diff --git a/src/App.tsx b/src/App.tsx
index 4f1c551..63208cd 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -14,7 +14,6 @@ import { Workspaces, workspaceShortcuts } from './components/Workspaces'
 import { AgentTracker } from './components/AgentTracker'
 import { SettingsModal } from './components/SettingsModal'
 import { ProjectSettingsModal } from './components/ProjectSettingsModal'
-import { DocViewer } from './components/DocViewer'
 import { TopBar } from './components/TopBar'
 import { workspaceEntries } from './components/Workspaces'
 
@@ -37,7 +36,7 @@ export function App() {
   })
   const toast = useStore(s => s.toast)
   const trackerRunId = useStore(s => s.ui.trackerRunId)
-  const viewingArtifact = useStore(s => s.ui.viewingArtifact)
+  const previewExpanded = previewOpen && 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')
@@ -143,14 +142,16 @@ export function App() {
         </div>
       )}
 
-      <div className="main">
+      <div className="main" hidden={previewExpanded}>
         <Conversation />
       </div>
 
       {previewOpen && (
         <>
-          <div className="divider" onMouseDown={onDividerDown('preview')} title="拖动调整预览区宽度" />
-          <div className="preview-slot" style={{ width: ui.previewWidth }}>
+          {!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>
         </>
@@ -180,7 +181,6 @@ export function App() {
       {ui.projectSettingsId && <ProjectSettingsModal />}
       {ui.adminZoneOpen && <AdminZone />}
       {ui.changePwOpen && <ChangePasswordModal onClose={() => store.setUI({ changePwOpen: false })} />}
-      {viewingArtifact && <DocViewer artifact={viewingArtifact} />}
       {toast && <div className="toast">{toast}</div>}
     </div>
   )
diff --git a/src/components/ArtifactsPanel.tsx b/src/components/ArtifactsPanel.tsx
index 2f0fd7c..c502ecd 100644
--- a/src/components/ArtifactsPanel.tsx
+++ b/src/components/ArtifactsPanel.tsx
@@ -37,7 +37,7 @@ 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。弹层盖住主区，先收起再打开。
+            // 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。
             <div key={a.id} className="artifact-row" data-artifact-row={a.id}
               onClick={() => { store.closeWorkspace(); store.requestPreview(a) }} title={`预览 ${a.name}`}>
               <span className="ar-icon"><Icon name={artifactIcon(a.name, a.kind)} size={15} /></span>
@@ -46,7 +46,7 @@ export function ArtifactsPanel() {
                 <span className="meta">{a.kind} · {humanSize(a.size) || '—'} · {shortTime(a.updatedAt)}</span>
               </span>
               <span className="ar-acts">
-                <button className="icon-btn" title="全屏预览" onClick={e => { e.stopPropagation(); store.closeWorkspace(); store.requestPreview(a, 'full') }}><Icon name="eye" size={14} /></button>
+                <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>
                 <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/DocViewer.tsx b/src/components/DocViewer.tsx
deleted file mode 100644
index c164b0f..0000000
--- a/src/components/DocViewer.tsx
+++ /dev/null
@@ -1,68 +0,0 @@
-// 文档查看器（4.4 → 预览能力收敛）：格式渲染统一交给 @ui FilePreview
-// （md/图片/pdf/代码/数据/docx/xlsx/pptx/URL 一套分派），这里只保留 OverlayHost
-// 容器、工具栏与文本族的在线编辑保存。
-import { useEffect, useState } from 'react'
-import { api } from '../api'
-import { store } from '../store'
-import { OverlayHost, Icon, Btn, FilePreview } from '@ui'
-import type { Artifact } from '../contracts'
-import { humanSize } from '../messageparts'
-
-export function DocViewer({ artifact }: { artifact: Artifact }) {
-  const [content, setContent] = useState<string | null>(null)
-  const [editing, setEditing] = useState(false)
-  const [dirty, setDirty] = useState(false)
-
-  const textKind = isTextKind(artifact)
-  useEffect(() => {
-    if (!textKind) return
-    setContent(null)
-    fetch(api.artifactContentUrl(artifact.id)).then(r => r.text()).then(setContent).catch(() => setContent('（读取失败）'))
-  }, [artifact.id])
-
-  const source = {
