fix(tui): bound diff rendering work

.agents/notes/implemented/bug-fix/2026-07-31-tui-diff-context-line-accounting.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write .agents/notes/implemented/bug-fix/2026-07-31-tui-diff-context-line-accounting.md
-2026-07-31-tui-diff-context-line-accounting.md: 71593022b56d9e675025f3a7a6d1e5e3edfa9b57
-2026-07-31-tui-diff-context-line-accounting.zh.md: df374c23b73fc5667cf733b4916d9d0d2ecb9198
+2026-07-31-tui-diff-context-line-accounting.md: d1bc72ea030abd46f809ca3e746e6043f717baeb
+2026-07-31-tui-diff-context-line-accounting.zh.md: a2a1dcce1325bca68c92cb4f206bfa35671e9d86

.agents/notes/implemented/bug-fix/2026-07-31-tui-diff-context-line-accounting.md

@@ -10,7 +10,9 @@ Result-time filesystem diffs carry the applied change with three surrounding con
 
 ## Decision
 
-The TUI compares each non-create `FileDiff.oldText` and `FileDiff.newText` at render time. 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. A create (`oldText: null`) continues to classify every non-empty new-content row as added.
+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.
+
+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.
 
@@ -22,8 +24,10 @@ This remains a consumer-side interpretation of the existing `FileDiff` contract.
 
 **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 their `+A -R` footer reports the actual line delta. Replaying an existing contextual diff gains the corrected rendering without a migration. Rendering performs one additional line comparison per non-create hunk; result-time hunks are already context-bounded, while create cards bypass the comparison.
+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 test covers neutral context and exact totals. The assembled `advanced-cards` terminal snapshots pin the neutral context style, semantic change colors, and `+1 -1` footer through collapsed and expanded card states.
+The focused TUI tests cover neutral context, exact totals, an empty create, bounded fallback, and 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.

.agents/notes/implemented/bug-fix/2026-07-31-tui-diff-context-line-accounting.zh.md

@@ -10,7 +10,9 @@ Status: implemented
 
 ## 决策
 
-对于每个不对应文件创建的 `FileDiff`，TUI 在渲染时比较 `FileDiff.oldText` 和 `FileDiff.newText`。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。创建操作（`oldText: null`）仍将新内容中的每个非空行归类为新增行。
+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。
+
+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。
 
@@ -22,8 +24,10 @@ Status: implemented
 
 **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，其 `+A -R` 页脚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。渲染每个不对应文件创建的 hunk 时，会额外执行一次逐行比较；结果时刻的 hunk 本就受上下文范围限制，创建卡片则会跳过比较。
+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和精确合计值。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，以及 `+1 -1` 页脚。
+聚焦的 TUI 测试覆盖中性上下文、精确合计值、空文件创建、有界回退和缓存复用。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。