When browsing /doc/ckout files which are present in the filesystem but not added in the repository are shown.

$ fossil new test.fossil
$ fossil open test.fossil
$ fossil server&

http://127.0.0.1:8080/doc/ckout/index.wiki now should show an error as should http://127.0.0.1:8080/doc/tip/index.wiki

$ echo Hello World! > index.wiki

http://127.0.0.1:8080/doc/ckout/index.wiki now should show "Hello World!"

$ fossil commit

Now since the file was not added it is not committed and hence http://127.0.0.1:8080/doc/tip/index.wiki still shows an error.
http://127.0.0.1:8080/doc/ckout/index.wiki should have been showing something like "file not added to repository" all the time so that it is consistent with the committed state created by committing the checkout.

browsing /doc/ckout shows files not added to repository