harden release promotion fallback on conflict

src/apps/apps.service.ts

@@ -726,7 +726,11 @@ export class AppsService {
                 commitSha,
               ], { cwd: workDir });
             } catch {
-              await this.resolveReleaseMergeByTakingSourceOnConflict(gitBin, workDir, mergeOptions, commitSha, repository);
+              try {
+                await this.resolveReleaseMergeByTakingSourceOnConflict(gitBin, workDir, mergeOptions, commitSha, repository);
+              } catch {
+                await this.promoteReleaseBySourceSnapshot(gitBin, workDir, mergeOptions, commitSha, targetBranch, repository);
+              }
             }
           }
         } else {
@@ -774,6 +778,31 @@ export class AppsService {
     await execFileAsync(gitBin, ['commit', '--allow-empty', '-m', `${repository} release promotion merge`], { cwd: workDir });
   }
 
+  private async promoteReleaseBySourceSnapshot(
+    gitBin: string,
+    workDir: string,
+    mergeOptions: string[],
+    commitSha: string,
+    targetBranch: string,
+    repository: string,
+  ) {
+    await this.resetPromotionWorktree(gitBin, workDir);
+    await execFileAsync(gitBin, [
+      'checkout',
+      '-B',
+      targetBranch,
+      `origin/${targetBranch}`,
+    ], { cwd: workDir });
+    await execFileAsync(gitBin, ['reset', '--hard', `origin/${targetBranch}`], { cwd: workDir }).catch(() => undefined);
+    await execFileAsync(gitBin, ['read-tree', '--reset', '-u', commitSha], { cwd: workDir });
+    await execFileAsync(gitBin, ['add', '-A'], { cwd: workDir });
+    const { stdout } = await execFileAsync(gitBin, ['status', '--porcelain'], { cwd: workDir });
+    if (!stdout.trim()) {
+      return;
+    }
+    await execFileAsync(gitBin, ['commit', '--allow-empty', '-m', `${repository} release promotion snapshot`], { cwd: workDir });
+  }
+
   private async resetPromotionWorktree(gitBin: string, workDir: string) {
     await execFileAsync(gitBin, ['merge', '--abort'], { cwd: workDir }).catch(() => undefined);
     await execFileAsync(gitBin, ['rebase', '--abort'], { cwd: workDir }).catch(() => undefined);