One Checkbox, Three Kinds of State in a Chrome MV3 Extension

I thought I had a settings bug. What I actually had was three different kinds of state pretending to be one boolean. While building a Chrome Manifest V3 email-tracker blocker, I expected a simple flow: you flip Gmail on in the settings, and the extension starts working in Gmail. That was the theory, anyway. The problem showed up when I was testing on a second Chrome profile. I'd enabled Gmail on my main profile, and Chrome Sync helpfully carried that preference over to the other one. But the optional permission for mail.google.com didn't come along — host grants live in the local profile and never sync. Profile number two now believed Gmail was enabled while lacking the host grant needed to inject the inbox content script or inspect its DOM. Depending on how you write your code, that's either a silent no-op or an extension quietly behaving as if access exists when it does not. Neither is great. Once I stopped and wrote it down, the picture got clearer. There are three separate things here: the inbox the user wants enabled, the host access Chrome has actually granted in this profile, and the dynamic DNR rules that are currently installed . Collapsing them into one flag is convenient. It's also wrong. The manifest is a menu, not an order The extension declares each webmail origin under optional_host_permissions . Every inbox gets activated on its own, and Chrome only asks the user for access when they turn that particular integration on. Here's the thing I had to internalize: declaring an optional origin means nothing by itself. Until the live grant exists, the extension has no business registering a content script for that inbox, poking at its DOM, or — by its own scoping policy — activating client-scoped blocking rules for it. Why bother with per-inbox prompts at all? Mostly trust. A tracker blocker that asks for all your webmail up front looks exactly like the thing it's supposed to protect you from. Asking for Gmail when you enable Gmail — and nothing more — is an