chore(vendor): import pi 1.3.0

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: 71023aec1546d6d677a65669c5665c0927ce0dd0

third_party/pi/packages/durable/test/examples/14-chat.ts

@@ -0,0 +1,45 @@
+// A chat turn.
+// Run from packages/durable:
+//   node --conditions=source --experimental-strip-types test/examples/14-chat.ts
+import { BACKGROUND_CONTEXT } from "@earendil-works/chord/context";
+import { createModels } from "@earendil-works/pi-ai/models";
+import { fauxAssistantMessage, fauxProvider } from "@earendil-works/pi-ai/providers/faux";
+import { AssistantEntry, createRegistry, defineExtension, Harness, MemoryStorage, section } from "../../src/index.ts";
+
+const context = BACKGROUND_CONTEXT;
+
+// The faux provider stands in for a real model (see 16-real-model.ts).
+const faux = fauxProvider();
+const models = createModels();
+models.setProvider(faux.provider);
+faux.setResponses([fauxAssistantMessage("Paris.")]);
+
+const registry = createRegistry();
+registry.install(
+	defineExtension({
+		name: "terse",
+		sections: [section("preamble", () => "You answer in one word.", { tag: false })],
+	}),
+);
+const harness = await Harness.open(new MemoryStorage(), { models, registry }, context);
+const root = await harness.root(context, { agent: { model: { provider: "faux", modelId: "faux-1" } } });
+
+// submit() durably admits user input and returns a Submission. The built-in
+// pi.generation task prepares the system prompt from the agent's sections,
+// calls the model, and appends the answer; wait() resolves once the input is
+// answered or has failed.
+const capital = await root.submit({ type: "input", content: "Capital of France?" }, context);
+const answered = await capital.wait(context);
+if (answered.status === "done" && answered.type === "input") {
+	const entry = await root.commit((tx) => tx.entry(AssistantEntry, answered.answer), context);
+	const reply = entry?.model?.[0];
+	console.log("answer:", reply?.role === "assistant" ? reply.content : reply);
+}
+
+// The transcript holds the user input, the positional system prompt, and the answer.
+const transcript = await root.entries({}, 10, undefined, context);
+console.log(
+	"transcript:",
+	[...transcript.items].reverse().map((entry) => entry.kind),
+);
+await harness.close(context);