diff --git a/src/App.tsx b/src/App.tsx
index e919916..2addeab 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -8,7 +8,6 @@ import { Icon } from '@ui'
 import { store, useStore } from './store'
 import { TaskSidebar } from './components/TaskSidebar'
 import { Conversation } from './components/Conversation'
-import { PreviewPane } from './components/PreviewPane'
 import { previewTabsKey } from './previewtabs'
 import { Workbench } from './components/Workbench'
 import { Workspaces, workspaceShortcuts } from './components/Workspaces'
@@ -18,7 +17,8 @@ import { ProjectSettingsModal } from './components/ProjectSettingsModal'
 import { TopBar } from './components/TopBar'
 import { workspaceEntries } from './components/Workspaces'
 
-// 布局：左（项目会话）/ 中（对话）/ 预览区（有标签时）/ 右（工作台）。
+// 布局（三栏工作台）：左（项目与会话）/ 中（对话）/ 第三栏（工作｜文件双入口）。
+// 文件预览不再是独立第四栏——预览在第三栏「文件」入口内，展开态铺满主区。
 const LEFT_MIN = 220, LEFT_MAX = 420, LEFT_OVERSHOOT = 40
 const RIGHT_MIN = 280, RIGHT_MAX = 560
 const PREVIEW_MIN = 420, PREVIEW_MAX = 1100
@@ -32,11 +32,15 @@ export function App() {
 
   const ui = useStore(s => s.ui)
   // 预览键与 requestPreview 的落点一致（previewTabsKey）：空态（未选会话）点开
-  // 工件也要渲染预览区，否则点击只剩工件弹层关闭、毫无反馈。
+  // 工件也要能进文件入口，否则点击只剩工件弹层关闭、毫无反馈。
   const previewOpen = useStore(s => (s.previewTabs[previewTabsKey(s.currentConvId)]?.length ?? 0) > 0)
+  const rightTab = useStore(s => s.ui.rightTab)
   const toast = useStore(s => s.toast)
   const trackerRunId = useStore(s => s.ui.trackerRunId)
-  const previewExpanded = previewOpen && ui.previewExpanded
+  // 文件入口 + 预览标签在场时，第三栏用「阅读档」宽度（420–1100），不受工作档上限约束。
+  const filesWide = rightTab === 'files' && previewOpen
+  const rightPanelWidth = filesWide ? ui.previewWidth : ui.rightWidth
+  const previewExpanded = filesWide && ui.previewExpanded
   const pendingBadge = useStore(s => s.cards.filter(c => c.status === 'action_required').length)
   // authState：checking → login（登录）→ mustchange（首登强制改密）→ ok（放行）。
   const [authState, setAuthState] = useState<'checking' | 'login' | 'mustchange' | 'ok'>('checking')
@@ -64,28 +68,31 @@ export function App() {
     store.refreshPlugins()
   }, [authState])
 
-  const drag = useRef<{ side: 'left' | 'right' | 'preview'; startX: number; startW: number; overshoot: boolean } | null>(null)
+  const drag = useRef<{ side: 'left' | 'right'; startX: number; startW: number; overshoot: boolean; min: number; max: number; key: 'leftWidth' | 'rightWidth' | 'previewWidth' } | null>(null)
 
-  const onDividerDown = (side: 'left' | 'right' | 'preview') => (e: React.MouseEvent) => {
+  const onDividerDown = (side: 'left' | 'right') => (e: React.MouseEvent) => {
     e.preventDefault()
-    const startW = side === 'left' ? ui.leftWidth : side === 'preview' ? ui.previewWidth : ui.rightWidth
-    drag.current = { side, startX: e.clientX, startW, overshoot: false }
+    // 右侧分隔条按当前入口选宽度档：文件+预览在场走阅读档，否则工作档。
+    const wide = side === 'right' && rightTab === 'files' && previewOpen
+    const key = side === 'left' ? 'leftWidth' : wide ? 'previewWidth' : 'rightWidth'
+    drag.current = {
+      side, startX: e.clientX, startW: ui[key], overshoot: false,
+      min: side === 'left' ? LEFT_MIN : wide ? PREVIEW_MIN : RIGHT_MIN,
+      max: side === 'left' ? LEFT_MAX : wide ? PREVIEW_MAX : RIGHT_MAX,
+      key,
+    }
     const move = (ev: MouseEvent) => {
       const d = drag.current
       if (!d) return
       if (d.side === 'left') {
         const w = d.startW + (ev.clientX - d.startX)
-        if (w < LEFT_MIN - LEFT_OVERSHOOT) { d.overshoot = true; return }
+        if (w < d.min - LEFT_OVERSHOOT) { d.overshoot = true; return }
         d.overshoot = false
-        store.setUI({ leftCollapsed: false, leftWidth: Math.min(LEFT_MAX, Math.max(LEFT_MIN, w)) })
-      } else if (d.side === 'preview') {
-        const w = d.startW - (ev.clientX - d.startX)
-        if (w < PREVIEW_MIN) return
-        store.setUI({ previewWidth: Math.min(PREVIEW_MAX, w) })
+        store.setUI({ leftCollapsed: false, leftWidth: Math.min(d.max, Math.max(d.min, w)) })
       } else {
         const w = d.startW - (ev.clientX - d.startX)
-        if (w < RIGHT_MIN) return
-        store.setUI({ rightCollapsed: false, rightWidth: Math.min(RIGHT_MAX, w) })
+        if (w < d.min) return
+        store.setUI({ rightCollapsed: false, [d.key]: Math.min(d.max, w) } as Partial<typeof ui>)
       }
     }
     const up = () => {
@@ -146,30 +153,21 @@ export function App() {
         <Conversation />
       </div>
 
