fix(raft): preserve stdlib logger writer in bolt filter; propagate ctx through ResignLeader

- suppressBoltNoise.Do now wraps log.Writer() instead of os.Stderr so any
  existing stdlib logger redirection is preserved rather than clobbered
- ResignLeader now accepts a context.Context: leadershipTransfer runs in a
  goroutine and a select abandons the caller at ctx.Done(), returning
  ctx.Err(); the goroutine itself exits once the inner raft transfer
  completes (bounded by ElectionTimeout)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: auricom

pkg/raft/node.go

@@ -93,7 +93,7 @@ func buildRaftConfig(cfg *Config) *raft.Config {
 
 func NewNode(cfg *Config, logger zerolog.Logger) (*Node, error) {
 	suppressBoltNoise.Do(func() {
-		log.SetOutput(&boltTxClosedFilter{w: os.Stderr})
+		log.SetOutput(&boltTxClosedFilter{w: log.Writer()})
 	})
 	if err := os.MkdirAll(cfg.RaftDir, 0755); err != nil {
 		return nil, fmt.Errorf("create raft dir: %w", err)
@@ -278,11 +278,19 @@ func (n *Node) leadershipTransfer() error {
 // It is a no-op when the node is nil or not currently the leader.
 // Call this before cancelling the node context on graceful shutdown to minimise
 // the window where a dying leader could still serve blocks.
-func (n *Node) ResignLeader() error {
+// The transfer is abandoned and ctx.Err() is returned if ctx expires first.
+func (n *Node) ResignLeader(ctx context.Context) error {
 	if n == nil || !n.IsLeader() {
 		return nil
 	}
-	return n.leadershipTransfer()
+	done := make(chan error, 1)
+	go func() { done <- n.leadershipTransfer() }()
+	select {
+	case err := <-done:
+		return err
+	case <-ctx.Done():
+		return ctx.Err()
+	}
 }
 
 func (n *Node) Config() Config {

pkg/raft/node_test.go

@@ -183,13 +183,13 @@ func TestNodeStartNilNoop(t *testing.T) {
 
 func TestNodeResignLeader_NilNoop(t *testing.T) {
 	var n *Node
-	assert.NoError(t, n.ResignLeader())
+	assert.NoError(t, n.ResignLeader(context.Background()))
 }
 
 func TestNodeResignLeader_NotLeaderNoop(t *testing.T) {
 	// Non-nil node with nil raft field — IsLeader() returns false, no transfer attempted.
 	n := &Node{}
-	assert.NoError(t, n.ResignLeader())
+	assert.NoError(t, n.ResignLeader(context.Background()))
 }
 
 func TestNewNode_SnapshotConfigApplied(t *testing.T) {