diff --git a/main.js b/main.js
index d2a17d2..d3aec4e 100644
--- a/main.js
+++ b/main.js
@@ -41,6 +41,7 @@ const {
   // GitHub
   listGithubRepos,
   getGithubCurrentUser,
+  githubRepoExists,
   getGithubUserHeatmap,
   getGithubRepoContents,
   getGithubFileContent,
@@ -56,6 +57,7 @@ const {
   editGithubRelease,
   deleteGithubRelease,
   updateGithubRepoVisibility,
+  updateGithubRepoDefaultBranch,
   updateGithubRepoTopics,
   deleteGithubRepo
 } = require('./src/git/apiHandler.js');
@@ -3507,6 +3509,7 @@ ipcMain.handle('check-clone-target-collisions', async (_event, data) => {
 
 ipcMain.handle('sync-repo-to-github', async (event, data) => {
   let mirrorDir = null;
+  let sourceDefaultBranch = '';
   try {
     const creds = readCredentials();
     if (!creds?.githubToken) {
@@ -3542,8 +3545,16 @@ ipcMain.handle('sync-repo-to-github', async (event, data) => {
       repoCreated = true;
     } catch (e) {
       const msg = String(e?.message || e || '');
-      if (!/already exists|existiert bereits|name already exists/i.test(msg)) {
-        throw e;
+      if (!/already exists|already_exists|existiert bereits|name already exists/i.test(msg)) {
+        // Falls GitHub mit einer unscharfen Meldung antwortet, explizit auf Existenz pruefen.
+        const exists = await githubRepoExists({
+          token: creds.githubToken,
+          owner: targetOwner,
+          repo
+        }).catch(() => false);
+        if (!exists) {
+          throw e;
+        }
       }
     }
 
@@ -3575,29 +3586,133 @@ ipcMain.handle('sync-repo-to-github', async (event, data) => {
     } catch (_) {}
 
     mirrorDir = fs.mkdtempSync(ppath.join(os.tmpdir(), 'git-manager-sync-'));
-    const cloneArgs = cloneNeedsGiteaHeader
-      ? ['-c', `http.${sourceOrigin}.extraheader=AUTHORIZATION: token ${creds.giteaToken}`, 'clone', '--mirror', sourceCloneUrl, mirrorDir]
-      : ['clone', '--mirror', sourceCloneUrl, mirrorDir];
 
+    // --bare statt --mirror: lädt alle Branches/Tags ohne mirror-Flag zu setzen,
+    // damit anschließende Refspec-Pushes (Force) funktionieren.
+    const cloneArgs = cloneNeedsGiteaHeader
+      ? ['-c', `http.${sourceOrigin}.extraheader=AUTHORIZATION: token ${creds.giteaToken}`, 'clone', '--bare', sourceCloneUrl, mirrorDir]
+      : ['clone', '--bare', sourceCloneUrl, mirrorDir];
+
+    // runGit: gibt stdout zurück, loggt stderr immer (git push schreibt Status auf stderr)
     const runGit = (args, cwd) => {
       const res = spawnSync('git', args, {
         cwd,
         encoding: 'utf8',
         windowsHide: true
       });
+      const out = (res.stdout || '').trim();
+      const err = (res.stderr || '').trim();
+      if (err) console.log(`[sync-repo-to-github][git] ${err}`);
       if (res.status !== 0) {
-        throw new Error((res.stderr || res.stdout || 'Git-Fehler').trim());
+        throw new Error((err || out || 'Git-Fehler').trim());
       }
-      return (res.stdout || '').trim();
+      return out;
     };
 
+    console.log(`[sync-repo-to-github] Klone Quell-Repo (bare): ${sourceCloneUrl}`);
     runGit(cloneArgs, process.cwd());
+    console.log('[sync-repo-to-github] Bare-Clone abgeschlossen');
+
+    // Alle lokalen Branches auflisten
+    const allBranchesRaw = runGit(['for-each-ref', '--format=%(refname:short)', 'refs/heads/'], mirrorDir);
+    const allBranches = (allBranchesRaw || '').split('\n').map(s => s.trim()).filter(s => s && isSafeGitRef(s));
+    console.log(`[sync-repo-to-github] Lokale Branches: ${allBranches.join(', ') || '(keine)'}`);
+
+    // Default-Branch ermitteln
+    try {
+      const headRef = runGit(['symbolic-ref', '--short', 'HEAD'], mirrorDir);
+      sourceDefaultBranch = String(headRef || '').replace(/^refs\/heads\//, '').trim();
+      if (!isSafeGitRef(sourceDefaultBranch)) sourceDefaultBranch = '';
+    } catch (_) {
+      sourceDefaultBranch = allBranches[0] || '';
+    }
+    if (!sourceDefaultBranch && allBranches.length > 0) sourceDefaultBranch = allBranches[0];
+    console.log(`[sync-repo-to-github] Quell-Default-Branch: "${sourceDefaultBranch || '(unbekannt)'}"`);
 
     const githubRemoteUrl = `https://github.com/${targetOwner}/${repo}.git`;
     const githubAuthHeader = `AUTHORIZATION: basic ${Buffer.from(`x-access-token:${creds.githubToken}`, 'utf8').toString('base64')}`;
+    const ghAuthArgs = ['-c', 'credential.helper=', '-c', `http.https://github.com/.extraheader=${githubAuthHeader}`];
 