-      {previewOpen && (
-        <>
-          {!previewExpanded && (
-            <div className="divider" onMouseDown={onDividerDown('preview')} title="拖动调整预览区宽度" />
-          )}
-          <div className={`preview-slot mk-panel-grow${previewExpanded ? ' expanded' : ''}`} style={previewExpanded ? undefined : { width: ui.previewWidth }}>
-            <PreviewPane />
-          </div>
-        </>
-      )}
-
       {!ui.rightCollapsed ? (
         <>
           <div className="divider" onMouseDown={onDividerDown('right')} onDoubleClick={store.toggleRight} title="拖动调整宽度；双击收起" />
-          <div className="right-panel" style={{ width: ui.rightWidth }}>
+          <div className={`right-panel mk-panel-grow${previewExpanded ? ' expanded' : ''}`}
+            style={previewExpanded ? undefined : { width: rightPanelWidth }}>
             <Workbench />
           </div>
         </>
       ) : (
         <div className="right-panel collapsed" style={{ width: 44 }}>
           <div className="icon-only">
-            <button title="展开收件箱" onClick={store.toggleRight}>◧
+            <button title="展开右栏" onClick={store.toggleRight}>◧
               {pendingBadge > 0 && <span className="rail-badge" data-testid="rail-badge">{pendingBadge}</span>}
             </button>
+            <button title="文件（搜索、预览、编辑、下载）" onClick={() => store.openFiles()}><Icon name="folder" size={16} /></button>
           </div>
         </div>
       )}
diff --git a/src/components/ArtifactsPanel.tsx b/src/components/ArtifactsPanel.tsx
index c502ecd..99ffcf1 100644
--- a/src/components/ArtifactsPanel.tsx
+++ b/src/components/ArtifactsPanel.tsx
@@ -1,5 +1,5 @@
-// 工件面板（工作区文件管理）：搜索 + kind 过滤 + 上传；行内打开预览区或下载。
-// ⌘1 弹层与右栏「文件」页签共用这一份。删除仍是保留能力，系统默认不提供入口。
+// 文件列表（第三栏「文件」入口的主视图）：搜索 + kind 过滤 + 上传；
+// 行内打开预览（同入口切到预览子视图）或下载。删除仍是保留能力，系统默认不提供入口。
 import { useState } from 'react'
 import { store, useStore } from '../store'
 import { api } from '../api'
@@ -37,16 +37,16 @@ export function ArtifactsPanel() {
         : visible.length === 0
           ? <div className="empty-note">没有匹配「{q}」的文件</div>
           : visible.map(a => (
-            // 预览落在对话右侧预览区。工作区弹层盖住主区，先收起再打开。
+            // 预览落位在第三栏「文件」入口：requestPreview 会切到预览子视图。
             <div key={a.id} className="artifact-row" data-artifact-row={a.id}
-              onClick={() => { store.closeWorkspace(); store.requestPreview(a) }} title={`预览 ${a.name}`}>
+              onClick={() => store.requestPreview(a)} title={`预览 ${a.name}`}>
               <span className="ar-icon"><Icon name={artifactIcon(a.name, a.kind)} size={15} /></span>
               <span className="ar-main">
                 <span className="name">{a.name}</span>
                 <span className="meta">{a.kind} · {humanSize(a.size) || '—'} · {shortTime(a.updatedAt)}</span>
               </span>
               <span className="ar-acts">
-                <button className="icon-btn" title="展开预览" onClick={e => { e.stopPropagation(); store.closeWorkspace(); store.requestPreview(a); store.setUI({ previewExpanded: true }) }}><Icon name="maximize" size={14} /></button>
+                <button className="icon-btn" title="展开预览（铺满主区）" onClick={e => { e.stopPropagation(); store.requestPreview(a); store.setUI({ previewExpanded: true }) }}><Icon name="maximize" size={14} /></button>
                 <a className="icon-btn" title="下载" href={api.artifactDownloadUrl(a.id)} download={a.name}
                   onClick={e => e.stopPropagation()}><Icon name="download" size={14} /></a>
               </span>
diff --git a/src/components/Conversation.tsx b/src/components/Conversation.tsx
index fc13d81..72b4948 100644
--- a/src/components/Conversation.tsx
+++ b/src/components/Conversation.tsx
@@ -4,7 +4,7 @@
 import { Icon, Avatar, BrandMark, Collapsible, getPersistedOpen, setPersistedOpen, SafeMarkdown } from '@ui'
 import { useEffect, useMemo, useRef, useState } from 'react'
 import { api } from '../api'
-import { store, useStore, activeRun, type LiveState, type ContextObs } from '../store'
+import { store, useStore, activeRun, isTerminal, type LiveState, type ContextObs } from '../store'
 import { scrollRatio, scrollTopForRatio } from '../scrollsync'
 import { liveToMessage, livePhaseLabel, showProcessInline } from '../live'
 import { deriveShellPhase, isShellBusy, showLiveBubble, type ShellPhase } from '../runstate'
@@ -484,6 +484,8 @@ export function Conversation() {
   })
   const busy = isShellBusy(phase)
   const showStop = phase === 'running'
+  // 慢通道在跑的后台子代理：前台回合结束后仍在执行，完成后经通知回到对话汇报。
+  const bgRunning = runs.filter(r => r.kind === 'subagent' && !isTerminal(r.status)).length
 
   useEffect(() => {
     if (!stickRef.current) return
@@ -553,7 +555,6 @@ export function Conversation() {
         <SessionNoteField convId={currentConvId} note={conversation?.sessionNote ?? ''} />
         <span title={connected ? '事件流已连接' : '重连中'} className={`conn-dot ${connected ? 'on' : 'off'}`} />
         {!connected && <span className="conn-label">重连中</span>}
-        {showStop && <button className="btn ghost" onClick={() => store.cancelActive()}>停止</button>}
       </div>
 
       <div className="chat-body" ref={bodyRef}
@@ -615,6 +616,19 @@ export function Conversation() {
 