-    kind: 'artifact' as const,
-    id: artifact.id,
-    name: artifact.name,
-    mime: artifact.mime,
-    contentUrl: api.artifactContentUrl(artifact.id),
-    downloadUrl: api.artifactDownloadUrl(artifact.id),
-  }
-
-  return (
-    <OverlayHost title={artifact.name} icon="📄" onClose={() => store.viewArtifact(null)}>
-      <div className="docv">
-        <div className="docv-toolbar">
-          <span className="docv-meta">{artifact.kind}{humanSize(artifact.size) ? ` · ${humanSize(artifact.size)}` : ''}</span>
-          <span className="spacer" />
-          {dirty && <span className="docv-dirty">未保存</span>}
-          {textKind && (
-            <>
-              <Btn variant="ghost" icon={editing ? 'eye' : 'list'} onClick={() => setEditing(e => !e)}>{editing ? '预览' : '编辑'}</Btn>
-              {editing && <Btn variant="primary" icon="check" disabled={!dirty} onClick={async () => {
-                await api.saveArtifactContent(artifact.id, content ?? '')
-                setDirty(false)
-                store.toast('已保存')
-              }}>保存</Btn>}
-            </>
-          )}
-          <a className="btn v-ghost docv-dl" href={api.artifactDownloadUrl(artifact.id)} download={artifact.name}>
-            <Icon name="download" size={14} /> 下载
-          </a>
-        </div>
-        <div className="docv-body">
-          {editing && textKind ? (
-            <textarea className="search-input docv-editor" value={content ?? ''}
-              onChange={e => { setContent(e.target.value); setDirty(true) }} />
-          ) : (
-            <FilePreview source={source} />
-          )}
-        </div>
-      </div>
-    </OverlayHost>
-  )
-}
-
-function isTextKind(a: Artifact): boolean {
-  return a.kind === 'document' && /\.(md|txt|csv|log|json)$/i.test(a.name)
-}
diff --git a/src/components/PreviewPane.tsx b/src/components/PreviewPane.tsx
index f185bc7..fed98c7 100644
--- a/src/components/PreviewPane.tsx
+++ b/src/components/PreviewPane.tsx
@@ -1,6 +1,10 @@
-// 对话右侧预览区：多标签、可关、全屏与下载。宽度由 App 的分隔条控制。
-import { FilePreview, TabStrip, Icon } from '@ui'
+// 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。
+import { useEffect, useState } from 'react'
+import { Btn, FilePreview, Icon, TabStrip } from '@ui'
 import { api } from '../api'
+import type { Artifact } from '../contracts'
+import { humanSize } from '../messageparts'
 import { store, useStore } from '../store'
 
 export function PreviewPane() {
@@ -8,9 +12,28 @@ export function PreviewPane() {
   const tabs = useStore(s => (convId ? s.previewTabs[convId] : undefined) ?? [])
   const activeId = useStore(s => (convId ? s.previewActive[convId] : null) ?? null)
   const artifacts = useStore(s => s.artifacts)
+  const expanded = useStore(s => s.ui.previewExpanded)
   const active = tabs.find(t => t.id === activeId) ?? tabs[0]
+  const art = active ? artifacts.find(a => a.id === active.id) : undefined
+  const textKind = !!art && isTextKind(art)
+  const [content, setContent] = useState<string | null>(null)
+  const [editing, setEditing] = useState(false)
+  const [dirty, setDirty] = useState(false)
+
+  useEffect(() => {
+    setEditing(false)
+    setDirty(false)
+    setContent(null)
+    if (!art || !isTextKind(art)) return
+    let cancelled = false
+    fetch(api.artifactContentUrl(art.id))
+      .then(r => r.text())
+      .then(text => { if (!cancelled) setContent(text) })
+      .catch(() => { if (!cancelled) setContent('（读取失败）') })
+    return () => { cancelled = true }
+  }, [art?.id])
+
   if (!active) return null
-  const art = artifacts.find(a => a.id === active.id)
   return (
     <div className="preview-pane">
       <TabStrip
@@ -21,11 +44,25 @@ export function PreviewPane() {
       />
       <div className="preview-pane-bar">
         <span className="preview-pane-name" title={active.name}>{active.name}</span>
+        {art && (
+          <span className="preview-pane-meta">{art.kind}{humanSize(art.size) ? ` · ${humanSize(art.size)}` : ''}</span>
+        )}
