feat: allow session-only delete on the main worktree

cmd/errors.go

@@ -39,6 +39,8 @@ func herdErr(project, branch string, err error) error {
 				sesErr.Ref.Project, sesErr.Ref.Branch, sesErr.Type, sesErr.Ref.Project, sesErr.Ref.Branch)
 		}
 		return err
+	case errors.Is(err, herd.ErrMainWorktree):
+		return fmt.Errorf("cannot delete the main worktree %s/%s — delete its sessions with 'ch delete session %s <branch>'", project, branch, project)
 	default:
 		return err
 	}

cmd/errors_internal_test.go

@@ -2,6 +2,8 @@ package cmd
 
 import (
 	"errors"
+	"fmt"
+	"strings"
 	"testing"
 
 	"github.com/xico42/codeherd/internal/herd"
@@ -51,6 +53,20 @@ func TestHerdErr_sessionExists_carriesRefFromTypedError(t *testing.T) {
 	}
 }
 
+func TestHerdErr_mainWorktree(t *testing.T) {
+	err := herdErr("myapp", "main", fmt.Errorf("%w: myapp/main", herd.ErrMainWorktree))
+	if err == nil {
+		t.Fatal("herdErr returned nil")
+	}
+	msg := err.Error()
+	if !strings.Contains(msg, "main worktree") {
+		t.Errorf("message = %q, should mention the main worktree", msg)
+	}
+	if !strings.Contains(msg, "ch delete session") {
+		t.Errorf("message = %q, should point at 'ch delete session'", msg)
+	}
+}
+
 func TestHerdErr_unknownSentinel_passesThrough(t *testing.T) {
 	raw := errors.New("boom")
 	got := herdErr("myapp", "feat", raw)