Under the hood
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Message-history schema gains an optional attached_by: "server" field
What
The schema Claude Code uses for chat/session messages (which already includes fields like id, in_reply_to, and author) now accepts an optional attached_by field, whose only currently allowed value is "server".
Why
This appears to let a message record note that something in it was attached by the server rather than by the user or the model, which could support features that add server-side content to a message after the fact, though the finding does not say what specifically uses this field.
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The writer flagged doubt
What content or feature actually sets attached_by, and how it is used once present, is not stated.