* I don't understand how IndexedDB and WebCrypto have anything to do with a distributed chat system like Slack*
Uh, what? The OP didn't mention Slack at all. I mean, you could make this kind of...comment on anything: "What does X have to do with Y?" (In this case, X=(WebCrypto & IndexedDB) and Y=(Slack)). But it's not very useful.
Yes, you're right. I missed it. I guess he's making a point about wanting his own chat history searchable on his client, and yet opaque to the server-side Slack operators. I agree it's not a great application, though.
Uh, what? The OP didn't mention Slack at all. I mean, you could make this kind of...comment on anything: "What does X have to do with Y?" (In this case, X=(WebCrypto & IndexedDB) and Y=(Slack)). But it's not very useful.