Refined the Codex-CORE fix: the happy-path (already-stored session) guard rejects
only an explicit read_only flag — a stored messaging session already owns its
sidecar, so the messaging-fork risk is specific to the materialize FALLBACK
(which creates a sidecar) where the _is_messaging_session_record check stays.
Also completed test_issue1436's _stub_session MagicMock (read_only=False,
_loaded_metadata_only=False) — bare MagicMock auto-attrs were truthy, tripping
the new read-only guard + _ensure_full_session_before_mutation reload.
Codex caught two data-integrity gaps in the contributor's guard: (1) the
get_session() happy path returned a stored session without checking read_only/
messaging, so an already-imported read-only session could be mutated via
rename/update/move; (2) the fallback only checked cli_meta.read_only, but agent
rows normalize messaging sources WITHOUT setting read_only — materializing a
writable sidecar for a state.db-owned messaging session forks its title/state.
Now reject getattr(s,'read_only') OR _is_messaging_session_record on the happy
path, and cli_meta.read_only OR _is_messaging_session_record(cli_meta) in the
fallback. Replaced the messaging-stub test with 3 regression tests (stored
read-only, stored messaging, messaging cli_meta without read_only flag).
nesquena-hermes