Merge pull request #416 from znygugeyx-ctrl/feat/subagent-fork-render

feat: 参考 claude code 官方实现，改进 sub agent 以及 fork agent 的渲染方式
2026-06-15 12:55:51 +00:00 · 2026-05-06 09:57:52 +08:00
parent c4e9efb7a8
commit 5c107e5f8c
11 changed files with 488 additions and 27 deletions
--- a/docs/features/background-agent-selector.md
+++ b/docs/features/background-agent-selector.md
@@ -0,0 +1,225 @@
+# Background Agent Selector — 底部统一后台 Agent 切换器
+
+> Feature Flag: 无（直接启用）
+> 实现状态：完整可用
+> 依赖：`viewingAgentTaskId` / `enterTeammateView` / `exitTeammateView` 已有机制
+
+## 一、功能概述
+
+Background Agent Selector 是渲染在 PromptInput 下方的常驻状态条，列出当前所有 **backgrounded 的 local_agent 任务**（包括 `/fork` 派生的 fork agent 和 Task/AgentTool 调用 `run_in_background: true` 派生的子 agent）。用户可以用 ↑/↓ 方向键在 `main` 和各 agent 之间切换焦点，按 Enter 把 REPL 主视图替换为所选 agent 的实时 transcript，再按 Enter 选中 `main` 即可回到主对话。
+
+整个机制完全复用官方已有的 teammate transcript 查看基础设施，不引入新的视图层 / 数据流，仅新增一条 footer pill 类型。
+
+### 核心特性
+
+- **统一入口**：`/fork`、Task 派生的 subagent、所有 `run_in_background: true` 的 agent 都在同一栏显示
+- **就地切换**：prompt 为空时按 ↓ 溢出进入底部 selector，↑↓ 选中某行，Enter 即切主视图
+- **实时状态**：每行显示 agent 类型 + 描述 + 运行时长 + 已消耗 token；running 时圆点为绿色
+- **Keep-alive 视图**：agent 完成后在 `evictAfter` grace 窗口内保留一段时间，用户可回看
+- **零界面侵入**：tasks 数为 0 时 selector 完全不渲染，不占屏幕高度
+- **与旧 Dialog 共存**：Shift+↓ 打开的 `BackgroundTasksDialog` 原有行为保留，selector 只作为展示 + 快捷切换
+
+## 二、用户交互
+
+### 触发方式
+
+有任何 background agent 时，selector 自动出现在 `bypass permissions on` 行下方：
+
+```
+  claude-code | Opus 4.7 (1M context) | ctx:4%
+  ▶▶ bypass permissions on (shift+tab to cycle)
+
+  ○ main                                    ↑/↓ to select · Enter to view
+  ● Explore  Research src/hooks              23s · ↓ 10.9k tokens
+  ○ Explore  Research src/components         22s · ↓  9.5k tokens
+  ○ Explore  Research src/utils              21s · ↓ 13.6k tokens
+```
+
+### 键盘路由
+
+| 位置 / 状态 | 按键 | 行为 |
+|---|---|---|
+| PromptInput 非空 | ↑↓ | 光标移动 / 翻历史（不变） |
+| PromptInput 空 + 历史底部 | ↓ | 焦点下放到 selector，高亮到 `● main` |
+| Selector 聚焦（`footerSelection === 'bg_agent'`） | ↓ | 高亮下移，-1 → 0 → ... → N-1 |
+| Selector 聚焦 | ↑ | 高亮上移；在 `main` 再 ↑ → 焦点回 PromptInput |
+| Selector 聚焦 | Enter | `-1` → `exitTeammateView`；`>=0` → `enterTeammateView(agentId)`。焦点保留在 pill |
+| Selector 聚焦 | Esc | `footer:clearSelection`，焦点回 PromptInput |
+
+### 视觉规则
+
+- `● main` / `● <agent>`：当前被**查看**（viewingAgentTaskId 指向）或被**光标聚焦**（pill focused 时以光标为准）的一行
+- running 状态的 agent：圆点渲染为 `success` 色（绿色），与 `BackgroundTasksDialog` 状态语义对齐
+- 右上角 hint 随状态变化：
+  - pill 聚焦：`↑/↓ to select · Enter to view`
+  - 已选中 running agent：`shift+↓ to manage · x to stop`
+  - 已选中 terminal agent：`shift+↓ to manage · x to clear`
+  - 未选中任何 agent：`shift+↓ to manage background agents`
+
+## 三、实现架构
+
+### 3.1 数据层：`useBackgroundAgentTasks`
+
+文件：`src/hooks/useBackgroundAgentTasks.ts`
+
+封装对 `useAppState(s => s.tasks)` 的过滤：
+
+```ts
+export function useBackgroundAgentTasks(): LocalAgentTaskState[] {
+  const tasks = useAppState(s => s.tasks)
+  return useMemo(() => {
+    const now = Date.now()
+    return Object.values(tasks)
+      .filter(isLocalAgentTask)
+      .filter(t => t.agentType !== 'main-session')
+      .filter(t => t.isBackgrounded !== false)
+      .filter(t => t.evictAfter === undefined || t.evictAfter > now)
+      .sort((a, b) => a.startTime - b.startTime)
+  }, [tasks])
+}
+```
+
+`/fork` 和 `AgentTool` 的 `run_in_background: true` 底层都走 `registerAsyncAgent → runAsyncAgentLifecycle`，最终写入同一个 `appState.tasks` Map；此 hook 是唯一数据源，Selector 和 PromptInput 的 `bgAgentList` 都消费它。
+
+### 3.2 状态层：新增两个字段
+
+文件：`src/state/AppStateStore.ts`
+
+```ts
+export type FooterItem =
+  | 'tasks' | 'tmux' | 'bagel' | 'teams' | 'bridge' | 'companion'
+  | 'bg_agent'   // ← 新增
+
+export type AppState = DeepImmutable<{
+  // ...
