Poll or wait for completion of async PDF generation job

[lizadaly]

Generating a PDF title will trigger the following workflow:

• An HTTP request to the "generate PDF" endpoint
• A celery job will be queued to start the Playwright (#1801)

The job will either write a completed PDF, error, or time out.

If the job succeeds:

• A PDF will be available on block storage.
• A URL to the PDF should be delivered to the end user that they have permission to access.

If the job errors:

• The user should be notified and the error should be propagated.

If the job times out:

• The user should be notified and the timeout should be raised as an error.

[lizadaly]

There are lots of implementation options for polling for job completion. What do the other projects do?

[rebeccacremona]

There are lots of implementation options for polling for job completion. What do the other projects do?

Perma tracks every request to make a Perma Link in a CaptureJob table. As the job runs, we update its status field, along with some progress indicators. That info is exposed in an API route. The frontend's JS hits that route every so often and advances a progress bar; we've heard some feedback that the progress bar isn't the best design choice.

The prototype capture service is set up the same way, but is tidier, including a Vue frontend.

As far as I know, CAP doesn't have any user-facing tasks or polling; probably worth confirming that with someone else.

[lizadaly]

This is done!