Not fully clear died notebooks files in runtime_dir

After not good closing of running jupyter notebook, and after new launch some files cleared like nbserver-(.+).json. But in this folder also store files like nbserver-(.+)-open.html and kernel-(.+).json.

My opinion is that when deletes nbserver-(.+).json also should delete nbserver-(.+)-open.html
Or if nbserver-(.+)-open.html has no pair nbserver-(.+).json

For files kernel-(.+).json I don't find where it checks that file is not needed.

Start by locating the runtime_dir cleanup logic for nbserver-(.+).json, nbserver-(.+)-open.html, and kernel-(.+).json files. Trace when each file is considered unused and verify that orphaned files are handled consistently; done means stale runtime files are removed without affecting active notebook or kernel sessions.

Written by the indexing model from the issue text.