Unclear It is not clear which mod calls this applies to.
What
A mod is a user-written add-on, and a hook is code a mod runs when something happens. Some sessions are started ahead of time by the host, the program running Claude Code. In those sessions, certain calls made from a classic.SessionStart hook are now refused. The message says to run the code from session.start or a later event such as turn.complete.
Why
These calls would wait for start-up to finish, but start-up is itself waiting for the hook, so the session would hang. Mod authors whose code is refused should move it to one of the later events.
Documented inclaude-code/plugins/mods/interface
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
It is not clear which mod calls this applies to.