diff --git a/core/common/nameidmapper.go b/core/common/nameidmapper.go
index a2c8dd0..9577b00 100644
--- a/core/common/nameidmapper.go
+++ b/core/common/nameidmapper.go
@@ -15,7 +15,10 @@
 package common
 
 // NameIDMapper assigns stable int32 IDs to string names on demand.
-// IDs are assigned sequentially starting from 0.
+// IDs are assigned sequentially starting from 1. Zero is reserved as the
+// proto3 "unset" sentinel so consumers using encoding/json (which honors
+// `omitempty` on int32 fields) or any client that treats GetId() == 0 as
+// missing never silently lose real entries.
 type NameIDMapper struct {
 	nameToID map[string]int32
 	nextID   int32
@@ -25,7 +28,7 @@ type NameIDMapper struct {
 func NewNameIDMapper() *NameIDMapper {
 	return &NameIDMapper{
 		nameToID: make(map[string]int32),
-		nextID:   0,
+		nextID:   1,
 	}
 }
 
diff --git a/core/common/nameidmapper_test.go b/core/common/nameidmapper_test.go
index 90f0ac6..008e2fc 100644
--- a/core/common/nameidmapper_test.go
+++ b/core/common/nameidmapper_test.go
@@ -15,6 +15,7 @@
 package common
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -24,15 +25,15 @@ func TestNameIDMapper_AssignsSequentialAndStableIDs(t *testing.T) {
 	mapper := NewNameIDMapper()
 
 	idA := mapper.ID("a")
-	assert.Equal(t, int32(0), idA)
+	assert.Equal(t, int32(1), idA, "first id must be 1; 0 is reserved as proto3 unspecified")
 	idB := mapper.ID("b")
-	assert.Equal(t, int32(1), idB)
+	assert.Equal(t, int32(2), idB)
 	// Re-requesting 'a' should return the same id
 	idA2 := mapper.ID("a")
 	assert.Equal(t, idA, idA2)
 	// A new, third name should get the next sequential id
 	idC := mapper.ID("c")
-	assert.Equal(t, int32(2), idC)
+	assert.Equal(t, int32(3), idC)
 }
 
 func TestNameIDMapper_MappingAndInvert(t *testing.T) {
@@ -44,18 +45,28 @@ func TestNameIDMapper_MappingAndInvert(t *testing.T) {
 
 	mapping := mapper.Mapping()
 	assert.Equal(t, 3, len(mapping))
-	assert.Equal(t, int32(0), mapping["x"])
-	assert.Equal(t, int32(1), mapping["y"])
-	assert.Equal(t, int32(2), mapping["z"])
+	assert.Equal(t, int32(1), mapping["x"])
+	assert.Equal(t, int32(2), mapping["y"])
+	assert.Equal(t, int32(3), mapping["z"])
 
 	inv := mapper.Invert()
 	assert.Equal(t, 3, len(inv))
-	assert.Equal(t, "x", inv[0])
-	assert.Equal(t, "y", inv[1])
-	assert.Equal(t, "z", inv[2])
+	assert.Equal(t, "x", inv[1])
+	assert.Equal(t, "y", inv[2])
+	assert.Equal(t, "z", inv[3])
+	_, hasZero := inv[0]
+	assert.False(t, hasZero, "id 0 must remain reserved")
 
 	// Mutating the inverted map should not affect the original mapping
-	inv[3] = "extra"
+	inv[4] = "extra"
 	_, ok := mapping["extra"]
 	assert.False(t, ok)
 }
+
+func TestNameIDMapper_NeverAssignsZero(t *testing.T) {
+	mapper := NewNameIDMapper()
+	for i := 0; i < 1000; i++ {
+		id := mapper.ID(fmt.Sprintf("name-%d", i))
+		assert.NotEqual(t, int32(0), id)
+	}
+}
diff --git a/core/common/utils.go b/core/common/utils.go
index 4dd3b7a..91a45ac 100644
--- a/core/common/utils.go
+++ b/core/common/utils.go
@@ -147,9 +147,11 @@ func HashRequestOptions(opts *tangopb.RequestOptions) string {
 // ResultToGetTargetGraphResponse converts a Result to a GetTargetGraphResponse
 func ResultToGetTargetGraphResponse(result targethasher.Result) ([]*tangopb.GetTargetGraphResponse, error) {
 	// Map target names to ids. This list is topologically sorted, so the ids are stable.
+	// IDs start at 1 — 0 is reserved as the proto3 "unset" sentinel so consumers using
+	// encoding/json (which honors `omitempty` on int32 fields) never silently lose a target.
 	targetNamesMapping := make(map[string]int32, len(result.TargetNames))
 	for i, name := range result.TargetNames {
-		targetNamesMapping[name] = int32(i)
+		targetNamesMapping[name] = int32(i + 1)
 	}
 
 	ruleTypeMapper := NewNameIDMapper()