Guard against nil attachments in processing form

[jazairi]

Why these changes are being introduced:

ThesisController#deleted_file_list calls .blob on a potentially nil Active Storage attachment.
The processing form can trigger a race condition
when a background process deletes a file that is
still visible on the form. If a user attempts to
delete that file and the attachment no longer
exists, the app throws a 422 error.

Relevant ticket(s):

• USE-710

How this addresses that need:

This adds a guard clause to check for the presence of the attachment before calling .blob.

Side effects of this change:

None.

Developer

Accessibility

• ANDI or WAVE has been run in accordance to our guide.
• This PR contains no changes to the view layer.
• New issues flagged by ANDI or WAVE have been resolved.
• New issues flagged by ANDI or WAVE have been ticketed (link in the Pull Request details above).
• No new accessibility issues have been flagged.

New ENV

• All new ENV is documented in README.
• All new ENV has been added to Heroku Pipeline, Staging and Prod.
• ENV has not changed.

Approval beyond code review

• UXWS/stakeholder approval has been confirmed.
• UXWS/stakeholder review will be completed retroactively.
• UXWS/stakeholder review is not needed.

Additional context needed to review

E.g., if the PR includes updated dependencies and/or data
migration, or how to confirm the feature is working.

Code Reviewer

Code

• I have confirmed that the code works as intended.
• Any CodeClimate issues have been fixed or confirmed as
  added technical debt.

Documentation

• The commit message is clear and follows our guidelines
  (not just this pull request message).
• The documentation has been updated or is unnecessary.
• New dependencies are appropriate or there were no changes.

Testing

• There are appropriate tests covering any new functionality.
• No additional test coverage is required.

[Copilot]

🟡 Changes recommended

Add coverage verifying stale attachment submissions complete without a 422/error.

Get a fresh assessment by requesting another Copilot review.

Pull request overview

Guards thesis processing against deleted Active Storage attachments.

Changes:

• Checks attachment existence before accessing its blob.
• Skips stale attachment entries safely.

File summaries

File	Description
app/controllers/thesis_controller.rb	Adds a nil attachment guard in deleted_file_list.

The stale-attachment regression path lacks controller test coverage and should be tested.

Review details

Suppressed comments (1)

app/controllers/thesis_controller.rb:182

• This guard only skips building the flash-message entry; the same stale id remains in thesis_params and is passed to thesis.update at line 124. Because Thesis enables accepts_nested_attributes_for :files_attachments, Rails can still raise ActiveRecord::RecordNotFound while applying _destroy for an attachment that disappeared, so the reported 422 race is not fully prevented. Remove or ignore missing attachment entries before the update (and add a regression test for the stale id).

      next unless attachment

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Lite

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[coveralls]

coverage: 98.287% (+0.001%) from 98.286% — etd-710 into main