Where the agent's view and the requester's view come apart.
Most of this is about Assets, and about the fact that the parts you need are not in the public API documentation. Uploading an attachment to an asset. Ingesting users from Microsoft Graph into Assets on a schedule. Both were worked out by watching what the product does and then checking it holds.
The rest is customer identity and the portal: what actually clears a duplicate customer once somebody has changed their email address, and an honest assessment of Refined Sites written after running it on a real service desk.