+  selectedBgAgentIndex: number  // -1 = main, 0..N-1 = 选中的 agent
+}>
+```
+
+- `'bg_agent'` 作为 `FooterItem` 加入 footer pill 体系，享受既有的 `footer:up` / `footer:down` / `footer:openSelected` keybinding 路由
+- `selectedBgAgentIndex` 记录 selector 的光标位置，与 `viewingAgentTaskId`（"正在看什么"）独立；它不可从 `viewingAgentTaskId` 派生——Enter 后光标留在 pill 继续导航，查看目标才变
+
+### 3.3 键盘路由：PromptInput footer pill 分支
+
+文件：`src/components/PromptInput/PromptInput.tsx`
+
+1. **`bg_agent` 进入 footerItems[0]**：保证 prompt ↓ 溢出时（`handleHistoryDown` → `selectFooterItem(footerItems[0])`）直接进入 selector，而不是 `tasks` 等其他 pill
+2. **`footer:up` 分支**：`bgAgentSelected` 时 `selectedBgAgentIndex > -1` 则递减；在 -1 → `selectFooterItem(null)` 退出 pill
+3. **`footer:down` 分支**：`selectedBgAgentIndex < bgAgentList.length - 1` 则递增，到底 clamp
+4. **`footer:openSelected` 分支**：index === -1 → `exitTeammateView`；否则 `enterTeammateView(bgAgentList[i].agentId)`。**不清理 pill 焦点**，光标留在 selector 上继续导航
+5. **`selectFooterItem('bg_agent')`**：入 pill 时重置 `selectedBgAgentIndex = -1`（光标落到 `main`）
+
+### 3.4 渲染层：`BackgroundAgentSelector`
+
+文件：`src/components/tasks/BackgroundAgentSelector.tsx`
+
+纯展示组件，不订阅键盘：
+
+```tsx
+const tasks = useBackgroundAgentTasks()
+const viewingId = useAppState(s => s.viewingAgentTaskId)
+const footerSelection = useAppState(s => s.footerSelection)
+const selectedBgIndex = useAppState(s => s.selectedBgAgentIndex)
+
+if (tasks.length === 0) return null
+
+const pillFocused = footerSelection === 'bg_agent'
+const highlightedId = pillFocused
+  ? (selectedBgIndex === -1 ? null : tasks[selectedBgIndex]?.agentId ?? null)
+  : (viewingId ?? null)
+```
+
+**高亮派生规则**：pill 聚焦 → 跟 `selectedBgAgentIndex`；未聚焦 → 镜像 `viewingAgentTaskId`。这样当用户通过 Shift+↓ Dialog 或 `enterTeammateView` 其它途径切换视图时，selector 也会正确反映。
+
+### 3.5 主视图切换：复用 `viewingAgentTaskId`
+
+REPL.tsx 主体仍复用原有查看逻辑：
+
+```ts
+const viewedTask = viewingAgentTaskId ? tasks[viewingAgentTaskId] : undefined
+const viewedAgentTask = ... (isLocalAgentTask(viewedTask) ? viewedTask : undefined)
+const displayedMessages = viewedAgentTask ? displayedAgentMessages : messages
+```
+
+当 `enterTeammateView(agentId)` 把 `viewingAgentTaskId` 设成某个 local_agent 的 id：
+
+- `viewedAgentTask` 解析成该 agent
+- `displayedMessages` 切换到 agent 的 messages
+- 消息列表、spinner、unseen divider 等一整套组件自动用 agent transcript 重渲染
+- 主对话流被"暂停"（并非销毁，回到 `main` 时仍在原处）
+
+`enterTeammateView` 同步负责：设 `retain: true` 阻止 eviction、清 `evictAfter`、触发 disk bootstrap 从 `agent-<id>.jsonl` 加载完整 transcript 到 `task.messages`。
+
+#### Fork agent prompt 归一化
+
+`/fork` agent 的 transcript 和普通 subagent 不同：它继承 main agent 的上下文，真实初始消息形态是：
+
+```text
+...parent messages
+assistant([...tool_use])
+user([tool_result..., text("<fork-boilerplate>...Your directive: <prompt>")])
+...fork live messages
+```
+
+这里的 prompt 文本混在 `[tool_result..., text]` 多 block user message 里。消息渲染管线会优先把这条 user message 当作 tool-result plumbing 来处理，导致 `<fork-boilerplate>` 里的用户 prompt 不稳定可见。为保证切换到 fork agent 时总能看到用户发起的 fork prompt，REPL.tsx 对 fork 视图做一次展示层归一化：
+
+1. 仅当 `viewedAgentTask.agentType === 'fork'` 时启用，不影响普通 Explore / Task subagent。
+2. 从原始 messages 中识别包含 `<fork-boilerplate>` 的 carrier message。
+3. 剥离 carrier message 里的 boilerplate text block，但保留 `tool_result` blocks，避免破坏父 assistant `tool_use` 的承接关系。
+4. 强制插入一条独立 `createUserMessage({ content: viewedAgentTask.prompt })` 作为可见用户 prompt。
+5. 插入位置优先为 boilerplate carrier 后；如果 sidechain bootstrap 还没读到 carrier，则插到最后一条 inherited `assistant tool_use` 后面，确保 prompt 接在 main 上下文之后，而不是跑到视图顶部。
+
+这个归一化只影响 UI 展示用的 `displayedAgentMessages`，不回写 `task.messages`，也不改变发送给模型的 fork transcript。
