cancelInFlightChain: Stop all tasks and unobserve their content fields before starting a new chain. Prevents observer stacking and halts unnecessary in-flight work (network, processing) when loadParts() or loadPersonVideos() is called while a previous chain is still running.

loadParts: Start the extras loading chain appropriate for the item type.

Chain by type: Movie / Video / Recording → AdditionalParts → People → LikeThis → SpecialFeatures MusicVideo / Episode → People → LikeThis Series → Seasons → People → LikeThis Season → Episodes ("Season X") → People → LikeThis BoxSet → BoxSetItems ("Movies") → People → LikeThis m.top.type must be set before calling this function (done by ShowScenes.bs).

onBoxSetItemsLoaded: Build "Movies" row then chain to People → LikeThis (BoxSet only)

onSeasonAllEpisodesLoaded: Build "Episodes" row then chain to People (Season only)

onSeasonEpisodesLoaded: Build "More from Season X" row with current episode first, then episodes that follow it in order, then episodes that precede it (wrapping around). E.g. viewing ep 3 of 9 → [3, 4, 5, 6, 7, 8, 9, 1, 2]

onSeasonsLoaded: Build "Seasons" row then chain to People (Series only)

populateRow: Reuse an existing row ContentNode (clearing its children) or create a new one. Creating appends the row to m.top.content at the current end — correct since the async chain fires in display order. m.rowHeights is reset at chain start and rebuilt here on every call, keeping it in sync with m.top.content across refreshes where rows may appear or disappear. Returns the row for the caller to store as a named ref.