       <div className="input-bar">
         <OutboxPanel />
+        {/* 轻量状态提示（方案：快慢通道连续体验）：忙碌时可继续输入排队；
+            后台任务在回合结束后仍在执行，完成后回到对话汇报。 */}
+        {(busy || bgRunning > 0) && (
+          <div className="input-status" data-testid="input-status">
+            <span className="live-dot" />
+            {busy
+              ? <span className="mk-sweep">助手工作中{bgRunning > 0 ? ` · ${bgRunning} 个后台任务` : ''}</span>
+              : <span>{bgRunning} 个后台任务进行中</span>}
+            <span className="input-status-note">{busy ? '输入仍可排队' : '完成后回到对话汇报'}</span>
+            <span style={{ flex: 1 }} />
+            <button type="button" className="input-status-link" onClick={() => store.openInbox()}>在工作里查看</button>
+          </div>
+        )}
         {attachmentNames.length > 0 && (
           <div className="attachments">
             {attachmentNames.map((n, i) => <span className="attach-chip" key={i}><Icon name='paperclip' size={12} /> {n}
diff --git a/src/components/PreviewPane.tsx b/src/components/PreviewPane.tsx
index 75fec5e..19d9e02 100644
--- a/src/components/PreviewPane.tsx
+++ b/src/components/PreviewPane.tsx
@@ -1,5 +1,5 @@
-// 对话右侧预览区：多标签、可关、展开与下载。宽度由 App 的分隔条控制；
-// 展开态铺满主区。文本类文件在这里编辑保存。
+// 第三栏「文件」入口的多标签预览：打开/切换/关闭标签、编辑保存、展开铺满与下载。
+// 列表 ⇄ 预览在同一入口内切换；宽度档（阅读档 420–1100）由 App 的分隔条控制。
 import { useEffect, useState } from 'react'
 import { Btn, FilePreview, Icon, TabStrip } from '@ui'
 import { api } from '../api'
@@ -44,6 +44,9 @@ export function PreviewPane() {
         onClose={id => store.closePreview(id)}
       />
       <div className="preview-pane-bar">
+        <button type="button" className="icon-btn" title="返回文件列表" onClick={() => store.setUI({ filesView: 'list', previewExpanded: false })}>
+          <Icon name="list" size={14} />
+        </button>
         <span className="preview-pane-name" title={active.name}>{active.name}</span>
         {art && (
           <span className="preview-pane-meta">{art.kind}{humanSize(art.size) ? ` · ${humanSize(art.size)}` : ''}</span>
diff --git a/src/components/TaskSidebar.tsx b/src/components/TaskSidebar.tsx
index 591f600..4bdcbac 100644
--- a/src/components/TaskSidebar.tsx
+++ b/src/components/TaskSidebar.tsx
@@ -1,4 +1,4 @@
-// 左栏：项目列表、当前项目的会话、体系工具、账户。
+// 左栏（找上下文）：顶部切换项目，中间放会话与搜索，底部放文件、工作区和账户。
 // 创建、搜索、置顶与归档仍在会话段里；领域工具由服务端工作区声明，没有时装上说明行。
 import { useEffect, useRef, useState } from 'react'
 import { store, useStore } from '../store'
@@ -40,6 +40,7 @@ export function TaskSidebar() {
   const projects = useStore(s => s.projects)
   const tasks = useStore(s => s.tasks)
   const me = useStore(s => s.me)
+  const artifacts = useStore(s => s.artifacts)
   const currentConvId = useStore(s => s.currentConvId)
   const currentProjectId = useStore(s => s.currentProjectId)
   const showArchived = useStore(s => s.ui.showArchived)
@@ -50,7 +51,7 @@ export function TaskSidebar() {
     s.projectCards.filter(c => c.status === 'action_required').length)
 
   const [q, setQ] = useState('')
-  const [menu, setMenu] = useState<{ kind: 'new' | 'account' | `row:${string}`; anchor: HTMLElement } | null>(null)
+  const [menu, setMenu] = useState<{ kind: 'new' | 'account' | 'project' | `row:${string}`; anchor: HTMLElement } | null>(null)
   const [creatingProject, setCreatingProject] = useState(false)
   const [newProjectName, setNewProjectName] = useState('')
 
@@ -70,6 +71,7 @@ export function TaskSidebar() {
   const pinned = visible.filter(t => t.pinned)
   const rest = visible.filter(t => !t.pinned)
   const currentProject = projects.find(p => p.id === currentProjectId)
+  const stage = projectStage(currentProject?.settings)
   const rowTask = menu?.kind.startsWith('row:') ? tasks.find(t => t.id === menu.kind.slice(4)) : null
   const rowMenuAnchor = menu && menu.kind.startsWith('row:') ? menu.anchor : null
 
@@ -86,6 +88,14 @@ export function TaskSidebar() {
     </span>
   )
 
+  /** 切换项目：优先恢复该项目下正在看的会话，否则进第一个未归档会话。 */
+  const switchProject = (pid: string) => {
+    const next = tasks.find(t => t.projectId === pid && t.id === currentConvId)
+      ?? tasks.find(t => t.projectId === pid && !t.archived)
+    if (next) store.openTask(next.id)
+    else store.openProject(pid)
+  }
+
   const taskRow = (t: Conversation) => (
     <div key={t.id} className={`tsb-task ${t.id === currentConvId ? 'active' : ''} ${t.archived ? 'archived' : ''}`}
       onClick={() => store.openTask(t.id)}
@@ -99,8 +109,15 @@ export function TaskSidebar() {
 
   return (
     <>
+      {/* 项目身份唯一落点：顶部切换项目（方案：项目导航置顶）。 */}
       <div className="tsb-brand">
-        <span className="tsb-name">项目</span>
+        <button className="tsb-projrow" title="切换项目"
+          onClick={e => { const el = e.currentTarget; setMenu(m => m?.kind === 'project' ? null : { kind: 'project', anchor: el }) }}>
+          <Icon name="folder" size={15} />
+          <span className="tsb-projrow-name">{currentProject?.name ?? '选择项目'}</span>
+          {stage && <span className="tsb-projrow-stage">{stage}</span>}
+          <span className="tsb-user-chev"><Icon name="chevron-down" size={13} /></span>
+        </button>
         <span style={{ flex: 1 }} />
         <button className="tsb-iconbtn" title="收起侧栏（⌘B）" onClick={store.toggleLeft}><Icon name="panel-left" /></button>
       </div>
@@ -127,6 +144,7 @@ export function TaskSidebar() {
           onClick={() => { store.setUI({ showArchived: !showArchived }); store.refreshTasks(!showArchived) }}><Icon name="archive" size={15} /></button>
       </div>
 
