Add test showing StartPty fails on Windows when given a zero size

CreatePseudoConsole rejects zero dimensions with E_INVALIDARG, so
starting a pty sized after a hidden (and thus zero-sized) view fails.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/commands/oscommands/pty_windows_test.go

@@ -0,0 +1,28 @@
+package oscommands
+
+import (
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// The requested size can legitimately be zero: the pty inherits the main
+// view's dimensions, and that view is zero-sized while hidden, e.g. in
+// full-screen mode with a side panel focused.
+func TestStartPtyWithZeroSize(t *testing.T) {
+	// The command deliberately produces no output: go test runs with
+	// redirected std handles, which CreateProcess duplicates into the child
+	// in place of handles to the attached pseudoconsole, so command output
+	// would bypass the pty and pollute the test log.
+	sp, err := StartPty(exec.Command("cmd", "/c", "exit 0"), 0, 0)
+	/* EXPECTED:
+	assert.NoError(t, err)
+	ACTUAL: */
+	assert.Error(t, err)
+
+	if err == nil {
+		_ = sp.Wait()
+		_ = sp.Pty.Close()
+	}
+}