* Add username onboarding prompt for new signups
New users (especially via OAuth/Google) are redirected to /onboarding
to choose a display username before accessing the app. Adds unique
constraint on users.username and case-insensitive uniqueness validation.
https://claude.ai/code/session_01UinBMAy9d6dQzzbcUAdq8J
* Address all code review issues on username onboarding
- Replace case-sensitive unique constraint with functional unique index on
lower(username) so DB-level uniqueness is case-insensitive (fix#1)
- Share USERNAME_RE from models/user.ts; add same format + uniqueness
validation to the settings update-profile action (fix#2)
- Wrap updateUser calls in try/catch to handle race-condition DB errors
gracefully in both onboarding and settings (fix#3)
- Add unit tests for suggestUsername, safeRedirectTo, USERNAME_RE, and
isOnboardingExempt (fix#4)
- Guard suggestUsername against returning strings shorter than 3 chars (fix#5)
- Preserve the user's intended destination via redirectTo query param
through the onboarding flow (fix#6)
- Treat empty username in settings as a validation error instead of a
silent no-op (fix#7)
- Use exact/sub-path matching in isOnboardingExempt to prevent
false-positive prefix matches like /loginpage (fix#8)
https://claude.ai/code/session_01UinBMAy9d6dQzzbcUAdq8J
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Co-authored-by: Claude <noreply@anthropic.com>
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