+      {/* 中段（方案：会话与搜索）。项目切换在顶部，文件与工作区沉底。 */}
       <div className="tsb-scroll">
         {creatingProject && (
           <div className="tsb-newproject">
@@ -143,25 +161,6 @@ export function TaskSidebar() {
           </div>
         )}
 
-        <div className="tsb-seclabel">项目</div>
-        {projects.map(p => {
-          const stage = projectStage(p.settings)
-          const count = tasks.filter(t => t.projectId === p.id && !t.archived).length
-          return (
-            <button key={p.id} className={`tsb-project ${p.id === currentProjectId ? 'active' : ''}`}
-              onClick={() => {
-                const next = tasks.find(t => t.projectId === p.id && t.id === currentConvId)
-                  ?? tasks.find(t => t.projectId === p.id && !t.archived)
-                if (next) store.openTask(next.id)
-                else store.openProject(p.id)
-              }}>
-              <span className="tsb-project-name">{p.name}</span>
-              <span className="tsb-project-meta">{stage ? `${stage} · ` : ''}{count} 个会话</span>
-            </button>
-          )
-        })}
-        {projects.length === 0 && <div className="tsb-empty">还没有项目——从「新建任务」旁的菜单创建</div>}
-
         {pinned.length > 0 && (
           <>
             <div className="tsb-seclabel">置顶</div>
@@ -173,11 +172,15 @@ export function TaskSidebar() {
           <div className="tsb-empty">这个项目还没有会话——点击「新建任务」开始</div>
         )}
         {rest.map(t => taskRow(t))}
+      </div>
 
-        <div className="tsb-seclabel">
-          体系工具
-          {pendingBadge > 0 && <span className="tsb-tool-badge" title="待处理">{pendingBadge}</span>}
-        </div>
+      {/* 底部（方案：文件、工作区、账户沉底）。 */}
+      <div className="tsb-bottom">
+        <button className="tsb-tool" title="文件搜索、预览、编辑与下载（第三栏「文件」入口）" onClick={() => store.openFiles()}>
+          <span className="tsb-tool-icon"><Icon name="folder" size={14} /></span>
+          <span className="tsb-tool-name">文件</span>
+          {artifacts.length > 0 && <span className="tsb-group-cnt">{artifacts.length}</span>}
+        </button>
         {tools.map(entry => (
           <button key={entry.key} className="tsb-tool" title={entry.shortcut} onClick={() => store.openWorkspace(entry.key)}>
             <span className="tsb-tool-icon">{entry.icon}</span>
@@ -209,6 +212,22 @@ export function TaskSidebar() {
       </div>
 
       {/* 弹出菜单们 */}
+      <Menu anchor={menu?.kind === 'project' ? menu.anchor : null} onClose={() => setMenu(null)}>
+        {projects.map(p => {
+          const count = tasks.filter(t => t.projectId === p.id && !t.archived).length
+          const pstage = projectStage(p.settings)
+          return (
+            <MenuItem key={p.id} icon="folder" onClick={() => { switchProject(p.id); setMenu(null) }}>
+              {p.name}
+              <kbd>{p.id === currentProjectId ? '当前' : pstage ? `${pstage} · ` : ''}{count} 会话</kbd>
+            </MenuItem>
+          )
+        })}
+        {projects.length === 0 && <div className="tsb-tool-note">还没有项目</div>}
+        <div className="tsb-menu-div" />
+        <MenuItem icon="plus" onClick={() => { setCreatingProject(true); setMenu(null) }}>新建项目…</MenuItem>
+      </Menu>
+
       <Menu anchor={menu?.kind === 'new' ? menu.anchor : null} onClose={() => setMenu(null)}>
         <MenuItem icon="plus" onClick={() => { store.createTask(); setMenu(null) }}>新建任务 · 当前项目<kbd>⌘N</kbd></MenuItem>
         <div className="tsb-menu-div" />
diff --git a/src/components/TopBar.tsx b/src/components/TopBar.tsx
index 7363502..068c979 100644
--- a/src/components/TopBar.tsx
+++ b/src/components/TopBar.tsx
@@ -1,20 +1,16 @@
-// 顶栏：产品标识、当前项目与阶段徽章、待处理铃铛。不参与具体操作。
+// 顶栏：产品标识与待处理铃铛。项目身份在左栏顶部切换器集中显示一次（方案），
+// 阶段徽章随切换器；本栏不再重复。
 import { BrandMark, Icon, pendingCount } from '@ui'
 import { store, useStore } from '../store'
-import { projectStage } from '../projectmeta'
 
 export function TopBar() {
-  const project = useStore(s => s.projects.find(p => p.id === s.currentProjectId))
   const pending = useStore(s => pendingCount(s.cards) + pendingCount(s.projectCards))
-  const stage = projectStage(project?.settings)
   return (
     <header className="topbar">
       <BrandMark size={22} />
       <span className="topbar-name">Agent-System</span>
-      {project && <span className="topbar-project" title="当前项目">{project.name}</span>}
-      {stage && <span className="topbar-stage" title="当前阶段">{stage}</span>}
       <span className="topbar-spacer" />
-      <button className="topbar-bell" title={pending > 0 ? `待处理 ${pending}，打开收件箱` : '收件箱'}
+      <button className="topbar-bell" title={pending > 0 ? `待处理 ${pending}，打开工作入口` : '工作入口'}
         onClick={() => store.focusPending()}>
         <Icon name="inbox" size={16} />
         {pending > 0 && <span className="rail-badge" data-testid="topbar-pending">{pending}</span>}
diff --git a/src/components/Workbench.tsx b/src/components/Workbench.tsx
index 80dd77b..0cd9f87 100644
--- a/src/components/Workbench.tsx
+++ b/src/components/Workbench.tsx
@@ -1,12 +1,16 @@
-// 右栏：卡片流。全部 / 待处理筛选、收纳、本会话与项目范围。
-// 文件不占右栏页签——工件走体系工具（⌘）与预览区，一个对象一个入口。
+// 右栏（第三栏）：「工作 / 文件」双入口。
+// 工作 = 当前任务卡 + 收件箱（待处理事项、后台任务卡、执行记录）；
+// 文件 = 文件列表（搜索/上传）与多标签预览（预览、编辑、下载）——预览不再是独立第四栏。
 import { store, useStore } from '../store'
 import type { Run } from '../contracts'
 import { InboxList, pendingCount, type ActivityCard, type DocBridge, type InboxFilter } from '@ui'
 import { Icon } from '@ui'
+import { previewTabsKey } from '../previewtabs'
+import { ArtifactsPanel } from './ArtifactsPanel'
+import { PreviewPane } from './PreviewPane'
 
