diff --git a/index.html b/index.html
index 8dd588c..d10c42d 100644
--- a/index.html
+++ b/index.html
@@ -196,8 +196,22 @@
           <ul id="members" class="members"></ul>
         </aside>
 
-        <div class="center-col">
+        <div class="center-col workspace" id="plan-workspace" data-stage="plan">
+          <div class="workspace-tools" aria-label="계획 화면 배치 조절">
+            <div class="layout-switch" role="group" aria-label="모델과 입력창 배치">
+              <button type="button" class="btn small" data-layout="stack" aria-pressed="true">상하</button>
+              <button type="button" class="btn small" data-layout="side" aria-pressed="false">좌우</button>
+            </div>
+            <label class="model-height-control" for="plan-model-height"><span data-size-label>모델 높이</span>
+              <input id="plan-model-height" type="range" min="180" max="560" step="20" value="400" />
+              <output id="plan-model-height-value" for="plan-model-height">400 px</output>
+            </label>
+            <button id="plan-model-toggle" class="btn small" type="button" aria-expanded="true" aria-controls="slot-plan">모델 접기</button>
+            <span class="layout-note muted small" aria-live="polite"></span>
+          </div>
           <div class="viewer-slot" id="slot-plan"></div>
+          <div class="workspace-splitter" role="separator" tabindex="0" aria-controls="slot-plan" aria-label="모델 크기 조절"></div>
+          <div class="workspace-pane">
           <!-- ② 교대 부재 카드 (시안, 2026-11-03): the card of the row picked in 부재 · 교대, under the 3D view. -->
           <section id="abut-panel-plan" class="panel viewer abut-card" hidden aria-labelledby="abut-panel-plan-title">
             <div class="viewer-head">
@@ -260,6 +274,7 @@
                     </footer>
                   </section>
         </section>
+          </div>
         </div>
 
         <aside class="panel results" aria-labelledby="changes-title">
@@ -298,22 +313,30 @@
           <ul id="rebar-tabs" class="members"></ul>
           <p class="pnote">형상은 ② 형상계획 기준입니다. 형상이 바뀌면 "형상 바뀜"으로 표시합니다.</p>
         </aside>
-        <div class="center-col review-workspace" id="review-workspace">
+        <div class="center-col workspace review-workspace" id="review-workspace" data-stage="rebar">
           <div class="workspace-tools" aria-label="검토 공간 조절">
-            <label class="model-height-control" for="review-model-height">모델 높이
+            <div class="layout-switch" role="group" aria-label="모델과 철근표 배치">
+              <button type="button" class="btn small" data-layout="stack" aria-pressed="true">상하</button>
+              <button type="button" class="btn small" data-layout="side" aria-pressed="false">좌우</button>
+            </div>
+            <label class="model-height-control" for="review-model-height"><span data-size-label>모델 높이</span>
               <input id="review-model-height" type="range" min="180" max="560" step="20" value="240" />
               <output id="review-model-height-value" for="review-model-height">240 px</output>
             </label>
             <button id="review-model-toggle" class="btn small" type="button" aria-expanded="true" aria-controls="slot-rebar">모델 접기</button>
             <button id="review-inputs" class="btn small" type="button">입력 보기</button>
             <button id="review-table" class="btn small" type="button">철근표 보기</button>
+            <span class="layout-note muted small" aria-live="polite"></span>
           </div>
           <div class="viewer-slot" id="slot-rebar"></div>
+          <div class="workspace-splitter" role="separator" tabindex="0" aria-controls="slot-rebar" aria-label="모델 크기 조절"></div>
+          <div class="workspace-pane">
         <section class="panel viewer" aria-labelledby="rebar-title">
           <div class="viewer-head"><h2 id="rebar-title">철근표</h2><button id="rebar-materials" class="btn-o" type="button">재료표·수량산출 보기</button></div>
           <p id="rebar-note" class="num"></p>
           <div id="rebar-table"></div>
         </section>
+          </div>
         </div>
         <aside class="panel results" aria-labelledby="rebar-issues-title">
           <h2 id="rebar-issues-title">알림</h2>
diff --git a/scripts/review-design-a.cjs b/scripts/review-design-a.cjs
index 673c9a6..71393f2 100644
--- a/scripts/review-design-a.cjs
+++ b/scripts/review-design-a.cjs
@@ -40,10 +40,10 @@ const delay=ms=>new Promise(r=>setTimeout(r,ms));let ws;
  await click('#review-tasks button');report.taskJump=await ev(`({focused:document.activeElement?.innerText,selected:document.querySelector('#rebar-table').innerText.includes('강조 중')})`);
  await ev(`[...document.querySelectorAll('#rebar-tabs button')].find(b=>b.textContent.includes('확대기초')).click()`);
