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/chord/test/provider-cost.test.ts

@@ -0,0 +1,83 @@
+// Entry 8: what a change costs the provider. The diff is computed once per change; each feed (one per connection and
+// member) encodes it with its own stateful encoder and its link serializes it.
+import assert from "node:assert/strict";
+import { Type } from "typebox";
+import { describe, it, vi } from "vitest";
+import type * as delta from "../src/delta/index.ts";
+import { type Ctx, createHost, hostNamed, memoryLinkPair, method, remote } from "../src/index.ts";
+import { CountingLink, stateFrames } from "./fixtures/counting.ts";
+
+const counts = vi.hoisted(() => ({ encoders: 0, encodes: 0 }));
+
+vi.mock("../src/delta/index.ts", async (importOriginal) => {
+	const original = await importOriginal<typeof delta>();
+	return {
+		...original,
+		encoder: () => {
+			counts.encoders++;
+			const inner = original.encoder();
+			return {
+				encode: (ops: Parameters<typeof inner.encode>[0]) => {
+					counts.encodes++;
+					return inner.encode(ops);
+				},
+			};
+		},
+	};
+});
+
+const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
+
+const List = remote("t.e8-cost", {
+	version: 1,
+	input: Type.Object({}),
+	host: hostNamed("server"),
+	variants: { main: { state: { items: Type.Array(Type.String()) }, methods: { add: method(Type.String()) } } },
+});
+
+describe("provider cost", () => {
+	it("one change to K clients: K encodes (one per feed), one frame per link, the same ops on every link", async () => {
+		const server = createHost({ self: { kind: "host" }, name: "server", onError: () => {} });
+		server.serve(List, (_input, _principal, self) => {
+			const items = self.state("items", Type.Array(Type.String()), []);
+			return {
+				variant: "main",
+				items,
+				add: (text: string, ctx: Ctx) => {
+					items.change(ctx, (draft) => {
+						draft.push(text);
+					});
+				},
+			};
+		});
+		const K = 4;
+		const clients = Array.from({ length: K }, (_, i) => {
+			const [down, up] = memoryLinkPair();
+			// One principal: every client reaches the same object.
+			server.accept(down, { principal: { user: "u" } });
+			const link = new CountingLink(up);
+			const host = createHost({
+				self: { kind: "host" },
+				name: `browser${i}`,
+				kind: "client",
+				upstream: { link, principal: { kind: "server" } },
+				onError: () => {},
+			});
+			return { host, link, ref: host.hold(List, {}) };
+		});
+		await Promise.all(clients.map((client) => client.ref.ready));
+		const encoders = counts.encoders;
+		const encodes = counts.encodes;
+		const before = clients.map((client) => stateFrames(client.link.received).length);
+		await clients[0]!.ref.add("x");
+		await sleep(10);
+		assert.equal(counts.encodes - encodes, K, "one encode per feed");
+		assert.equal(counts.encoders, encoders, "no new streams for a change");
+		const frames = clients.map((client, i) => stateFrames(client.link.received).slice(before[i]));
+		for (const list of frames) assert.equal(list.length, 1);
+		const ops = frames.map((list) => JSON.stringify(list[0]?.ops));
+		assert.equal(new Set(ops).size, 1, "every link carries the same ops");
+		for (const client of clients) assert.deepEqual(client.ref.items.value, ["x"]);
+		await server.close();
+	});
+});