fix(agent): decouple agent streams from compat

closes #6851

packages/coding-agent/test/agent-session-compaction.test.ts

@@ -12,7 +12,7 @@ import { existsSync, mkdirSync, rmSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { Agent } from "@earendil-works/pi-agent-core";
-import { getModel } from "@earendil-works/pi-ai/compat";
+import { getModel, streamSimple } from "@earendil-works/pi-ai/compat";
 import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { AgentSession, type AgentSessionEvent } from "../src/core/agent-session.ts";
 import { AuthStorage } from "../src/core/auth-storage.ts";
@@ -49,6 +49,7 @@ describe.skipIf(!API_KEY)("AgentSession compaction e2e", () => {
 		const model = getModel("anthropic", "claude-sonnet-4-5")!;
 		const agent = new Agent({
 			getApiKey: () => API_KEY,
+			streamFunction: streamSimple,
 			initialState: {
 				model,
 				systemPrompt: "You are a helpful assistant. Be concise.",