 // 工件解析/打开注入：渲染器纯展示，doc-ref 词汇经此桥接本仓状态（D29）。
-// 打开语义走 requestPreview 唯一入口（预览区）。
+// 打开语义走 requestPreview 唯一入口（第三栏「文件」入口）。
 export const docBridge: DocBridge = {
   resolveDoc: id => store.getState().artifacts.find(a => a.id === id),
   onOpenDoc: id => {
@@ -47,32 +51,67 @@ function ProjectInbox({ cards, filter }: { cards: ActivityCard[]; filter: InboxF
 }
 
 export function Workbench() {
+  const rightTab = useStore(s => s.ui.rightTab)
   const cards = useStore(s => s.cards)
   const plan = useStore(s => s.plan)
   const todos = useStore(s => s.todos)
   const inboxScope = useStore(s => s.inboxScope)
   const projectCards = useStore(s => s.projectCards)
   const filter = useStore(s => s.ui.inboxFilter)
+  const previewOpen = useStore(s => (s.previewTabs[previewTabsKey(s.currentConvId)]?.length ?? 0) > 0)
   const visible = inboxScope === 'project' ? projectCards : cards
   const pending = pendingCount(visible)
+  // 离开文件入口时收回全屏展开，避免出现「工作」铺满主区的怪态。
+  const switchTab = (tab: 'work' | 'files') =>
+    store.setUI({ rightTab: tab, previewExpanded: tab === 'files' ? store.getState().ui.previewExpanded : false })
   return (
     <>
       <div className="tabs">
-        <button className={`tab ${filter === 'all' ? 'active' : ''}`} onClick={() => store.setUI({ inboxFilter: 'all' })}
-          title="全部卡片">全部</button>
-        <button className={`tab ${filter === 'todo' ? 'active' : ''}`} onClick={() => store.setUI({ inboxFilter: 'todo' })}
-          title="只看待处理">待处理{pending > 0 ? ` ${pending}` : ''}</button>
+        <button className={`tab ${rightTab === 'work' ? 'active' : ''}`} onClick={() => switchTab('work')}
+          title="待处理事项、后台任务与执行记录">工作{pending > 0 ? ` ${pending}` : ''}</button>
+        <button className={`tab ${rightTab === 'files' ? 'active' : ''}`} onClick={() => switchTab('files')}
+          title="文件搜索、预览、编辑与下载">文件</button>
         <span className="spacer" style={{ flex: 1 }} />
-        <button className="tab tab-action" title="收纳已完成卡（done→关闭；已确认卡留痕不动）" onClick={() => store.tidyCards()}><Icon name="check" size={13} /> 收纳</button>
-        <button className="tab" title="收起收件箱" onClick={store.toggleRight}><Icon name="chevron-right" size={14} /></button>
+        {rightTab === 'work' && (
+          <button className="tab tab-action" title="收纳已完成卡（done→关闭；已确认卡留痕不动）" onClick={() => store.tidyCards()}><Icon name="check" size={13} /> 收纳</button>
+        )}
+        <button className="tab" title="收起右栏" onClick={store.toggleRight}><Icon name="chevron-right" size={14} /></button>
       </div>
+      {rightTab === 'files'
+        ? <FilesTab />
+        : <WorkTab plan={plan} todos={todos} filter={filter} inboxScope={inboxScope} projectCards={projectCards} cards={cards} />}
+    </>
+  )
+}
+
+/** 文件入口：有预览标签且处于预览子视图时展示预览；否则展示文件列表（搜索/上传）。 */
+function FilesTab() {
+  const previewOpen = useStore(s => (s.previewTabs[previewTabsKey(s.currentConvId)]?.length ?? 0) > 0)
+  const filesView = useStore(s => s.ui.filesView)
+  if (previewOpen && filesView === 'preview') return <PreviewPane />
+  return <div className="tab-body"><ArtifactsPanel /></div>
+}
+
+function WorkTab({ plan, todos, filter, inboxScope, projectCards, cards }: {
+  plan: Parameters<typeof CurrentTaskCard>[0]['plan']
+  todos: Parameters<typeof CurrentTaskCard>[0]['todos']
+  filter: InboxFilter
+  inboxScope: 'conv' | 'project'
+  projectCards: ActivityCard[]
+  cards: ActivityCard[]
+}) {
+  return (
+    <>
       <div className="tab-body" data-scroll-sync="inbox">
         <CurrentTaskCard plan={plan} todos={todos} />
-        <div className="inbox-scope" role="tablist" aria-label="收件箱范围">
+        <div className="inbox-scope" role="tablist" aria-label="收件箱范围与筛选">
           <button className={inboxScope === 'conv' ? 'active' : ''} onClick={() => store.setInboxScope('conv')}>本会话</button>
           <button className={inboxScope === 'project' ? 'active' : ''} onClick={() => store.setInboxScope('project')}>
             项目{pendingCount(projectCards) > 0 ? ` ${pendingCount(projectCards)}` : ''}
           </button>
+          <span style={{ flex: 1 }} />
+          <button className={filter === 'todo' ? 'active' : ''} title="只看待处理" onClick={() => store.setUI({ inboxFilter: 'todo' })}>待处理</button>
+          <button className={filter === 'all' ? 'active' : ''} title="全部卡片" onClick={() => store.setUI({ inboxFilter: 'all' })}>全部</button>
         </div>
         {inboxScope === 'project'
           ? <ProjectInbox cards={projectCards} filter={filter} />
diff --git a/src/components/Workspaces.tsx b/src/components/Workspaces.tsx
index e9cda44..b63bcc0 100644
--- a/src/components/Workspaces.tsx
+++ b/src/components/Workspaces.tsx
@@ -1,11 +1,11 @@
 // 工作区弹层（提案 T4/D25）：深读经 OverlayHost 单层呈现。
 // 服务端声明的工作区（领域插件槽位）对所有用户可见；插件管理面板仍只在系统管理区。
+// 文件浏览已并入第三栏「文件」入口，本弹层只承载代理与领域工作区。
 import { store, useStore } from '../store'
 import type { Run } from '../contracts'
 import { OverlayHost, type DocBridge } from '@ui'
 import { docBridge } from './Workbench'
 import { AgentRow } from './Workbench'
-import { ArtifactsPanel } from './ArtifactsPanel'
 import { buildWorkspaceEntries, type WorkspaceEntry } from '../workspaces'
 