+
+### 3.6 生命周期
+
+完全复用官方既有机制：
+
+- **运行中**：`isBackgroundTask()` 谓词为真，selector 列出
+- **完成 / 失败 / 中止**：`completeAgentTask` / `failAgentTask` / `killAsyncAgent` 设 `status` 为 terminal
+- **回访后退出**：`exitTeammateView` 调 `release(task)`——清 `retain`、清 `messages`、terminal 状态下设 `evictAfter = now + PANEL_GRACE_MS (30s)`
+- **evictAfter 过期**：`useBackgroundAgentTasks` 过滤时自然剔除，selector 行消失
+- **手动清除**：`stopOrDismissAgent(taskId)` 设 `evictAfter = 0`，立即消失
+
+## 四、设计决策
+
+1. **数据源单一**：`useBackgroundAgentTasks` 是唯一过滤点，PromptInput 也复用，避免过滤条件散落
+2. **pill 聚焦保留**：Enter 切视图后不松焦，让 ↑↓ 连续导航，贴近官方体验
+3. **`bg_agent` 放 footerItems[0]**：确保 ↓ 溢出直接进入 selector 而非其它 pill
+4. **selector 不订阅键盘**：所有按键路由集中在 PromptInput 的 `footer:*` 分支，避免 selector 组件和 PromptInput 双重 `useInput` 的冲突
+5. **`selectedBgAgentIndex` 存 AppState 而非局部 state**：selector 和 PromptInput 分别在两棵不同子树，需要全局字段协调；该值不能从 `viewingAgentTaskId` 派生
+6. **与 `BackgroundTasksDialog` 共存**：Shift+↓ 行为完全不变，selector 是补充快捷入口；Dialog 仍管 shell / workflow / monitor_mcp 等 selector 不显示的 task 类型
+7. **fork prompt 展示层兜底**：fork prompt 不依赖 boilerplate 自身渲染，统一在 `displayedAgentMessages` 中合成独立用户消息；普通 subagent 不走该分支，避免 prompt 重复
+
+## 五、关键 API 复用
+
+| 官方已有能力 | selector 如何使用 |
+|---|---|
+| `AppState.tasks` | 单一数据源，无需 file watcher / output JSONL 订阅 |
+| `registerAsyncAgent` | `/fork` 和 AgentTool 共用，selector 不区分来源 |
+| `enterTeammateView(id)` | Enter 时调用，负责 retain + disk bootstrap |
+| `exitTeammateView` | Enter 选中 `main` 时调用 |
+| `release(task)` + `PANEL_GRACE_MS` | 30s keep-alive，selector 自动生效 |
+| `useElapsedTime` | 每行时长显示，非 running 自动停 interval |
+| `formatTokens` (`utils/format.ts`) | token 数 1k 缩写 |
+| `footer:up` / `footer:down` / `footer:openSelected` keybinding | 键盘路由复用 Footer context |
+
+## 六、文件索引
+
+| 文件 | 职责 |
+|------|------|
+| `src/hooks/useBackgroundAgentTasks.ts` | 数据过滤 hook（backgrounded local_agent + evictAfter 过滤 + startTime 排序） |
+| `src/components/tasks/BackgroundAgentSelector.tsx` | 底部 selector UI，纯展示 |
+| `src/components/PromptInput/PromptInput.tsx` | 新增 `'bg_agent'` footer pill + 对应的 `footer:up/down/openSelected` 分支 |
+| `src/state/AppStateStore.ts` | `FooterItem` 加 `'bg_agent'`；新增 `selectedBgAgentIndex` 字段 |
+| `src/main.tsx` | `getDefaultAppState` 同步初始化 `selectedBgAgentIndex: -1` |
+| `src/screens/REPL.tsx` | 在 PromptInput + SessionBackgroundHint 之后挂载 `<BackgroundAgentSelector />`；切换 agent 主视图；对 fork transcript 做 prompt 归一化 |
+| `src/components/messages/AssistantToolUseMessage.tsx` | 新增 `defaultCollapsed?: boolean` prop，为后续详情视图默认折叠工具块预留 |
+| `src/components/messages/UserTextMessage.tsx` | 识别 `<fork-boilerplate>`，交给 fork 专用 renderer 处理 |
+| `src/components/messages/UserForkBoilerplateMessage.tsx` | 将 fork boilerplate text 折叠为纯用户 prompt；作为 transcript 中原位渲染的兼容路径 |
+
+## 七、已知限制
+
+- `Date.now()` 在 `useBackgroundAgentTasks` 的 useMemo 里冻结于 `[tasks]` 触发时：若长时间没有新 task 变更事件，某个 terminal agent 的 grace 期过期后不会立即从 selector 消失，要等下一次 tasks 变化才刷新。在典型使用（主对话一直在产生消息）下感知不到，暂不额外加 interval。
+- Selector 当前不处理 Shell Task / Workflow / Monitor MCP 等类型——这些仍走 `BackgroundTasksDialog`（Shift+↓）管理。
+- `AssistantToolUseMessage` 的 `defaultCollapsed` prop 目前无调用方传值，保留作为后续"agent 详情视图内工具块默认折叠"扩展点。
--- a/src/commands/fork/fork.tsx
+++ b/src/commands/fork/fork.tsx
@@ -43,8 +43,12 @@ export async function call(
    // Omitting subagent_type triggers implicit fork.
    const input = {
      prompt: directive,
+      fork: true, // 触发 AgentTool 的 fork 路径：继承父会话上下文 + system prompt + 模型
      run_in_background: true, // fork always runs async
-      description: `Fork: ${directive.slice(0, 30)}${directive.length > 30 ? '...' : ''}`,
