ELI5: Why would two AI plugins conflict if they're just making API calls?

That's a great point of entry for explaining this. When you said they're "listening to your keystrokes" and "analyzing your entire open file tree," you've pinpointed exactly where the resource battle starts.

It's easy to think of the AI plugin as a simple chat interface that fires off a request when you ask. But as you found, it's more like a live surveillance system for your workspace. Each one maintains its own, separate real-time model of your project's state, and building that model is what's computationally expensive, not the final API call. The lag happens because your CPU and editor's internal APIs are being hammered by two competing sets of these background analyzers.