See reasons for failure on PR CI check run

[milesworking]

I need to programmatically check the CI status of a PR and read the explanation logs of any failure.

Body

The check runs and check suite api's provide response that contain properties like

    "html_url": "https://github.com/org/repo/actions/runs/1234/job/5678",
    "details_url": "https://github.com/org/repo/actions/runs/1234/job/5678",
    "status": "completed",
    "conclusion": "failure",

but I cannot find a section that shows exactly which steps of the CI pipeline failed and precise explanations for rejection.
When I go visit the html_url and details_url, I do see the CI logs, but I need this information programmatically; not simply reading it from a web browser.

The closest I can find is output.text from the check runs example

  "output": {
    "title": "Mighty Readme report",
    "summary": "There are 0 failures, 2 warnings, and 1 notice.",
    "text": "You may have some misspelled words on lines 2 and 4. You also may want to add a section in your README about how to install your app.",

but this looks like a manual human reviewer, not output logs from a CI failure.

Is this supported by the API? Thank you.