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The agent harness belongs outside the sandbox

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Re: The agent harness belongs outside the sandbox

#31
post #27

Earlier quoted context omitted.

But what is an agent without tools?

Code.

Like as in what its made out of, or what it makes? Neither really makes sense here? Lots of things are made out of code and not necessarily agents, but also (from my decidedly outside observer perspective) "agents" are not limited to being code producers either.

Re: The agent harness belongs outside the sandbox

#32

I am not sure anyone knows what a harness is at this point. I've heard 17 different definitions of it at this point. It's almost like a buzzword in search of a problem.

I don’t even know what an agent means, let alone harness.

Agent is currently defined as "what I want it to mean given whatever I am talking about".

Personally, for me it embodies a level of autonomy. I define that as, an AI model with potential to interact with something external to itself based on its output, where that includes its own future behavior.

Re: The agent harness belongs outside the sandbox

#33

I am not sure anyone knows what a harness is at this point. I've heard 17 different definitions of it at this point. It's almost like a buzzword in search of a problem.

If you use cloud models.. the harness is what runs in your computer

AI companies would love if everything ran in their cloud, but arguably there are latency reasons or other reasons to run at least some stuff in your own computer

Re: The agent harness belongs outside the sandbox

#34
post #28

Personally, I find it fascinating to watch how, whenever a new technology appears, people start competing to define and own its standards. Manus rebuilt its harness five times in six months. The model stayed the same, but the architecture changed five times. LangChain re-architected Deep Research four times in one year. Anthropic also ripped out Claude Code’s agent harness whenever the model improved. Ever since Mitc…

> Ever since Mitchell Hashimoto mentioned the harness in February

What. The idea is as old as anyone can remember, and wrt. LLMs, it was known to be important since at least as early as ChatGPT being first released.

Re: The agent harness belongs outside the sandbox

#35
Two points:

-What remains unsolved is what should an Agent reasonably have access to in what context and for how long (etc).

Probabilistic code that can run far faster than human driven code, we don’t have a great model yet. We all should spend our energy there…

- Separating / putting controls on the FS resource is no different than putting the agent behind a firewall / allow-deny list.

It doesn’t invalidate running a sandbox in a sandbox to have better security.

Re: The agent harness belongs outside the sandbox

#36
post #28

Personally, I find it fascinating to watch how, whenever a new technology appears, people start competing to define and own its standards. Manus rebuilt its harness five times in six months. The model stayed the same, but the architecture changed five times. LangChain re-architected Deep Research four times in one year. Anthropic also ripped out Claude Code’s agent harness whenever the model improved. Ever since Mitc…

> Ever since Mitchell Hashimoto mentioned the harness in February What. The idea is as old as anyone can remember, and wrt. LLMs, it was known to be important since at least as early as ChatGPT being first released.

Yes, the concept itself is not new. Around 2022, people would usually have called it the orchestration layer.

But I think the term started being used closer to its current meaning around this point:

https://www.softwareimprovementgroup.com/blog/what-is-harnes...

In a way, the sequence was something like:

prompt engineering(23~4) -> context engineering(25) ->harness engineering(26)

At first, it was mostly understood as a correction or extension of prompt engineering. But the idea of “harness” as the layer that corrects, constrains, and operationalizes agents seems to have emerged much more clearly around 2026.

So yes, there is definitely some terminological confusion in the early phase. That is normal. New technical fields often begin with several competing names for almost the same layer, and only later does one term become stable.

Re: The agent harness belongs outside the sandbox

#37
> A lot of what an agent does doesn't need a sandbox at all: thinking, calling APIs, summarizing, waiting for CI.

I don’t get it. Calling an API requires a sandbox in most cases. The others could be abused in service of an un-sandboxed agent with API access.

If the harness is outside the sandbox then it’s just an ambiguous and confusing security model and boundary.

Re: The agent harness belongs outside the sandbox

#38
post #28

Personally, I find it fascinating to watch how, whenever a new technology appears, people start competing to define and own its standards. Manus rebuilt its harness five times in six months. The model stayed the same, but the architecture changed five times. LangChain re-architected Deep Research four times in one year. Anthropic also ripped out Claude Code’s agent harness whenever the model improved. Ever since Mitc…

Author here.

In my opinion, the main driver here is how fast models have evolved in the past 12 months. It makes the architecture of everything around them obsolete, very fast.

We went from using models as a building block, wrapping them in heavy workflow code, to now models being smart enough to drive their own workflows and planning.

Re: The agent harness belongs outside the sandbox

#39
post #28

Personally, I find it fascinating to watch how, whenever a new technology appears, people start competing to define and own its standards. Manus rebuilt its harness five times in six months. The model stayed the same, but the architecture changed five times. LangChain re-architected Deep Research four times in one year. Anthropic also ripped out Claude Code’s agent harness whenever the model improved. Ever since Mitc…

Author here. In my opinion, the main driver here is how fast models have evolved in the past 12 months. It makes the architecture of everything around them obsolete, very fast. We went from using models as a building block, wrapping them in heavy workflow code, to now models being smart enough to drive their own workflows and planning.

Really enjoyed your post, by the way. The idea of putting skills and memories in a database while keeping the file shaped interface for the agent is clean. One read/write surface, two backends, invisible to the modle that's a nice piece of design, and the candor in the "what's still hard" section made me trust the rest of the post. My comment above was meant as a joke, not about your architecture. If this pattern becomes the standard, I'll happily migrate my workflow again.

One thing I wonder about is whether path routing alone is enough.

If `/workspace` goes to the sandbox and `/memory` or `/skills` goes to the database, the path tells you where to send the request. But it does not tell you whether this user, session, or agent is allowed to access it.

When I built something similar with an MCP filesystem, I found that I needed a scope check before actually running the operation. In my case, I was using GPT dev mode through a Cloudflare tunnel to control my local environment/model, so this kind of boundary became important.

So I like the path-routing idea, but I wonder if it eventually needs a scope or permission layer as well.

Re: The agent harness belongs outside the sandbox

#40
> Three engineers trigger the agent on the same incident, and they all see stale state until their sessions end. Conflict resolution, eventual consistency, cache invalidation.

Arguably this is a feature not a bug. Conflict resolution forces the need for a process to come to agreement on a common source of truth - one of the reasons why most Git repos don’t allow users to push to main directly. Writing directly to a shared memory database seems like it would result in chaos and a host of side effects once the number of users scales.

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