different-ai/openwork · error

MCP_APP_DOCUMENT_RUNTIME_ERROR

MCP_APP_DOCUMENT_RUNTIME_ERROR

Error message

stage + ": " + safeMessage(value)

What it means

This error originates inside the generated Artifact application document sandbox: the report helper posts a ui/notifications/sandbox-diagnostic message with code MCP_APP_DOCUMENT_RUNTIME_ERROR to the parent window whenever the generated app throws at runtime. The message text is built as stage + ': ' + safeMessage(value), where stage identifies where it fired (e.g. 'document-error' from the window error listener). It means the generated interactive view's document-level JavaScript failed while executing.

Source

Thrown at ee/apps/den-api/src/generated-artifact-view-builder.ts:187

        loader: "js",
        resolveDir: process.cwd(),
      }))
    },
  }
}

const GENERATED_ARTIFACT_RUNTIME_REPORTER = `
(() => {
  const safeMessage = (value) => {
    if (value instanceof Error) return value.message.slice(0, 1000);
    if (typeof value === "string") return value.slice(0, 1000);
    return "The generated Artifact application failed at runtime.";
  };
  const report = (stage, value) => {
    window.parent.postMessage({
      method: "ui/notifications/sandbox-diagnostic",
      params: {
        code: "MCP_APP_DOCUMENT_RUNTIME_ERROR",
        message: stage + ": " + safeMessage(value),
      },
    }, "*");
  };
  window.__openworkReportArtifactRuntimeError = report;
  window.addEventListener("error", (event) => report("document-error", event.error || event.message));
  window.addEventListener("unhandledrejection", (event) => report("unhandled-rejection", event.reason));
})();
`.trim().replace(/<\/script/giu, "<\\/script")

async function buildClientBundle(reactSource: string): Promise<string> {
  const entry = `
    import React from "react";
    import { createRoot } from "react-dom/client";
    import { App, PostMessageTransport } from "@modelcontextprotocol/ext-apps";
    const ArtifactView = React.lazy(() => import("artifact:view"));
    const mount = document.getElementById("openwork-artifact-view-root");
    const reportRuntimeError = (stage, error) => {

View on GitHub (pinned to 2b7df46e8a)

Solutions

1. Read the stage prefix and message in the sandbox-diagnostic notification to locate where the document threw.
2. Fix the generated artifact code at the reported stage (guard null/undefined values, wrap async work in try/catch).
3. Regenerate the artifact and confirm the document loads without a document-error report.
4. If generated by a model, harden the generation prompt/template against the specific runtime failure.

Example fix

// before: unguarded access in generated doc
render(data.items[0].title)
// after: defensive access
const title = data?.items?.[0]?.title ?? ''; render(title)

window.addEventListener('error', (event) => report('document-error', event.error || event.message));
window.addEventListener('unhandledrejection', (event) => report('unhandled-rejection', event.reason));

function hasMessage(v: unknown): v is { message: string } {
  return typeof v === 'object' && v !== null && typeof (v as { message?: unknown }).message === 'string';
}

try { render(data); } catch (err) {
  window.__openworkReportArtifactRuntimeError?.('render', err);
  showFallbackView();
}

When it happens

Trigger: An uncaught exception in the generated artifact document (window 'error' event), or code explicitly calling window.__openworkReportArtifactRuntimeError(stage, value): runtime errors in generated render code, undefined references, failed fetches inside the sandbox, errors during initial document evaluation.

Common situations: Generated app code referencing data that turned out null/undefined; schema drift between the artifact generator output and runtime APIs; unhandled promise rejections in the sandbox; syntax-valid but logically broken generated code hitting an edge case with real data.

Related errors

• Number.${name} is not available in CodeMode.
• path_escape
• The right-hand side of 'instanceof' must be a constructor Co
• String method '${name}' is not available in CodeMode.
• Array.from(...) does not support a map function in CodeMode;

AI-assisted analysis of different-ai/openwork@2b7df46e8a (2026-09-01). Data as JSON: /api/errors/cf2177a00353f955. Report an issue: GitHub.