feat(ui-conversation): implement finalized IconActions with clock for user and assistant messages

.agents/notes/implemented/feature/2026-07-29-web-message-icon-actions-and-clock.i18n.yaml

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+# Bilingual-pair consistency record (docs/i18n/README.md): the git blob hash of each
+# 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/feature/2026-07-29-web-message-icon-actions-and-clock.md
+2026-07-29-web-message-icon-actions-and-clock.md: ac0c2624d4980f33a01d67cf699259b5913cb274
+2026-07-29-web-message-icon-actions-and-clock.zh.md: 8ec7d8a3d93a51e4a4d315caa067a649ec483120

.agents/notes/implemented/feature/2026-07-29-web-message-icon-actions-and-clock.md

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+# Agent Note: Web message IconActions and clocks
+
+Status: implemented
+
+English | [中文](2026-07-29-web-message-icon-actions-and-clock.zh.md)
+
+## Problem
+
+The web chat user bubble already had copy / branch / edit IconActions but no clock. Finalized assistant narration had no under-body action chrome at all, even though the Harness design shows a copy / branch / clock row after the answer settles. Streaming replies must not flash that chrome mid-token.
+
+## Decision
+
+**User bubbles prepend a date-aware local clock to the existing IconActions row; finalized assistant nodes append a copy / branch / clock row with `margin-top: 16px`.**
+
+Both seats format `node.time` through `formatMessageClock`: same calendar day → `HH:mm`, earlier this year → `M月D日 HH:mm`, other years → `YYYY年M月D日 HH:mm`. `MessageItem` places the label before copy (figma `388:20051`). `AssistantMarkdown` places it after branch (figma `43:32997`) and only when `streaming` is false with a known event time; the streaming tail omits the row. Copy writes joined text blocks. Branch stays a chrome stub. Hover-capable pointers keep both footers opacity-hidden until hover/focus-within. Clipboard write and the clock helper live in `message-chrome.ts`.
+
+## Alternatives considered
+
+**Show assistant IconActions during streaming.** Rejected: the request is to reveal the row only after output completes; mid-stream chrome would flicker and invite copying a partial answer.
+
+**Wire branch to a real session fork.** Rejected for this change: same rationale as the archived [user IconActions note](../../archived/feature/2026-07-27-user-message-icon-actions.md) — the mutation path is unspecified; the button reserves the design seat.
+
+## Consequences
+
+Settled assistant answers expose copy and the event clock immediately; branch stays a stub. User and assistant clocks share the same day/year widening rules. Per-message paging remains a deferred footer seat in the package README. Tests pin the three clock shapes, assistant footer presence only when not streaming, and copy payload (text blocks only).

.agents/notes/implemented/feature/2026-07-29-web-message-icon-actions-and-clock.zh.md

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+# Agent Note: Web 消息 IconActions 与时钟
+
+Status: implemented
+
+[English](2026-07-29-web-message-icon-actions-and-clock.md) | 中文
+
+## 问题
+
+Web 聊天的用户气泡已有复制／分支／编辑 IconActions，但没有时钟。已定稿的 assistant 叙述下方完全没有操作栏，尽管 Harness 设计稿在回答结束后展示复制／分支／时钟。流式回复不得在 token 中途闪出该栏。
+
+## 决策
+
+**用户气泡在既有 IconActions 行前追加感知日期的本地时钟；已定稿的 assistant 节点在正文下追加带 `margin-top: 16px` 的复制／分支／时钟。**
+
+两边都通过 `formatMessageClock` 格式化 `node.time`：同一日历日 → `HH:mm`，同年更早 → `M月D日 HH:mm`，跨年 → `YYYY年M月D日 HH:mm`。`MessageItem` 把标签放在复制之前（figma `388:20051`）。`AssistantMarkdown` 把它放在分支之后（figma `43:32997`），且仅在 `streaming` 为 false 且已知事件时间时渲染；流式尾部省略该行。复制写入拼接后的 text 块。分支仍是 chrome stub。具备 hover 能力的指针在 hover／focus-within 前保持两条 footer 透明。剪贴板写入与时钟辅助函数放在 `message-chrome.ts`。
+
+## 曾考虑的方案
+
+**在流式过程中展示 assistant IconActions。** 否决：需求是输出完成后才展示该行；中途 chrome 会闪烁，并诱使复制半截回答。
+
+**把分支接到真实的会话 fork。** 本次否决：与已归档的[用户 IconActions 笔记](../../archived/feature/2026-07-27-user-message-icon-actions.md)同一理由——变更路径尚未规定；按钮只预留设计座位。
+
+## 后果
+
+已定稿的 assistant 回答立刻暴露复制与事件时钟；分支仍为 stub。用户与 assistant 时钟共用同一套跨天／跨年加宽规则。逐消息分页仍是包 README 中的暂缓 footer 座位。测试钉住三种时钟形态、仅在非流式时出现 assistant footer，以及复制载荷（仅 text 块）。