From d85a836ba7fcd505b1ea3c8b6e02d5dca9af6529 Mon Sep 17 00:00:00 2001
From: Charles Packer <packercharles@gmail.com>
Date: Mon, 16 Feb 2026 19:52:17 -0800
Subject: [PATCH] test: lock SDK session reuse contract for follow-up sends
 (#314)

---
 src/core/sdk-session-contract.test.ts | 83 +++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 src/core/sdk-session-contract.test.ts

diff --git a/src/core/sdk-session-contract.test.ts b/src/core/sdk-session-contract.test.ts
new file mode 100644
index 0000000..7231737
--- /dev/null
+++ b/src/core/sdk-session-contract.test.ts
@@ -0,0 +1,83 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { mkdtempSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+
+vi.mock('@letta-ai/letta-code-sdk', () => ({
+  createAgent: vi.fn(),
+  createSession: vi.fn(),
+  resumeSession: vi.fn(),
+  imageFromFile: vi.fn(),
+  imageFromURL: vi.fn(),
+}));
+
+import { createSession, resumeSession } from '@letta-ai/letta-code-sdk';
+import { LettaBot } from './bot.js';
+
+describe('SDK session contract', () => {
+  let dataDir: string;
+  let originalDataDir: string | undefined;
+  let originalAgentId: string | undefined;
+  let originalRailwayMount: string | undefined;
+
+  beforeEach(() => {
+    dataDir = mkdtempSync(join(tmpdir(), 'lettabot-sdk-contract-'));
+    originalDataDir = process.env.DATA_DIR;
+    originalAgentId = process.env.LETTA_AGENT_ID;
+    originalRailwayMount = process.env.RAILWAY_VOLUME_MOUNT_PATH;
+
+    process.env.DATA_DIR = dataDir;
+    process.env.LETTA_AGENT_ID = 'agent-contract-test';
+    delete process.env.RAILWAY_VOLUME_MOUNT_PATH;
+
+    vi.clearAllMocks();
+  });
+
+  afterEach(() => {
+    if (originalDataDir === undefined) delete process.env.DATA_DIR;
+    else process.env.DATA_DIR = originalDataDir;
+
+    if (originalAgentId === undefined) delete process.env.LETTA_AGENT_ID;
+    else process.env.LETTA_AGENT_ID = originalAgentId;
+
+    if (originalRailwayMount === undefined) delete process.env.RAILWAY_VOLUME_MOUNT_PATH;
+    else process.env.RAILWAY_VOLUME_MOUNT_PATH = originalRailwayMount;
+
+    rmSync(dataDir, { recursive: true, force: true });
+  });
+
+  it('reuses the same SDK session across follow-up sendToAgent calls', async () => {
+    const mockSession = {
+      initialize: vi.fn(async () => undefined),
+      send: vi.fn(async (_message: unknown) => undefined),
+      stream: vi.fn(() =>
+        (async function* () {
+          yield { type: 'assistant', content: 'ack' };
+          yield { type: 'result', success: true };
+        })()
+      ),
+      close: vi.fn(() => undefined),
+      agentId: 'agent-contract-test',
+      conversationId: 'conversation-contract-test',
+    };
+
+    vi.mocked(createSession).mockReturnValue(mockSession as never);
+    vi.mocked(resumeSession).mockReturnValue(mockSession as never);
+
+    const bot = new LettaBot({
+      workingDir: join(dataDir, 'working'),
+      allowedTools: [],
+    });
+
+    await bot.sendToAgent('first message');
+    await bot.sendToAgent('second message');
+
+    expect(vi.mocked(resumeSession)).not.toHaveBeenCalled();
+    expect(vi.mocked(createSession)).toHaveBeenCalledTimes(1);
+    expect(mockSession.initialize).toHaveBeenCalledTimes(1);
+    expect(mockSession.send).toHaveBeenCalledTimes(2);
+    expect(mockSession.send).toHaveBeenNthCalledWith(1, 'first message');
+    expect(mockSession.send).toHaveBeenNthCalledWith(2, 'second message');
+    expect(mockSession.stream).toHaveBeenCalledTimes(2);
+  });
+});