deepseek-ai/deepseek-harness · error · Error

output.render returned ${describeReturn(value)} — it must re

Error message

output.render returned ${describeReturn(value)} — it must return an ARRAY of content blocks:
  ✓ return [{ type: 'text', text: String(value) }]

What it means

Error "output.render returned ${describeReturn(value)} — it must return an ARRAY of content blocks: ✓ return [{ type: 'text', text: String(value) }]" thrown in deepseek-ai/deepseek-harness.

Source

Thrown at packages/extensions/cordis-host-runner/src/guard.ts:536

 * Compact JSON preview of an invalid execute return for the teaching error
 * (`String(…)` for the un-stringifiable undefined case), truncated to
 * {@link RETURN_PREVIEW_LIMIT}.
 */
function describeReturn(value: JsonValue): string {
  // The caller has already crossed cloneJson, so this value is lossless JSON
  // and serialization cannot produce undefined.
  const json = JSON.stringify(value)
  return json.length > RETURN_PREVIEW_LIMIT ? `${json.slice(0, RETURN_PREVIEW_LIMIT)}…` : json
}

/**
 * Validate and host-materialize a sandbox renderer's content blocks.
 */
function assertRenderedContent(value: JsonValue): ContentBlock[] {
  if (Array.isArray(value) && value.every(isContentBlockShape)) {
    return value as unknown as ContentBlock[]
  }
  throw new Error(
    `output.render returned ${describeReturn(value)} — it must return an ARRAY of content blocks:\n`
    + '  ✓ return [{ type: \'text\', text: String(value) }]',
  )
}

/**
 * The `harness.defineTool` handed into the sandbox: the real DSL, with `parameters` normalized
 * into a fresh host-realm ParameterSchemaSpec (raw object wrappers unwrapped,
 * required arrays mapped, and explicit DSL object openness enforced) and the tool's `execute` return normalized into the host realm
 * via a JSON round-trip. Non-JSON or wrong-shape output fails that call instead of poisoning
 * the session log.
 * @param options - the standard `defineTool` options; `parameters` may be the ParameterSchemaSpec DSL or a JSON-Schema-style wrapper.
 * @returns the marker-tagged definition `harness.registerTool` (and the guarded `ctx.tools.register`) accepts.
 */
export function sandboxDefineTool(options: unknown): ToolDefinition {
  if (!isPlainRecord(options)) throw new Error('harness.defineTool options must be an object')
  const normalized = normalizeParameterSchemaSpec(options.parameters)
  if (!isPlainRecord(options.output)) {

View on GitHub (pinned to b150a551b8)

When it happens

Trigger: Thrown at packages/extensions/cordis-host-runner/src/guard.ts:536 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of deepseek-ai/deepseek-harness@b150a551b8 (2026-08-24). Data as JSON: /api/errors/4a30b1302e061207. Report an issue: GitHub.