What causes "Vela ${label} did not write the requested output file" in nexu-io/open-design?

Run the same Vela command with --output manually and check whether the file appears

nexu-io/open-design · error · Error

Vela ${label} did not write the requested output file

Error message

Vela ${label} did not write the requested output file

What it means

Thrown by readNonEmptyOutput() when stat() on the expected output file throws — meaning Vela's --output path was never created. The daemon tells Vela where to write the result (outputPath), then reads it back; a missing file means the CLI accepted the request but produced no output artifact.

Source

Thrown at apps/daemon/src/media/vela.ts:120

  // A configured OD alias is already the provider-facing wire name. Only
  // remove the catalogue namespace when the alias layer left the id intact.
  if (wireModel !== model) return wireModel;
  return model.startsWith('vela/') ? model.slice('vela/'.length) : model;
}

function extensionForImageMime(mime: string): string {
  if (mime === 'image/jpeg') return '.jpg';
  if (mime === 'image/webp') return '.webp';
  if (mime === 'image/png') return '.png';
  throw new Error(`Vela image returned unsupported mime_type ${mime}`);
}

async function readNonEmptyOutput(outputPath: string, label: string): Promise<Buffer> {
  let outputStat;
  try {
    outputStat = await stat(outputPath);
  } catch {
    throw new Error(`Vela ${label} did not write the requested output file`);
  }
  if (!outputStat.isFile() || outputStat.size <= 0) {
    throw new Error(`Vela ${label} wrote an empty output file`);
  }
  return readFile(outputPath);
}

function assertInputImageCount(imageRefs: VelaMediaImageRef[]): void {
  if (imageRefs.length > VELA_MAX_INPUT_IMAGES) {
    throw new Error(
      `Vela media accepts at most ${VELA_MAX_INPUT_IMAGES} input images; received ${imageRefs.length}`,
    );
  }
}

async function stageInputImages(
  imageRefs: VelaMediaImageRef[],
  tempDir: string,

View on GitHub (pinned to 5be4028344)

Solutions

Run the same Vela command with --output <path> manually and check whether the file appears
Verify the temp directory (os.tmpdir()) is writable and not full
Check the Vela CLI version for known --output regressions
Inspect Vela stderr/logs for write errors

Defensive patterns

Strategy: try-catch

Validate before calling

import { stat } from 'node:fs/promises';

async function outputExists(p: string): Promise<boolean> {
  try { return (await stat(p)).isFile(); } catch { return false; }
}

Try / catch

try {
  const bytes = await readNonEmptyOutput(outputPath, label);
} catch (err) {
  if (err instanceof Error && /did not write the requested output file/.test(err.message)) {
    // rerun the vela command, or inspect stderr for the write failure
  } else throw err;
}

Prevention

Confirm the temp directory is writable and has free space before the Vela call
Capture Vela stderr so a missing-output failure has a diagnostic
Pin the Vela CLI version and test --output behavior after upgrades

When it happens

Trigger: Vela image gen/edit or video command completed (returned JSON) but did not write to the --output path the daemon supplied. The label identifies which command (e.g. 'image gen', 'image edit').

Common situations: Vela CLI bug where --output is ignored under certain flags; permissions issue on the temp directory; the CLI wrote to a different path; disk full; the CLI was killed mid-write.

Related errors

AI-assisted analysis of nexu-io/open-design@5be4028344 (2026-08-12). Data as JSON: /api/errors/7585d7f837c25d6a. Report an issue: GitHub.