I built plugins for three editors. Everywhere, you're a guest in someone else's house

Over the last while I've built integrations for three places where people work with text and images: Obsidian , VS Code, and Figma. Doing a few of them back to back, I noticed something you don't see from a single one. They're all desktop apps. For your integration to exist at all, the person first installs a program on their machine, and then, inside it, your plugin. You're not writing for the web. You're writing code locked inside someone else's app — and each app has its own runtime, its own rules, and its own wall for you to walk into. The web trained us to think an HTTP request is one line. Inside someone else's sandbox, it turns out even that has to be earned. Figma was the strictest host of the three. I'll tell it through Figma, because it's locked down tighter than Obsidian or VS Code, and everything shows up on it at once. The task was almost comically simple: select a frame, write a caption, pick your social accounts, publish — without exporting the image and opening a second app. We already had the publishing API, so I expected the Figma side to be small. And it was: the main plugin file is 120 lines. The work wasn't in them. It was around them. Figma gives you bytes, not a file The first version came together easily. When the selection changes, the plugin checks whether there's one exportable node and tells the UI what it found. For the preview it exports a small copy; for publishing, separately, at 2×. const bytes = await nodes [ 0 ]. exportAsync ({ format : " PNG " , constraint : { type : " SCALE " , value : 2 }, }); 2× because the image still has a journey ahead of it: social networks recompress what you upload, and small text on a design goes noticeably softer by the time it lands in a feed. Then the first quirk of the foreign house. Figma hands the plugin not a file but raw PNG bytes — exportAsync() returns a Uint8Array . Our normal API won't eat that — it doesn't take a giant image stuffed into a JSON body. It creates a post first, hands the client