Implement Backup Submission Flow 526 Lighthouse Submissions

[tblackwe]

Issue Description

When 526 is cutover from using EVSS to Lighthouse APIs, our current mechanism for generating a PDF in backup submissions will no longer function. The Backup submission needs to implement an alternate path based on the Primary submission target API

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Tasks

• Implement backup submission that generates PDF using code added by PR #16411 Ticket Toxic Exposure - [Lighthouse API] generatePdf hook up #80773
• implement spec tests new backup submission path

Acceptance Criteria

• Backup submission updated to support diverging PDF generation
• 100% Passing spec tests
• 90% testing line coverage of new code

Breadcrumbs:

• Benefits Claims Service Implementation

• Disability Compensation Claims Documentation

[SamStuckey]

It looks like the flipper logic is all in place in the backup submission processor. I think all we need to do here is implement the logic you've linked above in this API provider factory. TL;DR @aurora-a-k-a-lightning did the hard stuff, we just need to flesh out the API provider and test.

[tblackwe]

nice. ty for the analysis Sam

[SamStuckey]

WIP DRAFT PR:
department-of-veterans-affairs/vets-api#16876

[SamStuckey]

HAND OFF: @tblackwe is taking this over due to an increased code yellow work load

[SamStuckey]

For posterity this slack thread has a bunch of useful context about how to test