Tip: Use SubagentStop's additionalContext to Extend a Subagent Instead of Failing It
Anthropic·medium signal
The SubagentStop hook fires when a subagent finishes and before its summary reaches the lead agent. Its payload now includes hookSpecificOutput.additionalContext, so you can inject new context and extend the subagent's turn rather than treating completion as a binary stop/error. This turns SubagentStop into a verification-loop primitive — re-feed a rubric or missing requirement and let the subagent continue.