fix: Handle existing branch in worktree creation

When re-dispatching tasks, the branch from a previous run may still
exist. Instead of failing with "a branch named X already exists",
reset the existing branch to the base and check it out.

apps/server/git/manager.ts

@@ -61,16 +61,16 @@ export class SimpleGitWorktreeManager implements WorktreeManager {
     const worktreePath = path.join(this.worktreesDir, id);
     log.info({ id, branch, baseBranch }, 'creating worktree');
 
-    // Create worktree with new branch
+    // Create worktree — reuse existing branch or create new one
+    const branchExists = await this.branchExists(branch);
+    if (branchExists) {
+      // Branch exists from a previous run — reset it to baseBranch and check it out
+      await this.git.raw(['branch', '-f', branch, baseBranch]);
+      await this.git.raw(['worktree', 'add', worktreePath, branch]);
+    } else {
       // git worktree add -b <branch> <path> <base-branch>
-    await this.git.raw([
-      'worktree',
-      'add',
-      '-b',
-      branch,
-      worktreePath,
-      baseBranch,
-    ]);
+      await this.git.raw(['worktree', 'add', '-b', branch, worktreePath, baseBranch]);
+    }
 
     const worktree: Worktree = {
       id,
@@ -327,6 +327,18 @@ export class SimpleGitWorktreeManager implements WorktreeManager {
     return worktrees;
   }
 
+  /**
+   * Check if a local branch exists in the repository.
+   */
+  private async branchExists(branch: string): Promise<boolean> {
+    try {
+      await this.git.raw(['rev-parse', '--verify', `refs/heads/${branch}`]);
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
   /**
    * Parse the output of git diff --name-status.
    */