 /** 体系工具（顺序即 ⌘ 序号）。服务端工作区全员可见；插件管理面板只在系统管理区。 */
@@ -15,7 +15,6 @@ export function workspaceEntries(): WorkspaceEntry[] {
 
 export function Workspaces() {
   const active = useStore(s => s.ui.activeWorkspace)
-  const artifacts = useStore(s => s.artifacts)
   const runs = useStore(s => s.runs)
   const pluginPanels = useStore(s => s.pluginPanels)
   const serverWorkspaces = useStore(s => s.serverWorkspaces)
@@ -23,11 +22,6 @@ export function Workspaces() {
   const entry = workspaceEntries().find(e => e.key === active)
   const close = () => store.closeWorkspace()
 
-  if (active === 'artifacts') {
-    return <OverlayHost title="工件" icon="📦" shortcut={entry?.shortcut ?? '⌘1'} sayHint="打开工件" badge={artifacts.length || undefined} onClose={close}>
-      <ArtifactsPanel />
-    </OverlayHost>
-  }
   if (active === 'agents') {
     const convRuns = runs.filter(r => r.kind !== 'tool')
     return <OverlayHost title="代理" icon="🤖" shortcut={entry?.shortcut ?? '⌘2'} sayHint="打开代理" onClose={close}>
diff --git a/src/store.ts b/src/store.ts
index 5eeabb2..915aa94 100644
--- a/src/store.ts
+++ b/src/store.ts
@@ -43,7 +43,10 @@ export interface UIState {
   leftCollapsed: boolean
   rightWidth: number
   rightCollapsed: boolean
-  rightTab: string
+  /** 第三栏双入口：工作（当前任务/收件箱）/ 文件（搜索、预览、编辑、下载）。 */
+  rightTab: 'work' | 'files'
+  /** 文件入口子视图：列表 / 预览（预览标签存在时才有意义）。 */
+  filesView: 'list' | 'preview'
   /** 收件箱筛选：全部 / 待处理。铃铛打开时切到待处理。 */
   inboxFilter: 'all' | 'todo'
   theme: ThemeChoice
@@ -106,9 +109,10 @@ interface AppState {
 const DEFAULT_UI: UIState = {
   leftWidth: 260,
   leftCollapsed: false,
-  rightWidth: 340,
+  rightWidth: 360,
   rightCollapsed: false,
-  rightTab: 'inbox',
+  rightTab: 'work',
+  filesView: 'list',
   inboxFilter: 'all',
   activeWorkspace: null,
   theme: 'dark',
@@ -134,6 +138,9 @@ function loadUI(): UIState {
       if (!isThemeChoice(ui.theme)) ui.theme = 'dark'
       if (!isFontSizeChoice(ui.fontSize)) ui.fontSize = 14
       if (ui.inboxFilter !== 'all' && ui.inboxFilter !== 'todo') ui.inboxFilter = 'all'
+      // 旧本地偏好里存的是 'inbox'——第三栏双入口上线时归一到 'work'。
+      if (ui.rightTab !== 'work' && ui.rightTab !== 'files') ui.rightTab = 'work'
+      if (ui.filesView !== 'list' && ui.filesView !== 'preview') ui.filesView = 'list'
       // 预览标签不进本地偏好。展开态若随刷新残留，会在没有标签时藏起对话。
       ui.previewExpanded = false
       return ui
@@ -160,19 +167,14 @@ function set(patch: Partial<AppState>) {
   listeners.forEach(l => l())
 }
 
-// 预览区打开前右栏是否收起。null = 当前没有因为预览而改过右栏。
-let previewRightWasCollapsed: boolean | null = null
-
-function syncPreviewRail(hasTabs: boolean) {
+// 第三栏「文件」入口联动（方案：预览并入第三栏）：开第一张标签自动切到文件入口的
+// 预览子视图并展开右栏；关掉最后一张回到文件列表。不再收起右栏——预览与工作同居第三栏。
+function syncFilesEntry(hasTabs: boolean) {
   if (hasTabs) {
-    if (previewRightWasCollapsed === null) previewRightWasCollapsed = state.ui.rightCollapsed
-    if (!state.ui.rightCollapsed) setUI({ rightCollapsed: true })
+    setUI({ rightTab: 'files', rightCollapsed: false, filesView: 'preview' })
     return
   }
-  if (previewRightWasCollapsed === null) return
-  const restore = previewRightWasCollapsed
-  previewRightWasCollapsed = null
-  setUI({ rightCollapsed: restore })
+  if (state.ui.filesView === 'preview') setUI({ filesView: 'list' })
 }
 
