Desktop session rows are created on the first submit (_ensure_session_db_row),
after _hydrate_session_cwd has already run against a missing row, so no git
probe was ever claimed and git_branch/git_repo_root stayed NULL. The sidebar
then labelled the lane with the DEFAULT_BRANCH_LABEL "main" fallback, and "+"
ran `git switch main`, which fails on a master-trunk repo.
- _ensure_session_db_row schedules the generation-scoped git probe once per
live session when the row has a cwd but lacks git metadata.
- "+" on a main-checkout lane switches only when git lists the label as a
branch (laneSwitchTarget); otherwise the session opens on the current checkout.
Fixes#108694Fixes#108784
3da330fe23