  await ev(`document.querySelector('#review-model-height').value='180';document.querySelector('#review-model-height').dispatchEvent(new Event('input',{bubbles:true}))`);
- await click('#review-inputs');report.inputJump=await ev(`({focused:document.activeElement?.id,scroll:document.querySelector('#review-workspace > .viewer').scrollTop})`);
+ await click('#review-inputs');report.inputJump=await ev(`({focused:document.activeElement?.id,scroll:document.querySelector('#review-workspace .workspace-pane > .viewer').scrollTop})`);
  await click('#review-model-toggle');await click('#review-table');
  await ev(`document.querySelector('#view-rebar > .results').scrollTop=250`);await cap('05-collapsed-table-material-1280');
- report.end=await ev(`({modelHidden:getComputedStyle(document.querySelector('#slot-rebar')).display,expanded:document.querySelector('#review-model-toggle').getAttribute('aria-expanded'),focused:document.activeElement.tagName,frames:[...document.querySelectorAll('#view-rebar > .panel,#review-workspace,#review-workspace > .viewer')].map(e=>({id:e.id,class:e.className,overflow:getComputedStyle(e).overflow,clientHeight:e.clientHeight,scrollHeight:e.scrollHeight,scrollTop:e.scrollTop}))})`);
+ report.end=await ev(`({modelHidden:getComputedStyle(document.querySelector('#slot-rebar')).display,expanded:document.querySelector('#review-model-toggle').getAttribute('aria-expanded'),focused:document.activeElement.tagName,frames:[...document.querySelectorAll('#view-rebar > .panel,#review-workspace,#review-workspace .workspace-pane > .viewer')].map(e=>({id:e.id,class:e.className,overflow:getComputedStyle(e).overflow,clientHeight:e.clientHeight,scrollHeight:e.scrollHeight,scrollTop:e.scrollTop}))})`);
  report.finished=new Date().toISOString();fs.writeFileSync(path.join(out,'raw.json'),JSON.stringify(report,null,2));console.log(JSON.stringify(report));
  await send('Page.close');ws.close();
 })().catch(e=>{report.failure=String(e.stack||e);fs.writeFileSync(path.join(out,'raw.json'),JSON.stringify(report,null,2));console.error(e);if(ws)ws.close();process.exitCode=1});
diff --git a/scripts/verify-design-fixes.cjs b/scripts/verify-design-fixes.cjs
index 56caa68..ec39f86 100644
--- a/scripts/verify-design-fixes.cjs
+++ b/scripts/verify-design-fixes.cjs
@@ -56,7 +56,7 @@ async function main() {
     await until(`!document.getElementById('dlg-apply').disabled && document.getElementById('import-abut-A1')?.checked === true`);
   };
   const member = async (label) => { await click(`[...document.querySelectorAll('#rebar-tabs button')].find(b => b.textContent.startsWith(${JSON.stringify(label)}))`); await delay(100); };
-  const lower = () => ev(`document.querySelector('#review-workspace > section').getBoundingClientRect().height`);
+  const lower = () => ev(`document.querySelector('#review-workspace .workspace-pane > section').getBoundingClientRect().height`);
   await send('Page.enable'); await send('Runtime.enable'); await send('DOM.enable');
   await send('Emulation.setDeviceMetricsOverride', { width: 1600, height: 1000, deviceScaleFactor: 1, mobile: false });
   await until(`!!document.querySelector('[data-card="excel"] button') && typeof window.loadBytesToApp === 'function'`);
@@ -94,7 +94,7 @@ async function main() {
   report.layoutCollapsed = await lower();
   check('collapse adds model area to evidence', report.layoutCollapsed > report.layoutResized + 150);
   await click(`document.getElementById('review-table')`);
-  check('table shortcut focuses and reveals table', await ev(`document.activeElement.matches('#rebar-table table.rebar-table') && document.activeElement.getBoundingClientRect().top >= document.querySelector('#review-workspace > section').getBoundingClientRect().top - 2`));
+  check('table shortcut focuses and reveals table', await ev(`document.activeElement.matches('#rebar-table table.rebar-table') && document.activeElement.getBoundingClientRect().top >= document.querySelector('#review-workspace .workspace-pane > section').getBoundingClientRect().top - 2`));
   await shot('03-table-laptop');
   await click(`document.getElementById('review-inputs')`);
   check('input shortcut preserves keyboard tab order', await ev(`document.activeElement.matches('#rebar-table input') && document.activeElement.tabIndex === 0`));
diff --git a/scripts/verify-workspace-layout.cjs b/scripts/verify-workspace-layout.cjs
new file mode 100644
index 0000000..45ecb57
--- /dev/null
+++ b/scripts/verify-workspace-layout.cjs
@@ -0,0 +1,135 @@
+// Run with Windows Node and an isolated Chrome on CDP 9444; Vite must be on 5173.
+// ②·③ center workspace: stacked ↔ side-by-side, splitter drag/keyboard, persistence, width fallback.