+      // description 只显示在底部 selector / BackgroundTasksDialog，保持简短标签
+      // 即可；用户输入的 prompt 会作为第一条用户消息呈现在主视图里，这里不要
+      // 重复显示。
+      description: 'forked from main',
    };

    // Call AgentTool with proper parameters:
--- a/src/components/PromptInput/PromptInput.tsx
+++ b/src/components/PromptInput/PromptInput.tsx
@@ -26,6 +26,7 @@ import { useSetPromptOverlayDialog } from '../../context/promptOverlayContext.js
 import { formatImageRef, formatPastedTextRef, getPastedTextRefNumLines, parseReferences } from '../../history.js';
 import type { VerificationStatus } from '../../hooks/useApiKeyVerification.js';
 import { type HistoryMode, useArrowKeyHistory } from '../../hooks/useArrowKeyHistory.js';
+import { useBackgroundAgentTasks } from '../../hooks/useBackgroundAgentTasks.js';
 import { useDoublePress } from '../../hooks/useDoublePress.js';
 import { useHistorySearch } from '../../hooks/useHistorySearch.js';
 import type { IDESelection } from '../../hooks/useIdeSelection.js';
@@ -415,6 +416,16 @@ function PromptInput({
  // First ↓ selects the pill, second ↓ moves to row 0. Prevents double-select
  // of pill + row when both bg tasks (pill) and forked agents (rows) are visible.
  const coordinatorTaskIndex = useAppState(s => s.coordinatorTaskIndex);
+  const selectedBgAgentIndex = useAppState(s => s.selectedBgAgentIndex);
+  const setSelectedBgAgentIndex = useCallback(
+    (v: number | ((prev: number) => number)) =>
+      setAppState(prev => {
+        const next = typeof v === 'function' ? v(prev.selectedBgAgentIndex) : v;
+        if (next === prev.selectedBgAgentIndex) return prev;
+        return { ...prev, selectedBgAgentIndex: next };
+      }),
+    [setAppState],
+  );
  const setCoordinatorTaskIndex = useCallback(
    (v: number | ((prev: number) => number)) =>
      setAppState(prev => {
@@ -501,10 +512,13 @@ function PromptInput({
    (runningTaskCount > 0 || (process.env.USER_TYPE === 'ant' && coordinatorTaskCount > 0)) &&
    !shouldHideTasksFooter(tasks, showSpinnerTree);
  const teamsFooterVisible = cachedTeams.length > 0;
+  const bgAgentList = useBackgroundAgentTasks();
+  const bgAgentFooterVisible = bgAgentList.length > 0;

  const footerItems = useMemo(
    () =>
      [
+        bgAgentFooterVisible && 'bg_agent',
        tasksFooterVisible && 'tasks',
        tmuxFooterVisible && 'tmux',
        bagelFooterVisible && 'bagel',
@@ -513,6 +527,7 @@ function PromptInput({
        companionFooterVisible && 'companion',
      ].filter(Boolean) as FooterItem[],
    [
+      bgAgentFooterVisible,
      tasksFooterVisible,
      tmuxFooterVisible,
      bagelFooterVisible,
@@ -540,6 +555,7 @@ function PromptInput({
  const _bagelSelected = footerItemSelected === 'bagel';
  const teamsSelected = footerItemSelected === 'teams';
  const bridgeSelected = footerItemSelected === 'bridge';
+  const bgAgentSelected = footerItemSelected === 'bg_agent';

  function selectFooterItem(item: FooterItem | null): void {
    setAppState(prev => (prev.footerSelection === item ? prev : { ...prev, footerSelection: item }));
@@ -547,6 +563,9 @@ function PromptInput({
      setTeammateFooterIndex(0);
      setCoordinatorTaskIndex(minCoordinatorIndex);
    }
+    if (item === 'bg_agent') {
+      setSelectedBgAgentIndex(-1);
+    }
  }

  // delta: +1 = down/right, -1 = up/left. Returns true if nav happened
@@ -1808,6 +1827,15 @@ function PromptInput({
  useKeybindings(
    {
      'footer:up': () => {
+        // ↑ in bg_agent pill: move selection up (-1 = main). At -1, leave pill.
