Add team tasks: several agents in one worktree sharing a board

internal/workflow/workflow.go

@@ -62,7 +62,14 @@ func Validate(def api.WorkflowDefinition) error {
 		}
 		seen[s.Name] = true
 
-		if strings.TrimSpace(s.Model) == "" {
+		switch {
+		case s.Agents != nil && strings.TrimSpace(s.Model) != "":
+			problems = append(problems, fmt.Sprintf("%s: model can't be given with agents, which name their own", where))
+		case s.Agents != nil:
+			for _, p := range TeamProblems(*s.Agents) {
+				problems = append(problems, fmt.Sprintf("%s: %s", where, p))
+			}
+		case strings.TrimSpace(s.Model) == "":
 			problems = append(problems, fmt.Sprintf("%s: model is required", where))
 		}
 
@@ -103,6 +110,32 @@ func Validate(def api.WorkflowDefinition) error {
 	return nil
 }
 
+func TeamProblems(members []api.TeamMember) []string {
+	problems := []string{}
+	if len(members) < 2 {
+		problems = append(problems, "a team needs at least two agents")
+	}
+	seen := map[string]bool{}
+	for i, mem := range members {
+		where := fmt.Sprintf("agent %d (%q)", i+1, mem.Name)
+		p := nameProblem(mem.Name)
+		if p != "" {
+			problems = append(problems, fmt.Sprintf("%s: name %s", where, p))
+		}
+		if seen[mem.Name] {
+			problems = append(problems, fmt.Sprintf("%s: another agent has the same name", where))
+		}
+		seen[mem.Name] = true
+		if strings.TrimSpace(mem.Model) == "" {
+			problems = append(problems, fmt.Sprintf("%s: model is required", where))
+		}
+		if strings.TrimSpace(mem.Prompt) == "" {
+			problems = append(problems, fmt.Sprintf("%s: prompt is empty", where))
+		}
+	}
+	return problems
+}
+
 func graphProblems(def api.WorkflowDefinition) []string {
 	problems := []string{}
 	finals := []string{}