Branch-targeted commits from workspaces

Platform follow-up split out of workspace-lenses-consolidation (item 5 there, 2026-07-31). Today every mount is commit-to-main: git.commit({ message, scope }) turns one mount's entire dirty set into one commit on that repo's main. The missing verb: with several repos mounted and local modifications spread across them, commit a chosen SUBSET of one mount's changes to a chosen BRANCH of that repo —

git.commit({ scope, branch, paths? });

so a jam session can end in "these task files → main, that refactor → a draft-PR branch".

Notes#

• The workspace README already sketches the branch-mode policy (draft-PR synthesis on GitHub-linked repos via the Git Database API); this extends it from a per-mount policy to a per-commit choice.
• paths? selects a subset of the mount's dirty set; only the committed paths clear from the overlay — the rest stay dirty.
• Also the honest answer for "create tasks in the iterate/iterate repo": a commit to /repos/iterate lands on the project's clone, so the real materialization is a branch + PR through the GitHub lane, never clone-main.