/focus works in SDK and headless sessions, and hosts are told the view mode

What

/focus switches the focus view, which shows only your last prompt, a one-line summary of the work and the final response. It can now be used in non-interactive sessions, meaning SDK and headless runs where another program drives Claude Code.

• A second /focus command, with argument hint [on|off], is available only when the session is not interactive. With no argument it flips the current state; other arguments get "Unknown argument ... Use: /focus [on|off]".
• It writes viewMode into the flag-settings layer and sends apply_flag_settings with briefTranscript.
• If a managed viewMode setting overrides the choice, it replies that focus view is set by that setting and stays on or off.
• Submitted from local standard input, it refuses with "/focus isn't available here yet".
• The interactive /focus now says it needs the fullscreen renderer when not in fullscreen.
• The session start message sent to SDK hosts now includes view_mode ("focus" or "default") and per_turn_effort_active, an internal field marking whether a per-turn effort setting is active.

Why

SDK and remote hosts can switch focus view per session without editing settings.json, and can mirror the current view. The effort field lets a host tell when changing effort would invalidate the prompt cache.