Reject a truncated video and retry only the artifact download

01Prepare environment and inputs

1. Prepare Node.js and FFmpeg. The original two-second 320×180 source has twenty frames; its byte size and expected SHA-256 are captured in artifact-manifest.json.
2. Inspect truncated.mp4: it is an actual byte-prefix truncation of the original source, not a fabricated error label. The first local download returns those broken bytes.
3. Run in a fresh directory. All HTTP requests use one ephemeral 127.0.0.1 artifact URL, with a three-second timeout, a 2-MB response cap and finally cleanup. No production task is called.

02Run the recipe

Run command

node run-recipe.mjs --out ./my-run

1. Keep the existing task and artifact identity

   Read the manifest for local-paid-once and /artifact/local-paid-once. The fixture exposes an intentionally forbidden /generate route solely to count accidental resubmissions; the successful path never calls it. This local name does not represent an actual paid task.

2. Reject the first complete HTTP response as broken media

   The first response is HTTP 200 but contains 17,775 bytes, half of the 35,550-byte source. Run FFmpeg with -xerror and explode error detection through the entire video decode. The actual decoder failure is retained in the negative receipt.

3. Retry the same artifact URL once

   Fetch the exact same artifact identity a second time. The local server returns the complete original bytes. Check SHA-256 against the manifest, then fully decode twenty frames instead of accepting the network status alone.

4. Audit the boundary between retries

   Check exactly two downloads, zero generation requests and a closed local server. The bounded fixture has no backoff, signed-URL renewal or provider error classification; a real downloader must use its own service’s documented recovery rules.

03Check the result

• The first HTTP 200 response contains the actual truncated byte prefix and differs from the expected SHA-256.
• Full FFmpeg decode of the truncated attempt exits with a recorded error.
• The second fetch uses the same artifact URL and the total download count is exactly two.
• The second file’s SHA-256 equals the complete artifact manifest.
• The recovered file fully decodes to twenty 320×180 frames.
• No /generate request occurs and the loopback server closes; all seven checks pass.

04Troubleshoot and deliver

The local replay proves recovery from this truncated MP4 while preserving artifact identity. It does not show a provider retry promise or a real payment, generation or signed-download execution.

05Download scripts and fixtures

• Original task-specific local-fixture diagram ↓
• Complete runnable kit with original inputs and real receipts ↓
• Task-specific standard-library fixture runner ↓
• Bounded local execution and receipt helpers ↓
• English execution and acceptance guide ↓
• English machine-readable task brief ↓
• Chinese execution and acceptance guide ↓
• Chinese machine-readable task brief ↓
• Actual complete passing execution receipt ↓
• Actual expected-rejection receipt ↓
• Named task-specific check results ↓
• SHA-256 inventory for distributed files ↓
• Recorded fixture: artifact-manifest.json ↓
• Recorded fixture: complete-source.mp4 ↓
• Recorded fixture: truncated.mp4 ↓
• Recorded fixture: download-attempt-1.mp4 ↓
• Recorded fixture: download-attempt-2.mp4 ↓