From 1bc3f85d6a24699f049f86a84dba21e4b5dbbde4 Mon Sep 17 00:00:00 2001
From: Lukas May <lukas.may@carealytix.com>
Date: Fri, 6 Mar 2026 10:54:42 +0100
Subject: [PATCH] fix: Merge worktree conflict when target branch already
 checked out

Use a temp branch + update-ref to avoid "already checked out" error
when merging into the default branch. Also show actual branch name
in the Merge & Push button instead of "Default".
---
 apps/server/git/simple-git-branch-manager.ts   | 18 +++++++++++++++---
 .../src/components/review/InitiativeReview.tsx |  2 +-
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/apps/server/git/simple-git-branch-manager.ts b/apps/server/git/simple-git-branch-manager.ts
index 0c73ce7..a7678e7 100644
--- a/apps/server/git/simple-git-branch-manager.ts
+++ b/apps/server/git/simple-git-branch-manager.ts
@@ -31,19 +31,27 @@ export class SimpleGitBranchManager implements BranchManager {
   }
 
   async mergeBranch(repoPath: string, sourceBranch: string, targetBranch: string): Promise<MergeResult> {
-    // Use an ephemeral worktree for merge safety
+    // Use an ephemeral worktree with a temp branch for merge safety.
+    // We can't check out targetBranch directly — it may already be checked out
+    // in the clone's main working tree or an agent worktree.
     const tmpPath = mkdtempSync(join(tmpdir(), 'cw-merge-'));
     const repoGit = simpleGit(repoPath);
+    const tempBranch = `cw-merge-${Date.now()}`;
 
     try {
-      // Create ephemeral worktree on target branch
-      await repoGit.raw(['worktree', 'add', tmpPath, targetBranch]);
+      // Create worktree with a temp branch starting at targetBranch's commit
+      await repoGit.raw(['worktree', 'add', '-b', tempBranch, tmpPath, targetBranch]);
 
       const wtGit = simpleGit(tmpPath);
 
       try {
         await wtGit.merge([sourceBranch, '--no-edit']);
 
+        // Update the real target branch ref to the merge result.
+        // update-ref bypasses the "branch is checked out" guard.
+        const mergeCommit = (await wtGit.revparse(['HEAD'])).trim();
+        await repoGit.raw(['update-ref', `refs/heads/${targetBranch}`, mergeCommit]);
+
         log.info({ repoPath, sourceBranch, targetBranch }, 'merge completed cleanly');
         return { success: true, message: `Merged ${sourceBranch} into ${targetBranch}` };
       } catch (mergeErr) {
@@ -73,6 +81,10 @@ export class SimpleGitBranchManager implements BranchManager {
         try { rmSync(tmpPath, { recursive: true, force: true }); } catch { /* ignore */ }
         try { await repoGit.raw(['worktree', 'prune']); } catch { /* ignore */ }
       }
+      // Delete the temp branch
+      try {
+        await repoGit.raw(['branch', '-D', tempBranch]);
+      } catch { /* ignore — may already be cleaned up */ }
     }
   }
 
diff --git a/apps/web/src/components/review/InitiativeReview.tsx b/apps/web/src/components/review/InitiativeReview.tsx
index fc0cd7a..a23a83a 100644
--- a/apps/web/src/components/review/InitiativeReview.tsx
+++ b/apps/web/src/components/review/InitiativeReview.tsx
@@ -214,7 +214,7 @@ export function InitiativeReview({ initiativeId, onCompleted }: InitiativeReview
               ) : (
                 <GitMerge className="h-3.5 w-3.5" />
               )}
-              Merge & Push to Default
+              Merge & Push to {targetBranch || "default"}
             </Button>
           </div>
         </div>