write
abstract suspend fun writeTile(z: Int, x: Int, y: Int, rows: Flow<CachedFeatureRow>, sector: Sector? = null)
Atomically replace rows for one tile. Pass an empty flow to record "tile has no features" — that's the negative cache for ocean / empty Overpass responses. sector is the tile's true geographic bounds (null → slippy bounds from (z, x, y)).