+const fs = require('node:fs'), path = require('node:path'), assert = require('node:assert/strict');
+const root = path.resolve(__dirname, '..');
+const out = path.resolve(root, '.verify/workspace-layout-20261109');
+fs.mkdirSync(out, { recursive: true });
+const report = { checks: [], errors: [], metrics: {} };
+let ws, send;
+const delay = ms => new Promise(r => setTimeout(r, ms));
+let target;
+(async () => {
+  target = await (await fetch('http://127.0.0.1:9444/json/new?about:blank', { method: 'PUT' })).json();
+  ws = new WebSocket(target.webSocketDebuggerUrl);
+  await new Promise((r, j) => { ws.onopen = r; ws.onerror = j; });
+  let seq = 0; const pending = new Map();
+  ws.onmessage = ({ data }) => {
+    const m = JSON.parse(data), p = pending.get(m.id);
+    if (p) { clearTimeout(p.timer); pending.delete(m.id); m.error ? p.reject(new Error(JSON.stringify(m.error))) : p.resolve(m.result); }
+    if (m.method === 'Page.javascriptDialogOpening') ws.send(JSON.stringify({ id: 900000 + (++seq), method: 'Page.handleJavaScriptDialog', params: { accept: true } }));
+    if (m.method === 'Runtime.exceptionThrown') report.errors.push(m.params.exceptionDetails.exception?.description || m.params.exceptionDetails.text);
+  };
+  send = (method, params = {}) => new Promise((resolve, reject) => {
+    const id = ++seq, timer = setTimeout(() => reject(new Error('Timeout ' + method)), 8000);
+    pending.set(id, { resolve, reject, timer }); ws.send(JSON.stringify({ id, method, params }));
+  });
+  const ev = async expression => {
+    const r = await send('Runtime.evaluate', { expression, awaitPromise: true, returnByValue: true });
+    if (r.exceptionDetails) throw new Error(r.exceptionDetails.exception?.description || r.exceptionDetails.text);
+    return r.result.value;
+  };
+  const until = async (expression, tries = 120) => {
+    for (let i = 0; i < tries; i++) { try { if (await ev(expression)) return; } catch { /* navigating */ } await delay(150); }
+    throw new Error('Wait ' + expression);
+  };
+  const check = (name, value) => { assert.ok(value, name); report.checks.push(name); console.log('PASS', name); };
+  const click = expression => ev(`(()=>{const e=${expression};if(!e||e.disabled)throw new Error('Missing target');e.click();})()`);
+  const shot = async name => { await delay(250); const r = await send('Page.captureScreenshot', { format: 'png' }); fs.writeFileSync(path.join(out, name + '.png'), Buffer.from(r.data, 'base64')); };
+  const viewport = (width, height) => send('Emulation.setDeviceMetricsOverride', { width, height, deviceScaleFactor: 1, mobile: false });
+  const rects = ws_ => ev(`(()=>{const w=document.getElementById('${ws_}'),r=e=>{const b=e.getBoundingClientRect();return{l:Math.round(b.left),t:Math.round(b.top),r:Math.round(b.right),b:Math.round(b.bottom),w:Math.round(b.width),h:Math.round(b.height)};};const c=document.querySelector('#viewer-block canvas');return{ws:r(w),slot:r(w.querySelector('.viewer-slot')),split:r(w.querySelector('.workspace-splitter')),pane:r(w.querySelector('.workspace-pane')),canvas:c?r(c):null,side:w.classList.contains('layout-side'),note:w.querySelector('.layout-note').textContent,label:w.querySelector('[data-size-label]').textContent,value:w.querySelector('output').textContent};})()`);
+  const drag = async (sel, dx, dy) => {
+    const b = await ev(`(()=>{const r=document.querySelector('${sel}').getBoundingClientRect();return{x:r.left+r.width/2,y:r.top+r.height/2};})()`);
+    await send('Input.dispatchMouseEvent', { type: 'mousePressed', x: b.x, y: b.y, button: 'left', buttons: 1, clickCount: 1 });
+    for (let i = 1; i <= 5; i++) await send('Input.dispatchMouseEvent', { type: 'mouseMoved', x: b.x + dx * i / 5, y: b.y + dy * i / 5, button: 'left', buttons: 1 });
+    await send('Input.dispatchMouseEvent', { type: 'mouseReleased', x: b.x + dx, y: b.y + dy, button: 'left', buttons: 0, clickCount: 1 });
+    await delay(250);
+  };
+  const key = async (k, code, vk) => { for (const type of ['keyDown', 'keyUp']) await send('Input.dispatchKeyEvent', { type, key: k, code, windowsVirtualKeyCode: vk }); await delay(120); };
+
+  await send('Page.enable'); await send('Runtime.enable'); await send('DOM.enable');
+  await viewport(1600, 1000);
+  await send('Page.navigate', { url: process.env.PIERZAINER_URL || 'http://127.0.0.1:5173/' });
+  await until(`!!document.querySelector('[data-card="excel"] button') && typeof window.loadBytesToApp === 'function'`);
+  await ev(`Object.keys(localStorage).filter(k=>k.startsWith('pierzainer.workspace-layout')||k==='pierzainer.review-layout').forEach(k=>localStorage.removeItem(k))`);
+  await send('Page.reload'); await delay(2500);
+  await until(`!!document.querySelector('[data-card="excel"] button') && typeof window.loadBytesToApp === 'function'`);
+  await click(`document.querySelector('[data-card="excel"] button')`);
+  await ev(`document.getElementById('project-name').value='배치 검증';document.getElementById('project-name').dispatchEvent(new Event('input'));`);
+  const doc = await send('DOM.getDocument');
