diff --git a/codeagent-wrapper/backend.go b/codeagent-wrapper/backend.go
index 59e3ef9..5a0c79a 100644
--- a/codeagent-wrapper/backend.go
+++ b/codeagent-wrapper/backend.go
@@ -43,7 +43,8 @@ func (ClaudeBackend) BuildArgs(cfg *Config, targetArg string) []string {
 
 	if cfg.Mode == "resume" {
 		if cfg.SessionID != "" {
-			args = append(args, "--session-id", cfg.SessionID)
+			// Claude CLI uses -r <session_id> for resume.
+			args = append(args, "-r", cfg.SessionID)
 		}
 	} else {
 		args = append(args, "-C", workdir)
diff --git a/codeagent-wrapper/backend_test.go b/codeagent-wrapper/backend_test.go
index abb550b..ffc69da 100644
--- a/codeagent-wrapper/backend_test.go
+++ b/codeagent-wrapper/backend_test.go
@@ -29,7 +29,7 @@ func TestClaudeBuildArgs_ModesAndPermissions(t *testing.T) {
 	t.Run("resume mode uses session id and omits workdir", func(t *testing.T) {
 		cfg := &Config{Mode: "resume", SessionID: "sid-123", WorkDir: "/ignored"}
 		got := backend.BuildArgs(cfg, "resume-task")
-		want := []string{"-p", "--session-id", "sid-123", "--output-format", "stream-json", "--verbose", "resume-task"}
+		want := []string{"-p", "-r", "sid-123", "--output-format", "stream-json", "--verbose", "resume-task"}
 		if !reflect.DeepEqual(got, want) {
 			t.Fatalf("got %v, want %v", got, want)
 		}