Purpose
-------
Integration tests for ``oct git branch`` (Phase 4F — G-F1).
Responsibilities
----------------
- Verify ``--create`` creates a branch with naming validation.
- Verify ``--switch`` switches to an existing branch.
- Verify mutual exclusivity of ``--create`` and ``--switch``.
- Verify JSON output.
- Verify audit trail.
- Verify error cases (duplicate, non-existent, uncommitted changes).
Diagnostics
-----------
Domain: GIT-TESTS
Levels:
L2 -- test lifecycle
L3 -- assertion details
L4 -- deep tracing
Contracts
---------
- All tests use subprocess invocation (same pattern as test_git_commit.py).
- All tests use tmp_path fixtures so they are automatically cleaned up.