checkpoint_manager_profile_rename.py (merged from main) reaches for
_store_has_head/_ref_tip/_list_project_refs/_unlink_quiet, which main
extracted from checkpoint_manager after this branch diverged; a profile
rename with checkpoints raised AttributeError. Add the same helpers here.
Also: tests follow this branch's contracts (model_metadata_http.get instead
of a requests module, no agent.ssl_guard, backup excludes PM trees too,
_safe_restore_plan), and run_tests.sh forwards SSL_CERT_FILE/DIR so network
tests verify TLS with the pinned interpreter on hosts without a compiled-in
bundle path.
30bf9ab47c