         <span className="preview-pane-spacer" />
         {art && (
           <>
-            <button type="button" className="icon-btn" title="全屏预览" onClick={() => store.requestPreview(art, 'full')}>
-              <Icon name="eye" size={14} />
+            {dirty && <span className="preview-pane-dirty">未保存</span>}
+            {textKind && (
+              <>
+                <Btn variant="ghost" icon={editing ? 'eye' : 'list'} onClick={() => setEditing(e => !e)}>{editing ? '预览' : '编辑'}</Btn>
+                {editing && <Btn variant="primary" icon="check" disabled={!dirty} onClick={async () => {
+                  await api.saveArtifactContent(art.id, content ?? '')
+                  setDirty(false)
+                  store.toast('已保存')
+                }}>保存</Btn>}
+              </>
+            )}
+            <button type="button" className="icon-btn" title={expanded ? '还原预览' : '展开预览'} aria-pressed={expanded} onClick={() => store.togglePreviewExpanded()}>
+              <Icon name={expanded ? 'minimize' : 'maximize'} size={14} />
             </button>
             <a className="icon-btn" title="下载" href={api.artifactDownloadUrl(art.id)} download={art.name}>
               <Icon name="download" size={14} />
@@ -34,7 +71,10 @@ export function PreviewPane() {
         )}
       </div>
       <div className="preview-pane-body">
-        {art ? (
+        {editing && textKind ? (
+          <textarea className="search-input preview-pane-editor" value={content ?? ''}
+            onChange={e => { setContent(e.target.value); setDirty(true) }} />
+        ) : art ? (
           <FilePreview source={{
             kind: 'artifact',
             id: art.id,
@@ -48,3 +88,7 @@ export function PreviewPane() {
     </div>
   )
 }
+
+function isTextKind(a: Artifact): boolean {
+  return a.kind === 'document' && /\.(md|txt|csv|log|json)$/i.test(a.name)
+}
diff --git a/src/messageparts.ts b/src/messageparts.ts
index b571e4d..124fda2 100644
--- a/src/messageparts.ts
+++ b/src/messageparts.ts
@@ -126,7 +126,7 @@ export function workedLabel(createdAt?: string, endedAt?: string): string {
   return text ? `已工作 ${text}` : '已工作'
 }
 
-/** 文件大小人类可读（工件面板/DocViewer 共用）。 */
+/** 文件大小人类可读（工件面板/预览栏共用）。 */
 export function humanSize(n: number | undefined): string {
   if (!n || n <= 0) return ''
   const units = ['B', 'KB', 'MB', 'GB']
diff --git a/src/previewfit.ts b/src/previewfit.ts
index ba975f5..73e0b01 100644
--- a/src/previewfit.ts
+++ b/src/previewfit.ts
@@ -32,6 +32,9 @@ export function fitPagesToWidth(host: HTMLElement, el: HTMLElement): () => void
   }
   const observer = new ResizeObserver(() => apply())
   observer.observe(el)
+  // 页内图片后加载只改变页纸高度，不改变栏宽。el 变宽和 wrapper 变高都要重算宿主高度。
+  const wrapper = host.querySelector<HTMLElement>('.docx-wrapper')
+  if (wrapper && wrapper !== el) observer.observe(wrapper)
   return () => {
     observer.disconnect()
     clearFit(host)
diff --git a/src/store.ts b/src/store.ts
index 0021e51..5a52da7 100644
--- a/src/store.ts
+++ b/src/store.ts
@@ -43,9 +43,10 @@ export interface UIState {
   autoCollapseProcess: boolean
   settingsOpen: boolean
   trackerRunId: string | null
-  viewingArtifact: Artifact | null
   /** 预览区宽度。标签列表按会话放在 AppState，不进本地偏好。 */
   previewWidth: number
+  /** 预览栏铺满主区。标签不持久化，这个标志在 loadUI 时强制复位。 */
+  previewExpanded: boolean
   activeWorkspace: string | null
   taskOrg: 'project' | 'timeline'
   showArchived: boolean
@@ -105,8 +106,8 @@ const DEFAULT_UI: UIState = {
   autoCollapseProcess: true,
   settingsOpen: false,
   trackerRunId: null,
-  viewingArtifact: null,
   previewWidth: 640,
+  previewExpanded: false,
   taskOrg: 'project',
   showArchived: false,
   lastProjectId: null,
@@ -122,6 +123,8 @@ function loadUI(): UIState {
       const ui = { ...DEFAULT_UI, ...JSON.parse(raw) } as UIState
       if (!isThemeChoice(ui.theme)) ui.theme = 'dark'
       if (ui.inboxFilter !== 'all' && ui.inboxFilter !== 'todo') ui.inboxFilter = 'all'
+      // 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
