Nginx SPA Fallback Checklist
Single-page apps need direct routes to return index.html. Static assets, however, should still return 404 if missing so deployment mistakes are visible.
Subdirectory fallback
Scope try_files fallback to the deployed app path instead of masking every missing file on the domain.
Before reload
Run an Nginx syntax check and keep a rollback path before reloading production configuration.
Verify
Test the app root, one deep page, and real JS/CSS assets for correct status codes and content types.