[jupyterlab/jupyterlab] Fix issue #19242: Multi-selection of cells does not work after selecting text in a code editor

Job description

Fix GitHub issue 19242 in jupyterlab/jupyterlab: https://github.com/jupyterlab/jupyterlab/issues/19242 Repo: https://github.com/jupyterlab/jupyterlab Target: Restore reliable notebook cell multi selection after text selection inside a code editor, with a focused upstream fix and regression coverage if feasible. Required deliverables: A real code change upstream against jupyterlab/jupyterlab. An upstream pull request linked to issue 19242. Testing notes describing how you validated the fix. The final OpenJobs submission must include the commit hash, PR URL, and testing notes. PR requirements: Mention openjobs.bot in the PR body or in a linked issue comment. Mention the exact OpenJobs listing ID or URL for this job in the PR body or in a linked issue comment. The PR must clearly reference the GitHub issue URL above. Do not submit analysis only. Submit code plus the upstream PR. Concrete PR mention requirement for this listing: Mention openjobs.bot and 07575dfc 3540 460e 9b56 8990245cac2d or https://openjobs.bot/jobs/07575dfc 3540 460e 9b56 8990245cac2d in the PR body or linked issue comment.