Failed tool calls and turns now show up in Insights

@sanity/context now saves agent failures to your conversation transcripts, so they show up in Insights. Failed tool calls are saved with their error. On AI SDK v7, failed turns are saved too, along with the transcript up to the failure. AI SDK v6 has no hook for failed turns, so those aren't saved.

Classification sees these errors as well, so a failed turn is no longer treated as an empty reply. No code changes are needed. See Add insights to Sanity Context.