fix: clear stale upstream state on disconnect

pool/impl.go

@@ -164,8 +164,9 @@ func (c *StratumClient) Disconnect() {
 		return
 	}
 	c.closedOnce.Do(func() {
-		if c.conn != nil {
-			_ = c.conn.Close()
+		conn := c.resetConnectionState()
+		if conn != nil {
+			_ = conn.Close()
 		}
 		if c.listener != nil {
 			c.listener.OnDisconnect()
@@ -175,12 +176,28 @@ func (c *StratumClient) Disconnect() {
 
 func (c *StratumClient) notifyDisconnect() {
 	c.closedOnce.Do(func() {
+		c.resetConnectionState()
 		if c.listener != nil {
 			c.listener.OnDisconnect()
 		}
 	})
 }
 
+func (c *StratumClient) resetConnectionState() net.Conn {
+	if c == nil {
+		return nil
+	}
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	conn := c.conn
+	c.conn = nil
+	c.tlsConn = nil
+	c.sessionID = ""
+	c.active = false
+	c.pending = make(map[int64]struct{})
+	return conn
+}
+
 func (c *StratumClient) writeJSON(payload any) error {
 	c.sendMu.Lock()
 	defer c.sendMu.Unlock()
@@ -472,6 +489,7 @@ func (s *FailoverStrategy) OnDisconnect() {
 		return
 	}
 	s.mu.Lock()
+	s.client = nil
 	closing := s.closing
 	if closing {
 		s.closing = false

pool/strategy_disconnect_test.go

@@ -1,6 +1,7 @@
 package pool
 
 import (
+	"net"
 	"sync/atomic"
 	"testing"
 	"time"
@@ -63,3 +64,58 @@ func TestFailoverStrategy_Disconnect_Ugly(t *testing.T) {
 		t.Fatalf("expected repeated intentional disconnects to remain silent, got %d listener calls", got)
 	}
 }
+
+func TestStratumClient_NotifyDisconnect_ClearsState_Good(t *testing.T) {
+	serverConn, clientConn := net.Pipe()
+	defer serverConn.Close()
+
+	spy := &disconnectSpy{}
+	client := &StratumClient{
+		conn:      clientConn,
+		listener:  spy,
+		sessionID: "session-1",
+		active:    true,
+		pending: map[int64]struct{}{
+			7: {},
+		},
+	}
+
+	client.notifyDisconnect()
+
+	if got := spy.disconnects.Load(); got != 1 {
+		t.Fatalf("expected one disconnect notification, got %d", got)
+	}
+	if client.conn != nil {
+		t.Fatalf("expected pooled connection to be cleared")
+	}
+	if client.sessionID != "" {
+		t.Fatalf("expected session id to be cleared, got %q", client.sessionID)
+	}
+	if client.IsActive() {
+		t.Fatalf("expected client to stop reporting active after disconnect")
+	}
+	if len(client.pending) != 0 {
+		t.Fatalf("expected pending submit state to be cleared, got %d entries", len(client.pending))
+	}
+}
+
+func TestFailoverStrategy_OnDisconnect_ClearsClient_Bad(t *testing.T) {
+	spy := &disconnectSpy{}
+	strategy := &FailoverStrategy{
+		listener: spy,
+		client:   &StratumClient{active: true, pending: make(map[int64]struct{})},
+	}
+
+	strategy.OnDisconnect()
+	time.Sleep(10 * time.Millisecond)
+
+	if strategy.client != nil {
+		t.Fatalf("expected strategy to drop the stale client before reconnect")
+	}
+	if strategy.IsActive() {
+		t.Fatalf("expected strategy to report inactive while reconnect is pending")
+	}
+	if got := spy.disconnects.Load(); got != 1 {
+		t.Fatalf("expected one disconnect notification, got %d", got)
+	}
+}