One thing I'd add from building a shell plugin that routes natural language to agents: the detection heuristic matters way more than flag conventions.

We spent a lot of time on when to run something as a shell command vs send it to an LLM. The hard lesson: false positives are much worse than false negatives. "git push --force" accidentally going to an LLM instead of executing is the kind of thing that kills user trust instantly. Our heuristic ended up very conservative.

The bigger surprise was the real-time visual indicator. We added a small color signal showing "this goes to shell" vs "this goes to agent" as you type, and it changed how people wrote more than anything else. Before it, people hedged natural language queries with shell-like syntax just in case. After it, they wrote normally.

On the isatty point — right for automation. But there's a third mode worth thinking about: "orchestrated interactive," where a human is watching the agent use your CLI and needs to step in. Pure non-interactive breaks that entirely.