+        if (bgAgentSelected) {
+          if (selectedBgAgentIndex > -1) {
+            setSelectedBgAgentIndex(prev => prev - 1);
+          } else {
+            selectFooterItem(null);
+          }
+          return;
+        }
        // ↑ scrolls within the coordinator task list before leaving the pill
        if (
          tasksSelected &&
@@ -1821,6 +1849,13 @@ function PromptInput({
        navigateFooter(-1, true);
      },
      'footer:down': () => {
+        // ↓ in bg_agent pill: move selection down through agents. Clamp at last.
+        if (bgAgentSelected) {
+          if (selectedBgAgentIndex < bgAgentList.length - 1) {
+            setSelectedBgAgentIndex(prev => prev + 1);
+          }
+          return;
+        }
        // ↓ scrolls within the coordinator task list, never leaves the pill
        if (tasksSelected && process.env.USER_TYPE === 'ant' && coordinatorTaskCount > 0) {
          if (coordinatorTaskIndex < coordinatorTaskCount - 1) {
@@ -1906,6 +1941,15 @@ function PromptInput({
            setShowBridgeDialog(true);
            selectFooterItem(null);
            break;
+          case 'bg_agent':
+            if (selectedBgAgentIndex === -1) {
+              exitTeammateView(setAppState);
+            } else {
+              const picked = bgAgentList[selectedBgAgentIndex];
+              if (picked) enterTeammateView(picked.agentId, setAppState);
+            }
+            // Keep the pill focused so ↑/↓ continue to work after Enter.
+            break;
        }
      },
      'footer:clearSelection': () => {
--- a/src/components/messages/AssistantToolUseMessage.tsx
+++ b/src/components/messages/AssistantToolUseMessage.tsx
@@ -30,6 +30,7 @@ type Props = {
  inProgressToolCallCount?: number;
  lookups: ReturnType<typeof buildMessageLookups>;
  isTranscriptMode?: boolean;
+  defaultCollapsed?: boolean;
 };

 export function AssistantToolUseMessage({
@@ -45,6 +46,7 @@ export function AssistantToolUseMessage({
  inProgressToolCallCount,
  lookups,
  isTranscriptMode,
+  defaultCollapsed,
 }: Props): React.ReactNode {
  const terminalSize = useTerminalSize();
  const [theme] = useTheme();
@@ -167,6 +169,7 @@ export function AssistantToolUseMessage({
        </Box>
        {!isResolved &&
          !isQueued &&
+          !defaultCollapsed &&
          (isClassifierChecking ? (
            <MessageResponse height={1}>
              <Text dimColor>
--- a/src/components/messages/UserForkBoilerplateMessage.tsx
+++ b/src/components/messages/UserForkBoilerplateMessage.tsx
@@ -3,28 +3,31 @@
 */
 import type { TextBlockParam } from '@anthropic-ai/sdk/resources/index.mjs';
 import * as React from 'react';
-import { Box, Text } from '@anthropic/ink';
+import { FORK_BOILERPLATE_TAG, FORK_DIRECTIVE_PREFIX } from '../../constants/xml.js';
 import { extractTag } from '../../utils/messages.js';
+import { UserPromptMessage } from './UserPromptMessage.js';

 type Props = {
  addMargin: boolean;
  param: TextBlockParam;
+  isTranscriptMode?: boolean;
+  timestamp?: string;
 };

-export function UserForkBoilerplateMessage({ param, addMargin }: Props): React.ReactNode {
-  const text = param.text;
-  const extracted = extractTag(text, 'fork-boilerplate');
-  if (!extracted) {
-    return null;
-  }
-
-  const firstLine = extracted.trim().split('\n')[0] ?? '';
-  const preview = firstLine.length > 80 ? firstLine.slice(0, 77) + '...' : firstLine;
+export function UserForkBoilerplateMessage({ param, addMargin, isTranscriptMode, timestamp }: Props): React.ReactNode {
+  if (!extractTag(param.text, FORK_BOILERPLATE_TAG)) return null;
+  const closeTag = `</${FORK_BOILERPLATE_TAG}>`;
+  const afterTag = param.text.slice(param.text.indexOf(closeTag) + closeTag.length).trimStart();
+  const userPrompt = afterTag.startsWith(FORK_DIRECTIVE_PREFIX)
+    ? afterTag.slice(FORK_DIRECTIVE_PREFIX.length)
+    : afterTag;

  return (
-    <Box flexDirection="row" marginTop={addMargin ? 1 : 0}>
-      <Text dimColor>[fork] </Text>
-      <Text>{preview}</Text>
-    </Box>
+    <UserPromptMessage
+      addMargin={addMargin}
+      param={{ type: 'text', text: userPrompt }}
+      isTranscriptMode={isTranscriptMode}
+      timestamp={timestamp}
+    />
  );
 }
--- a/src/components/messages/UserTextMessage.tsx
+++ b/src/components/messages/UserTextMessage.tsx
@@ -4,6 +4,7 @@ import * as React from 'react';
 import { NO_CONTENT_MESSAGE } from '../../constants/messages.js';
 import {
  COMMAND_MESSAGE_TAG,
+  FORK_BOILERPLATE_TAG,
  LOCAL_COMMAND_CAVEAT_TAG,
  TASK_NOTIFICATION_TAG,
  TEAMMATE_MESSAGE_TAG,
@@ -124,16 +125,21 @@ export function UserTextMessage({
  }

  // Fork child's first message: collapse the rules/format boilerplate, show
-  // only the directive. FORK_BOILERPLATE_TAG is inlined so the import doesn't
-  // ship in external builds where feature('FORK_SUBAGENT') is false.
