Account synchronization across multiple devices

[vlita]

I have noticed that when I complete a challenge and then switch to a different computer, my code (and challenge completion data) isnt always available on the second computer. Specifically, the total "challenges completed" count on my user profile is accurate, but the check-mark badges on the challenges page disappear for some of the challenges I completed on the other computer, along with the code I wrote. Let me know if more information/screenshots is needed to resolve this issue.

[kunal-mansukhani]

Investigation notes (root cause + proposed fix)

Investigated across leetgpu-client and leetgpu-infra for the report: profile “challenges completed” looks right, but challenge-page checkmarks (and code) are missing on a second machine.

What is stored where

Data	Storage	Cross-device?
Challenge draft code	Browser localStorage key challengeCodes (src/features/challenges/utils/challengeStorage.ts, written from CodeEditorContainer)	No
Successful/failed submissions + code files	Server (submissions / submission_files)	Yes
Challenge-page checkmarks	Server GET /api/v1/challenges/progress → ListChallengeProgress	Yes (when query matches)
Profile solved counts	Server ListUserDifficultyStats / related profile queries	Yes

Editor load path (ChallengeEditor): prefer localStorage.challengeCodes[challengeId][language], else starter code. It does not hydrate from the user’s latest server submission.

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Root cause A — missing code (by design today)

Drafts never leave the browser. On a second machine, localStorage is empty → editor shows starter code. Submitted solutions are on the server, but you only get them by opening Submissions and clicking a tile (fetchSubmissionCode).

Worse UX on a fresh device:

1. Preferred language is also local (localStorage.challengeLanguage). Without it, the client currently defaults new sessions toward JAX (temporary experiment in ChallengeEditor).
2. Submissions list is filtered by language + GPU. Default language/GPU on machine 2 often won’t match where you submitted on machine 1 → “No submissions available for the selected filters,” which feels like code vanished.

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Root cause B — profile count vs challenge checkmarks (semantic mismatch)

Progress badges (ListChallengeProgress in libs/leetgpu/schema/queries/challenges.sql):

AND s.action = 'submit'
-- completed iff BOOL_OR(st.name = 'success') among submit rows

Documented by TestChallengeProgress: a successful run must not mark attempted/completed.

Profile solved counts (ListUserDifficultyStats in users.sql) count distinct challenge_id with st.name = 'success' and do not filter action = 'submit'.

Since runs are persisted (finalizeSubmission stores every execution with action), a challenge you only Run successfully (or mix of runs + submits) can inflate profile “solved” while the challenges page shows no checkmark. That matches “profile accurate, badges missing for some.”

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Proposed fix

1. Infra (consistency) — leetgpu-infra

• Add AND s.action = 'submit' to profile solved aggregations that should mean “completed,” at least:
  • ListUserDifficultyStats (solved CTE)
  • optionally ListUserLanguageStats solved filter
• Keeps profile totals aligned with /challenges/progress and TestChallengeProgress.

2. Client (cross-device code) — leetgpu-client

When opening a challenge, if there is no local draft (or draft === starter):

• Fetch latest submit for that challengeId + selected language (new endpoint or extend submissions API to return latest across GPUs / best effort).
• Seed editor + challengeCodes from that code.

Optional follow-ups:

• Server-backed drafts (proper sync).
• Submissions panel: if empty for current GPU, fall back to “any GPU for this language” or show a hint.
• Revert/remove the temporary JAX default so fresh devices don’t hide CUDA submissions.

3. Client (hardening)

• fetchChallengeProgress currently treats HTTP 401 as { progressByChallengeId: {} } (success). Prefer throw/retry so React Query doesn’t cache “no badges” for staleTime (5 min) after a blip.

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Why no PR from this pass

GitHub MCP here can read + comment/create issues, but cannot commit/push file changes (gh is not authenticated on this runner). Happy to implement the above in a PR once push access is available.

Key refs

• Issue: Account synchronization across multiple devices #328
• Client storage: leetgpu-client src/features/challenges/utils/challengeStorage.ts
• Client progress UI: ChallengesPage.tsx + fetchChallengeProgress
• Infra progress SQL: ListChallengeProgress
• Infra profile SQL: ListUserDifficultyStats
• Intent test: TestChallengeProgress in libs/leetgpu/test/challenges_test.go

[vlita]

Is there a plan to implement some of the proposed fixes?