote_agent.ts b/tests/integration/a2a/input_required/test_agents/multi_hop_remote_agent.ts
index 652644f08..acd1b484b 100644
--- a/tests/integration/a2a/input_required/test_agents/multi_hop_remote_agent.ts
+++ b/tests/integration/a2a/input_required/test_agents/multi_hop_remote_agent.ts
@@ -6,7 +6,37 @@
 
 import {RemoteA2AAgent} from '@google/adk';
 
-const port = process.env.TEST_API_SERVER_PORT || '40000';
+const PORT_ENV_VAR = 'TEST_API_SERVER_PORT';
+
+/**
+ * Returns the port of the test ADK API server this agent is loaded into.
+ *
+ * The harness picks that port at random and this agent points back at its own
+ * server, so no default could ever be right.
+ *
+ * @throws If the environment variable is unset or not a positive integer.
+ */
+function requireServerPort(): number {
+  const raw = process.env[PORT_ENV_VAR];
+  if (!raw) {
+    throw new Error(
+      `${PORT_ENV_VAR} is not set. This agent points back at the test ADK ` +
+        `API server it runs inside, so it has no default port to fall back ` +
+        `to; AdkTsApiServer must propagate ${PORT_ENV_VAR}.`,
+    );
+  }
+
+  const port = Number(raw);
+  if (!Number.isInteger(port) || port <= 0) {
+    throw new Error(
+      `${PORT_ENV_VAR} must be a positive integer, got "${raw}".`,
+    );
+  }
+
+  return port;
+}
+
+const port = requireServerPort();
 
 export const rootAgent = new RemoteA2AAgent({
   name: 'multi_hop',