perf(cli): defer Playwright and isomorphic-git until a command needs them

Load browser composition after CLI scenario validation and load Git support only for local reference trees with Git metadata. Preserve default outputs and actual command behavior.

Refs #1065.

Co-authored-by: Kaoru0822 <208281322+kaoru0822-kitauji@users.noreply.github.com>

src/application/ReferenceSourceVcsAdapter.ts

@@ -2,8 +2,6 @@ import fs from "node:fs";
 import { lstat, readFile } from "node:fs/promises";
 import { join, resolve } from "node:path";
 
-import { resolveRef } from "isomorphic-git";
-
 export type ReferenceSourceVcsInfo =
   | {
       readonly kind: "git";
@@ -42,6 +40,8 @@ export const readReferenceSourceVcs = async (
 };
 
 const resolveSourceHead = async (root: string): Promise<string> => {
+  // isomorphic-git is loaded on first use so CLI and MCP startup skip it.
+  const { resolveRef } = await import("isomorphic-git");
   const dotgit = join(root, ".git");
   if (!(await lstat(dotgit)).isFile())
     return resolveRef({ fs, dir: root, ref: "HEAD" });

src/cliBrowserScenarioCommands.ts

@@ -2,7 +2,6 @@ import { Cli } from "incur";
 import { z } from "zod";
 
 import { captureBrowserScenario } from "./application/BrowserScenarioCaptureService.js";
-import { createBrowserScenarioProvider } from "./composition/browserScenario.js";
 import { CLI_COMMANDS } from "./cliCommandNames.js";
 import { parseCliJsonInput, resolveCliJsonPaths } from "./cliJsonInput.js";
 import { logCliCommand } from "./cliLogging.js";
@@ -44,6 +43,9 @@ export const registerBrowserScenarioCommands = (
               projectInputIssues(scenario.error.issues, input.value),
             ),
           );
+        // Load Playwright only for this command, not during CLI startup.
+        const { createBrowserScenarioProvider } =
+          await import("./composition/browserScenario.js");
         const result = await captureBrowserScenario(
           createBrowserScenarioProvider(environment),
           scenario.data,

tests/boundary/cli/cliStartupImports.test.ts

@@ -0,0 +1,76 @@
+import { execFile } from "node:child_process";
+import { mkdir } from "node:fs/promises";
+import { join } from "node:path";
+import { promisify } from "node:util";
+
+import { describe, expect, it } from "vitest";
+
+import { createTestTempDirectory } from "../../fixtures/temporaryDirectory.js";
+
+const execute = promisify(execFile);
+const MARKER = "REA_TEST_RESOLVED ";
+// Dependencies that only one command uses; startup must not resolve them.
+const DEFERRED_PACKAGES = ["playwright-core", "isomorphic-git"] as const;
+// Report each resolved deferred package on stderr without changing resolution.
+const RESOLUTION_HOOK = `data:text/javascript,${encodeURIComponent(`
+import { registerHooks } from "node:module";
+const packages = ${JSON.stringify(DEFERRED_PACKAGES)};
+registerHooks({
+  resolve(specifier, context, next) {
+    const resolved = next(specifier, context);
+    const name = packages.find((item) =>
+      resolved.url.includes("/node_modules/" + item + "/"),
+    );
+    if (name !== undefined)
+      process.stderr.write(${JSON.stringify(MARKER)} + name + "\\n");
+    return resolved;
+  },
+});
+`)}`;
+
+const resolvedPackages = async (
+  arguments_: readonly string[],
+): Promise<ReadonlySet<string>> => {
+  const { stderr } = await execute(
+    process.execPath,
+    [`--import=${RESOLUTION_HOOK}`, ...arguments_],
+    { cwd: process.cwd(), maxBuffer: 16 * 1_024 * 1_024 },
+  );
+  return new Set(
+    stderr
+      .split("\n")
+      .filter((line) => line.startsWith(MARKER))
+      .map((line) => line.slice(MARKER.length)),
+  );
+};
+
+const evaluate = (source: string): readonly string[] => [
+  "--input-type=module",
+  "--eval",
+  source,
+];
+
+describe("CLI startup imports", () => {
+  it("detects each deferred package when its command code loads", async () => {
+    await expect(
+      resolvedPackages(
+        evaluate('await import("./dist/composition/browserScenario.js");'),
+      ),
+    ).resolves.toContain("playwright-core");
+    const source = await createTestTempDirectory("rea-startup-imports-");
+    await mkdir(join(source, ".git"));
+    await expect(
+      resolvedPackages(
+        evaluate(
+          `const { readReferenceSourceVcs } = await import("./dist/application/ReferenceSourceVcsAdapter.js"); await readReferenceSourceVcs(${JSON.stringify(source)});`,
+        ),
+      ),
+    ).resolves.toContain("isomorphic-git");
+  });
+
+  it("does not load command-specific packages to register commands", async () => {
+    await expect(
+      resolvedPackages(["scripts/rea.mjs", "--help"]),
+    ).resolves.toEqual(new Set());
+  });
+});