feat(ai): lazy-load provider modules for faster startup fixes #2297

packages/ai/test/lazy-module-load.test.ts

@@ -0,0 +1,102 @@
+import { spawnSync } from "node:child_process";
+import { createRequire } from "node:module";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, expect, it } from "vitest";
+
+const require = createRequire(import.meta.url);
+const tsxLoader = require.resolve("tsx/esm");
+const packageRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const aiEntryUrl = new URL("../src/index.ts", import.meta.url).href;
+
+const SDK_SPECIFIERS = [
+	"@anthropic-ai/sdk",
+	"openai",
+	"@google/genai",
+	"@mistralai/mistralai",
+	"@aws-sdk/client-bedrock-runtime",
+] as const;
+
+type ProbeResult = {
+	loadedSpecifiers: string[];
+};
+
+function runProbe(action: string): ProbeResult {
+	const script = `
+		import { registerHooks } from "node:module";
+
+		const targets = new Set(${JSON.stringify(SDK_SPECIFIERS)});
+		const loaded = [];
+
+		registerHooks({
+			resolve(specifier, context, nextResolve) {
+				if (targets.has(specifier)) {
+					loaded.push(specifier);
+				}
+				return nextResolve(specifier, context);
+			},
+		});
+
+		const mod = await import(${JSON.stringify(aiEntryUrl)});
+		${action}
+		console.log(JSON.stringify({ loadedSpecifiers: [...new Set(loaded)] }));
+	`;
+
+	const result = spawnSync(process.execPath, ["--import", tsxLoader, "--input-type=module", "--eval", script], {
+		cwd: packageRoot,
+		encoding: "utf8",
+	});
+
+	if (result.status !== 0) {
+		throw new Error(`Probe failed (exit ${result.status})\nSTDOUT:\n${result.stdout}\nSTDERR:\n${result.stderr}`);
+	}
+
+	const stdoutLines = result.stdout
+		.split(/\r?\n/)
+		.map((line) => line.trim())
+		.filter((line) => line.length > 0);
+	const lastLine = stdoutLines.at(-1);
+	if (!lastLine) {
+		throw new Error(`Probe produced no output\nSTDERR:\n${result.stderr}`);
+	}
+
+	return JSON.parse(lastLine) as ProbeResult;
+}
+
+describe("lazy provider module loading", () => {
+	it("does not load provider SDKs when importing the root barrel", () => {
+		const result = runProbe("");
+		expect(result.loadedSpecifiers).toEqual([]);
+	});
+
+	it("loads only the Anthropic SDK when calling the root lazy wrapper", () => {
+		const result = runProbe(`
+			const model = {
+				id: "claude-sonnet-4-20250514",
+				name: "Claude Sonnet 4",
+				api: "anthropic-messages",
+				provider: "anthropic",
+				baseUrl: "https://api.anthropic.com",
+				reasoning: true,
+				input: ["text"],
+				cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0 },
+				contextWindow: 200000,
+				maxTokens: 8192,
+			};
+			const context = { messages: [{ role: "user", content: "hi" }] };
+			await mod.streamSimpleAnthropic(model, context).result();
+		`);
+
+		expect(result.loadedSpecifiers).toEqual(["@anthropic-ai/sdk"]);
+	});
+
+	it("loads only the Anthropic SDK when dispatching through streamSimple", () => {
+		const result = runProbe(`
+			const model = mod.getModel("anthropic", "claude-sonnet-4-20250514");
+			const context = { messages: [{ role: "user", content: "hi" }] };
+			await mod.streamSimple(model, context).result();
+		`);
+
+		expect(result.loadedSpecifiers).toEqual(["@anthropic-ai/sdk"]);
+	});
+});