[Parked until product proof] In-browser Pyodide playground

Summary

contextweaver's demos are deterministic, network-free, and CPU-light —
the rare Python library that can run entirely in the browser. Add a
"Playground" page to the MkDocs site that loads contextweaver in Pyodide
(WebAssembly CPython) and lets visitors route a 100-tool catalog, firewall
a 16 KB payload, and inspect BuildStats — editable code, live output, no
install, no backend, no API keys.

Why this matters

• "Try it in your browser" collapses the adoption funnel from
  README → install → quickstart to README → click. For a library whose
  pitch is a before/after number, letting visitors generate that number
  themselves in 10 seconds is the strongest possible demo.
• Zero infrastructure: Pyodide runs client-side; GitHub Pages hosts it.
  Determinism means every visitor sees exactly the documented numbers.
• Few projects in this category have anything comparable — it is a
  memorable differentiator and instantly shareable.

Proposed scope

• docs/playground.md + JS glue: Pyodide bootstrap, micropip.install
  of the contextweaver wheel, a code editor (CodeMirror) preloaded with
  scenario snippets, and an output pane.
• Scenario presets via tabs: (1) route 100 tools → ChoiceCards,
  (2) firewall + drilldown, (3) phase-budgeted build with BuildStats,
  (4) free-form editor.
• Feasibility gate (first task): confirm the dependency story under
  Pyodide — PyYAML, jsonschema, rank-bm25 availability;
  tiktoken (Rust) will likely be unavailable, which the existing
  deterministic offline token-counter fallback (contextweaver.tokens,
  see the troubleshooting note on the tiktoken-unavailable path) is
  designed for; typer/rich/mcp are unused by the library paths the
  playground exercises but are import-time dependencies — if imports
  block, evaluate micropip's dependency handling or a documented
  playground-specific install step. Document findings in the issue
  before building UI.
• CI: a Playwright (or similar) smoke test that loads the page and runs
  preset 1, gating the docs deploy; pin the Pyodide version.
• Link prominently from README and docs/index.md.

Implementation notes

• The wheel is pure-Python (py3-none-any) — installable by micropip
  directly from PyPI or a docs-hosted copy.
• MkDocs material supports custom JS/CSS per page
  (extra_javascript); keep the playground self-contained under
  docs/assets/playground/.
• Heuristic token counts will differ from tiktoken's — print a one-line
  note in playground output and link the troubleshooting entry; numbers
  must still be deterministic.
• Keep load fast: lazy-load Pyodide on first interaction, show progress;
  total cold start on broadband should be < 15 s.

Acceptance criteria

• Playground page on the docs site runs all three preset scenarios
  client-side with no backend and no keys.
• Output for preset scenarios is deterministic across reloads.
• Cold-start load is acceptable (lazy-loaded, with progress UI).
• CI smoke test gates docs deployment; Pyodide version pinned.
• README links the playground next to the install one-liner.

Out of scope

• Running the MCP gateway/CLI in-browser (library APIs only).
• Persistence, sharing links, or user accounts.
• Mobile-optimized editor UX beyond what CodeMirror gives by default.

References

• Pyodide: https://pyodide.org/en/stable/
• micropip: https://micropip.pyodide.org/
• Offline token-counter fallback:
  docs/troubleshooting.md#offline-air-gapped-tiktoken-warning
• Related: #435 (Colab gallery — the heavier-weight sibling)

Priority: P1 · Effort: L · Impact: Transformational

Start with the Pyodide dependency feasibility gate, checking the library paths, contextweaver.tokens fallback, and the tiktoken-unavailable note in docs/troubleshooting.md. If viable, map the work across docs/playground.md, docs/assets/playground/, README, docs/index.md, and the proposed Playwright smoke test. Done means the feasibility findings are documented and the page meets the listed client-side, deterministic, loading, CI, and linking criteria.