Defer expensive context to intent. The page renders only what every reader needs; the rest waits behind a hover, a focus, or a long press.
The event happened in one timezone, was stored as UTC (RFC 3339), and you're reading it in a third. Render in the viewer's locale with the tz abbreviation always visible; reveal the source and UTC on intent.
Mentions, avatar stacks, reviewer chips. Anywhere a person appears, the page might want to show who they are. Fetching every profile up front wastes bandwidth and rate limit. Defer the fetch until the reader points at a name or a face; cache the result per session so repeat hovers are instant.