diff --git a/content-editor.js b/content-editor.js
index 1db5b97..6f0e16c 100644
--- a/content-editor.js
+++ b/content-editor.js
@@ -274,6 +274,18 @@ const server = http.createServer(async (req, res) => {
           return;
         }
         const data = JSON.parse(body);
+        // Optimistic locking: the editor echoes the fingerprint of the content it
+        // loaded. If the file changed since (deploy, another tab, git), a blind
+        // save would silently overwrite those changes — reject with 409 instead.
+        const clientHash = req.headers['x-content-hash'];
+        const currentOnDisk = fs.readFileSync(FILES[activeFile], 'utf8').trim();
+        const currentHash = crypto.createHash('sha256').update(currentOnDisk).digest('hex');
+        if (typeof clientHash !== 'string' || clientHash !== currentHash) {
+          writeAudit('content_saved', { clientAddress, user: CMS_USER, file: activeFile, result: 'conflict' });
+          res.writeHead(409, { 'Content-Type': 'application/json' });
+          res.end(JSON.stringify({ ok: false, error: 'A tartalom megváltozott, mióta ezt a lapot megnyitottad (pl. deploy vagy másik fül mentett). Frissítsd az oldalt, és végezd el újra a módosításokat.' }));
+          return;
+        }
         const validation = validateContent(activeFile, data);
         if (!validation.ok) {
           writeAudit('content_saved', { clientAddress, user: CMS_USER, file: activeFile, result: 'validation_failed' });
@@ -335,9 +347,14 @@ const server = http.createServer(async (req, res) => {
   } catch (e) {
     message = { type: 'err', text: 'Fájl olvasási hiba: ' + e.message };
   }
+  // WHY: fingerprint of the file content at page load. The editor sends it back
+  // on save (X-Content-Hash); a mismatch means the file changed since this tab
+  // was opened (deploy, another tab, git) and a blind save would silently
+  // overwrite those changes.
+  const contentHash = crypto.createHash('sha256').update(jsonData).digest('hex');
 
   res.writeHead(200, { 'Content-Type': 'text/html; charset=utf-8' });
-  res.end(HTML(activeFile, jsonData, message, CSRF_TOKEN, FILE_LABELS, clientJs));
+  res.end(HTML(activeFile, jsonData, message, CSRF_TOKEN, FILE_LABELS, clientJs, contentHash));
 });
 
 if (require.main === module) {
diff --git a/docs/felhasznaloi-utmutato.md b/docs/felhasznaloi-utmutato.md
index b013ea4..a234c83 100644
--- a/docs/felhasznaloi-utmutato.md
+++ b/docs/felhasznaloi-utmutato.md
@@ -65,6 +65,7 @@ A dokumentum a repó része, és **folyamatosan karbantartott**: minden funkció
 ### 💾 Mentés
 
 - A Mentés **ellenőrzi a tartalmat**: hiányzó vagy rossz típusú mező esetén hibaüzenetet kapsz, és a mentés nem történik meg — az oldal így nem tud elromlani.
+- **Ha a tartalom megváltozott, mióta a lapot megnyitottad** (pl. közben deploy történt vagy egy másik fülben mentett valaki), a Mentés figyelmeztet: ilyenkor döntsd el, hogy frissíted a lapot az új tartalomra (a szerkesztésed elvész), vagy megszakítod. Ezzel a védelemmel nem írható véletlenül felül senki módosítása.
 - Minden sikeres mentés **biztonsági mentést** készít a szerveren (`.content-backups/`), és naplózza a műveletet.
 - Ha a Mentés sikeres, a mentett állapotot **Előnézet** gombbal nézheted meg a staging oldalon.
 
