Handle /page/ redirects for subprojects

[ericholscher]

Summary

• document the spike to restore /page/ redirects on subprojects
• make ServePageRedirect resolve subprojects from either the current project, alias, or slug
• add a regression test covering /projects/<subproject>/page/ redirects
• document how to run the subproject page-redirect test with the proxito settings
• fix a ruff lint warning in ServePageRedirect by removing an unused import

Testing

• ✅ DJANGO_SETTINGS_MODULE=readthedocs.settings.proxito.test uv run pytest readthedocs/proxito/tests/test_old_redirects.py::InternalRedirectTests::test_page_redirect_on_subproject -vv -s
• ✅ uv run ruff check readthedocs/proxito/views/serve.py readthedocs/proxito/tests/test_old_redirects.py

---

Codex Task

[read-the-docs-community]

Documentation build overview

📚 dev | 🛠️ Build #30541339 | 📁 Comparing 58191a4 against latest (1292c9f)

🔍 Preview build

Show files changed (6 files in total): 📝 6 modified | ➕ 0 added | ➖ 0 deleted

File	Status
contribute.html	📝 modified
install.html	📝 modified
search-integration.html	📝 modified
style-guide.html	📝 modified
design/embed-api.html	📝 modified
design/theme-context.html	📝 modified

[read-the-docs-community]

Documentation build overview

📚 docs | 🛠️ Build #30541340 | 📁 Comparing 58191a4 against latest (1292c9f)

🔍 Preview build

Show files changed (20 files in total): 📝 17 modified | ➕ 0 added | ➖ 3 deleted

File	Status
build-customization.html	📝 modified
link-previews.html	📝 modified
support.html	📝 modified
visual-diff.html	📝 modified
about/index.html	📝 modified
config-file/v2.html	📝 modified
intro/antora.html	📝 modified
intro/doctools.html	📝 modified
intro/docusaurus.html	📝 modified
intro/markdoc.html	📝 modified
intro/mdbook.html	📝 modified
intro/mkdocs.html	📝 modified
intro/mystmd.html	➖ deleted
intro/sphinx.html	📝 modified
intro/vitepress.html	📝 modified
intro/zensical.html	➖ deleted
reference/main-content-detection.html	➖ deleted
server-side-search/index.html	📝 modified
tutorial/index.html	📝 modified
tutorials/index.html	📝 modified

[humitos]

We should probably add a test case for a project with a custom /projects/ prefix in the URL as well.

[stsewd]

Not really sure what type of problem this is solving? Using the parent project with /projects//page/? Not really sure if we should support that, the parent project isn't a subproject of itself, we don't have those types of URLs anywhere. I'm also not sure if we should support looking by slug, all doc URLs use the alias.

[ericholscher]

@stsewd This was requested by a user: https://app.frontapp.com/open/msg_1ywmnguf?key=jm1YcL6gOAX1QmsaqmZTk3mxMvR2geLL

Also I want it for our docs, for example https://docs.readthedocs.com/platform/page/reference/git-integration.html

[stsewd]

We already support page redirects for subprojects, the URL should be https://docs.readthedocs.com/projects/platform/page/reference/git-integration.html. What is not supported is using a custom prefix.

[ericholscher]

Huh... ok 🤔

[ericholscher]

I will close this then, and let the user know.