Omit lastLogForTick from Kafka JSON when false

Add omitempty tag to LastLogForTick so the field is excluded from
serialized messages when its value is false, keeping payloads lean.
Add tests verifying the marshaling behavior.

Author: 0xluk

bob-events-bridge/internal/kafka/message.go

@@ -18,7 +18,7 @@ type EventMessage struct {
 	Timestamp       uint64         `json:"timestamp"`
 	TransactionHash string         `json:"transactionHash"`
 	Body            map[string]any `json:"body"`
-	LastLogForTick  bool           `json:"lastLogForTick"`
+	LastLogForTick  bool           `json:"lastLogForTick,omitempty"`
 }
 
 // TransformEventBody converts a typed bob event body into the Kafka body format

bob-events-bridge/internal/kafka/message_test.go

@@ -1,6 +1,7 @@
 package kafka
 
 import (
+	"encoding/json"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -303,3 +304,28 @@ func TestBuildEventMessage_LastLogForTick(t *testing.T) {
 	assert.True(t, msg.LastLogForTick)
 }
 
+func TestEventMessage_JSON_OmitsLastLogForTickWhenFalse(t *testing.T) {
+	msg := EventMessage{
+		Index:      1,
+		Type:       0,
+		TickNumber: 100,
+	}
+
+	data, err := json.Marshal(msg)
+	require.NoError(t, err)
+	assert.NotContains(t, string(data), "lastLogForTick")
+}
+
+func TestEventMessage_JSON_IncludesLastLogForTickWhenTrue(t *testing.T) {
+	msg := EventMessage{
+		Index:          1,
+		Type:           0,
+		TickNumber:     100,
+		LastLogForTick: true,
+	}
+
+	data, err := json.Marshal(msg)
+	require.NoError(t, err)
+	assert.Contains(t, string(data), `"lastLogForTick":true`)
+}
+