WASM: add a WebAssembly/JupyterLite smoke-test job to CI

[mmcky]

Part of #925 (Phase 3 — keep it working).

Goal

Browser support must not regress once established: add a wasm job to GitHub Actions that runs a smoke suite in the real browser stack.

Approach

• Build the Phase 0 JupyterLite site in CI — the deployment config from WASM: JupyterLite proof-of-concept deployment and browser smoke suite #928 is the seed.
• Execute the smoke suite in the xeus-python kernel: headless Chromium via Playwright, or the pytester harness pattern used inside emscripten-forge recipes.
• pandas and pytest are both packaged for WASM, so meaningful portions of the real test suite can eventually run in-browser — start with the smoke list from WASM: JupyterLite proof-of-concept deployment and browser smoke suite #928 and grow from there.
• Track the emscripten-forge numba/llvmlite versions in the job the way conda-forge versions are tracked today.

This job is also the natural watchpoint for upstreaming: the blog post signals intent to merge the WASM engine into Numba mainline, and once that ships, the patched-recipe caveats (no ParallelAccelerator fallback, disabled ufunc caching) may start dissolving.

Acceptance criteria

• A CI job builds a JupyterLite deployment containing quantecon and runs the smoke suite in a headless browser
• Failures are actionable — per-function results rather than a monolithic pass/fail

[mmcky]

Parking the Emscripten/JupyterLite runner job removed from PR #938 in the split (see the review there for context). Below is that job with the review fixes already folded in, ready to seed this issue's PR — it drops --with-deps (the browser install hung at apt-get for the full 6-hour job limit on the one run), adds pytest-timeout (the --timeout flag was previously passed without its plugin), makes the native gate real via needs: native, drops the _site cache (unpinned quantecon made the key meaningless and the build re-ran regardless), adds a server-readiness check before Playwright starts, bumps setup-python to v7, and puts upper bounds on the unpinned build tools (the one run resolved jupyterlite-xeus to 5.0.0, which the --XeusAddon.environment_file flag has never been exercised against).

Development approach: iterate in the PR under a pull_request trigger so each attempt shows red/green, then flip to schedule + workflow_dispatch just before merge — workflow_dispatch only works once the workflow file exists on the default branch, and after merge gh workflow run --ref <branch> can still exercise branch versions. Note the job tests the released conda-forge quantecon (not repo source) until the package lands on emscripten-forge-4x, so per-PR triggering isn't useful long-term.

The Playwright harness it runs (ci/wasm/test_jupyterlite.py, reworked to sentinel-driven execution in PR #938) and the kernel env (ci/wasm/environment.yml) are already on main once #938 merges. The job to append to .github/workflows/ci_wasm_smoke.yml:

  # ------------------------------------------------------------------
  # Emscripten / JupyterLite.
  # Builds a real JupyterLite site from emscripten-forge packages
  # (xeus-python WASM kernel + numba + quantecon), then drives it
  # headlessly with Playwright to verify the stack end-to-end.
  # ------------------------------------------------------------------
  wasm:
    name: Smoke suite (Emscripten / JupyterLite)
    runs-on: ubuntu-latest
    timeout-minutes: 45
    needs: native
    steps:
    - uses: actions/checkout@v7

    - uses: actions/setup-python@v7
      with:
        python-version: "3.11"

    - name: Install micromamba
      uses: mamba-org/setup-micromamba@v2
      with:
        micromamba-binary-path: /usr/local/bin/micromamba
        init-shell: none
        generate-run-shell: false

    - name: Install JupyterLite build tools
      run: |
        pip install \
          "jupyterlite-core>=0.4,<0.9" \
          "jupyterlite-xeus>=4.5,<6" \
          pytest \
          pytest-timeout \
          pytest-playwright

    - name: Install Playwright browser
      run: python -m playwright install chromium

    - name: Build JupyterLite site
      run: |
        jupyter lite build \
          --XeusAddon.environment_file=ci/wasm/environment.yml \
          --output-dir=_site

    - name: Start local server
      run: |
        python -m http.server 8000 --directory _site &
        until curl -sf http://localhost:8000/ >/dev/null; do sleep 1; done

    - name: Run Playwright smoke tests (Emscripten kernel)
      run: |
        pytest ci/wasm/test_jupyterlite.py \
          --browser chromium \
          --timeout=900 \
          -v

Remaining known unknowns for the first iterations: the JupyterLab selectors in test_jupyterlite.py (launcher card, console prompt, output area) have never executed against a real JupyterLite build, and neither has the jupyterlite-xeus 5.x build flag — expect a few rounds. Once the job is green, record the per-function results table in #928.