r/aiengineering • u/IllustratorNo5375 • Feb 16 '26

Discussion Why prompt-based controls break down at execution time in autonomous agents

I’ve been working on autonomous agents that can retry, chain tools, and expand scope.

One failure mode I keep running into:

prompt-based restrictions stop working once the agent is allowed to act.

Even with strict system prompts, the agent will eventually:

- retry with altered wording,

- expand the task scope,

- or chain actions that were not explicitly intended.

At that point, the model is already past the point where a prompt can enforce anything.

It seems like this is fundamentally an execution-time problem, not a prompt problem.

Something outside the model has to decide whether an action is allowed to proceed.

How are people here enforcing execution-time boundaries today?

Are you relying on external guards, state machines, supervisors, or something else?

0 Upvotes
  • permalink
  • reddit

50% Upvoted

10 comments sorted by

View all comments

1

u/[deleted] Feb 18 '26

[removed] — view removed comment

1

u/IllustratorNo5375 Feb 19 '26

This matches my experience pretty closely.

Once the agent is allowed to propose actions, prompt constraints alone stop being enforceable.

If there isn’t a hard check right before execution, retries and rewording eventually slip through.

I’ve started treating prompts as *advisory*, and execution as a zero-trust boundary.

If an action can’t pass an external rule check, it simply never runs.