The durable _last_known_cwd anchor is keyed by the shared 'default' container,
so a non-owning worktree session could inherit the owning session's cwd through
it — breaking the wrong-worktree-routing fix (test_file_tools_cwd_resolution::
test_resolution_routes_to_resolving_sessions_worktree).
Reorder _authoritative_workspace_root so the session-specific registered cwd
override (keyed by raw session id) is checked BEFORE the shared-container
_last_known_cwd fallback. A non-owning session now resolves into its own
registered worktree; the durable anchor only fills in when there's no
session-specific override (the #26211 single-session case). Adds a regression
test covering the owner-mirrors-then-other-session-resolves interaction.
457c8a0a7c