Remote sessions keep track of foreground tasks

A remote session is a Claude Code session that runs on another machine. Remote sessions already kept a list of background tasks, which are tasks that keep running while the conversation goes on. They now also keep a list of foreground tasks. The list is filled when the session starts, updated each time a task reports a result, and cleared when the worker running the session is reported gone.

Some other changes come with it:

• A new event marks a reply as held.
• The record of a finished reply is reset at the start of each turn.
• A new version of Claude's instructions tells it to wait in the foreground for a result it needs before replying. A check decides when this version is used.