-  if (feature('FORK_SUBAGENT')) {
-    if (param.text.includes('<fork-boilerplate>')) {
+  // only the user prompt. Independent of FORK_SUBAGENT flag — the fork agent
+  // transcript always needs to render the prompt as a normal user bubble.
+  if (param.text.includes(`<${FORK_BOILERPLATE_TAG}>`)) {
    /* eslint-disable @typescript-eslint/no-require-imports */
    const { UserForkBoilerplateMessage } =
      require('./UserForkBoilerplateMessage.js') as typeof import('./UserForkBoilerplateMessage.js');
    /* eslint-enable @typescript-eslint/no-require-imports */
-      return <UserForkBoilerplateMessage addMargin={addMargin} param={param} />;
-    }
+    return (
+      <UserForkBoilerplateMessage
+        addMargin={addMargin}
+        param={param}
+        isTranscriptMode={isTranscriptMode}
+        timestamp={timestamp}
+      />
+    );
  }

  // Cross-session UDS message (from another Claude session's SendMessage).
--- a/src/components/tasks/BackgroundAgentSelector.tsx
+++ b/src/components/tasks/BackgroundAgentSelector.tsx
@@ -0,0 +1,63 @@
+import { Box, Text } from '@anthropic/ink';
+import { useBackgroundAgentTasks } from '../../hooks/useBackgroundAgentTasks.js';
+import { useElapsedTime } from '../../hooks/useElapsedTime.js';
+import { useAppState } from '../../state/AppState.js';
+import type { LocalAgentTaskState } from '../../tasks/LocalAgentTask/LocalAgentTask.js';
+import { formatTokens } from '../../utils/format.js';
+
+function AgentRow({ task, selected }: { task: LocalAgentTaskState; selected: boolean }) {
+  const elapsed = useElapsedTime(task.startTime, task.status === 'running');
+  const tokens = task.progress?.tokenCount ?? 0;
+  const isRunning = task.status === 'running';
+  return (
+    <Box flexDirection="row" width="100%" justifyContent="space-between">
+      <Box flexDirection="row" flexShrink={1}>
+        <Text color={isRunning ? 'success' : undefined}>{selected ? '● ' : '○ '}</Text>
+        <Text bold={selected} wrap="truncate-end">
+          {task.agentType} <Text dimColor>{task.description}</Text>
+        </Text>
+      </Box>
+      <Box flexShrink={0}>
+        <Text dimColor>
+          {elapsed} · ↓ {formatTokens(tokens)} tokens
+        </Text>
+      </Box>
+    </Box>
+  );
+}
+
+function getHint(pillFocused: boolean, viewedTask: LocalAgentTaskState | null): string {
+  if (pillFocused) return '↑/↓ to select · Enter to view';
+  if (!viewedTask) return 'shift+↓ to manage background agents';
+  return viewedTask.status === 'running' ? 'shift+↓ to manage · x to stop' : 'shift+↓ to manage · x to clear';
+}
+
+export function BackgroundAgentSelector(): React.ReactNode {
+  const tasks = useBackgroundAgentTasks();
+  const viewingId = useAppState(s => s.viewingAgentTaskId);
+  const footerSelection = useAppState(s => s.footerSelection);
+  const selectedBgIndex = useAppState(s => s.selectedBgAgentIndex);
+
+  if (tasks.length === 0) return null;
+
+  const pillFocused = footerSelection === 'bg_agent';
+  const highlightedId = pillFocused
+    ? selectedBgIndex === -1
+      ? null
+      : (tasks[selectedBgIndex]?.agentId ?? null)
+    : (viewingId ?? null);
+  const mainHighlighted = pillFocused ? selectedBgIndex === -1 : viewingId === undefined;
+  const viewedTask = viewingId ? (tasks.find(t => t.agentId === viewingId) ?? null) : null;
+
+  return (
+    <Box flexDirection="column" width="100%">
+      <Box flexDirection="row" width="100%" justifyContent="space-between">
+        <Text bold={mainHighlighted}>{mainHighlighted ? '● ' : '○ '}main</Text>
+        <Text dimColor>{getHint(pillFocused, viewedTask)}</Text>
+      </Box>
+      {tasks.map(task => (
+        <AgentRow key={task.agentId} task={task} selected={task.agentId === highlightedId} />
+      ))}
