Backend: Add cursor-based pagination for high-volume campaign lists

[CelestinaBeing]

Summary

The backend uses offset/limit pagination (?page=1&limit=10). At scale with thousands of campaigns, offset pagination becomes slow (full table scan + skip) and unreliable when records are inserted between pages (page drift). Cursor-based pagination is the scalable solution for production.

Problem

In backend/src/pagination.js:

// offset/limit approach
items.slice(offset, offset + limit)

Issues:

• SELECT * OFFSET N requires scanning and skipping N rows — O(N) cost
• Campaign insertions between page fetches cause duplicate or missing items
• No stable cursor for re-fetching from a known position

Acceptance Criteria

• Add cursor-based pagination support in paginateItems(): if ?cursor= is provided, use it instead of page/offset
• Cursor encodes: { id, createdAt } base64-encoded so it's opaque to clients
• Implement in sqliteCampaignRepository.list(): WHERE (createdAt, id) < (cursor.createdAt, cursor.id) with ORDER BY createdAt DESC, id DESC LIMIT N+1
• Response includes: { items, nextCursor, hasMore }
• Keep backward compat: offset/limit pagination still works when ?cursor= is absent
• Update frontend/src/components/Pagination.tsx to support cursor-mode (load more / infinite scroll option)
• Add unit tests for cursor encoding/decoding, boundary conditions (first page, last page, empty), and consistency under concurrent inserts
• Update backend/openapi.yaml

References

• backend/src/pagination.js
• backend/src/dal/sqliteCampaignRepository.js
• frontend/src/components/Pagination.tsx

[Kaycee276]

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Hi maintainer i'd love to work on this issue

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[Malcolm-Wander]

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Hello maintainer,I’d love to work on this issue…thank you in advance🙏🏽

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[michaelvic123]

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[dotmantissa]

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Hi 👋 I'm a full-stack developer
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[prodbycorne]

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