feat(rstest): add @midscene/rstest package

[fi3ework]

Summary

Introduce @midscene/rstest — Midscene exposed as native rstest fixtures. Destructure agent, page, browser, agentForPage directly from the test signature; the package handles browser lifecycle, per-test agent construction, and per-file HTML report merging.

import { test as base } from '@midscene/rstest/playwright';
import { expect } from '@rstest/core';

const test = base.extend({ url: 'http://localhost:5173/' });

test('adds a todo', async ({ agent }) => {
  await agent.aiAct("type 'Study AI' in the input and press Enter");
  await agent.aiAssert('the list contains exactly one item: "Study AI"');
});

Two browser providers ship behind subpath exports:

• @midscene/rstest/playwright
• @midscene/rstest/puppeteer

Fixtures

Fixture	Notes
midsceneOptions	headless / viewport / launchOptions / contextOptions / gotoOptions / agentOptions. Repo-wide defaults via defineMidsceneDefaults in a setupFile; per-file override via test.extend({ midsceneOptions }).
url	Target URL the default page fixture navigates to. Empty string disables auto-navigation.
browser	File-scoped, lazy — not launched unless something destructures it (or anything depending on it).
context (playwright only)	Fresh BrowserContext per test. Override for custom storage / state.
page	Auto-navigated to url. Override the fixture for custom page lifecycles (persistent context, trace orchestration, …). Code after await use(page) is teardown.
agent	PlaywrightAgent / PuppeteerAgent bound to page. Report collection automatic.
agentForPage(page, opts?)	Build secondary agents for popups / additional contexts. Reports merged alongside the primary's.

Reporter

MidsceneReporter prints Midscene report: midscene_run/report/<file>.html after each test file. Wire into reporters: ['default', new MidsceneReporter()] in rstest.config.ts.

Notes for reviewers

• rstest 0.9.9 doesn't export TestAPIs / TestContext / Fixtures — `packages/rstest/src/test-api-types.ts` mirrors the public surface from public types only, so the emitted `.d.ts` doesn't leak unexported internals. Delete the file when rstest exposes those types.
• Browser singleton is promise-based to stay correct under `test.concurrent` (two concurrent tests would otherwise both see `_browser === null` and double-launch).
• `__reportMeta` private fixture is shared between `agent` and `agentForPage` so the timestamp baked into report filenames stays consistent within one test. Hidden from the public type via the final cast in each provider.
• `isolate: true` is required (rstest default). The package keeps file-scoped state at module top-level, which only works because each test file evaluates its own module graph.

Validation

• `pnpm -w run lint`
• `npx nx typecheck @midscene/rstest`
• `npx nx test @midscene/rstest` — 18 / 18
• `npx nx build @midscene/rstest` (d.ts inspection confirms `__reportMeta` is omitted from public types)

Test plan

• `npx rstest run` against the example demo project
• Midscene HTML report path is printed after each test file
• `test.extend({ page })` with `chromium.launchPersistentContext` works end-to-end
• Puppeteer subpath works without Playwright installed
• `test.concurrent` doesn't double-launch the browser
• A file with only non-AI tests doesn't launch a browser at all (lazy guarantee)