In-page execution broken: JupyterLite kernel never connects after quantecon-theme v2.0.0 upgrade

[mmcky]

Summary

After the quantecon-theme v2.0.0 + mystmd 1.9.1 upgrade (#45), clicking the in-page execution ⏻ power button hangs indefinitely at:

⚡ Connecting to JupyterLite ⚡
[client] Connecting…

The kernel never becomes ready, so no executable cell can run on any lecture. In-page execution is effectively broken site-wide.

Reproduction

1. Open a lecture built with the v2.0.0 toolchain, e.g. https://pr-45--beautiful-dodol-cb9543.netlify.app/inflation-history/
2. Click the ⏻ power button (top-right of the content).
3. The "Connecting to JupyterLite… [client] Connecting…" banner appears and never completes.

Scope — what this is NOT

• Not the local PyPI warehouse (Add local PyPI warehouse for piplite #44). Reproduces identically on the ci: upgrade to mystmd 1.9.1 + Node 20 for quantecon-theme v2.0.0 #45 preview, which ships no pypi/ warehouse. The warehouse is only read at %pip install time after a successful connect (see piplite 404 warnings on pip install cells (missing local PyPI warehouse) #42), so it cannot affect connection. PR Add local PyPI warehouse for piplite #44 is unaffected and orthogonal.
• Distinct from the "Cannot render output node" static-render bug, which ci: upgrade to mystmd 1.9.1 + Node 20 for quantecon-theme v2.0.0 #45 (mystmd 1.9.1) already fixed. This is a runtime kernel-connection failure, not a rendering one.

When it started

Introduced with #45 (v2.0.0 upgrade: mystmd 1.9.1 + Node 20 + the unpinned quantecon-theme bundle). Before the upgrade the kernel connected — see #42, where connect succeeded and only the %pip install step emitted a 404.

Suspected cause (unconfirmed)

The CI install line pins mystmd but leaves the thebe runtime deps unpinned:

npm install -g mystmd@1.9.1 thebe-core thebe thebe-lite

This is the same "unpinned dependency vs. theme bundle" mismatch that broke output-node rendering until mystmd was pinned. If the thebe-lite runtime is out of sync with what the v2.0.0 theme client (@myst-theme 1.x) expects, the kernel handshake may never complete. Two candidate fix locations:

1. lecture-wasm build config — pin thebe-core / thebe / thebe-lite to versions compatible with quantecon-theme v2.0.0 (fix here).
2. Theme bundle — the v2.0.0 @myst-theme thebe-lite integration is itself broken (fix upstream in QuantEcon/quantecon-theme-src).

Next diagnostic step

Capture DevTools Network + Console while clicking power:

• Which request goes red / stays pending (thebe-lite worker, pyodide, *-kernel*.js, .whl/.data)?
• Any red console errors?

This disambiguates (1) vs (2) above.

Refs

• Introduced by ci: upgrade to mystmd 1.9.1 + Node 20 for quantecon-theme v2.0.0 #45 (v2.0.0 upgrade)
• Relates to piplite 404 warnings on pip install cells (missing local PyPI warehouse) #42 — the warehouse only matters once the kernel connects again
• Adjacent: Improve interactive power button UX #39 (power button UX)
• Probable upstream: QuantEcon/quantecon-theme-src (quantecon-theme v2.0.0 / @myst-theme 1.x)

[mmcky]

Resolved as transient — not an actual kernel failure.

In-page execution works under the v2.0.0 theme — confirmed connecting and running cells in both Chrome and Safari. The "stuck at Connecting to JupyterLite" symptom was intermittent and cleared by a page refresh, so this was not the universal failure the title implied.

Likely cause (consistent with "fixed on refresh"):

• a stale / half-registered Service Worker from the theme-version transition (v1.x → v2.0.0) intercepting requests on first load, and/or
• a cold first Pyodide load (~10 MB WASM) that hadn't completed on the first attempt.

During triage every required asset was verified served correctly (thebe-core.min.js / thebe-lite.min.js, service-worker.js, Pyodide v0.27.0, piplite defaults), consistent with a caching/transient cause rather than a missing-asset bug.

Closing. Upstream report (also closed as transient): QuantEcon/quantecon-theme.mystmd#74. If a genuinely cold load (fresh profile / cleared site data + unregistered service worker) ever reliably hangs, reopen with that evidence.