fix(client): state each step-brief tooltip in its time window

The three rows draw from different slices of the log, and the tag bubbles only named the content, never the window — scrubbing read like the rows did not match up. Each bubble now opens with its window and closes with the one cross-bar fact that explains the half-step offset: inputs are what entered after the previous reply (nothing new on a turn opener), calls made here land in the NEXT bar's In row, and the opener recalls itself on every step of its turn.

src/client/i18n.ts

@@ -57,9 +57,9 @@ export const DICT_ZH: Record<string, string> = {
   'brief.more': '+{n}',
   'brief.noInputs': '（无新增）',
   'brief.locate': '在上下文浏览器中查看',
-  'brief.turnTip': '这一轮开场时用户发送的消息',
-  'brief.inputTip': '这一步新进入上下文的内容（通常是上一步工具调用的结果）',
-  'brief.replyTip': '这一步模型返回的内容（文本回复或工具调用）',
+  'brief.turnTip': '这一轮开场时用户发送的消息；回合内的每一步都会回显同一条',
+  'brief.inputTip': '上一步回复之后、本次请求发出前新进入上下文的内容——通常是上一步所调工具的结果；每轮的第一步无新增',
+  'brief.replyTip': '这一步模型返回的内容（文本回复或工具调用）；此步发起的调用，其结果会出现在下一柱的「输入」行',
   'events.title': '上下文事件',
   'events.empty': '暂无上下文事件（压缩、注入、模型切换会出现在这里）',
   'events.at': '第 {t} 轮 · 第 {s} 步',
@@ -217,9 +217,9 @@ export const DICT_EN: Record<string, string> = {
   'brief.more': '+{n}',
   'brief.noInputs': '(nothing new)',
   'brief.locate': 'Reveal in Context Browser',
-  'brief.turnTip': 'The user message that opened this turn',
-  'brief.inputTip': 'What newly entered the context for this step (usually results of the previous tool calls)',
-  'brief.replyTip': 'What the model returned on this step (a text reply or tool calls)',
+  'brief.turnTip': 'The user message that opened this turn — every step of the turn recalls it',
+  'brief.inputTip': 'What entered after the previous reply and before this request went out — usually the previous tool-call results; a turn opener has nothing new',
+  'brief.replyTip': 'What the model returned on this step (a text reply or tool calls) — results of calls made here appear in the In row of the next bar',
   'events.title': 'Context Events',
   'events.empty': 'No context events yet (compaction, injections, model switches appear here)',
   'events.at': 'Turn {t} · Step {s}',