fix(submissions): fix unhandled 404s in assessment/submission routes

[adi-herwana-nus]

Problem

Two dead ends in the submission and assessment routes:

/submissions/:id rendered a blank page. The :submissionId route has children but no element
of its own. React Router still creates a match branch for a parent route, so an exact
/submissions/5 matched it and rendered a default <Outlet /> with nothing inside — it never fell
through to the not-found route.

A submission or assessment ID that doesn't exist showed no 404. The backend returns 404, but the
frontend swallowed it:

Page	Fetch	What the user saw
Attempt (submissions/:id/edit)	fetchSubmission	Blank page — the catch only flipped isLoading off, leaving the page to render against an empty store
Assessment (assessments/:id)	fetchAssessment via Preload	Generic red "fetching error" note and toast
Access logs (submissions/:id/logs)	fetchLogs via Preload	Same generic error note

The existing response interceptor only redirects on the 404 whose body says "component not found"
(a disabled course component). A missing record raises ActiveRecord::RecordNotFound, whose response
doesn't match, so nothing redirected.

Change

An index route under :submissionId redirects to edit, matching the pattern already used for
marketplace/listings.

A redirectToNotFoundIfMissing helper in api/ErrorHandling.ts redirects to the not-found page on a
404 and returns whether it did, so callers can skip their own error handling. It is applied at the
three fetches above.

Note this covers more than a typo'd ID. Resources are loaded through their parent — through: :course
in Course::Assessment::Controller, through: :assessment in
Course::Assessment::Submission::Controller — so CanCanCan scopes the find to
@course.assessments / @assessment.submissions. An assessment that exists in another course
raises RecordNotFound before authorization ever runs, and so 404s rather than 403s. That is the
right split, and it means the not-found path leaks no existence information across courses.

Why the helper is opt-in

The obvious alternative is to redirect on every 404 inside redirectIfMatchesErrorIn, in the
response interceptor. That would break callers that treat a 404 as a normal outcome — sendOldSessions
in the video submission actions uses it to detect a session the backend has already dropped. Keeping
it opt-in also leaves the existing local handling in RubricPlaygroundPage coherent.

Preload's own onErrorDo was not usable for the two Preload pages: it receives
error.response?.data, not the status, so the check has to sit at the call site.

[Copilot]

Pull request overview

This PR improves UX and correctness for invalid/missing assessment/submission routes by ensuring they redirect to the Not Found page (instead of rendering blank pages or generic fetch errors), and by adding an index redirect for the /submissions/:id parent route.

Changes:

• Add an index route under :submissionId that redirects /submissions/:id to /submissions/:id/edit.
• Introduce redirectToNotFoundIfMissing to opt-in redirect-to-404 behavior for missing-record 404s.
• Apply the helper to submission attempt, assessment show, and submission logs fetch paths to avoid “blank page” / generic error states.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
client/app/routers/course/assessments/submissions.tsx	Adds an index redirect under :submissionId to avoid rendering an empty outlet.
client/app/bundles/course/assessment/submission/actions/logs.ts	Redirects missing submission-log requests to Not Found when backend returns 404.
client/app/bundles/course/assessment/submission/actions/index.js	Redirects missing submission attempts to Not Found on 404 instead of leaving an empty page state.
client/app/bundles/course/assessment/pages/AssessmentShow/index.tsx	Redirects missing assessments to Not Found rather than showing Preload’s generic fetch error UI.
client/app/api/ErrorHandling.ts	Adds an opt-in helper to redirect on missing-record 404 responses.

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