What
A new control message kind, remote_tools_reannounce, was added to the remote-session protocol. When a replacement remote-tool worker gets a tool call naming a machine it doesn't recognize, it can send this request, identified by a worker epoch and a deadline, to ask the attached client (the one serving the session's tools) to re-announce itself. The client side handles this with rate limiting and epoch checks, and the message kind is included in the reject-list for otherwise-unhandled message kinds.
Why
This keeps a remote session's list of available tools and machines in sync even after a worker is replaced, avoiding stale or unrecognized machine references.
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The writer flagged doubt
The finding does not say what user-visible problem this fixes or when a worker gets replaced.