Add cron schedules and sync docs

agent/internal/config/config_test.go

@@ -48,9 +48,84 @@ func TestLoadMinimal(t *testing.T) {
 	}
 }
 
+func TestLoadCronCheck(t *testing.T) {
+	c, err := Load(writeTmp(t, `
+	agent_id = "host-1"
+	state_dir = "/tmp/x"
+
+	[server]
+	enabled = true
+	url = "http://localhost"
+
+	[[checks]]
+	id = "c1"
+	command = "true"
+	cron = "CRON_TZ=UTC 0 6 * * *"
+	timeout = "5m"
+	`))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !c.Checks[0].UsesCron() || c.Checks[0].UsesInterval() {
+		t.Fatalf("unexpected schedule mode: %+v", c.Checks[0])
+	}
+}
+
+func TestValidateCheckScheduleChoice(t *testing.T) {
+	for name, body := range map[string]string{
+		"both_interval_and_cron": `
+	interval = "10s"
+	cron = "0 * * * *"
+	timeout = "5s"
+	`,
+		"neither_interval_nor_cron": `
+	timeout = "5s"
+	`,
+		"invalid_cron": `
+	cron = "not a cron"
+	timeout = "5s"
+	`,
+		"seconds_cron": `
+	cron = "0 0 * * * *"
+	timeout = "5s"
+	`,
+		"every_cron": `
+	cron = "@every 10s"
+	timeout = "5s"
+	`,
+		"tz_every_cron": `
+	cron = "CRON_TZ=UTC @every 10s"
+	timeout = "5s"
+	`,
+		"reboot_cron": `
+	cron = "@reboot"
+	timeout = "5s"
+	`,
+	} {
+		t.Run(name, func(t *testing.T) {
+			_, err := Load(writeTmp(t, `
+	agent_id = "host-1"
+	state_dir = "/tmp/x"
+
+	[server]
+	enabled = true
+	url = "http://localhost"
+
+	[[checks]]
+	id = "c1"
+	command = "true"
+	`+body+`
+	`))
+			if err == nil {
+				t.Fatal("expected schedule validation error")
+			}
+		})
+	}
+}
+
 func TestLoadResourceLimits(t *testing.T) {
 	c, err := Load(writeTmp(t, `
-agent_id = "host-1"
+	agent_id = "host-1"
 state_dir = "/tmp/x"
 
 [server]