-    runGit(['remote', 'set-url', '--push', 'origin', githubRemoteUrl], mirrorDir);
-    runGit(['-c', 'credential.helper=', '-c', `http.https://github.com/.extraheader=${githubAuthHeader}`, 'push', '--mirror'], mirrorDir);
+    // GitHub als Push-Remote setzen
+    runGit(['remote', 'set-url', 'origin', githubRemoteUrl], mirrorDir);
+
+    // Lokale Commit-SHAs loggen (= Gitea-Stand)
+    for (const branch of allBranches) {
+      try {
+        const localSha = runGit(['rev-parse', `refs/heads/${branch}`], mirrorDir);
+        console.log(`[sync-repo-to-github] Gitea  ${branch}: ${localSha}`);
+      } catch (_) {}
+    }
+
+    // Remote (GitHub) Commit-SHAs VOR dem Push ermitteln und vergleichen
+    try {
+      const remoteRefsRaw = runGit([...ghAuthArgs, 'ls-remote', '--heads', 'origin'], mirrorDir);
+      const remoteMap = {};
+      (remoteRefsRaw || '').split('\n').forEach(line => {
+        const parts = line.trim().split(/\s+/);
+        if (parts.length === 2) {
+          const branch = parts[1].replace('refs/heads/', '');
+          remoteMap[branch] = parts[0];
+        }
+      });
+      for (const branch of allBranches) {
+        const remoteSha = remoteMap[branch] || '(nicht vorhanden)';
+        console.log(`[sync-repo-to-github] GitHub ${branch}: ${remoteSha}`);
+      }
+    } catch (lsErr) {
+      console.warn('[sync-repo-to-github] ls-remote Warnung:', lsErr?.message || lsErr);
+    }
+
+    // Jeden Branch einzeln force-pushen für maximale Zuverlässigkeit
+    console.log(`[sync-repo-to-github] Force-Push ${allBranches.length} Branch(es) nach GitHub: ${githubRemoteUrl}`);
+    let pushedCount = 0;
+    for (const branch of allBranches) {
+      console.log(`[sync-repo-to-github] Pushe Branch: ${branch}`);
+      runGit([...ghAuthArgs, 'push', '--force', 'origin', `refs/heads/${branch}:refs/heads/${branch}`], mirrorDir);
+      pushedCount++;
+    }
+    console.log(`[sync-repo-to-github] ${pushedCount} Branch(es) erfolgreich gepusht`);
+
+    // Auf GitHub nicht mehr vorhandene Branches aufräumen (prune via API, non-fatal)
+    try {
+      const remoteRefsRaw = runGit([...ghAuthArgs, 'ls-remote', '--heads', 'origin'], mirrorDir);
+      const remoteHeads = (remoteRefsRaw || '').split('\n')
+        .map(l => { const m = l.match(/refs\/heads\/(.+)$/); return m ? m[1].trim() : null; })
+        .filter(Boolean);
+      const localSet = new Set(allBranches);
+      for (const remoteBranch of remoteHeads) {
+        if (!localSet.has(remoteBranch) && isSafeGitRef(remoteBranch)) {
+          console.log(`[sync-repo-to-github] Lösche veralteten Remote-Branch: ${remoteBranch}`);
+          runGit([...ghAuthArgs, 'push', 'origin', `--delete`, remoteBranch], mirrorDir);
+        }
+      }
+    } catch (pruneErr) {
+      console.warn('[sync-repo-to-github] Prune-Warnung:', pruneErr?.message || pruneErr);
+    }
+
+    // Tags mit Force-Push übertragen (non-fatal)
+    try {
+      runGit([...ghAuthArgs, 'push', 'origin', '--tags', '--force'], mirrorDir);
+      console.log('[sync-repo-to-github] Tags erfolgreich gepusht');
+    } catch (tagsErr) {
+      console.warn('[sync-repo-to-github] Tags-Push Warnung:', tagsErr?.message || tagsErr);
+    }
+
+    // Default-Branch auf GitHub per API angleichen
+    if (sourceDefaultBranch) {
+      console.log(`[sync-repo-to-github] Setze GitHub Default-Branch auf: ${sourceDefaultBranch}`);
+      try {
+        await updateGithubRepoDefaultBranch({
+          token: creds.githubToken,
+          owner: targetOwner,
+          repo,
+          defaultBranch: sourceDefaultBranch
+        });
+        console.log('[sync-repo-to-github] Default-Branch aktualisiert');
+      } catch (defaultBranchErr) {
+        console.warn('sync-repo-to-github: default-branch update warning', defaultBranchErr?.message || defaultBranchErr);
+      }
+    }
 
     // Optional: Topics auf GitHub angleichen (nur falls übergeben)
     const topics = Array.isArray(data?.topics) ? data.topics.filter(Boolean) : [];
@@ -3617,7 +3732,8 @@ ipcMain.handle('sync-repo-to-github', async (event, data) => {
     return {
       ok: true,
       repoCreated,
-      githubRepo: `${targetOwner}/${repo}`
+      githubRepo: `${targetOwner}/${repo}`,
+      sourceDefaultBranch: sourceDefaultBranch || null
     };
   } catch (e) {
     console.error('sync-repo-to-github error', e);