fix: Handle platform specific PTY polling for terminal copy (#279)

* fix: Handle platform specific PTY polling for terminal copy

* fix: Code review fixes

* fix: Code review fixes

internal/pty/output_copy.go

@@ -0,0 +1,40 @@
+package pty
+
+import (
+	"context"
+	"errors"
+	"io"
+)
+
+const outputCopyBufferSize = 32 * 1024
+
+// copyWithContext is a plain context-aware copy used as a fallback when the
+// source is not a *os.File (e.g. mocks in tests) and on platforms without a
+// poll-based reader. Cancellation is observed between reads.
+func copyWithContext(ctx context.Context, dst io.Writer, src io.Reader) error {
+	buf := make([]byte, outputCopyBufferSize)
+	for {
+		select {
+		case <-ctx.Done():
+			return nil
+		default:
+		}
+
+		nr, err := src.Read(buf)
+		if nr > 0 {
+			nw, werr := dst.Write(buf[:nr])
+			if werr != nil {
+				return werr
+			}
+			if nw < nr {
+				return io.ErrShortWrite
+			}
+		}
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				return nil
+			}
+			return err
+		}
+	}
+}