TUI diff context lines stay neutral
TUI diff 上下文行保持中性
Result-time filesystem diffs carry the applied change with three surrounding context lines in each `FileDiff.oldText` and `FileDiff.newText`. The TUI rendered every old-side row as removed and every new-side row as added, including the identical context present on both sides. A one-line edit therefore appeared as seven removals plus seven additions, and the footer repeated those inflated totals.
English
Problem
Result-time filesystem diffs carry the applied change with three surrounding context lines in each FileDiff.oldText and FileDiff.newText. The TUI rendered every old-side row as removed and every new-side row as added, including the identical context present on both sides. A one-line edit therefore appeared as seven removals plus seven additions, and the footer repeated those inflated totals.
Decision
The TUI compares each FileDiff whose old and new text are both available. Added and removed rows retain their green + and red - markers; equal context rows use the recessed body tone with a neutral two-space prefix. The footer sums only the rows classified as added or removed. maxDiffEditLength bounds the exact comparison by its combined added and removed line count; the default is 1000. Exceeding the bound renders the complete old side as removed and the complete new side as added, marks the footer approximate, and caches that result so redraws do not repeat the comparison. A tool result clears the pending-view cache before deriving the settled view, including when a presenter mutates and reuses the same view object.
When oldText is null, the renderer cannot distinguish a create from a pending overwrite or an argument fallback whose prior text is unavailable. It therefore shows every non-empty new-side row as added, without claiming those rows were absent from an existing file. Empty new content renders no synthetic added row.
This remains a consumer-side interpretation of the existing FileDiff contract. Filesystem tools continue to persist contextual before/after snippets, so other consumers keep their placement context and existing session logs replay with corrected TUI presentation. The TUI uses the same maintained diff package as dsh-tool-fs instead of introducing a second line-diff implementation.
Alternatives considered
Remove context from filesystem result metadata. Rejected: contextual applied hunks are intentional producer output used by capable editors, and changing them would weaken every consumer while leaving old session logs misleading in the TUI.
Extend FileDiff with persisted per-line tags. Rejected: the tags can be derived deterministically from the existing before/after pair; persisting them would widen the cross-package and session-log contract solely for one renderer.
Match equal lines by position without a diff algorithm. Rejected: insertions and deletions shift subsequent context, so positional pairing would misclassify valid hunks.
Run every comparison to completion. Rejected: pending tool views can contain unrestricted model-authored old and new strings, and an unbounded Myers comparison can block the synchronous terminal renderer.
Consequences
TUI diff cards distinguish evidence-bearing context from the mutation itself, and an exact +A -R footer reports the actual line delta. Replaying an existing contextual diff gains the corrected rendering without a migration. Result-time filesystem hunks are context-bounded; unrestricted pending views either complete within the configured edit-length budget or degrade to an explicitly approximate linear rendering.
The focused TUI tests cover neutral context, exact totals, an empty create, bounded fallback, result-time cache invalidation, and redraw cache reuse. The assembled advanced-cards terminal snapshots pin the neutral context style, semantic change colors, exact footer, and approximate fallback through collapsed and expanded card states.
中文
问题
文件系统 diff 返回结果时，每个 FileDiff.oldText 和 FileDiff.newText 都会包含已应用的变更及其前后各 3 行上下文。TUI 将旧侧的每一行都渲染为删除行，将新侧的每一行都渲染为新增行，其中包括两侧相同的上下文。因此，一行编辑会显示为删除 7 行并新增 7 行，页脚还会重复这些虚高的合计值。
决策
TUI 会比较每个变更前后文本均可用的 FileDiff。新增行和删除行仍分别使用绿色 + 和红色 - 标记；相同的上下文行则使用弱化的正文色调，并带有由两个空格构成的中性前缀。页脚只汇总归类为新增或删除的行。maxDiffEditLength 以新增行与删除行的合计数为精确比较设置上限，默认值为 1000。超过上限时，TUI 会把完整旧侧渲染为删除内容、把完整新侧渲染为新增内容，将页脚标记为近似结果，并缓存该结果，避免后续重绘重复比较。工具结果会在派生已结算视图前清除待处理视图缓存，即使 presenter 修改并复用同一个视图对象也一样。
当 oldText 为 null 时，渲染器无法区分文件创建、待处理覆写，以及旧文本不可用的参数回退。因此，它会把新侧的每个非空行显示并计作新增行，但不会声称这些行原先不存在于已有文件中。新内容为空时，不会渲染虚构的新增行。
该行为仍然只是消费方对现有 FileDiff 契约的解释。文件系统工具仍会持久化带上下文的变更前后片段，因此其他消费方仍能获得定位上下文，已有会话日志在回放时也会采用修正后的 TUI 呈现。TUI 与 dsh-tool-fs 共用同一个受维护的 diff 包（package），无需引入第二套逐行 diff 实现。
考虑过的替代方案
从文件系统结果元数据中移除上下文。 不予采纳：带上下文的已应用 hunk 是有意保留的生产方输出，供具备相应能力的编辑器使用；更改这些内容会让所有消费方丢失信息，同时旧会话日志在 TUI 中仍会产生误导。
为 FileDiff 扩展持久化的逐行标签。 不予采纳：这些标签可以根据现有的变更前后文本对确定性派生；仅为一个渲染器持久化标签，会扩大跨包契约和会话日志契约。
不使用 diff 算法，按位置匹配相同行。 不予采纳：插入和删除会使后续上下文发生位移，因此按位置配对会把有效 hunk 错误分类。
让所有比较都运行至完成。 不予采纳：待处理工具视图可能包含由模型生成且长度不受限制的新旧字符串，无界的 Myers 比较可能阻塞同步终端渲染器。
后果
TUI diff 卡片会区分用于佐证的上下文与变更本身，精确的 +A -R 页脚会报告实际的行变更量。回放已有的上下文 diff 无需迁移即可获得修正后的渲染。结果时刻的文件系统 hunk 受上下文范围限制；不受限制的待处理视图要么在配置的编辑长度预算内完成比较，要么降级为明确标注为近似结果的线性渲染。
聚焦的 TUI 测试覆盖中性上下文、精确合计值、空文件创建、有界回退、结果到达时的缓存失效和重绘缓存复用。组装后的 advanced-cards 终端快照在卡片折叠和展开状态下固定了中性上下文样式、变更行的语义色彩、精确结果页脚和近似回退。