> AI excels at problem-solving, it's conceivable that Muse simply found a path to the data.

No. What you're missing here is that Muse for Mac is a native, compiled, code signed, notarized app, with specified entitlements. It can't simply rewrite its own executable code, so it can't do whatever it wants. You can even reverse engineer the app. Muse looks in ~/Library/Messages for the messages database; this is actually hard-coded in the executable file. Whatever ideas the remote LLM may come up with cannot automatically be translated into instructions that are executed by the Mac app. That's not how it works.