diff --git a/pkg/cardinal/debug.go b/pkg/cardinal/debug.go
index e3378ecfb..6921125c8 100644
--- a/pkg/cardinal/debug.go
+++ b/pkg/cardinal/debug.go
@@ -48,11 +48,15 @@ func newDebugModule(world *World) debugModule {
 		commands:   make(map[string]*structpb.Struct),
 		events:     make(map[string]*structpb.Struct),
 		components: make(map[string]*structpb.Struct),
-		reflector: &jsonschema.Reflector{
+		reflector:  &jsonschema.Reflector{
 			Anonymous:      true, // Don't add $id based on package path
 			ExpandedStruct: true, // Inline the struct fields directly
+			// FieldNameTag="msgpack" makes advertised field names match the shamaton wire
+			// format (msgpack tag, else Go field name; see internal/schema); the json-tag
+			// default would mismatch and silently drop fields on decode.
+			FieldNameTag:   "msgpack",
 		},
-		perf: perf,
+		perf:       perf,
 	}
 }
 
diff --git a/pkg/cardinal/debug_internal_test.go b/pkg/cardinal/debug_internal_test.go
new file mode 100644
index 000000000..42b3373b5
--- /dev/null
+++ b/pkg/cardinal/debug_internal_test.go
@@ -0,0 +1,70 @@
+package cardinal
+
+import (
+	"testing"
+
+	"github.com/invopop/jsonschema"
+	"github.com/shamaton/msgpack/v3"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/types/known/structpb"
+)
+
+// schemaSample mixes the tag cases that decide a field's wire name: a msgpack
+// tag, a json-only tag whose value differs from the field name, an untagged
+// field, and an explicitly excluded field.
+type schemaSample struct {
+	Tagged   string `json:"tagged"   msgpack:"nickname"` // msgpack tag wins
+	JSONOnly string `json:"jsonOnly"`                    // json tag ignored -> field name
+	Plain    int    // no tags -> field name
+	Skipped  string `msgpack:"-"` // excluded from the wire
+}
+
+func (schemaSample) Name() string { return "schema-sample" }
+
+// TestIntrospectSchemaNamesMatchWireFormat guards the introspect↔serialize
+// contract: the field names advertised by the introspection schema must equal
+// the keys shamaton/msgpack actually reads and writes, so a client that fills a
+// command/component from the schema isn't silently dropped on the wire.
+// Regression for the create-player "nickname" mismatch.
+func TestIntrospectSchemaNamesMatchWireFormat(t *testing.T) {
+	t.Parallel()
+
+	// Names the wire format actually uses.
+	encoded, err := msgpack.Marshal(schemaSample{Tagged: "a", JSONOnly: "b", Plain: 1, Skipped: "x"})
+	require.NoError(t, err)
+	var wire map[string]any
+	require.NoError(t, msgpack.Unmarshal(encoded, &wire))
+
+	// Names introspection advertises, via the real register() path.
+	d := &debugModule{
+		commands:  make(map[string]*structpb.Struct),
+		reflector: &jsonschema.Reflector{
+			Anonymous:      true, // Don't add $id based on package path
+			ExpandedStruct: true, // Inline the struct fields directly
+			FieldNameTag:   "msgpack",
+		},
+	}
+	require.NoError(t, d.register("command", schemaSample{}))
+	schemaMap := d.commands["schema-sample"].AsMap()
+	props, ok := schemaMap["properties"].(map[string]any)
+	require.True(t, ok, "schema should have properties")
+
+	assert.ElementsMatch(t, mapKeys(wire), mapKeys(props),
+		"introspect schema field names must match the msgpack wire keys")
+
+	// Spot-check the specifics the fix turns on.
+	assert.Contains(t, props, "nickname")   // msgpack tag wins over json
+	assert.Contains(t, props, "JSONOnly")   // json tag ignored; Go field name used
+	assert.Contains(t, props, "Plain")      // untagged -> field name
+	assert.NotContains(t, props, "Skipped") // msgpack:"-" excluded
+	assert.NotContains(t, props, "tagged")  // the json tag value must not leak through
+}
+
+func mapKeys(m map[string]any) []string {
+	out := make([]string, 0, len(m))
+	for k := range m {
+		out = append(out, k)
+	}
+	return out
+}