## Summary
- Start resource discovery from the rendered XML root because prebuild
removes the page body wrapper before generating the route.
- Add a regression test for a Sitemap resource used by a Collection on
an XML page.
## Verification
- The regression test failed before the fix: the generated request graph
omitted `sitemap-resource` from `rootIds`.
- `pnpm --filter webstudio test -- src/prebuild.test.ts` — 78 tests
passed.
- `pnpm --filter webstudio typecheck` — passed.
- Formatting, lint, and `git diff --check` passed.
- Rebuilt the imported Spazio Flow project locally. `/sitemap.xml` now
returns all 12 eligible URLs; before the fix it returned an empty
`<urlset>`.
- Documentation impact reviewed: no user workflow or documented behavior
changed, so no docs update is needed.
- Fixture impact reviewed: no fixture inputs or generated contracts
changed, so no fixture regeneration is needed.
Oleg Isonen
432ca1172d