PPR shell metadata added to Build Output

Minor Changes

• 01e18e8: Add hasFallback, htmlSize, and isDynamicRoute to Prerender

  These optional fields surface per-route PPR shell metadata in the Build Output so consumers can classify prerenders (e.g. full shell vs. empty shell vs. concrete prerender):

  • hasFallback — whether a dynamic route template had a static fallback (undefined for concrete prerenders)
  • htmlSize — byte size of the prerendered .html shell (0 for an empty shell, undefined when there's no .html)
  • isDynamicRoute — whether the entry came from a dynamic route template rather than a concrete prerender