Fix solution branch

Change-Id: I7de33c86485861c82f953ac161aa2d18b40134cb
diff --git a/server/tm/git_tm/git_task_manager.go b/server/tm/git_tm/git_task_manager.go
index 9806a07..e86ab76 100644
--- a/server/tm/git_tm/git_task_manager.go
+++ b/server/tm/git_tm/git_task_manager.go
@@ -594,11 +594,15 @@
 	// Build PR description from template
 	description := buildSolutionPRDescription(task, solution, gtm.config.Git.PRTemplate, agentName)
 
+	// Determine base branch (try main first, fallback to master)
+	baseBranch := gtm.determineBaseBranch(ctx, agentName)
+	gtm.logger.Info("Using base branch", slog.String("base_branch", baseBranch))
+
 	options := git.PullRequestOptions{
 		Title:       fmt.Sprintf("Task %s: %s", task.ID, task.Title),
 		Description: description,
 		HeadBranch:  branchName,
-		BaseBranch:  "main",
+		BaseBranch:  baseBranch,
 		Labels:      []string{"ai-generated"},
 		Draft:       false,
 	}
@@ -1003,7 +1007,7 @@
 	// Create branch
 	cmd = gitCmd("checkout", "-b", branchName)
 	if err := cmd.Run(); err != nil {
-		return fmt.Errorf("failed to create branch: %w", err)
+		return fmt.Errorf("failed to create branch %s: %w", branchName, err)
 	}
 
 	// Create solution file in agent's clone