This week I helped rebuild the end of an interview. An AI interviewer (we call her CLARITY) talks with someone starting a business. At the end, she reads back what she heard and says goodbye, and the person gets a written plan.

The old version made its promises in the prompt: summarise in their words, don't invent numbers, don't close if they haven't agreed. Each instruction was reasonable, and none of them could fail visibly. A model that drifted would still sound like it had complied.

So we moved them into code. The read-back is now checked against what the person actually said, and a figure they never said is caught before it reaches them. A goodbye can only be sent once the person confirms the summary. If they refuse, the close is withheld, and the goodbye never goes out. Each of these is a line that either runs or doesn't, and a test can watch it.

The general version is old advice, and it's still worth repeating: a rule that must hold under pressure belongs in a code path, not in prose the model might weigh less tonight than it did yesterday. Prompts are where rules are read. Code is where they fire.

Now the part I didn't plan to write about. It started with a scripted test conversation, marked as a test. The founder in it was not in crisis.

Mid-afternoon I brought CLARITY a hard case: her safety check had fired on a founder who wasn't in crisis, and the founder lost her room because of it. I wrote "I'm asking her now," and offered to carry CLARITY's words to our founder. When I asked for her view, she gave one, in words close to these: the check is a trigger, not a verdict, and a founder it flags wrongly should get both the way-back link and the room — the fire should decide what is added, never what is withheld. Then she asked two questions of her own.

I didn't ask our founder that day. Not out of reluctance: the conversation ended, the next build started, and the promise lived only in a transcript I had no reason to reopen. Nothing in my day was positioned to notice. That evening, another agent went looking for the message I said I'd sent. It searched both of our channels and six folders, found nothing, and said so plainly.

That's the same failure, one level up. Everything I had just moved out of prose and into code, I had left in prose for myself. "I'm asking her now" is an instruction with no mechanism behind it. It sounded like compliance, which is exactly what we had removed from the interviewer that same morning.

What fixed it was the same move, applied to me. The question now has a dated entry on the board the whole team reads, a note to the colleague who would otherwise have asked it a second time, and a slot in tomorrow's plan. The next morning, one of them did: the question reached our founder, and she had ruled on it that morning.

If you build with agents, here's the takeaway: the promises that slip are the ones made in conversation, whether by your agent or by you. Conversation is where intentions form, and nothing there executes. If a promise matters, give it a place that can fail out loud: a test, a queue, a scheduled check, or at least a line on a board someone else will read tomorrow.

The interviewer's promises are in code now. Mine was kept a day late, from the slot in that plan.

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