     }
   } catch { /* ignore */ }
@@ -778,13 +781,11 @@ export const store = {
     setTimeout(() => flashLocate('.chat', 'data-msg-id', messageId), 60)
   },
   openTracker(runId: string) { setUI({ trackerRunId: runId }) },
-  viewArtifact(a: Artifact | null) { setUI({ viewingArtifact: a }) },
   /**
-   * 工件预览唯一入口。默认在对话右侧预览区打开或激活标签；hint 'full' 落位全屏
-   * DocViewer。打开第一张标签时收起右栏，关掉最后一张时恢复。
+   * 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。
    */
-  requestPreview(a: Artifact, hint?: 'full') {
-    if (hint === 'full') { setUI({ viewingArtifact: a }); return }
+  requestPreview(a: Artifact) {
     const conv = state.currentConvId ?? '_'
     const opened = openPreviewTab(state.previewTabs[conv] ?? [], { id: a.id, name: a.name })
     set({
@@ -793,6 +794,7 @@ export const store = {
     })
     syncPreviewRail(true)
   },
+  togglePreviewExpanded() { setUI({ previewExpanded: !state.ui.previewExpanded }) },
   activatePreview(id: string) {
     const conv = state.currentConvId ?? '_'
     set({ previewActive: { ...state.previewActive, [conv]: id } })
@@ -804,6 +806,7 @@ export const store = {
       previewTabs: { ...state.previewTabs, [conv]: next.tabs },
       previewActive: { ...state.previewActive, [conv]: next.activeId },
     })
+    if (next.tabs.length === 0) setUI({ previewExpanded: false })
     syncPreviewRail(next.tabs.length > 0)
   },
   openSettings(open: boolean) { setUI({ settingsOpen: open }) },
diff --git a/src/styles.css b/src/styles.css
index 3016203..e66b4d5 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -196,13 +196,21 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 
 /* 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; }
 .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); }
 .preview-pane-spacer { flex: 1; }
 .preview-pane-body { flex: 1; min-height: 0; overflow: auto; }
-.preview-pane-body .ui-fp { height: 100%; }
+/* 只给下限，不钉死高度：内容超出时由本层滚动。PDF iframe 靠自身 flex:1 撑满。 */
+.preview-pane-body .ui-fp { min-height: 100%; }
 .preview-pane-body .ui-fp-pdf { height: 100%; min-height: 480px; border: none; }
+.preview-pane-meta { flex-shrink: 0; font-size: var(--fs-ui-xs); color: var(--text-faint); text-transform: capitalize; }
+.preview-pane-dirty { color: var(--warn); font-size: var(--fs-ui-sm); }
+.preview-pane-editor {
+  display: block; width: 100%; height: 100%; min-height: 0; resize: none;
+  font-family: var(--mono); font-size: var(--fs-ui-sm); background: var(--bg); color: var(--text);
+}
 .docx-wrapper { background: var(--bg-inset) !important; padding: 12px; display: flex; flex-direction: column; align-items: flex-start !important; }
 .docx-wrapper > section.docx { background: var(--paper) !important; color: var(--paper-ink); box-shadow: var(--shadow-md); }
 /* 过程段内联组（流式/关闭自动折叠时，按原位渲染的过程容器） */
@@ -318,18 +326,6 @@ button { font-family: inherit; font-size: inherit; color: inherit; }
 .effect-hot { color: var(--ok); border-color: var(--ok); }
 .effect-new-run { color: var(--warn); border-color: var(--warn); }
 
-/* ---- 文档查看器（单层 OverlayHost 内）---- */
-.docv { display: flex; flex-direction: column; min-height: 0; }
-.docv-toolbar { display: flex; align-items: center; gap: 8px; padding: 0 0 10px; border-bottom: 1px solid var(--border-soft); margin-bottom: 10px; }
-.docv-toolbar .spacer { flex: 1; }
-.docv-meta { font-size: var(--fs-ui-xs); color: var(--text-faint); text-transform: capitalize; }
-.docv-dirty { color: var(--warn); font-size: var(--fs-ui-sm); }
-.docv-dl { text-decoration: none; }
-.docv-body { flex: 1; min-height: 0; overflow: auto; }
-.docv-pdf { width: 100%; height: 100%; min-height: 60vh; border: 1px solid var(--border-soft); border-radius: var(--radius); background: var(--bg); }
-.docv-editor { width: 100%; height: 56vh; font-family: var(--mono); font-size: var(--fs-ui-sm); resize: vertical; }
-.docv-pre { font-family: var(--mono); font-size: var(--fs-ui-sm); white-space: pre-wrap; word-break: break-word; background: var(--bg-inset); border: 1px solid var(--border-soft); border-radius: var(--radius); padding: 12px 14px; }
