test(issue-57): the derivable audit-log root is recorded, not forwarded

New: prefix()/CLI forward three keys for a sibling binding and four for an
explicit root; create records the sibling on the row, omits it from the
pane's --env and still pins it in the injected publish commands; the
issue's scene (a pane with WORKSPACE_ROOT and MAM_JOBS_DIR only) moves its
audit log with --registry-dir and leaves the control root alone;
worktree_prepare's pane --env carries no DELEGATE_JOB_LOGS_DIR.

The three existing four-key forwarding assertions (user-approved) compare
FORWARDED_ENV = CP_ENV[:3]; CP_ENV and the negative assertions are kept.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/test_issue21_acceptance.py

@@ -21,7 +21,8 @@ import pytest
 from test_issue21_loop_b import LOCAL_ROWS, _drive, _reviews, _sidecars, _state
 from test_issue21_phase2_loop_a import (REM, _calls, _prepare, _resume, _rows, _run, _skill, _wt,  # noqa: F401
                                         ctl)
-from test_issue21_worktree_prereqs import (CP_ENV, WRAPPER, _assert_no_env_in_agent_args, _binding, _dry_submit,
+from test_issue21_worktree_prereqs import (CP_ENV, FORWARDED_ENV, WRAPPER, _assert_no_env_in_agent_args, _binding,  # noqa: F401
+                                           _dry_submit,
                                            _env, _env_flags, _injected, _kill_timer, _only_job_id)
 from test_issue21_worktree_prereqs import _git as _g
 from test_issue21_worktree_prereqs import wt_repo  # noqa: F401
@@ -70,7 +71,7 @@ def test_a2_pane_env_carries_the_binding_not_the_agent_args(ctl, mock_herdr, moc
     main = ctl
     wt, since, _ = _sibling(main, mock_herdr)
     flags = _env_flags(mock_herdr, since)
-    for k, v in zip(CP_ENV, _binding(main).values()):
+    for k, v in zip(FORWARDED_ENV, list(_binding(main).values())[:3]):
         assert f"{k}={v}" in flags, flags
     spawns = [c for c in _calls(mock_herdr) if c[:2] in (["pane", "split"], ["workspace", "create"])]
     assert spawns and any("--env" in c for c in spawns), "the binding rides on the pane-creating call"