When Claude runs a tool, such as reading a file or running a command, its reply contains the request and the next message holds the result. The saved record of a session, called the transcript, links these together. When you resume a session and a result is not linked to the reply that asked for it, Claude Code now looks up the right reply by the tool call's id, or by the result's sourceToolAssistantUUID, and reattaches the result there. This can happen with parallel tool calls, where several tools run at once, and with side conversations called sidechains.
A result is only moved when it and the reply belong to the same sidechain and the same agent. A new telemetry event, tengu_chain_tool_result_recovered_by_call_id, counts how many results were recovered this way.
Resumed sessions are more likely to come back with every tool result in the right place instead of losing some of them.