What
The subagent_type: "fork" value is now a named, explicitly-selectable agent type rather than the implicit default when no subagent_type is provided. This makes multi-agent code clearer and avoids accidental forking.
Details
- Omitting
subagent_type(when the fork experiment is active) previously implicitly created a fork; now the behavior is documented as explicit opt-in via"fork" - Remote sessions cannot use
isolation: "remote"with fork — a clear error is returned - Other named agent types still start with zero context
- The Agent tool description has been updated to reflect this
Evidence
Updated Agent tool description (search for "(except subagent_type: \"fork\")" and "Fork cannot use isolation: \"remote\"")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.