 function setUI(patch: Partial<UIState>) {
@@ -367,7 +369,6 @@ export const store = {
         previewActive: { ...state.previewActive, [convId]: active },
       })
     }
-    syncPreviewRail((state.previewTabs[convId] ?? []).length > 0)
     const resumeSeq = await store.reconcile()
     store.connectLive(resumeSeq ?? state.lastSeq)
   },
@@ -818,12 +819,14 @@ export const store = {
     const conv = state.cards.filter(c => c.status === 'action_required').length
     const proj = state.projectCards.filter(c => c.status === 'action_required').length
     if (conv === 0 && proj > 0) store.setInboxScope('project')
-    setUI({ rightCollapsed: false, rightTab: 'inbox', inboxFilter: 'todo' })
+    setUI({ rightCollapsed: false, rightTab: 'work', inboxFilter: 'todo' })
   },
   openInbox(cardId?: string) {
-    setUI({ rightCollapsed: false, rightTab: 'inbox' })
+    setUI({ rightCollapsed: false, rightTab: 'work' })
     if (cardId) setTimeout(() => flashLocate('.right-panel', 'data-card-id', cardId), 60)
   },
+  /** 左栏/收起轨的「文件」入口：打开第三栏文件入口（列表或既有预览）。 */
+  openFiles() { setUI({ rightTab: 'files', rightCollapsed: false }) },
   // 卡→消息互定位另一半（D32）：从收件箱卡滚回产生它的对话消息。
   locateMessage(messageId?: string) {
     if (!messageId) return
@@ -831,8 +834,8 @@ export const store = {
   },
   openTracker(runId: string) { setUI({ trackerRunId: runId }) },
   /**
-   * 工件预览唯一入口：在对话右侧预览区打开或激活标签。
-   * 打开第一张标签时收起右栏，关掉最后一张时恢复，并收回展开态。
+   * 工件预览唯一入口：在第三栏「文件」入口打开或激活标签（多文件多标签）。
+   * 打开第一张自动切到预览子视图；关掉最后一张回到文件列表，并收回展开态。
    */
   requestPreview(a: Artifact) {
     const conv = previewTabsKey(state.currentConvId)
@@ -841,7 +844,7 @@ export const store = {
       previewTabs: { ...state.previewTabs, [conv]: opened.tabs },
       previewActive: { ...state.previewActive, [conv]: opened.activeId },
     })
-    syncPreviewRail(true)
+    syncFilesEntry(true)
   },
   togglePreviewExpanded() { setUI({ previewExpanded: !state.ui.previewExpanded }) },
   activatePreview(id: string) {
@@ -856,7 +859,7 @@ export const store = {
       previewActive: { ...state.previewActive, [conv]: next.activeId },
     })
     if (next.tabs.length === 0) setUI({ previewExpanded: false })
-    syncPreviewRail(next.tabs.length > 0)
+    syncFilesEntry(next.tabs.length > 0)
   },
   openSettings(open: boolean) { setUI({ settingsOpen: open }) },
   openProjectSettings(id: string | null) { setUI({ projectSettingsId: id }) },
diff --git a/src/styles.css b/src/styles.css
index f0f98a6..40ceea0 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -24,11 +24,6 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
   border: 1px solid var(--border-sidebar);
 }
 .topbar-name { font-weight: 650; letter-spacing: .01em; }
-.topbar-project { color: var(--text-sidebar-dim); font-size: var(--fs-ui-sm); max-width: 240px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
-.topbar-stage {
-  font-size: var(--fs-ui-xs); padding: 2px 8px; border-radius: var(--radius-full);
-  border: 1px solid var(--border-sidebar); color: var(--text-sidebar);
-}
 .topbar-spacer { flex: 1; }
 .topbar-bell {
   position: relative; width: 28px; height: 28px; display: inline-flex; align-items: center; justify-content: center;
@@ -56,8 +51,12 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 .main { flex: 1; min-width: 0; display: flex; flex-direction: column; background: var(--bg); border: 1px solid var(--border-soft); border-radius: var(--radius-lg); }
 /* 作者 display 声明会压过 UA 的 [hidden]，此处显式恢复；展开预览靠它隐藏对话列 */
 .main[hidden] { display: none !important; }
+/* 第三栏（工作｜文件）：文件入口承载预览，展开态铺满主区 */
 .right-panel { background: var(--bg-panel); border: 1px solid var(--border-soft); border-radius: var(--radius-lg); display: flex; flex-direction: column; flex-shrink: 0; min-width: 0; }
+.right-panel.expanded { flex: 1 1 auto; width: auto; }
 .right-panel.collapsed { width: 44px !important; }
+/* 预览嵌进第三栏后去掉独立面板外壳（圆角/描边由右栏提供，纸面仍用 --bg） */
+.right-panel .preview-pane { flex: 1; min-height: 0; border: none; border-radius: 0; background: var(--bg); }
 
 /* ---- 通用控件 ---- */
 .btn {
@@ -196,9 +195,7 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 .tl-check { color: var(--text-dim); font-size: var(--fs-ui-sm); margin: 4px 0; }
 .tl-tools .status-error { margin-left: 8px; color: var(--err-text); }
 
