feat(vbgui-fe): JupyterLite scaffold + GitHub Pages deploy workflow

Stage F-E of the Visual Builder GUI epic (cppmega-mlx-o0k). Ships
the static-bundle hand-off so the visual builder can run from
GitHub Pages with no kernel server.

- vbgui/jupyterlite/: JupyterLite scaffold (jupyter_lite_config.json
  + content/demo.ipynb). Demo notebook documents the estimator-only
  constraint (MLX unavailable under Pyodide → build_model / dry_forward
  disabled; everything else works 1:1 through the same JSON-RPC
  contract). Verified locally with `jupyter lite build` (69 MB output).
- .github/workflows/vbgui-pages.yml: CI workflow that builds the
  Vite standalone bundle + the anywidget bundle + the JupyterLite
  site and pushes the assembled payload to GitHub Pages on every
  main push that touches the relevant paths. Uses
  actions/upload-pages-artifact + actions/deploy-pages.
- .gitignore (per-subdir): _out/ and the doit DB are build artefacts.

Tests (6): config + notebook validity + workflow contains required
steps (build:widget, jupyter lite build, deploy-pages action) + the
content/files subdirs exist.

Full v4 regression: 2068 passed / 5 skipped / 15 xfailed / 0 failed.

Closes cppmega-mlx-o0k.5.

Author: apstenku123

.github/workflows/vbgui-pages.yml

@@ -0,0 +1,84 @@
+name: Deploy Visual Builder static demo to GitHub Pages
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "vbgui/**"
+      - "cppmega_v4/widget/**"
+      - "cppmega_v4/spec/**"
+      - "cppmega_v4/buildspec/**"
+      - "cppmega_v4/parallelism/**"
+      - "cppmega_v4/fusion/**"
+      - "cppmega_v4/probe/**"
+      - "cppmega_v4/jsonrpc/**"
+      - "cppmega_v4/runner/**"
+      - ".github/workflows/vbgui-pages.yml"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Set up Node 22
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+          cache: "npm"
+          cache-dependency-path: vbgui/package-lock.json
+
+      - name: Set up Python 3.13
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install JupyterLite + Pyodide kernel
+        run: |
+          python -m pip install --upgrade pip
+          pip install jupyterlite-core jupyterlite-pyodide-kernel jupyter-server
+
+      - name: Build standalone Vite bundle
+        working-directory: vbgui
+        env:
+          NODE_ENV: development
+        run: |
+          npm ci
+          npm run typecheck
+          npm test
+          npm run build
+          npm run build:widget
+
+      - name: Build JupyterLite static site
+        working-directory: vbgui/jupyterlite
+        run: jupyter lite build --output-dir ../site/jupyterlite
+
+      - name: Stage Pages payload
+        run: |
+          mkdir -p vbgui/site
+          cp -r vbgui/dist/* vbgui/site/
+          test -d vbgui/site/jupyterlite
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: vbgui/site
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - id: deployment
+        uses: actions/deploy-pages@v4

tests/v4/test_jupyterlite_scaffold.py

@@ -0,0 +1,58 @@
+"""F-E JupyterLite scaffold tests — config validity + build pipeline.
+
+Lightweight: verify the static scaffold files exist and parse cleanly.
+The full `jupyter lite build` runs in CI (see
+.github/workflows/vbgui-pages.yml) — locally we just lint the inputs so
+a malformed notebook or config can't slip into main.
+"""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import pytest
+
+
+_VBGUI = Path("vbgui")
+_JLITE = _VBGUI / "jupyterlite"
+
+
+def test_jupyterlite_config_exists_and_parses():
+    cfg = _JLITE / "jupyter_lite_config.json"
+    assert cfg.is_file(), "missing jupyter_lite_config.json"
+    payload = json.loads(cfg.read_text())
+    assert "LiteBuildConfig" in payload
+    assert payload["LiteBuildConfig"]["contents"] == ["content"]
+
+
+def test_jupyterlite_demo_notebook_is_valid():
+    nb = _JLITE / "content" / "demo.ipynb"
+    assert nb.is_file()
+    data = json.loads(nb.read_text())
+    assert data["nbformat"] >= 4
+    assert "cells" in data and len(data["cells"]) >= 1
+    src = "".join("".join(c.get("source", [])) for c in data["cells"])
+    # Notebook must self-document the estimator-only mode constraint.
+    assert "estimator-only" in src.lower()
+
+
+def test_jupyterlite_demo_imports_widget_class():
+    nb = _JLITE / "content" / "demo.ipynb"
+    src = nb.read_text()
+    assert "VisualBuilderWidget" in src
+
+
+def test_pages_workflow_exists_and_has_required_jobs():
+    wf = Path(".github/workflows/vbgui-pages.yml")
+    assert wf.is_file(), "missing GitHub Pages deploy workflow"
+    text = wf.read_text()
+    assert "actions/upload-pages-artifact" in text
+    assert "actions/deploy-pages" in text
+    assert "build:widget" in text
+    assert "jupyter lite build" in text
+
+
+@pytest.mark.parametrize("subdir", ["content", "files"])
+def test_jupyterlite_subdirs_present(subdir):
+    assert (_JLITE / subdir).is_dir()

vbgui/jupyterlite/content/demo.ipynb

@@ -0,0 +1,33 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# cppmega Visual Builder — JupyterLite demo\n",
+    "\n",
+    "This static-site demo runs the visual builder in **estimator-only mode**:\n",
+    "VBSpec / MBSpec / PSpec / Fusion planning all work; `build_model` and `dry_forward` are disabled because MLX is not available under Pyodide.\n",
+    "\n",
+    "Use the Visual Builder GUI in **JupyterLab** (full mode) when you need to actually train."
+   ]
+  },
+  {
+   "cell_type": "code",
+   "metadata": {},
+   "source": [
+    "import piplite\n",
+    "await piplite.install([\"cppmega-mlx[gui,widget]\"])\n",
+    "from cppmega_v4.widget import VisualBuilderWidget\n",
+    "VisualBuilderWidget()"
+   ],
+   "outputs": [],
+   "execution_count": null
+  }
+ ],
+ "metadata": {
+  "kernelspec": {"display_name": "Python (Pyodide)", "language": "python", "name": "python"}
+ },
+ "nbformat": 4,
+ "nbformat_minor": 5
+}

vbgui/jupyterlite/jupyter_lite_config.json

@@ -0,0 +1,9 @@
+{
+  "LiteBuildConfig": {
+    "contents": ["content"],
+    "extra_http_headers": {
+      "Cross-Origin-Embedder-Policy": "require-corp",
+      "Cross-Origin-Opener-Policy": "same-origin"
+    }
+  }
+}