bf := b[:min(int64(len(b)), holeStart-sr.pos)]
			nf, err = tryReadFull(sr.fr, bf)
		} else { // In a hole fragment
			bf := b[:min(int64(len(b)), holeEnd-sr.pos)]
			nf, err = tryReadFull(zeroReader{}, bf)
		}
		b = b[nf:]
		sr.pos += int64(nf)
		if sr.pos >= holeEnd && len(sr.sp) > 1 {
			sr.sp = sr.sp[1:] // Ensure last fragment always remains
		}
	}

	n = len(b0) - len(b)
	switch {