App.tsx was 361 lines, and roughly sixty of them were one cohesive concern with nothing to do with laying out a page: fetching the catalogue for the current filters, debouncing it, and negotiating with the session before it could ask. Six pieces of state, four callbacks and two effects, sharing scope with the header, footer, filter drawer and auth modal that make up the rest of the file.
This is the same shape #81 dealt with once. That change took out the rendering half by extracting Catalogue and brought the file under the cognitive-complexity limit. The state half stayed.
App keeps the URL as the source of filter truth, because that genuinely belongs to the page: a reload, a shared link and the back button all have to restore the same view. What moves is the request, the debounce, and the auth negotiation — and that last one is the reason this is worth doing. The rule the comments explain at length, that firing before the session resolves would 401 and show an outage banner to someone who is in fact signed in, now has somewhere to live rather than being a pair of derived booleans in a page component.
The hook decides when the favorites filter needs a session; the page decides what to do about it, through an onAuthRequired callback, because the prompt is a modal the page owns.
The serialise-then-reparse of the filters is kept, with the reason written down rather than left to be rediscovered. Depending on a string is what keeps `load` referentially stable while the filters are value-equal, and `load` is what the debounce effect depends on — depending on the object would give a new `load` every render, restart the debounce each time, and fire a request per keystroke. The alternatives considered were a ref written during render and threading the key through the page, and both are worse than one honest comment.
filterKey is returned rather than recomputed by the caller: the page needs exactly that value to reset the catalogue's error boundary, so a crashed grid gets another chance when the filters change.
App.tsx is 300 lines. No behaviour change is intended, so the bar is the end-to-end suite unchanged — the storefront listing, the filters, the favorites-requires-sign-in prompt, the failure banner and the boundary reset all pass.
Also removes what the extraction left dead in App.tsx: the useEffect import, the debounce constant, and `authLoading`, which existed only to decide whether to fire the request.
Refs #98
bermudalamb
461ab01d4c