[jmgasper]

Summary

Fixes the remaining “Past competitions / Newest first” issue on topcoder-dev.com/opportunities after platform-ui #2421.

The deployed UI correctly requests sortBy=endDate&sortOrder=desc, but PostgreSQL puts null end dates first for a descending sort. The dev API's first ten results were all undated challenges, including “DS MM Dec 8” and “AI Screener t1.” The member-filtered in-memory comparator also inverted its missing-date handling for descending order.

End-date sorting now explicitly places missing dates last in both directions, with ascending challenge ID as a tie-breaker before pagination. Public and member-filtered searches use the same ordering. Undated records remain in the results and total count. No schema migration or additional UI change is required.

Validation

• Confirmed the deployed Opportunities JavaScript includes the merged end-date sorting change.
• Reproduced the null-first results directly against the dev Challenge API.
• PostgreSQL-backed regression passed for public/member searches, ascending/descending dates, equal dates, missing dates, and three two-item pages; the existing status-ordering regression also passed (2 tests).
• pnpm lint and pnpm build passed using Node 26.5.1. Local commands disabled pnpm's dependency auto-install check to reuse the existing matching dependencies in the isolated worktree.
• git diff --check passed.

This API change must be merged and deployed to dev before the reported site behavior is resolved.