+  const node = await send('DOM.querySelector', { nodeId: doc.root.nodeId, selector: '#file' });
+  await send('DOM.setFileInputFiles', { nodeId: node.nodeId, files: [path.resolve(root, '../../RAG/운곡교P1입력.xlsx')] });
+  await until(`!document.getElementById('dlg-apply').disabled`);
+  await click(`document.getElementById('dlg-apply')`);
+  await delay(800);
+
+  // ② 계획
+  await click(`document.getElementById('nav-plan')`); await delay(600);
+  let r = await rects('plan-workspace');
+  check('② default is stacked: model above the input pane', !r.side && r.slot.b <= r.pane.t && r.slot.w === r.pane.w);
+  check('② layout switch shows 상하 pressed', await ev(`document.querySelector('#plan-workspace [data-layout="stack"]').getAttribute('aria-pressed')==='true'`));
+  await shot('01-plan-stack');
+  await click(`document.querySelector('#plan-workspace [data-layout="side"]')`); await delay(500);
+  r = await rects('plan-workspace'); report.metrics.planSide = r;
+  check('② 좌우: model left, pane right, same top', r.side && r.slot.r <= r.pane.l && Math.abs(r.slot.t - r.pane.t) <= 1);
+  check('② 좌우 starts near 50 % and shows width label', Math.abs(r.slot.w / r.ws.w - 0.5) < 0.03 && r.label === '모델 폭' && r.value === '50%');
+  check('② 3D canvas follows the narrower slot', r.canvas && r.slot.w - r.canvas.w >= 0 && r.slot.w - r.canvas.w <= 40 && r.canvas.h > 300);
+  check('② pane scrolls independently', await ev(`(()=>{const p=document.querySelector('#plan-workspace .workspace-pane');return getComputedStyle(p).overflowY==='auto';})()`));
+  await shot('02-plan-side');
+  await drag('#plan-workspace .workspace-splitter', -Math.round(r.ws.w * 0.1), 0);
+  r = await rects('plan-workspace');
+  check('② splitter drag narrows model to about 40 %', r.value === '40%' && Math.abs(r.slot.w / r.ws.w - 0.4) < 0.03);
+  await ev(`document.querySelector('#plan-workspace .workspace-splitter').focus()`);
+  await key('ArrowRight', 'ArrowRight', 39);
+  check('② splitter keyboard step (+2 %)', (await rects('plan-workspace')).value === '42%' && await ev(`document.querySelector('#plan-workspace .workspace-splitter').getAttribute('aria-valuenow')==='42'`));
+  await send('Input.dispatchMouseEvent', { type: 'mousePressed', x: r.split.l + 6, y: r.split.t + 100, button: 'left', clickCount: 2 });
+  await send('Input.dispatchMouseEvent', { type: 'mouseReleased', x: r.split.l + 6, y: r.split.t + 100, button: 'left', clickCount: 2 });
+  await ev(`document.querySelector('#plan-workspace .workspace-splitter').dispatchEvent(new MouseEvent('dblclick',{bubbles:true}))`); await delay(200);
+  check('② double-click resets to 50 %', (await rects('plan-workspace')).value === '50%');
+  await click(`document.getElementById('plan-model-toggle')`); await delay(300);
+  r = await rects('plan-workspace');
+  check('② collapsed model: pane takes the full width', r.slot.w === 0 && Math.abs(r.pane.w - r.ws.w) <= 2);
+  await click(`document.getElementById('plan-model-toggle')`); await delay(300);
+
+  // ③ 배근 stays independent
+  await click(`document.getElementById('nav-rebar')`); await delay(700);
+  r = await rects('review-workspace');
+  check('③ preference is independent of ② (still stacked, 240 px)', !r.side && r.value === '240 px' && r.slot.b <= r.pane.t);
+  await drag('#review-workspace .workspace-splitter', 0, 100);
+  r = await rects('review-workspace');
+  check('③ stacked splitter drag grows model height', r.value === '340 px' && Math.abs(r.slot.h - 340) <= 2);
+  await click(`document.querySelector('#review-workspace [data-layout="side"]')`); await delay(500);
+  r = await rects('review-workspace'); report.metrics.rebarSide = r;
+  check('③ 좌우: model left, rebar table right', r.side && r.slot.r <= r.pane.l && r.canvas && r.slot.w - r.canvas.w >= 0 && r.slot.w - r.canvas.w <= 40);
+  await click(`document.getElementById('review-table')`); await delay(300);
+  check('③ 철근표 shortcut still reveals the table in 좌우', await ev(`(()=>{const t=document.activeElement,p=document.querySelector('#review-workspace .workspace-pane > section').getBoundingClientRect();return t.matches('#rebar-table table.rebar-table')&&t.getBoundingClientRect().top>=p.top-2;})()`));
+  await shot('03-rebar-side');
+
+  // persistence
+  await send('Page.reload'); await delay(2500); await until(`typeof window.loadBytesToApp==='function'`); await delay(800);
+  check('preferences persist per stage after reload', await ev(`(()=>{const p=JSON.parse(localStorage.getItem('pierzainer.workspace-layout.plan')),q=JSON.parse(localStorage.getItem('pierzainer.workspace-layout.rebar'));return p.mode==='side'&&p.width===50&&q.mode==='side'&&q.height===340;})()`));
+  await until(`typeof window.openSampleProject==='function'`); await ev('window.openSampleProject()'); await delay(1500);
+  await click(`document.getElementById('nav-plan')`); await delay(600);
+  check('② restored 좌우 when shown after reload', await ev(`document.getElementById('plan-workspace').classList.contains('layout-side')`));
+  await click(`document.getElementById('nav-rebar')`); await delay(600);