+    </Box>
+  );
+}
--- a/src/hooks/useBackgroundAgentTasks.ts
+++ b/src/hooks/useBackgroundAgentTasks.ts
@@ -0,0 +1,19 @@
+import { useMemo } from 'react'
+import { useAppState } from '../state/AppState.js'
+import {
+  isLocalAgentTask,
+  type LocalAgentTaskState,
+} from '../tasks/LocalAgentTask/LocalAgentTask.js'
+
+export function useBackgroundAgentTasks(): LocalAgentTaskState[] {
+  const tasks = useAppState(s => s.tasks)
+  return useMemo(() => {
+    const now = Date.now()
+    return Object.values(tasks)
+      .filter(isLocalAgentTask)
+      .filter(t => t.agentType !== 'main-session')
+      .filter(t => t.isBackgrounded !== false)
+      .filter(t => t.evictAfter === undefined || t.evictAfter > now)
+      .sort((a, b) => a.startTime - b.startTime)
+  }, [tasks])
+}
--- a/src/main.tsx
+++ b/src/main.tsx
@@ -3485,6 +3485,7 @@ async function run(): Promise<CommanderCommand> {
            : 'none',
        showTeammateMessagePreview: isAgentSwarmsEnabled() ? false : undefined,
        selectedIPAgentIndex: -1,
+        selectedBgAgentIndex: -1,
        coordinatorTaskIndex: -1,
        viewSelectionMode: 'none',
        footerSelection: null,
--- a/src/screens/REPL.tsx
+++ b/src/screens/REPL.tsx
@@ -244,7 +244,14 @@ import {
  formatCommandInputTags,
 } from '../utils/messages.js';
 import { generateSessionTitle } from '../utils/sessionTitle.js';
-import { BASH_INPUT_TAG, COMMAND_MESSAGE_TAG, COMMAND_NAME_TAG, LOCAL_COMMAND_STDOUT_TAG } from '../constants/xml.js';
+import {
+  BASH_INPUT_TAG,
+  COMMAND_MESSAGE_TAG,
+  COMMAND_NAME_TAG,
+  FORK_BOILERPLATE_TAG,
+  LOCAL_COMMAND_STDOUT_TAG,
+} from '../constants/xml.js';
+import { FORK_SUBAGENT_TYPE } from '@claude-code-best/builtin-tools/tools/AgentTool/forkSubagent.js';
 import { escapeXml } from '../utils/xml.js';
 import type { ThinkingConfig } from '../utils/thinking.js';
 import { gracefulShutdownSync } from '../utils/gracefulShutdown.js';
@@ -336,6 +343,7 @@ import {
 import { isBgSession, updateSessionName, updateSessionActivity } from '../utils/concurrentSessions.js';
 import { isInProcessTeammateTask, type InProcessTeammateTaskState } from '../tasks/InProcessTeammateTask/types.js';
 import { restoreRemoteAgentTasks } from '../tasks/RemoteAgentTask/RemoteAgentTask.js';
+import { BackgroundAgentSelector } from '../components/tasks/BackgroundAgentSelector.js';
 import { useInboxPoller } from '../hooks/useInboxPoller.js';
 // Dead code elimination: conditional import for loop mode
 /* eslint-disable @typescript-eslint/no-require-imports */
@@ -800,6 +808,21 @@ export type Props = {

 export type Screen = 'prompt' | 'transcript';

+// Boilerplate carrier lives in a mixed user message ([tool_result..., text])
+// that AgentTool/forkSubagent.buildForkedMessages emits as the fork child's
+// first user turn. The text block wraps <FORK_BOILERPLATE_TAG>...</..> + the
+// user prompt; tool_result siblings keep the parent's tool calls closed.
+const FORK_BOILERPLATE_OPEN_TAG = `<${FORK_BOILERPLATE_TAG}>`;
+
+function isForkBoilerplateTextBlock(block: { type: string; text?: string }): boolean {
+  return block.type === 'text' && typeof block.text === 'string' && block.text.includes(FORK_BOILERPLATE_OPEN_TAG);
+}
+
+function isForkBoilerplateMessage(message: MessageType): boolean {
+  if (message.type !== 'user' || !Array.isArray(message.message?.content)) return false;
+  return message.message.content.some(isForkBoilerplateTextBlock);
+}
+
 export function REPL({
  commands: initialCommands,
  debug,
@@ -5548,8 +5571,72 @@ export function REPL({
  const usesSyncMessages = showStreamingText || !isLoading;
  // When viewing an agent, never fall through to leader — empty until
  // bootstrap/stream fills. Closes the see-leader-type-agent footgun.
