fix(agent): decouple agent streams from compat

closes #6851

scripts/agent-treeshake-smoke-entry.ts

@@ -0,0 +1,13 @@
+import { Agent } from "@earendil-works/pi-agent-core";
+import { createModels } from "@earendil-works/pi-ai";
+import { anthropicProvider } from "@earendil-works/pi-ai/providers/anthropic";
+
+const models = createModels();
+models.setProvider(anthropicProvider());
+const model = models.getModel("anthropic", "claude-sonnet-4-5");
+if (!model) throw new Error("Anthropic smoke-test model not found");
+
+export const agent = new Agent({
+	initialState: { model },
+	streamFunction: models.streamSimple.bind(models),
+});