fix(scans): ignore stale polling responses

[eshaanag]

Description

Prevents stale Scans page polling responses from overwriting the current task list after a newer request has already completed.

The Scans page now aborts superseded /tasks requests and uses a latest-request sequence guard before updating tasks, pagination, or loading state. This keeps polling, filter changes, page changes, and visibility refreshes from racing each other. I am contributing this under GSSoC.

Related Issues

Closes #415

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• npm test -- --run testing/unit/pages/Scans.polling.test.tsx
• npm run typecheck
• npm run build
• git diff --check

Note: the existing Scans polling test suite emits React act(...) warnings that were present during the targeted run, but all assertions pass.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[utksh1]

Good direction, but this cannot merge while frontend-checks are failing. Please fix the Scans polling test/typecheck failures after the latest main changes, keep the abort/sequence guard behavior, and rerun the full frontend check job before re-review.

[eshaanag]

Thanks for the review. I fixed the frontend-checks failure by updating the Scans phase test fetch fixtures to reflect successful responses after the new non-OK response handling. I also updated the branch with latest main and reran the full PR checks; artifact-check, formatting-hygiene, backend-lint, backend-tests, benchmark, and frontend-checks are all passing now. Could you please re-review when you get a chance?

[utksh1]

Current re-review note: frontend-checks are failing on the latest branch. Please fix the Scans polling test/typecheck failures after current main, keep the abort/sequence guard behavior, and rerun the full frontend check job before re-review.

[eshaanag]

Thanks for checking again. I re-verified the latest branch state after syncing with current main, and GitHub currently shows all checks passing on this PR: artifact-check, backend-lint, backend-tests, benchmark, formatting-hygiene, and frontend-checks.

I also reproduced the frontend-checks steps locally on the current branch:

• npm run typecheck passed
• npm run quality passed with the existing non-blocking animation warning
• npm run test passed: 21 files / 189 tests
• npm run build passed

I do not see a current failing frontend-checks run attached to this PR now. If you are seeing a different failing run, please point me to that job URL and I will inspect that exact log.