Three tasks over the decisions recorded on the issue: the pure paging rules with their tests, the wiring into the catalogue, and the end-to-end cases including the two assertions this finally lets say what they mean.
Two decisions the issue left open are settled here. The page number goes in the URL beside the filters, because a numbered page being linkable is the whole reason numbered pages were chosen over infinite scroll, and the URL is already the single source of truth for what the storefront is showing. The page size deliberately does not, because it is a preference belonging to one person — putting it in the URL would mean sharing a link to an item also imposed your page size on whoever opened it. It lives in localStorage instead, which also keeps it inside the issue's own scope boundary of not touching the API.
The third open question, whether page size changes with viewport, is answered no and written down as such rather than left silent. A size that moved on rotation would fight the preference the customer had just set.
Everything testable is a pure function, because that is all this project can unit-test: vitest runs in a node environment with no jsdom and no testing-library, so a hook or a component is only reachable through Playwright. That is the same split filters.ts already uses, and it is why the React wrapper is thin enough to need no test of its own.
Writing it turned up one piece of luck worth not breaking: filtersToSearchParams builds a fresh URLSearchParams, so applying a filter already drops the page parameter and returns to page one, while paging copies the existing params and keeps the filters. The plan says so explicitly so nobody 'fixes' it later.
It also confirmed the issue's own warning. filters.spec.ts:165 asserts a named fixture is visible in the unfiltered grid, and favorites-filter.spec.ts:106 does the same — with ten items to a page over thousands, both would start failing the moment paging landed. They were always proxies for 'the result set got bigger', and a visible total lets them assert that directly.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
bermudalambandClaude Opus 5
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