求助大家图中阴影部分要怎么画?

这是源代码的文件。
\documentclass[tikz,border=5pt]{standalone}
\usepackage{amsmath}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}
\begin{scope}[x={(1cm,0cm)},y={(0cm,1cm)}]
\draw[-stealth](-4,0)--(4,0);
\draw[-stealth](0,-3)--(0,3)node[above]{$(z)$};
\draw[-](0,0)--(2.5,3);
\node[left]at(0.13,-0.15){$\scriptstyle O$};
\draw[-](3,-3)--(0,0);
\end{scope}
\draw[-{Stealth[scale=0.5]}](-50:0.24)arc(-50:60:0.24);
\node at(0.45,0.1){$\frac{\pi}{\alpha}$};
\end{tikzpicture}
\end{document}
Step1. 代码不要包含一大堆与原始问题无关的内容。
Step2. 可以考虑基于angles库绘制代码,简化并美化角度的标注
Step3. 基于patterns库实现阴影的绘制
\documentclass[tikz,border=5pt]{standalone}
\usepackage{amsmath}
\usepackage{fourier}
\usetikzlibrary{arrows.meta,angles,quotes,patterns,bending}
\begin{document}
\begin{tikzpicture}
\draw[-Stealth,thick] (-2,0)--(4,0);
\draw[-Stealth,thick] (0,-3)--(0,3) node[above]{$(z)$};
\draw (3,-3) -- coordinate[pos=.1] (A) (0,0) node[label=below left:$O$] (O) {} -- coordinate[pos=.9] (B) (2.5,3);
\draw[pattern=north west lines,pattern color=magenta!50] (A) -- (0,0) -- (B) -- (A) -- cycle;
\pic["$\pi/\alpha$", draw=teal, text=teal, fill=white, -Stealth, angle eccentricity=1.75] {angle = A--O--B};
\end{tikzpicture}
\end{document}