After 4 months solo: shipping a Windows tray AI hotkey on .NET 8 + WPF (and the Win32 paste-back rabbit hole)

I spent 4 months of nights and weekends building CapyBro — a Windows tray app that runs AI on any selected text via a global hotkey. Native .NET 8 + WPF (not Electron), MIT-licensed, ~49 MB installer. Two backends: cloud (OpenRouter) or fully local (Ollama). The hardest technical problem turned out to be Win32 paste-back into child controls. This post walks through that rabbit hole + the architecture decisions that paid off.

Why I built this

For most of 2025, my AI workflow was this loop:

1. Read something in Slack / a doc / a Telegram message

2. Alt+Tab → ChatGPT tab → paste