`Astro.url.pathname` returns different things in dev vs prod if `build.format` config option is set to `preserve`

### Astro Info ```block Astro v7.2.4 Vite v8.2.2 Node v22.20.0 System macOS (arm64) Package Manager npm Output static Adapter none Integrations none ``` ### If this issue only occurs in one browser, which browser is a problem? _No response_ ### Describe the Bug If the `build.format` config option is set to `preserve`, `Astro.url.pathname` will end in `.html` on non-index pages in prod. In dev, however, the `.html` is missing. ### What's the expected result? `Astro.url.pathname` should end in `.html` in dev as well. ### Link to Minimal Reproducible Example https://github.com/alexschcom/astro-pathname ### Participation - [ ] I am willing to submit a pull request for this issue.