+  check('③ restored 좌우 and 340 px height after reload', await ev(`document.getElementById('review-workspace').classList.contains('layout-side')&&getComputedStyle(document.getElementById('review-workspace')).getPropertyValue('--review-model-height').trim()==='340px'`));
+  await click(`document.getElementById('nav-plan')`); await delay(400);
+
+  // width fallback
+  await viewport(1280, 800); await delay(500);
+  check('1280 px: side request falls back to stacked with a note', await ev(`(()=>{const w=document.getElementById('plan-workspace');return !w.classList.contains('layout-side')&&w.querySelector('.layout-note').textContent.includes('좁아')&&w.querySelector('[data-layout="side"]').getAttribute('aria-pressed')==='true';})()`));
+  await viewport(1920, 1080); await delay(500);
+  check('1920 px: side-by-side restored automatically', await ev(`document.getElementById('plan-workspace').classList.contains('layout-side')`));
+  await viewport(1000, 900); await delay(500);
+  check('1000 px (mobile frame): stacked, splitter hidden', await ev(`(()=>{const w=document.getElementById('plan-workspace');return !w.classList.contains('layout-side')&&getComputedStyle(w.querySelector('.workspace-splitter')).display==='none';})()`));
+  for (const width of [1280, 1600, 1920]) {
+    await viewport(width, 1000); await delay(300);
+    check(`${width} px: no horizontal page scroll`, await ev(`document.documentElement.scrollWidth<=innerWidth`));
+  }
+  check('no runtime exceptions', report.errors.length === 0);
+  report.result = 'PASS';
+})().catch(e => { report.result = 'FAIL'; report.failure = e.stack; process.exitCode = 1; }).finally(() => {
+  fs.writeFileSync(path.join(out, 'report.json'), JSON.stringify(report, null, 2));
+  console.log(JSON.stringify({ result: report.result, failure: report.failure, errors: report.errors }));
+  if (target?.id) fetch('http://127.0.0.1:9444/json/close/' + target.id).catch(() => {});
+  ws?.close();
+});
diff --git a/src/main.ts b/src/main.ts
index 9f706c5..6579133 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -145,6 +145,7 @@ import type { Issue, PierInput, PierType, StrataRow } from './core/types';
 import { buildPierScene, setRebarView, setRebarViewOn, viewPosition, type PartName, type PierScene, type ViewKind } from './view/scene';
 import { buildAllPiers, type AllPiers } from './view/all-piers';
 import { buildTerrainMapGroup, disposeTerrainMapGroup, setTerrainMapMode } from './view/terrain-map';
+import { initWorkspaceLayout } from './view/workspace-layout';
 
 /** One pier as shown in the list. `checked` is the multi-select state (시안 ①). */
 interface Pier extends PierValues {
@@ -6383,28 +6384,10 @@ function restorePanel(id: string): void {
 restorePanel('parts-info');
 restorePanel('color-info');
 
-/** Viewer sizing is a local display preference, separate from project/design data. */
+/** Viewer sizing/arrangement is a local display preference, separate from project/design data. */
 function initReviewWorkspace(): void {
-  const workspace = $('review-workspace');
-  const slider = $<HTMLInputElement>('review-model-height');
-  const toggle = $<HTMLButtonElement>('review-model-toggle');
-  let collapsed = false;
-  try {
-    const saved = JSON.parse(localStorage.getItem('pierzainer.review-layout') ?? 'null');
-    if (saved && Number.isFinite(saved.height) && saved.height >= 180 && saved.height <= 560) slider.value = String(saved.height);
-    collapsed = saved?.collapsed === true;
-  } catch { /* A blocked store must not prevent resizing. */ }
-  const apply = () => {
-    workspace.style.setProperty('--review-model-height', `${slider.value}px`);
-    workspace.classList.toggle('model-collapsed', collapsed);
-    $('review-model-height-value').textContent = `${slider.value} px`;
-    toggle.textContent = collapsed ? '모델 펼치기' : '모델 접기';
-    toggle.setAttribute('aria-expanded', String(!collapsed));
-    slider.disabled = collapsed;
-    try { localStorage.setItem('pierzainer.review-layout', JSON.stringify({ height: Number(slider.value), collapsed })); } catch { /* Display preference only. */ }
-  };
-  slider.addEventListener('input', apply);
-  toggle.addEventListener('click', () => { collapsed = !collapsed; apply(); });
+  initWorkspaceLayout($('plan-workspace'));
+  initWorkspaceLayout($('review-workspace'));
   const jump = (selector: string) => {
     const node = document.querySelector<HTMLElement>(selector);
     if (!node) return;
@@ -6414,18 +6397,6 @@ function initReviewWorkspace(): void {
   };
   $('review-inputs').addEventListener('click', () => jump('#rebar-table .abut-rebar-inputs input, #rebar-table input[type="number"], #rebar-table select'));
   $('review-table').addEventListener('click', () => jump('#rebar-table table.rebar-table'));
-  apply();
-  new ResizeObserver(() => {
-    if (workspace.clientHeight === 0 || !window.matchMedia('(min-width: 1101px)').matches) return;
-    const available = workspace.clientHeight - workspace.querySelector<HTMLElement>('.workspace-tools')!.offsetHeight - 264;
-    const max = Math.max(180, Math.min(560, Math.floor(available / 20) * 20));
-    const next = Math.min(Number(slider.value), max);
-    if (slider.max !== String(max) || slider.value !== String(next)) {