diff --git a/scripts/cms-editor-client.js b/scripts/cms-editor-client.js
index 8aed686..22c53ea 100644
--- a/scripts/cms-editor-client.js
+++ b/scripts/cms-editor-client.js
@@ -233,10 +233,16 @@ async function save() {
   const data = collect();
   const res = await fetch('/save?file=' + FILE, {
     method: 'POST',
-    headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': CSRF_TOKEN },
+    headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': CSRF_TOKEN, 'X-Content-Hash': CONTENT_HASH },
     body: JSON.stringify(data, null, 2)
   });
   if (res.status === 401) { location.href = '/login'; return; }
+  if (res.status === 409) {
+    if (confirm('A tartalom megváltozott, mióta ez a lap megnyílt (pl. deploy vagy másik fül mentett).\n\nOK = lap frissítése az új tartalommal (a szerkesztésed elvész)\nMégse = maradsz ezen a lapon, a mentés nem történt meg.')) {
+      location.reload();
+    }
+    return;
+  }
   const json = await res.json();
   const status = document.getElementById('saveStatus');
   if (json.ok) {
diff --git a/scripts/cms-pages.js b/scripts/cms-pages.js
index 090e0ed..7c06642 100644
--- a/scripts/cms-pages.js
+++ b/scripts/cms-pages.js
@@ -4,7 +4,7 @@
 const isStaging = () => process.env.CMS_DEPLOY_ENV === 'staging';
 
 // FILE_LABELS is injected to avoid a circular dependency with the main file.
-const HTML = (activeFile, jsonData, message, csrfToken, fileLabels, clientJs) => `<!DOCTYPE html>
+const HTML = (activeFile, jsonData, message, csrfToken, fileLabels, clientJs, contentHash) => `<!DOCTYPE html>
 <html lang="hu">
 <head>
   <meta charset="UTF-8">
@@ -120,6 +120,7 @@ ${message ? `<div class="toast ${message.type === 'ok' ? 'ok' : 'err'}">${messag
 const DATA = JSON.parse(document.getElementById('page-data').textContent);
 const FILE = "${activeFile}";
 const CSRF_TOKEN = "${csrfToken}";
+const CONTENT_HASH = "${contentHash}";
 
