fix: Windows build failure due to missing SIGWINCH

Move SIGWINCH terminal resize handler into platform-specific
winchControl() function. Unix version handles resize via
syscall.SIGWINCH, Windows version returns nil (no resize).

Author: deevus

sandbox/incus/exec.go

@@ -6,11 +6,9 @@ import (
 	"fmt"
 	"io"
 	"os"
-	"os/signal"
 	"strings"
 	"time"
 
-	"github.com/gorilla/websocket"
 	"github.com/lxc/incus/v6/shared/api"
 	"golang.org/x/term"
 
@@ -175,27 +173,7 @@ func (i *Incus) Console(ctx context.Context, name string, opts sandbox.ConsoleOp
 		Stdout:   os.Stdout,
 		Stderr:   os.Stderr,
 		DataDone: dataDone,
-		Control: func(conn *websocket.Conn) {
-			// Handle SIGWINCH for terminal resize.
-			ch := make(chan os.Signal, 1)
-			signal.Notify(ch, sigWINCH())
-			defer signal.Stop(ch)
-
-			for range ch {
-				w, h, err := term.GetSize(fd)
-				if err != nil {
-					continue
-				}
-				msg := api.InstanceExecControl{
-					Command: "window-resize",
-					Args: map[string]string{
-						"width":  fmt.Sprintf("%d", w),
-						"height": fmt.Sprintf("%d", h),
-					},
-				}
-				_ = conn.WriteJSON(msg)
-			}
-		},
+		Control: winchControl(fd),
 	}
 
 	op, err := i.server.ExecInstance(full, execPost, args)

sandbox/incus/signal_unix.go

@@ -3,10 +3,35 @@
 package incus
 
 import (
+	"fmt"
 	"os"
+	"os/signal"
 	"syscall"
+
+	"github.com/gorilla/websocket"
+	"github.com/lxc/incus/v6/shared/api"
+	"golang.org/x/term"
 )
 
-func sigWINCH() os.Signal {
-	return syscall.SIGWINCH
+func winchControl(fd int) func(*websocket.Conn) {
+	return func(conn *websocket.Conn) {
+		ch := make(chan os.Signal, 1)
+		signal.Notify(ch, syscall.SIGWINCH)
+		defer signal.Stop(ch)
+
+		for range ch {
+			w, h, err := term.GetSize(fd)
+			if err != nil {
+				continue
+			}
+			msg := api.InstanceExecControl{
+				Command: "window-resize",
+				Args: map[string]string{
+					"width":  fmt.Sprintf("%d", w),
+					"height": fmt.Sprintf("%d", h),
+				},
+			}
+			_ = conn.WriteJSON(msg)
+		}
+	}
 }

sandbox/incus/signal_windows.go

@@ -0,0 +1,10 @@
+//go:build windows
+
+package incus
+
+import "github.com/gorilla/websocket"
+
+// winchControl returns nil on Windows where SIGWINCH does not exist.
+func winchControl(_ int) func(*websocket.Conn) {
+	return nil
+}