Diff

data class DiffChange(
    val currentStartLine: Int,
    val currentLineCount: Int,
    val originalStartLine: Int,
    val removedLines: List<String> = emptyList(),
)

fun setDiffChanges(changes: List<DiffChange>)
fun computeDiff(originalText: String)
fun setBatchDiffLineSpans(layer: EditorSpanLayer, spansByOriginalLine: Map<Int, List<StyleSpan>>)
fun clearDiff()

computeDiff 让内核把当前缓冲区与 originalText 做 diff，并绘制增删行号区。

setDiffChanges 推入宿主算好的 hunk 列表。

setBatchDiffLineSpans 按原始（删除侧）行号给 token 上色。

主题：diffAddedLineBackground、diffRemovedLineBackground、diffAddedGutterBackground、diffRemovedGutterBackground。