agent: Move thread history access behind AgentConnection trait (#46631)
This should move almost all access of the threadstore behind the trait,
which unlocks external agents supplying the list
Release Notes:
- N/A
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Co-authored-by: Zed Zippy <234243425+zed-zippy[bot]@users.noreply.github.com>
291611e3dbBen Brandt committed on 1/12/2026, 9:42:12 PM· committed by GitHubparentf651c4c