utils/bimap: drop json/v2 marshaler, keep type generic

BiMap is generic over comparable K,V — bolting on a json/v2
Marshaler/Unmarshaler bound the type to text I/O it has no business
caring about. Removed the marshaler interface and the dependent tests;
no consumer of BiMap in the node module relied on JSON.

Callers that need to persist a bimap should encode a typed snapshot at
the call site (ZAP for internal, JSON for external HTTP boundaries) —
one and only one way, at the boundary that owns the schema.

utils/bimap/bimap.go

@@ -1,26 +1,20 @@
 // Copyright (C) 2019-2025, Lux Industries Inc. All rights reserved.
 // See the file LICENSE for licensing terms.
 
+// Package bimap is an in-memory bi-directional map. Serialization is the
+// caller's concern — this type is generic over comparable K/V, and the
+// internal Lux wire format is ZAP, which is element-typed. Use a typed
+// ZAP schema (or a typed snapshot struct) at the call site to persist a
+// bimap; do not bolt a generic marshaler onto BiMap itself.
 package bimap
 
 import (
-	"bytes"
-	"github.com/go-json-experiment/json"
-	"errors"
 	"maps"
 	"slices"
 
 	"github.com/luxfi/node/utils"
 )
 
-var (
-	_ json.Marshaler   = (*BiMap[int, int])(nil)
-	_ json.Unmarshaler = (*BiMap[int, int])(nil)
-
-	nullBytes       = []byte("null")
-	errNotBijective = errors.New("map not bijective")
-)
-
 type Entry[K, V any] struct {
 	Key   K
 	Value V
@@ -127,28 +121,3 @@ func (m *BiMap[_, V]) Values() []V {
 func (m *BiMap[K, V]) Len() int {
 	return len(m.keyToValue)
 }
-
-func (m *BiMap[K, V]) MarshalJSON() ([]byte, error) {
-	return json.Marshal(m.keyToValue)
-}
-
-func (m *BiMap[K, V]) UnmarshalJSON(b []byte) error {
-	if bytes.Equal(b, nullBytes) {
-		return nil
-	}
-	var keyToValue map[K]V
-	if err := json.Unmarshal(b, &keyToValue); err != nil {
-		return err
-	}
-	valueToKey := make(map[V]K, len(keyToValue))
-	for k, v := range keyToValue {
-		valueToKey[v] = k
-	}
-	if len(keyToValue) != len(valueToKey) {
-		return errNotBijective
-	}
-
-	m.keyToValue = keyToValue
-	m.valueToKey = valueToKey
-	return nil
-}

utils/bimap/bimap_test.go

@@ -4,7 +4,6 @@
 package bimap
 
 import (
-	"github.com/go-json-experiment/json"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -338,29 +337,6 @@ func TestBiMapLenAndLists(t *testing.T) {
 	require.Empty(m.Values())
 }
 
-func TestBiMapJSON(t *testing.T) {
-	require := require.New(t)
-
-	expectedMap := New[int, int]()
-	expectedMap.Put(1, 2)
-	expectedMap.Put(2, 3)
-
-	jsonBytes, err := json.Marshal(expectedMap)
-	require.NoError(err)
-
-	expectedJSONBytes := []byte(`{"1":2,"2":3}`)
-	require.JSONEq(string(expectedJSONBytes), string(jsonBytes))
-
-	var unmarshalledMap BiMap[int, int]
-	require.NoError(json.Unmarshal(jsonBytes, &unmarshalledMap))
-	require.Equal(expectedMap, &unmarshalledMap)
-}
-
-func TestBiMapInvalidJSON(t *testing.T) {
-	require := require.New(t)
-
-	invalidJSONBytes := []byte(`{"1":2,"2":2}`)
-	var unmarshalledMap BiMap[int, int]
-	err := json.Unmarshal(invalidJSONBytes, &unmarshalledMap)
-	require.ErrorIs(err, errNotBijective)
-}
+// JSON marshal/unmarshal tests removed: BiMap no longer carries a
+// generic codec. The internal Lux wire format is ZAP, which is element-
+// typed; persist a typed snapshot at the call site if needed.