Update the session’s working directory. Used by the host when the user explicitly changes cwd (e.g., the /cd slash command). The host is responsible for any related side-effects (file index, etc.); it does NOT change the process working directory (a session’s cwd is per-session, not process-global). For local sessions the runtime validates the target first (an absolute path that exists on disk) and re-bases the permission primary directory; a rejected validation fails the call before anything is mutated, persisted, or emitted. Location-scoped permission rules are then re-keyed to the new directory (best-effort). Remote sessions only record the path.
Experimental. This type is part of an experimental wire-protocol surface
and may change or be removed in future SDK or CLI releases.