-      slider.max = String(max);
-      slider.value = String(next);
-      apply();
-    }
-  }).observe(workspace);
 }
 initReviewWorkspace();
 
diff --git a/src/style.css b/src/style.css
index 7f6e11f..b367ea1 100644
--- a/src/style.css
+++ b/src/style.css
@@ -776,8 +776,21 @@ body { background: #eef1f4; font-family: 'Noto Sans KR', system-ui, sans-serif;
   .grid > #viewer-block .canvas { flex: 1 1 auto; height: auto; min-height: 240px; }
   /* ②–④: the model keeps a fixed band at the top; the table scrolls below it. */
   .center-col { display: grid; grid-template-rows: clamp(280px, 48vh, 560px) minmax(0, 1fr); gap: 12px; }
-  .review-workspace { grid-template-rows: auto minmax(180px, var(--review-model-height, 240px)) minmax(0, 1fr); }
-  .review-workspace.model-collapsed { grid-template-rows: auto minmax(0, 1fr); }
+  /* ②·③ workspace: tools / model / splitter / pane (상하) or model | splitter | pane (좌우). */
+  .workspace { grid-template-columns: minmax(0, 1fr); grid-template-rows: auto minmax(180px, var(--review-model-height, clamp(280px, 48vh, 560px))) 12px minmax(0, 1fr); gap: 0; }
+  .workspace > .workspace-tools { margin-bottom: 8px; }
+  .workspace.model-collapsed { grid-template-rows: auto minmax(0, 1fr); }
+  .workspace.layout-side { grid-template-columns: minmax(0, var(--model-width, 50%)) 12px minmax(0, 1fr); grid-template-rows: auto minmax(0, 1fr); }
+  .workspace.layout-side > .workspace-tools { grid-column: 1 / -1; }
+  .workspace.layout-side > .viewer-slot { grid-column: 1; grid-row: 2; }
+  .workspace.layout-side > .workspace-splitter { grid-column: 2; grid-row: 2; }
+  .workspace.layout-side > .workspace-pane { grid-column: 3; grid-row: 2; }
+  .workspace.layout-side.model-collapsed { grid-template-columns: minmax(0, 1fr); }
+  .workspace.layout-side.model-collapsed > .workspace-pane { grid-column: 1 / -1; }
+  .workspace-pane { min-height: 0; overflow: auto; display: flex; flex-direction: column; gap: 12px; }
+  .workspace-pane > .viewer { flex: none; }
+  .review-workspace > .workspace-pane { overflow: hidden; }
+  .review-workspace > .workspace-pane > .viewer { flex: 1 1 auto; min-height: 0; overflow: auto; }
   .viewer-slot { min-height: 0; height: 100%; display: flex; flex-direction: column; }
   .viewer-slot > .viewer { flex: 1 1 auto; min-height: 0; display: flex; flex-direction: column; }
   .viewer-slot .canvas { flex: 1 1 auto; height: auto; min-height: 180px; }
@@ -793,11 +806,28 @@ body { background: #eef1f4; font-family: 'Noto Sans KR', system-ui, sans-serif;
   .viewer-slot .canvas { height: 60vh; min-height: 420px; flex: none; }
   .grid > .review-workspace { max-height: none; }
   .review-workspace .viewer-slot .canvas { height: var(--review-model-height, 240px); min-height: 180px; }
-  .review-workspace > .viewer { max-height: 75vh; overflow: auto; }
+  .review-workspace .workspace-pane > .viewer { max-height: 75vh; overflow: auto; }
+  .workspace-pane { display: flex; flex-direction: column; gap: 16px; }
+  .workspace-splitter { display: none; }
   .rebar-table thead th { position: sticky; top: 0; background: #ffffff; z-index: 1; }
 }
 
-.review-workspace.model-collapsed #slot-rebar { display: none; }
+.workspace.model-collapsed > .viewer-slot, .workspace.model-collapsed > .workspace-splitter { display: none; }
+
+/* ②·③ 배치 전환 · 분할선 (2026-11-09) */
+.layout-switch { display: inline-flex; border: 1px solid var(--line, #d5dde6); border-radius: 8px; overflow: hidden; }
+.layout-switch .btn { border: 0; border-radius: 0; min-width: 52px; }
+.layout-switch .btn + .btn { border-left: 1px solid var(--line, #d5dde6); }
+.layout-switch .btn[aria-pressed="true"] { background: #e8f1fb; color: #0b4f8a; font-weight: 700; }
+.layout-note:empty { display: none; }
+.workspace-splitter { position: relative; cursor: row-resize; touch-action: none; border-radius: 6px; outline: none; }
+.workspace-splitter::after { content: ""; position: absolute; left: 50%; top: 50%; width: 48px; height: 4px; transform: translate(-50%, -50%); border-radius: 2px; background: #c3cfdb; transition: background .15s; }
+.workspace.layout-side > .workspace-splitter { cursor: col-resize; }
+.workspace.layout-side > .workspace-splitter::after { width: 4px; height: 48px; }
+.workspace-splitter:hover::after, .workspace.is-resizing > .workspace-splitter::after { background: #2f7bc0; }
+.workspace-splitter:focus-visible { box-shadow: inset 0 0 0 2px #2f7bc0; }
+.workspace.is-resizing { user-select: none; cursor: row-resize; }
+.workspace.layout-side.is-resizing { cursor: col-resize; }
 
 /* 3D 영역 (승인 2026-10-23): 제목은 교각 목록으로. 좌측 스택(부재 표시 · 시점), 우측 스택(색 기준 · 원점)을 캔버스 위에 둠. */
 #viewer-block { position: relative; }
diff --git a/src/view/workspace-layout.ts b/src/view/workspace-layout.ts
new file mode 100644
index 0000000..aac3607
--- /dev/null
+++ b/src/view/workspace-layout.ts
@@ -0,0 +1,163 @@
+/**
+ * ②·③ center workspace layout: model above the pane (stack) or beside it (side),
+ * with a draggable / keyboard splitter. A per-stage display preference kept in
+ * localStorage only — never part of the project file.
