handle unrelated history promotion fallback

src/apps/apps.service.ts

@@ -714,13 +714,27 @@ export class AppsService {
             if (!isUnrelatedHistoryError(message)) {
               throw error;
             }
-            await execFileAsync(gitBin, [
+            try {
-              ...mergeOptions,
+              await execFileAsync(gitBin, [
-              'merge',
+                ...mergeOptions,
-              '--allow-unrelated-histories',
+                'merge',
-              '--no-ff',
+                '--allow-unrelated-histories',
-              commitSha,
+                '--no-ff',
-            ], { cwd: workDir });
+                '--no-edit',
+                commitSha,
+              ], { cwd: workDir });
+            } catch {
+              await execFileAsync(gitBin, [
+                ...mergeOptions,
+                'merge',
+                '--allow-unrelated-histories',
+                '--no-ff',
+                '--no-edit',
+                '-X',
+                'theirs',
+                commitSha,
+              ], { cwd: workDir });
+            }
           }
         } else {
           await execFileAsync(gitBin, [