next.js

b3512c2e - Separate route structure comparison from param comparison (#98974)

Separate route structure comparison from param comparison (#98974) Changing a page’s search params doesn’t change which page it is, but it may change the data that page needs. The router currently mixes these concerns by appending search params to `__PAGE__` segments. Remove that encoding so we can compare which route is being rendered separately from the param values used to render it. Param values are now compared through the existing VaryPath data structure, while route structure is compared during the existing tree traversals. Each traversal can decide which comparisons matter for the work it’s doing. Client-side comparisons and history restoration still need the search params, so store them in a separate FlightRouterState slot for now. As before, previous-page search params are stripped from normal request headers. This is a temporary step that lets us migrate incrementally. Eventually, FlightRouterState will be replaced by a type that represents the route and its params more directly. This is mostly a refactor, though it fixes an accidental inconsistency in search-param handling compared with regular route params, avoiding some redundant prefetch work. Fully cached pages already track their vary params correctly. This separation prepares us to do the same for partially dynamic segments during navigation, so changing an unrelated param won’t require rendering their dynamic content again.