-
 /* ---- 杂项 ---- */
 .toast { position: fixed; bottom: 24px; left: 50%; transform: translateX(-50%); background: var(--bg-raised); border: 1px solid var(--border); color: var(--text); padding: 9px 16px; border-radius: var(--radius-full); box-shadow: var(--shadow-lg); z-index: 90; font-size: var(--fs-ui-caption); }
 .conn-dot { width: 8px; height: 8px; border-radius: 50%; }
diff --git a/test/previewfit.test.ts b/test/previewfit.test.ts
index 31a9806..a6d43cf 100644
--- a/test/previewfit.test.ts
+++ b/test/previewfit.test.ts
@@ -1,5 +1,5 @@
-import { describe, it, expect } from 'vitest'
-import { computeFitScale } from '../src/previewfit'
+import { afterEach, describe, it, expect } from 'vitest'
+import { computeFitScale, fitPagesToWidth } from '../src/previewfit'
 
 describe('computeFitScale', () => {
   it('keeps the page at 100% when the column is wider than the page', () => {
@@ -19,3 +19,92 @@ describe('computeFitScale', () => {
     expect(computeFitScale(Number.NaN, 794, 24)).toBe(1)
   })
 })
+
+// node 测试环境没有 DOM。这里只实现 fitPagesToWidth 会碰到的查询与尺寸。
+class FakeEl {
+  style: { height: string; overflow: string; minHeight: string; transform: string; transformOrigin: string } = {
+    height: '', overflow: '', minHeight: '', transform: '', transformOrigin: '',
+  }
+  clientWidth = 0
+  offsetWidth = 0
+  offsetHeight = 0
+  className = ''
+  tag = 'div'
+  children: FakeEl[] = []
+  querySelector(sel: string): FakeEl | null {
+    const walk = (nodes: FakeEl[]): FakeEl | null => {
+      for (const node of nodes) {
+        if (matches(node, sel)) return node
+        const hit = walk(node.children)
+        if (hit) return hit
+      }
+      return null
+    }
+    return walk(this.children)
+  }
+}
+
+function matches(el: FakeEl, sel: string): boolean {
+  const classes = el.className.split(/\s+/).filter(Boolean)
+  if (sel.startsWith('.')) return classes.includes(sel.slice(1))
+  const [tag, cls] = sel.split('.')
+  return el.tag === tag && classes.includes(cls)
+}
+
+class FakeResizeObserver {
+  static observed: FakeEl[] = []
+  static instances: FakeResizeObserver[] = []
+  constructor(private callback: () => void) {
+    FakeResizeObserver.instances.push(this)
+  }
+  observe(el: FakeEl) { FakeResizeObserver.observed.push(el) }
+  disconnect() { /* dispose 只要求卸下监听 */ }
+  static fire() {
+    for (const instance of FakeResizeObserver.instances) instance.callback()
+  }
+  static reset() {
+    FakeResizeObserver.observed = []
+    FakeResizeObserver.instances = []
+  }
+}
+
+describe('fitPagesToWidth', () => {
+  const previous = globalThis.ResizeObserver
+
+  afterEach(() => {
+    FakeResizeObserver.reset()
+    globalThis.ResizeObserver = previous
+  })
+
+  it('recomputes the host height when the page wrapper grows and clears inline styles on dispose', () => {
+    globalThis.ResizeObserver = FakeResizeObserver as unknown as typeof ResizeObserver
+    const host = new FakeEl()
+    host.clientWidth = 420
+    const wrapper = new FakeEl()
+    wrapper.className = 'docx-wrapper'
+    wrapper.offsetHeight = 1000
+    const page = new FakeEl()
+    page.tag = 'section'
+    page.className = 'docx'
+    page.offsetWidth = 794
+    wrapper.children.push(page)
+    host.children.push(wrapper)
+
+    const dispose = fitPagesToWidth(host as unknown as HTMLElement, host as unknown as HTMLElement)
+    const scale = (420 - 24) / 794
+    expect(host.style.height).toBe(`${Math.round(1000 * scale)}px`)
+    expect(host.style.overflow).toBe('hidden')
+    expect(FakeResizeObserver.observed).toContain(wrapper)
+
+    wrapper.offsetHeight = 1500
+    FakeResizeObserver.fire()
+    expect(host.style.height).toBe(`${Math.round(1500 * scale)}px`)
+
+    dispose()
+    expect(host.style.height).toBe('')
+    expect(host.style.overflow).toBe('')
+    expect(host.style.minHeight).toBe('')
+    expect(wrapper.style.transform).toBe('')
+    expect(wrapper.style.transformOrigin).toBe('')
+  })
+})