feat(protocol): job messages, protocol version and job model (#7)

internal/protocol/protocol_test.go

@@ -47,3 +47,35 @@ func TestDecodeRejectsMalformedPayload(t *testing.T) {
 	_, err := Decode[Hello](Envelope{Type: TypeHello, Payload: json.RawMessage(`{"hostname": 5}`)})
 	assert.ErrorContains(t, err, "decode hello")
 }
+
+func TestEncodeJob_CarriesID(t *testing.T) {
+	in := JobStart{Kind: KindSwarm, SwarmService: "gitea_gitea", Ref: "gitea/gitea:1.27"}
+	env, err := EncodeJob(TypeJobStart, "42", 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, "42", back.ID)
+	assert.Equal(t, TypeJobStart, back.Type)
+	out, err := Decode[JobStart](back)
+	require.NoError(t, err)
+	assert.Equal(t, in, out)
+}
+
+func TestHello_PhaseOneDecodesAsVersionZero(t *testing.T) {
+	var h Hello
+	require.NoError(t, json.Unmarshal([]byte(`{"agent_version":"x","hostname":"h","swarm_manager":false}`), &h))
+	assert.Equal(t, 0, h.ProtocolVersion)
+	assert.Nil(t, h.KnownJobs)
+}
+
+func TestEnvelope_InventoryHasNoID(t *testing.T) {
+	env, err := Encode(TypeSnapshot, Snapshot{})
+	require.NoError(t, err)
+	raw, err := json.Marshal(env)
+	require.NoError(t, err)
+	assert.NotContains(t, string(raw), `"id"`)
+}