-/* 对话右侧预览区 */
-.preview-slot { flex-shrink: 0; min-width: 0; display: flex; }
-.preview-slot.expanded { flex: 1 1 auto; width: auto; }
+/* 第三栏「文件」入口内的多标签预览（外壳样式见 .right-panel .preview-pane） */
 .preview-pane { flex: 1; min-width: 0; display: flex; flex-direction: column; background: var(--bg); border: 1px solid var(--border-soft); border-radius: var(--radius-lg); overflow: hidden; }
 .preview-pane-bar { display: flex; align-items: center; gap: 8px; padding: 6px 10px; border-bottom: 1px solid var(--border-soft); }
 .preview-pane-name { min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: var(--fs-ui-sm); color: var(--text-dim); }
@@ -256,6 +253,11 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 
 /* 输入区：悬浮卡片式输入壳（16px 大圆角 = DESIGN.md 特批例外） */
 .input-bar { padding: 8px max(16px, 6%) 16px; background: var(--bg); border-radius: 0 0 var(--radius-lg) var(--radius-lg); }
+/* 轻量状态提示行（快慢通道）：一行以内，弱色；后台任务在回合结束后仍显示 */
+.input-status { display: flex; align-items: center; gap: 8px; padding: 0 4px 6px; color: var(--text-faint); font-size: var(--fs-ui-sm); }
+.input-status-note { color: var(--text-faint); }
+.input-status-link { border: none; background: none; color: var(--accent-text); font-size: var(--fs-ui-sm); cursor: pointer; padding: 0; }
+.input-status-link:hover { text-decoration: underline; }
 .outbox-trigger { width: 100%; text-align: left; background: var(--bg-inset); color: var(--text-dim); border: 1px solid var(--border-soft); border-radius: var(--radius-xs); padding: 6px 10px; font-size: var(--fs-ui-sm); cursor: pointer; }
 .outbox-list { list-style: none; margin: 6px 0 0; padding: 0; display: flex; flex-direction: column; gap: 6px; }
 .outbox-item { display: flex; gap: 6px; align-items: center; background: var(--bg-inset); border-radius: var(--radius-xs); padding: 6px 8px; }
@@ -345,8 +347,13 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 /* ---- 品牌标（侧栏 / 登录页 / 头像共用的星芒渐变底；辅色为品牌令牌 --brand-2） ---- */
 .brand-mark { background: linear-gradient(135deg, var(--accent), var(--brand-2)); color: var(--text-on-accent); display: inline-flex; align-items: center; justify-content: center; flex: none; box-shadow: inset 0 1px 0 rgba(255,255,255,.22); }
 
-/* ---- 左栏：任务中心（方案 A；Zai 复刻重造型） ---- */
-.tsb-brand { display: flex; align-items: center; gap: 9px; padding: 14px 14px 8px; }
+/* ---- 左栏：项目导航（方案 A；三栏工作台重排：切换置顶、会话居中、文件沉底） ---- */
+.tsb-brand { display: flex; align-items: center; gap: 6px; padding: 12px 12px 8px; }
+.tsb-projrow { flex: 1; min-width: 0; display: flex; align-items: center; gap: 7px; height: 32px; padding: 0 9px; border-radius: var(--radius); border: 1px solid var(--border); background: var(--bg-raised); color: var(--text); cursor: pointer; font-size: var(--fs-ui-caption); font-weight: 600; }
+.tsb-projrow:hover { border-color: var(--accent-sidebar); }
+.tsb-projrow-name { min-width: 0; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
+.tsb-projrow-stage { flex: none; font-size: var(--fs-ui-xs); font-weight: 450; color: var(--text-faint); border: 1px solid var(--border); border-radius: var(--radius-full); padding: 0 6px; }
+.tsb-projrow .tsb-user-chev { color: var(--text-faint); display: inline-flex; flex: none; }
 .tsb-logo { width: 24px; height: 24px; border-radius: var(--radius); background: linear-gradient(135deg, var(--accent), var(--brand-2)); color: var(--text-on-accent); font-size: var(--fs-ui-sm); font-weight: 700; display: flex; align-items: center; justify-content: center; flex: none; }
 .tsb-name { font-weight: 650; font-size: var(--fs-ui-caption); letter-spacing: -0.01em; }
 .tsb-iconbtn { width: 26px; height: 26px; border-radius: var(--radius-sm); background: none; border: none; color: var(--text-faint); cursor: pointer; font-size: var(--fs-ui-caption); display: inline-flex; align-items: center; justify-content: center; position: relative; }
@@ -404,6 +411,8 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 .tsb-row-act:hover { background: var(--bg-active); color: var(--text); }
 
 .tsb-footer { display: flex; align-items: center; gap: 4px; padding: 10px 12px; border-top: 1px solid var(--border-soft); border-radius: 0 0 var(--radius-lg) var(--radius-lg); }
+/* 底部沉底区（方案：文件、工作区在账户上方） */
+.tsb-bottom { display: flex; flex-direction: column; gap: 1px; padding: 6px 10px 2px; border-top: 1px solid var(--border-soft); }
 .tsb-user { flex: 1; display: flex; align-items: center; gap: 9px; min-width: 0; height: 40px; padding: 0 7px; border: none; border-radius: var(--radius); background: none; cursor: pointer; text-align: left; transition: background .12s; }
 .tsb-user:hover { background: var(--bg-hover); }
 .tsb-avatar { width: 27px; height: 27px; border-radius: 50%; background: linear-gradient(135deg, var(--accent), var(--brand-2)); color: var(--text-on-accent); font-size: var(--fs-ui-sm); font-weight: 600; display: flex; align-items: center; justify-content: center; flex: none; box-shadow: inset 0 1px 0 rgba(255,255,255,.2); }
diff --git a/src/workspaces.ts b/src/workspaces.ts
index 0f16af4..ddf96ef 100644
--- a/src/workspaces.ts
+++ b/src/workspaces.ts
@@ -1,5 +1,6 @@
 // 体系工具排位：服务端声明的工作区对所有用户可见，按 shortcut 数字占位；
-// 内置「工件」「代理」补进空位。插件管理面板不进这条清单。
+// 内置「代理」补进空位。文件浏览在第三栏「文件」入口（方案：入口收敛），不再占体系工具位。
+// 插件管理面板不进这条清单。
 
 export interface WorkspaceEntry {
   key: string
@@ -16,7 +17,6 @@ export interface WorkspaceSource {
 }
 
 const BUILTINS: Omit<WorkspaceEntry, 'shortcut'>[] = [
-  { key: 'artifacts', title: '工件', icon: '📦' },
   { key: 'agents', title: '代理', icon: '🤖' },
 ]
 
@@ -56,7 +56,6 @@ export function buildWorkspaceEntries(server: WorkspaceSource[]): WorkspaceEntry
     return 99
   }
   ranked.push({ rank: takeFree(1), entry: BUILTINS[0] })
-  ranked.push({ rank: takeFree(2), entry: BUILTINS[1] })
   for (const entry of unranked) ranked.push({ rank: takeFree(9), entry })
   return ranked
     .filter(item => item.rank <= 9)