+ */
+export type WorkspaceMode = 'stack' | 'side';
+export interface WorkspaceLayout { mode: WorkspaceMode; height: number | null; width: number; collapsed: boolean }
+
+export const HEIGHT_MIN = 180, HEIGHT_MAX = 560, HEIGHT_STEP = 20;
+export const WIDTH_MIN = 30, WIDTH_MAX = 70, WIDTH_STEP = 2, WIDTH_DEFAULT = 50;
+/** Below this center-column width each side-by-side pane would be under ~440 px. */
+export const SIDE_MIN_WIDTH = 900;
+const DESKTOP = '(min-width: 1101px)';
+
+const clamp = (v: number, lo: number, hi: number) => Math.min(hi, Math.max(lo, v));
+const snap = (v: number, step: number) => Math.round(v / step) * step;
+
+export function defaultLayout(stage: string): WorkspaceLayout {
+  return { mode: 'stack', height: stage === 'rebar' ? 240 : null, width: WIDTH_DEFAULT, collapsed: false };
+}
+
+/** Parse a stored value defensively; the old ③ key `pierzainer.review-layout` held {height, collapsed}. */
+export function parseLayout(stage: string, raw: unknown): WorkspaceLayout {
+  const base = defaultLayout(stage);
+  if (!raw || typeof raw !== 'object') return base;
+  const v = raw as Record<string, unknown>;
+  const height = typeof v.height === 'number' && Number.isFinite(v.height) && v.height >= HEIGHT_MIN && v.height <= HEIGHT_MAX ? v.height : base.height;
+  const width = typeof v.width === 'number' && Number.isFinite(v.width) ? clamp(v.width, WIDTH_MIN, WIDTH_MAX) : base.width;
+  return { mode: v.mode === 'side' ? 'side' : 'stack', height, width, collapsed: v.collapsed === true };
+}
+
+/** Side-by-side applies only when the user chose it and the column is wide enough on a desktop frame. */
+export function effectiveMode(layout: WorkspaceLayout, columnWidth: number, desktop: boolean): { mode: WorkspaceMode; forced: boolean } {
+  if (layout.mode === 'side' && (!desktop || columnWidth < SIDE_MIN_WIDTH)) return { mode: 'stack', forced: true };
+  return { mode: layout.mode, forced: false };
+}
+
+const storageKey = (stage: string) => `pierzainer.workspace-layout.${stage}`;
+
+function load(stage: string): WorkspaceLayout {
+  try {
+    const saved = localStorage.getItem(storageKey(stage));
+    if (saved) return parseLayout(stage, JSON.parse(saved));
+    if (stage === 'rebar') return parseLayout(stage, JSON.parse(localStorage.getItem('pierzainer.review-layout') ?? 'null'));
+  } catch { /* A blocked or corrupt store falls back to defaults. */ }
+  return defaultLayout(stage);
+}
+
+export function initWorkspaceLayout(workspace: HTMLElement): void {
+  const stage = workspace.dataset.stage ?? 'plan';
+  const tools = workspace.querySelector<HTMLElement>('.workspace-tools')!;
+  const slot = workspace.querySelector<HTMLElement>('.viewer-slot')!;
+  const splitter = workspace.querySelector<HTMLElement>('.workspace-splitter')!;
+  const slider = tools.querySelector<HTMLInputElement>('input[type="range"]')!;
+  const output = tools.querySelector<HTMLOutputElement>('output')!;
+  const sizeLabel = tools.querySelector<HTMLElement>('[data-size-label]')!;
+  const toggle = tools.querySelector<HTMLButtonElement>('button[aria-controls]')!;
+  const note = tools.querySelector<HTMLElement>('.layout-note')!;
+  const modeButtons = Array.from(tools.querySelectorAll<HTMLButtonElement>('[data-layout]'));
+  const layout = load(stage);
+  let heightMax = HEIGHT_MAX;
+  let current: WorkspaceMode = 'stack';
+
+  const save = () => { try { localStorage.setItem(storageKey(stage), JSON.stringify(layout)); } catch { /* Display preference only. */ } };
+  /** Without a saved height ② keeps its original responsive band; show what is on screen. */
+  const shownHeight = () => layout.height ?? clamp(snap(slot.getBoundingClientRect().height || 400, HEIGHT_STEP), HEIGHT_MIN, heightMax);
+
+  const apply = () => {
+    const desktop = window.matchMedia(DESKTOP).matches;
+    const { mode, forced } = effectiveMode(layout, workspace.clientWidth, desktop);
+    current = mode;
+    workspace.classList.toggle('layout-side', mode === 'side');
+    workspace.classList.toggle('model-collapsed', layout.collapsed);
+    if (layout.height == null) workspace.style.removeProperty('--review-model-height');
+    else workspace.style.setProperty('--review-model-height', `${Math.min(layout.height, heightMax)}px`);
+    workspace.style.setProperty('--model-width', `${layout.width}%`);
+    for (const b of modeButtons) b.setAttribute('aria-pressed', String(b.dataset.layout === layout.mode));
+    note.textContent = forced ? (desktop ? '화면이 좁아 상하로 표시 중' : '좁은 화면은 상하로 표시') : '';
+    toggle.textContent = layout.collapsed ? '모델 펼치기' : '모델 접기';
+    toggle.setAttribute('aria-expanded', String(!layout.collapsed));
+    const side = mode === 'side';
+    sizeLabel.textContent = side ? '모델 폭' : '모델 높이';
+    slider.min = String(side ? WIDTH_MIN : HEIGHT_MIN);
+    slider.max = String(side ? WIDTH_MAX : heightMax);
+    slider.step = String(side ? WIDTH_STEP : HEIGHT_STEP);
+    const value = side ? layout.width : Math.min(shownHeight(), heightMax);
+    slider.value = String(value);
+    output.textContent = side ? `${value}%` : `${value} px`;
+    slider.disabled = layout.collapsed;
+    splitter.hidden = layout.collapsed;