 ${clientJs}
 </script>
diff --git a/scripts/test-content-editor-conflict.js b/scripts/test-content-editor-conflict.js
new file mode 100644
index 0000000..32a8b08
--- /dev/null
+++ b/scripts/test-content-editor-conflict.js
@@ -0,0 +1,127 @@
+#!/usr/bin/env node
+
+/**
+ * Integration test for optimistic locking on CMS save (MITHOME-61):
+ *   1. save with the correct X-Content-Hash → 200
+ *   2. save with a stale hash (file changed on disk meanwhile) → 409, file untouched
+ *   3. save without any hash header → 409 (strict: must always send the fingerprint)
+ *   4. a follow-up save with the NEW hash succeeds → the editor can continue after refresh
+ */
+const assert = require('assert/strict');
+const crypto = require('crypto');
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const { spawn } = require('child_process');
+
+const ROOT = path.join(__dirname, '..');
+const PORT = 4128;
+const BASE = `http://127.0.0.1:${PORT}`;
+
+const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'cms-conflict-'));
+const auditFile = path.join(tmp, 'audit.jsonl');
+
+const child = spawn('node', ['content-editor.js'], {
+  cwd: ROOT,
+  env: {
+    ...process.env,
+    CONTENT_EDITOR_PORT: String(PORT),
+    CONTENT_EDITOR_AUDIT_FILE: auditFile,
+    CMS_USER: 'conflict-test-user',
+    CMS_PASS: 'conflict-test-pass',
+    CMS_DEPLOY_ENV: 'staging',
+  },
+  stdio: 'ignore',
+});
+
+async function waitForServer(timeoutMs = 10000) {
+  const deadline = Date.now() + timeoutMs;
+  while (Date.now() < deadline) {
+    try {
+      await fetch(`${BASE}/logout`);
+      return;
+    } catch {
+      await new Promise(r => setTimeout(r, 200));
+    }
+  }
+  throw new Error('server did not start');
+}
+
+const hashOf = s => crypto.createHash('sha256').update(s.trim()).digest('hex');
+
+async function call(method, pathName, { body, headers } = {}) {
+  const login = await fetch(`${BASE}/login`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ user: 'conflict-test-user', pass: 'conflict-test-pass' }),
+  });
+  const cookie = (login.headers.get('set-cookie') || '').split(';')[0];
+  if (method === 'GET') {
+    return fetch(`${BASE}${pathName}`, { headers: { Cookie: cookie, ...headers } });
+  }
+  const page = await (await fetch(`${BASE}${pathName.split('?')[0] || '/'}?file=contact`, { headers: { Cookie: cookie } })).text();
+  const csrf = page.match(/CSRF_TOKEN = "([a-f0-9]+)"/)[1];
+  return fetch(`${BASE}${pathName}`, { method, headers: { Cookie: cookie, 'X-CSRF-Token': csrf, ...headers }, body });
+}
+
+async function main() {
+  await waitForServer();
+  const contentFile = path.join(ROOT, 'proto', 'src', 'content', 'pages', 'contact.json');
+
+  // Baseline: read the page and capture the served fingerprint
+  const page = await (await call('GET', '/?file=contact')).text();
+  const servedHash = page.match(/const CONTENT_HASH = "([a-f0-9]+)"/)[1];
+  const diskBefore = fs.readFileSync(contentFile, 'utf8');
+  assert.equal(servedHash, hashOf(diskBefore), 'served fingerprint matches the file on disk');
+
+  const payload = diskBefore; // unchanged content is still a valid save payload
+  const jsonHeaders = { 'Content-Type': 'application/json' };
+
+  // 1. correct hash → 200
+  const ok = await call('POST', '/save?file=contact', {
+    headers: { ...jsonHeaders, 'X-Content-Hash': servedHash },
+    body: payload,
+  });
+  assert.equal(ok.status, 200);
+
+  // 2. stale hash: simulate the file changing on disk (deploy/other tab)
+  const savedContact = fs.readFileSync(contentFile, 'utf8'); // keep the exact bytes
+  try {
+    fs.writeFileSync(contentFile, diskBefore.replace('"responseTime"', '"responseTime" /*changed*/'));
+    const stale = await call('POST', '/save?file=contact', {
+      headers: { ...jsonHeaders, 'X-Content-Hash': servedHash },
+      body: payload,
+    });
+    assert.equal(stale.status, 409);
+    const body = await stale.json();
+    assert.match(body.error, /megváltozott/);
+    // file untouched by the rejected save (still the "changed" variant)
+    assert.ok(fs.readFileSync(contentFile, 'utf8').includes('/*changed*/'));
+  } finally {
+    fs.writeFileSync(contentFile, savedContact); // restore
+  }
+
+  // 3. missing hash → 409 (strict)
+  const noHash = await call('POST', '/save?file=contact', {
+    headers: jsonHeaders,
+    body: payload,
+  });
+  assert.equal(noHash.status, 409);
+
+  // 4. save with the fresh hash of the restored file succeeds
+  const freshHash = hashOf(fs.readFileSync(contentFile, 'utf8'));
+  const retry = await call('POST', '/save?file=contact', {
+    headers: { ...jsonHeaders, 'X-Content-Hash': freshHash },
+    body: payload,
+  });
+  assert.equal(retry.status, 200);
+
+  console.log('Content Editor optimistic-lock test: OK');
+}
+
+main()
+  .catch(err => { console.error('❌', err.message); process.exitCode = 1; })
+  .finally(() => {
+    child.kill('SIGTERM');
+    try { fs.rmSync(tmp, { recursive: true, force: true }); } catch { /* best effort */ }
+  });
diff --git a/scripts/test-content-editor-serializer.js b/scripts/test-content-editor-serializer.js
index 11a1e94..0aa839e 100644
--- a/scripts/test-content-editor-serializer.js
+++ b/scripts/test-content-editor-serializer.js
@@ -25,7 +25,8 @@ const fixture = {
   sections: [{ id: 'first', items: ['egy', 'kettő'], settings: { visible: false, weight: 1 } }],
 };
 const clientJs = fs.readFileSync('scripts/cms-editor-client.js', 'utf8');
-const html = serverContext.globalThis.renderContentEditor('home', JSON.stringify(fixture), null, 'csrf-test-token', { common: '⚙️ Közös' }, clientJs);
+const html = serverContext.globalThis.renderContentEditor('home', JSON.stringify(fixture), null, 'csrf-test-token', { common: '⚙️ Közös' }, clientJs, 'hash-test-value');
+assert.ok(html.includes('const CONTENT_HASH = "hash-test-value"'));
 const browserSource = [...html.matchAll(/<script(?: [^>]*)?>([\s\S]*?)<\/script>/g)].at(-1)[1]
   .replace("render(DATA, document.getElementById('editor'));", '')
   .replace("const toast = document.querySelector('.toast');", 'const toast = null;');