What
A monitor watch is Claude Code following the output of a running command. When a watch closes it now emits monitor_watch_closed. The event records closed_by, which is one of too_much_output, flushed, dropped or exited. It also records how many events were queued and how many were suppressed. The name was added to a list of event names, and it is emitted from one more place that was not read.
In the same area of code, a new constant MCP_APP_SANDBOX_BASE_HOST is set to sandbox.claudemcpcontent.com. It sits next to the existing wildcard host *.claudemcpcontent.com. MCP apps are add-ons served through MCP servers, and this host is where their sandboxed content is loaded from.
Why
The close event is reporting only and does not change what you see. The new host constant points to MCP app content using one fixed address alongside the wildcard. That may matter if your network filters which hosts Claude Code can reach.