feat(backends): add optional pi_embedded backend and config wiring

src/backends/piEmbedded.test.ts

@@ -0,0 +1,100 @@
+import { mkdtempSync, rmSync, writeFileSync } from 'fs';
+import { join } from 'path';
+import { tmpdir } from 'os';
+import { pathToFileURL } from 'url';
+import { describe, expect, it } from 'vitest';
+
+import { PiEmbeddedBackend } from './piEmbedded.js';
+
+function createModule(source: string): { moduleUrl: string; cleanup: () => void } {
+  const dir = mkdtempSync(join(tmpdir(), 'flynn-pi-embedded-'));
+  const file = join(dir, 'module.mjs');
+  writeFileSync(file, source, 'utf-8');
+  return {
+    moduleUrl: pathToFileURL(file).href,
+    cleanup: () => rmSync(dir, { recursive: true, force: true }),
+  };
+}
+
+describe('PiEmbeddedBackend', () => {
+  it('returns text from a createAgentSession/run response object', async () => {
+    const mod = createModule(`
+      export function createAgentSession() {
+        return {
+          run(payload) {
+            return { text: "pi says: " + payload.input };
+          },
+        };
+      }
+    `);
+
+    try {
+      const backend = new PiEmbeddedBackend({ module: mod.moduleUrl, timeoutMs: 2000 });
+      const result = await backend.process({ prompt: 'hello', history: [] });
+      expect(result).toBe('pi says: hello');
+    } finally {
+      mod.cleanup();
+    }
+  });
+
+  it('falls back to string payload when object payload is rejected', async () => {
+    const mod = createModule(`
+      export function createAgentSession() {
+        return {
+          run(payload) {
+            if (typeof payload !== "string") {
+              throw new Error("expected string payload");
+            }
+            return "echo " + payload;
+          },
+        };
+      }
+    `);
+
+    try {
+      const backend = new PiEmbeddedBackend({ module: mod.moduleUrl, timeoutMs: 2000 });
+      const result = await backend.process({ prompt: 'hello', history: [] });
+      expect(result).toContain('echo USER: hello');
+    } finally {
+      mod.cleanup();
+    }
+  });
+
+  it('throws when module has no supported session factory', async () => {
+    const mod = createModule('export const version = "0.0.0";');
+
+    try {
+      const backend = new PiEmbeddedBackend({ module: mod.moduleUrl, timeoutMs: 2000 });
+      await expect(backend.process({ prompt: 'hello', history: [] }))
+        .rejects.toThrow('supported session factory');
+    } finally {
+      mod.cleanup();
+    }
+  });
+
+  it('throws when module cannot be loaded', async () => {
+    const backend = new PiEmbeddedBackend({ module: '/definitely/missing/pi-module.mjs', timeoutMs: 2000 });
+    await expect(backend.process({ prompt: 'hello', history: [] }))
+      .rejects.toThrow('Failed to load Pi embedded runtime module');
+  });
+
+  it('times out slow Pi requests', async () => {
+    const mod = createModule(`
+      export function createAgentSession() {
+        return {
+          run() {
+            return new Promise(() => {});
+          },
+        };
+      }
+    `);
+
+    try {
+      const backend = new PiEmbeddedBackend({ module: mod.moduleUrl, timeoutMs: 10 });
+      await expect(backend.process({ prompt: 'hello', history: [] }))
+        .rejects.toThrow('timed out');
+    } finally {
+      mod.cleanup();
+    }
+  });
+});