fix(subtitle): 字幕列表打开时精准定位高亮——真实布局校正替代估算偏移 - #938
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打开列表时定位偏差根因：_findNearestSubtitleIndex 返回首条 startTimeMs>=position 的字幕，正在播的那条(start<=position<=end)被跳过； 台词间隙大时(如乐器段19:00->21:00无对白)高亮跳到几分钟后。 - cupertino pane: 区间内优先命中，间隙取已开始(start<=position)的最后一条 - nipaplay menu: 区间检查已有，间隙的|start-position|绝对最近改为同一语义， 两端主题行为对齐 Python 语义镜像 8/8 边界检查(subtitle_index_check.py)。
FurudeRika123
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The RenderBox-based correction is the right idea, and the gap-semantics change in _findNearestSubtitleIndex (cupertino_subtitle_list_pane.dart:283-304, subtitle_list_menu.dart:412-437) is a genuine improvement over the old "first start >= position / absolute-nearest" logic - the parsers sort by start time, so the early return lastIndex short-circuit is safe.
One correctness gap blocks approval: the comments at cupertino_subtitle_list_pane.dart:332-334 and subtitle_list_menu.dart:501-503 state that Scrollable.ensureVisible "only scrolls when the item is not visible". That is not true - the default alignmentPolicy is ScrollPositionAlignmentPolicy.explicit, whose implementation unconditionally targets getOffsetToReveal(object, alignment) and re-aligns the item to 30% of the viewport on every call. The code being replaced was conditional (itemOffset < visibleStart || itemOffset > visibleEnd - estimated); the new block is not, so the list now re-animates on every cue change and snaps back while the user is browsing manually. Restore the condition (measure the item's RenderBox against the viewport rect before calling, or pass ScrollPositionAlignmentPolicy.keepVisibleAtStart), or document the new follow-playback behaviour as intentional.
Minor: cupertino_subtitle_list_pane.dart:197-199 does .clamp(0, _visibleEntries.length - 1); if _visibleEntries is ever empty this throws ArgumentError (num.clamp requires lowerLimit <= upperLimit). The nipaplay twin guards this at subtitle_list_menu.dart:289 - please add the same guard for parity. Also, the retry in step 3 (cupertino:231-243, nipaplay:322-334) has no further retry, so if the keyed item is still unbuilt the highlight can stay off-screen until the next window change, since the inline ensureVisible only fires when localIndex != _currentLocalIndex.
问题
字幕列表打开时高亮定位用「行高估算 + 首条 start >= pos」推导：
方案
验证