It seems when a TypeScript-projected language is used in the VS Code Notebook, it doesn't work because URI Converter does not support the URIs of the notebook cells.

VS Code uses vscode-notebook-cell://<original-notebook-file-path>#<cellId> format for the cells. This way different URI fragments represent different cells.

When Volar converts this into filename, it doesn't preserve # fragment anywhere and then recovers it incorrectly.

Proposal

When fragment is present, add '/' + encodeURIComponent('#' + fragment) ('/%23' prefix) to the end of the file path.
To identify the fragment, the path should have last path component starting with %23 and do not contain more /.

It may conflict with filenames starting with %23 (eg, notebook filename %23andme.mynotebook).