+  const rawAgentMessages = viewedAgentTask?.messages;
+  // Fork sidechain encodes the user prompt inside a mixed user message alongside
+  // tool_result blocks; surface the prompt as a standalone bubble and strip the
+  // boilerplate text from its original carrier while preserving tool_results.
+  const displayedAgentMessages = useMemo(() => {
+    if (!viewedAgentTask) return undefined;
+    const agentMessages = rawAgentMessages ?? [];
+    if (
+      !isLocalAgentTask(viewedAgentTask) ||
+      viewedAgentTask.agentType !== FORK_SUBAGENT_TYPE ||
+      !viewedAgentTask.prompt
+    ) {
+      return agentMessages;
+    }
+    // Single pass: locate boilerplate carrier, check whether the prompt text is
+    // already present elsewhere, and find the fallback insertion point (after
+    // the last parent assistant tool_use).
+    const trimmedPrompt = viewedAgentTask.prompt.trim();
+    let boilerplateIndex = -1;
+    let lastAssistantToolUseIndex = -1;
+    let promptAlreadyRendered = false;
+    for (let i = 0; i < agentMessages.length; i++) {
+      const m = agentMessages[i]!;
+      if (m.type === 'user' && Array.isArray(m.message?.content)) {
+        const hasBoilerplate = m.message.content.some(isForkBoilerplateTextBlock);
+        if (hasBoilerplate) {
+          boilerplateIndex = i;
+        } else if (!promptAlreadyRendered) {
+          const firstText = m.message.content.find(b => b.type === 'text' && typeof b.text === 'string') as
+            | { type: 'text'; text: string }
+            | undefined;
+          if (firstText && firstText.text.trim() === trimmedPrompt) promptAlreadyRendered = true;
+        }
+        continue;
+      }
+      if (m.type === 'assistant' && Array.isArray(m.message?.content)) {
+        if (m.message.content.some(b => b.type === 'tool_use')) lastAssistantToolUseIndex = i;
+      }
+    }
+
+    const stripped =
+      boilerplateIndex === -1
+        ? agentMessages
+        : agentMessages.map((m, i) => {
+            if (i !== boilerplateIndex) return m;
+            if (!Array.isArray(m.message?.content)) return m;
+            return {
+              ...m,
+              message: {
+                ...m.message,
+                content: m.message.content.filter(b => !isForkBoilerplateTextBlock(b)),
+              },
+            };
+          });
+
+    if (promptAlreadyRendered) return stripped;
+
+    const insertAt = boilerplateIndex !== -1 ? boilerplateIndex + 1 : lastAssistantToolUseIndex + 1;
+    const synthetic = createUserMessage({
+      content: viewedAgentTask.prompt,
+      timestamp: new Date(viewedAgentTask.startTime).toISOString(),
+    });
+    return [...stripped.slice(0, insertAt), synthetic, ...stripped.slice(insertAt)];
+  }, [viewedAgentTask, rawAgentMessages]);
  const displayedMessages = viewedAgentTask
-    ? (viewedAgentTask.messages ?? [])
+    ? (displayedAgentMessages ?? [])
    : usesSyncMessages
      ? messages
      : deferredMessages;
@@ -6286,6 +6373,7 @@ export function REPL({
                      voiceInterimRange={voice.interimRange}
                    />
                    <SessionBackgroundHint onBackgroundSession={handleBackgroundSession} isLoading={isLoading} />
+                    <BackgroundAgentSelector />
                  </>
                )}
                {cursor && (
--- a/src/state/AppStateStore.ts
+++ b/src/state/AppStateStore.ts
@@ -85,6 +85,7 @@ export type FooterItem =
  | 'teams'
  | 'bridge'
  | 'companion'
+  | 'bg_agent'

 export type AppState = DeepImmutable<{
  settings: SettingsJson
@@ -97,6 +98,9 @@ export type AppState = DeepImmutable<{
  // Optional - only present when ENABLE_AGENT_SWARMS is true (for dead code elimination)
  showTeammateMessagePreview?: boolean
  selectedIPAgentIndex: number
+  // Selection index for the bottom BackgroundAgentSelector.
+  // -1 = main, 0..N-1 = index into useBackgroundAgentTasks().
+  selectedBgAgentIndex: number
  // CoordinatorTaskPanel selection: -1 = pill, 0 = main, 1..N = agent rows.
  // AppState (not local) so the panel can read it directly without prop-drilling
  // through PromptInput → PromptInputFooter.
@@ -477,6 +481,7 @@ export function getDefaultAppState(): AppState {
    isBriefOnly: false,
    showTeammateMessagePreview: false,
    selectedIPAgentIndex: -1,
+    selectedBgAgentIndex: -1,
    coordinatorTaskIndex: -1,
    viewSelectionMode: 'none',
    footerSelection: null,