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/06-harness.ts

@@ -0,0 +1,66 @@
+// Open a Harness with a registry of extensions.
+// Run from packages/durable:
+//   node --conditions=source --experimental-strip-types test/examples/06-harness.ts
+import { BACKGROUND_CONTEXT } from "@earendil-works/chord/context";
+import { Type } from "@earendil-works/pi-ai";
+import { createModels } from "@earendil-works/pi-ai/models";
+import {
+	AgentDoc,
+	createRegistry,
+	defineDoc,
+	defineExtension,
+	defineTool,
+	Harness,
+	MemoryStorage,
+} from "../../src/index.ts";
+
+const context = BACKGROUND_CONTEXT;
+
+// A Harness is a Session plus conversation handles and durable tasks. Extension
+// code (tools, prompt sections, hooks, tasks) comes in named extensions
+// installed in a registry the application owns. Nothing in the registry is
+// saved; it is this process's code.
+const read = defineTool({
+	name: "read",
+	description: "Read a file",
+	parameters: Type.Object({ path: Type.String() }),
+	execute: async (args) => ({ output: [{ type: "text", text: `contents of ${args.path}` }] }),
+});
+const Files = defineExtension({ name: "files", tools: [read] });
+const registry = createRegistry();
+registry.install(Files);
+
+// `models` is pi-ai's model access; generation calls models through it.
+const harness = await Harness.open(new MemoryStorage(), { models: createModels(), registry }, context);
+
+const Notes = defineDoc<{ text: string }>({
+	kind: "example.notes",
+	version: 1,
+	scope: "conversation",
+	history: "rewindable",
+	fork: "asOf",
+	initial: () => ({ text: "" }),
+});
+
+// The root conversation always has ID 1. The first root() call creates it,
+// its built-in documents, the `agent` choices, and whatever `init` writes, all
+// in one commit. Later calls, including after a restart, return it and ignore
+// both options.
+const root = await harness.root(context, {
+	agent: { thinkingLevel: "low" },
+	init: async (tx, rootId) => {
+		(await tx.doc(Notes, rootId)).text = "root notes";
+	},
+});
+console.log("root:", root.id, await harness.snapshot(Notes, root.id, context));
+// The stored choices are names; agent() resolves them against the registry.
+console.log("stored agent:", await harness.snapshot(AgentDoc, root.id, context));
+const agent = await root.agent(context);
+console.log(
+	"resolved:",
+	agent.thinkingLevel,
+	agent.extensions.map((extension) => extension.name),
+	agent.tools.map((tool) => tool.name),
+);
+
+await harness.close(context);