diff --git a/server/server.js b/server/server.js
index c260dac..107e284 100755
--- a/server/server.js
+++ b/server/server.js
@@ -346,64 +346,84 @@ const PYTHON_BIN     = process.env.PYTHON_BIN     || 'python3';
 const calibScriptPath = path.join(__dirname, '..', 'scripts', 'callibriate.py');
 
 app.post('/api/calibration/compute', async (req, res) => {
-  const { camera } = req.body ?? {};
-  if (!camera) return res.status(400).json({ error: '"camera" parameter fehlt' });
+  try {
+    const { camera } = req.body ?? {};
+    if (!camera) return res.status(400).json({ error: '"camera" parameter fehlt' });
 
-  const session = await findLatestCalibSession();
-  if (!session) return res.status(400).json({ error: 'Keine Kalibrierungs-Session vorhanden' });
+    const session = await findLatestCalibSession();
+    if (!session) return res.status(400).json({ error: 'Keine Kalibrierungs-Session vorhanden' });
 
-  const sessionDir = path.join(calibDataDir, session);
+    const sessionDir = path.join(calibDataDir, session);
 
-  // SSE-Header
-  res.setHeader('Content-Type',  'text/event-stream');
-  res.setHeader('Cache-Control', 'no-cache');
-  res.setHeader('Connection',    'keep-alive');
-  res.flushHeaders();
+    // SSE-Header – erst NACH den Validierungen senden
+    res.setHeader('Content-Type',  'text/event-stream');
+    res.setHeader('Cache-Control', 'no-cache');
+    res.setHeader('Connection',    'keep-alive');
+    res.flushHeaders();
 
-  const send = (obj) => res.write(`data: ${JSON.stringify(obj)}\n\n`);
+    // Schreibt nur wenn die Verbindung noch offen ist
+    const send = (obj) => {
+      if (!res.writableEnded) res.write(`data: ${JSON.stringify(obj)}\n\n`);
+    };
 
-  send({ type: 'log', text: `▶ Session:    ${session}` });
-  send({ type: 'log', text: `▶ Kamera:     ${camera}` });
-  send({ type: 'log', text: `▶ Script:     ${calibScriptPath}` });
-  send({ type: 'log', text: '' });
+    send({ type: 'log', text: `▶ Session:    ${session}` });
+    send({ type: 'log', text: `▶ Kamera:     ${camera}` });
+    send({ type: 'log', text: `▶ Script:     ${calibScriptPath}` });
+    send({ type: 'log', text: '' });
 
-  const proc = spawn(PYTHON_BIN, [
-    calibScriptPath,
-    '--camera',     camera,
-    '--input-dir',  sessionDir,
-    '--output-dir', sessionDir,
-  ]);
+    // -u = unbuffered (Python gibt jede Zeile sofort aus)
+    const proc = spawn(PYTHON_BIN, [
+      '-u',
+      calibScriptPath,
+      '--camera',     camera,
+      '--input-dir',  sessionDir,
+      '--output-dir', sessionDir,
+    ]);
 
-  // stdout zeilenweise weiterleiten
-  let stdoutBuf = '';
-  proc.stdout.on('data', (chunk) => {
-    stdoutBuf += chunk.toString();
-    const lines = stdoutBuf.split('\n');
-    stdoutBuf = lines.pop();                    // letztes (unvollständiges) Fragment behalten
-    for (const line of lines) send({ type: 'log', text: line });
-  });
+    let stdoutBuf = '';
+    proc.stdout.on('data', (chunk) => {
+      stdoutBuf += chunk.toString();
+      const lines = stdoutBuf.split('\n');
+      stdoutBuf = lines.pop();
+      for (const line of lines) send({ type: 'log', text: line });
+    });
 
-  // stderr als Warnung weiterleiten
-  let stderrBuf = '';
-  proc.stderr.on('data', (chunk) => {
-    stderrBuf += chunk.toString();
-    const lines = stderrBuf.split('\n');
-    stderrBuf = lines.pop();
-    for (const line of lines) send({ type: 'log', text: `[stderr] ${line}` });
-  });
+    let stderrBuf = '';
+    proc.stderr.on('data', (chunk) => {
+      stderrBuf += chunk.toString();
+      const lines = stderrBuf.split('\n');
+      stderrBuf = lines.pop();
+      for (const line of lines) send({ type: 'log', text: `[stderr] ${line}` });
+    });
 
-  proc.on('error', (err) => {
-    send({ type: 'log',  text: `Fehler beim Starten: ${err.message}` });
-    send({ type: 'done', exitCode: -1 });
-    res.end();
-  });
+    proc.on('error', (err) => {
+      console.error('calibration/compute spawn error:', err);
+      send({ type: 'log',  text: `Fehler beim Starten: ${err.message}` });
+      send({ type: 'done', exitCode: -1 });
+      if (!res.writableEnded) res.end();
+    });
 
-  proc.on('close', (code) => {
-    if (stdoutBuf) send({ type: 'log', text: stdoutBuf });   // Rest ausgeben
-    if (stderrBuf) send({ type: 'log', text: `[stderr] ${stderrBuf}` });
-    send({ type: 'done', exitCode: code });
-    res.end();
-  });
+    proc.on('close', (code) => {
+      if (stdoutBuf) send({ type: 'log', text: stdoutBuf });
+      if (stderrBuf) send({ type: 'log', text: `[stderr] ${stderrBuf}` });
+      send({ type: 'done', exitCode: code ?? -1 });
+      if (!res.writableEnded) res.end();
+    });
+
+  } catch (err) {
+    // Fehler VOR flushHeaders → normaler JSON-Fehler
+    // Fehler NACH flushHeaders → SSE-Fehlerevent + close
+    console.error('calibration/compute error:', err);
+    if (!res.headersSent) {
+      res.status(500).json({ error: String(err) });
+    } else {
+      try {
+        res.write(`data: ${JSON.stringify({ type: 'log', text: `Server-Fehler: ${err.message}` })}\n\n`);
+        res.write(`data: ${JSON.stringify({ type: 'done', exitCode: -1 })}\n\n`);
+        res.end();
+      } catch { /* Verbindung bereits geschlossen */ }
+    }
+  }
 });
 
 async function checkServiceReachability(name, url) {