When sending a message to a thread from the Agents chat UI, the run used
the OAuth profile email (which can be a personal account that isn't an org
member). For Slack-originated threads resumed from the UI, auth routes
through the email-based path and fails ("Could not find a LangSmith account").
Resolve the run email via the GitHub->email mapping first, falling back to
the profile email only when no mapping exists, matching the github-source
auth path.
