Package-level declarations

Screen-scoped pub/sub channel — the mechanism behind EventRunningScope.broadcastData(...) and TileRenderingScope's observeScreenTileBroadcastChannel. One fresh instance per screen (a plain field on MosaicScreenStateHolder, not a Koin single), reached in composition via LocalScreenTilesBroadcastChannel — unlike dev.catbit.mosaic.client.ui.sdui.foundation.system_broadcast.SystemBroadcastChannel, which is app-wide. This is the channel ScrollColumnTile/ScrollRowTile/ScrollPagerTile and the overlay open/close/dismiss commands (DisplayNavigationDrawer, DisplaySnackbar, etc.) publish on.

Base contract for every value published on a screen's own ScreenTilesBroadcastChannel — implemented by one data class per command kind (scroll-to, overlay open/close, etc.). tileId is what TileSchema.observeScreenTileBroadcastChannel(filterByTileId = true, ...) compares against a subscriber's own id to decide whether a given command is addressed to it.