Code Execution

Python fenced-code blocks can run in the renderer through Pyodide. Execution happens in a Web Worker so loading packages and running Python do not block the React UI thread.

Activation

CodeBlockView exposes the run tool only when both conditions hold:

• the block language is python;
• chat.code.execution.enabled is true.

The timeout comes from chat.code.execution.timeout_minutes and defaults to one minute. Clicking Run calls pyodideService.runScript(source, {}, timeoutMinutes * 60_000) using the latest source held by the workbench. The returned { text, image? } renders below the code surface in StatusBar.

Runtime flow

CodeBlockView
  → PyodideService.runScript
    → initialize one shared pyodide.worker
    → postMessage({ id, python, context })
      → loadPackagesFromImports(python)
      → runPythonAsync(python)
      → postMessage({ id, output })
    → formatOutput(output)
  → StatusBar text and optional image

PyodideService owns worker initialization, request IDs, response resolvers, timeouts, reset, and termination. Initialization is shared across calls and may retry up to five times. A run timeout rejects that request's resolver; it does not interrupt Python already executing inside the worker.

The service also listens for the legacy IpcChannel.Python_ExecutionRequest renderer event and replies on Python_ExecutionResponse, allowing a main-process caller to use the same worker.

Worker behavior

The worker loads Pyodide 0.28.0 from jsDelivr, so first use and newly imported packages require network access. For each request it:

1. creates a fresh Python globals dictionary;
2. calls loadPackagesFromImports for packages named by the source;
3. injects a Matplotlib shim when the source contains matplotlib;
4. runs the source with runPythonAsync;
5. converts proxy results into structured-cloneable JavaScript values;
6. captures stdout, stderr, execution errors, and an optional Matplotlib PNG;
7. destroys the per-request globals dictionary.

The context field is part of the service message shape but is not currently injected into the Python globals.

Output and failure semantics

PyodideService.formatOutput prefers stdout, otherwise formats the expression result, then appends stderr/errors. A run with no output returns Execution completed with no output. Initialization, timeout, and internal failures resolve to user-visible text instead of rejecting the UI call.

Matplotlib's patched show() saves the current figure to an in-memory PNG data URL. CodeBlockView displays that image together with any text result.

Security boundary

The worker isolates computation from the UI thread, but it is not a security sandbox for untrusted Python. It downloads the Pyodide runtime and imported packages, and executes the supplied source. The feature is therefore disabled by default and must remain an explicit user setting.

Verification

The UI contract is covered by:

pnpm test src/renderer/components/CodeBlockView/__tests__/CodeBlockView.test.tsx

Changes to the service or worker also require a manual run that covers initial runtime download, package loading, timeout reporting, stdout/stderr, and Matplotlib image output; those layers currently have no dedicated automated tests.