+    splitter.setAttribute('aria-orientation', side ? 'vertical' : 'horizontal');
+    splitter.setAttribute('aria-valuemin', slider.min);
+    splitter.setAttribute('aria-valuemax', slider.max);
+    splitter.setAttribute('aria-valuenow', String(value));
+    splitter.setAttribute('aria-valuetext', output.textContent);
+    splitter.title = side ? '끌어서 모델 폭 조절 · 두 번 클릭하면 기본값' : '끌어서 모델 높이 조절 · 두 번 클릭하면 기본값';
+  };
+  const setSize = (value: number) => {
+    if (current === 'side') layout.width = clamp(snap(value, WIDTH_STEP), WIDTH_MIN, WIDTH_MAX);
+    else layout.height = clamp(snap(value, HEIGHT_STEP), HEIGHT_MIN, heightMax);
+    apply(); save();
+  };
+
+  for (const b of modeButtons) b.addEventListener('click', () => { layout.mode = b.dataset.layout === 'side' ? 'side' : 'stack'; apply(); save(); });
+  slider.addEventListener('input', () => setSize(Number(slider.value)));
+  toggle.addEventListener('click', () => { layout.collapsed = !layout.collapsed; apply(); save(); });
+
+  splitter.addEventListener('pointerdown', (event) => {
+    if (event.button !== 0) return;
+    event.preventDefault();
+    splitter.setPointerCapture(event.pointerId);
+    workspace.classList.add('is-resizing');
+    const move = (e: PointerEvent) => {
+      if (current === 'side') {
+        const r = workspace.getBoundingClientRect();
+        setSize(((e.clientX - r.left) / r.width) * 100);
+      } else {
+        setSize(e.clientY - slot.getBoundingClientRect().top);
+      }
+    };
+    const end = () => {
+      workspace.classList.remove('is-resizing');
+      splitter.removeEventListener('pointermove', move);
+      splitter.removeEventListener('pointerup', end);
+      splitter.removeEventListener('pointercancel', end);
+    };
+    splitter.addEventListener('pointermove', move);
+    splitter.addEventListener('pointerup', end);
+    splitter.addEventListener('pointercancel', end);
+  });
+  splitter.addEventListener('keydown', (event) => {
+    const side = current === 'side';
+    const step = side ? WIDTH_STEP : HEIGHT_STEP;
+    const now = side ? layout.width : shownHeight();
+    const grow = side ? ['ArrowRight', 'ArrowDown'] : ['ArrowDown', 'ArrowRight'];
+    const shrink = side ? ['ArrowLeft', 'ArrowUp'] : ['ArrowUp', 'ArrowLeft'];
+    let next: number | null = null;
+    if (grow.includes(event.key)) next = now + step * (event.shiftKey ? 5 : 1);
+    else if (shrink.includes(event.key)) next = now - step * (event.shiftKey ? 5 : 1);
+    else if (event.key === 'Home') next = side ? WIDTH_MIN : HEIGHT_MIN;
+    else if (event.key === 'End') next = side ? WIDTH_MAX : heightMax;
+    if (next == null) return;
+    event.preventDefault();
+    setSize(next);
+  });
+  splitter.addEventListener('dblclick', () => {
+    if (current === 'side') layout.width = WIDTH_DEFAULT;
+    else layout.height = defaultLayout(stage).height;
+    apply(); save();
+  });
+
+  // Keep the stacked model band within the visible column and re-evaluate the side-by-side width rule.
+  new ResizeObserver(() => {
+    if (workspace.clientHeight === 0) return;
+    if (window.matchMedia(DESKTOP).matches) {
+      const available = workspace.clientHeight - tools.offsetHeight - 264;
+      heightMax = Math.max(HEIGHT_MIN, Math.min(HEIGHT_MAX, Math.floor(available / HEIGHT_STEP) * HEIGHT_STEP));
+    } else heightMax = HEIGHT_MAX;
+    apply();
+  }).observe(workspace);
+  window.matchMedia(DESKTOP).addEventListener('change', apply);
+  apply();
+}
diff --git a/tests/workspace-layout.test.ts b/tests/workspace-layout.test.ts
new file mode 100644
index 0000000..3b8ba05
--- /dev/null
+++ b/tests/workspace-layout.test.ts
@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { defaultLayout, effectiveMode, parseLayout, SIDE_MIN_WIDTH } from '../src/view/workspace-layout';
+
+describe('workspace layout preference', () => {
+  it('defaults: stacked, ③ model 240 px, ② keeps its responsive band', () => {
+    expect(defaultLayout('rebar')).toEqual({ mode: 'stack', height: 240, width: 50, collapsed: false });
+    expect(defaultLayout('plan').height).toBeNull();
+  });
+  it('migrates the old ③ {height, collapsed} value', () => {
+    expect(parseLayout('rebar', { height: 360, collapsed: true })).toEqual({ mode: 'stack', height: 360, width: 50, collapsed: true });
+  });
+  it('rejects out-of-range or corrupt values', () => {
+    expect(parseLayout('rebar', { mode: 'grid', height: 9999, width: 95 })).toEqual({ mode: 'stack', height: 240, width: 70, collapsed: false });
+    expect(parseLayout('plan', 'x')).toEqual(defaultLayout('plan'));
+  });
+  it('side-by-side only on a wide desktop column, otherwise stacked and marked forced', () => {
+    const side = { ...defaultLayout('plan'), mode: 'side' as const };
+    expect(effectiveMode(side, SIDE_MIN_WIDTH, true)).toEqual({ mode: 'side', forced: false });
+    expect(effectiveMode(side, SIDE_MIN_WIDTH - 1, true)).toEqual({ mode: 'stack', forced: true });
+    expect(effectiveMode(side, 1400, false)).toEqual({ mode: 'stack', forced: true });
+    expect(effectiveMode(defaultLayout('plan'), 400, true)).toEqual({ mode: 'stack', forced: false });
+  });
+});