Sprint 101 — Register 3 Pages + MEMORY.md Cleanup

Background

New user onboarding required a multi-step registration flow. The existing auth flow jumped directly from OAuth callback to the main dashboard with no profile setup step. Sprint 101 introduces a 3-page registration wizard and performs MEMORY.md housekeeping.

Goals

1. Create /register page (registration entry, OAuth provider selection)
2. Create /register/profile page (display name, avatar, study preferences)
3. Create /register/github page (GitHub account linking for submission tracking)
4. Clean up MEMORY.md entries older than 30 sprints

Work Summary

Changes

Page Structure

app/[locale]/register/
  layout.tsx          — RegisterLayout (stepper + progress indicator)
  page.tsx            — Step 1: Registration entry
  profile/
    page.tsx          — Step 2: Profile setup
  github/
    page.tsx          — Step 3: GitHub linking

Registration Flow

1. /register — Entry page. Displays "Complete your profile to get started" CTA. Shows current OAuth provider (Google/GitHub). "Continue" button advances to /register/profile.

2. /register/profile — Display name input (2–30 chars, profanity filter), avatar upload (≤2MB JPEG/PNG, cropped to 200×200), study timezone selection. "Save & Continue" → /register/github.

3. /register/github — GitHub OAuth2 PKCE flow to link a separate GitHub account for submission file tracking. "Skip for now" allowed — GitHub linking is optional.

Stepper Component

<RegisterStepper
  steps={[
    { label: t('stepRegister'), href: '/register' },
    { label: t('stepProfile'), href: '/register/profile' },
    { label: t('stepGithub'), href: '/register/github' },
  ]}
  currentStep={currentStep}
/>

MEMORY.md Cleanup

• Removed inline detail for sprints 60–70 (moved to topic files in .claude/projects/memory/)
• Reduced MEMORY.md from 28KB to 18KB
• Preserved sprint index entries (1-line summaries retained)

Verification

Decisions

• 3-page wizard over single form: Each step has distinct UX requirements and can fail independently. Multi-page is more resilient (partial completion survives refresh).
• GitHub linking optional: Forcing GitHub linking at registration would block users who use other hosting. Optional step with "skip" maintains accessibility.
• PKCE for GitHub OAuth2: PKCE (Proof Key for Code Exchange) is required for public clients (browser-side). No client secret stored in frontend.
• MEMORY.md cleanup: Files over 24KB trigger warnings. Pruning inline detail to topic files is the standard maintenance pattern.

Lessons Learned

• Registration wizards need back-navigation: Initial implementation had no "Back" button. Added after UX review — users need to edit previous steps.
• PKCE redirect URI must exactly match: GitHub OAuth app registered redirect URI must match the redirect_uri parameter character-for-character, including trailing slashes.
• MEMORY.md grows faster than expected: Sprint 101 was the first time the 24KB warning triggered. Establish a cleanup schedule (every 10 sprints or at 20KB).