[yuezengwu]

Selecting a Git subtree still materializes the entire repository in both read snapshots and isolated writes, which can exceed host workspace archive limits. Check out only the selected subtree with cone-mode sparse checkout and a full index; key snapshots by repository, subtree and commit so separate selections remain isolated.

New managed worktrees use the existing repository lock and require Git >= 2.36 before creation. Repository-root and directory sources keep full checkouts. Existing caches, snapshots and session records are retained; incomplete setup fails without registering a session. Public schemas and authorization behavior are unchanged.

Validation:

• pnpm check, pnpm typecheck, pnpm test (12 suites / 116 tests), pnpm check:package, and git diff --check pass.
• Real Git regressions cover same-commit paths/refs, nested and special-character paths, offline creation from a legacy cache, full root/directory sources, preexisting pending and committed sessions, publication preserving outside blobs, outside edits, abort and interrupted setup.
• Isolated comparison with one bare cache, one snapshot and one unpublished write: full checkout exceeds the unchanged 128 MiB compressed limit; sparse checkout archives successfully at 74,448,905 bytes (71.0 MiB). This is local capacity evidence; Cloud runtime acceptance remains pending the staged package and host dependency update.