feat(protocol): define agent-to-master wire messages

internal/protocol/protocol_test.go

@@ -0,0 +1,49 @@
+package protocol
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestServiceKey(t *testing.T) {
+	cases := []struct {
+		name string
+		svc  Service
+		want string
+	}{
+		{"compose", Service{Kind: KindCompose, ComposeProject: "slusk", ComposeService: "web"}, "compose|slusk|web"},
+		{"swarm", Service{Kind: KindSwarm, SwarmService: "gitea_gitea"}, "swarm|gitea_gitea"},
+		{"container", Service{Kind: KindContainer, ContainerName: "adhoc"}, "container|adhoc"},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			assert.Equal(t, c.want, c.svc.Key())
+		})
+	}
+}
+
+func TestEncodeDecodeRoundTrip(t *testing.T) {
+	in := Snapshot{Services: []Service{
+		{Kind: KindCompose, ComposeProject: "slusk", ComposeService: "web", Image: "slusk:1.4.2", Status: "running"},
+	}}
+	env, err := Encode(TypeSnapshot, in)
+	require.NoError(t, err)
+
+	raw, err := json.Marshal(env)
+	require.NoError(t, err)
+	var back Envelope
+	require.NoError(t, json.Unmarshal(raw, &back))
+
+	assert.Equal(t, TypeSnapshot, back.Type)
+	out, err := Decode[Snapshot](back)
+	require.NoError(t, err)
+	assert.Equal(t, in, out)
+}
+
+func TestDecodeRejectsMalformedPayload(t *testing.T) {
+	_, err := Decode[Hello](Envelope{Type: TypeHello, Payload: json.RawMessage(`{"hostname": 5}`)})
+	assert.ErrorContains(t, err, "decode hello")
+}