Ah come on, guys, let's talk pragmatically. "Malleable editor as an OS layer" has benefits beyond subjective reasoning. Emacs has had M-x shell-command and arbitrary elisp eval forever. A metacircular MCP isn't some new capability class. Even if I didn't use Emacs - my shell, my editor, my browser extensions, my npm install, my VSCode plugins, my curl | bash from yesterday - they all have the same access. Singling out the LLM in this context is like selection bias.
Of course, reasonable mitigations are a must - just like for any other tool. Narrowing MCP scope - tool routing rules, read-only git defaults, etc. "Docker or nothing" is a lazy answer - Docker-for-everything has real costs: friction, broken integrations, worse ergonomics.
Practical security is all about staying in the goldilocks zone. You shouldn't get relaxed about the basics - sandboxing, 2FA, password managers - they are worth doing, and you can get so paranoid about so many things, and yet against a targeted, well-resourced attacker, your sandboxing posture is mostly irrelevant. The interesting attacks bypass the threat model entirely. Read about Ben Nassi's team research¹ - pretty cool example. There are multitudes of other ways and your Docker container won't stop them. Defend against the boring 99%, and accept that the 1% is someone else's problem (or a much bigger problem than your dev environment)
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¹ https://www.nassiben.com/video-based-crypta
TLDR LLM Summary: Researchers showed that a device's power LED subtly flickers in brightness and color while the CPU performs cryptographic work, and these flickers leak information about the secret key. By pointing an ordinary video camera (an iPhone or an internet-connected security camera) at the LED and exploiting the camera's rolling shutter, they boosted the effective sampling rate from 60 to 60,000 measurements per second, enough to do cryptanalysis. Using only this video footage, they recovered full ECDSA and SIKE keys from a smartcard reader and a Samsung Galaxy S8, with no malware on the target devices.