Giving an AI coding agent a deterministic "architecture linter" so it stops faking "done"

Most architecture diagrams are dead artifacts. A pretty PNG in /docs, drawn once, stale in a month, verifying nothing — it'll happily show an arrow that isn't in the code and stay silent about the ones that are. So when I started having a coding agent "draw the architecture," I expected more of the same. It wasn't, and the reason is one property. I use Event Storming — the domain-modeling format where you lay the system out as a sequence in time: an event triggers a reaction, the reaction a command, the command a new event. The useful part isn't the sticky notes, it's the invariant underneath: everything has a cause and an effect. A domain event has a cause. A command has a result. A policy bridges someone else's event to your command. That turns into something an agent can actually check. So instead of asking the model to "look smart," I gave it a cheap deterministic graph check. It walks the cause→effect graph of the board and returns structured gaps: an event with no cause a command that produces no event a policy that bridges nothing an isolated card (someone sketched a thought and never finished it) Now the agent has a feedback loop that doesn't lie and doesn't tire: author the board → validate (read the gaps) → refine → re-validate. It iterates to zero gaps the same way it iterates to green tests. No more "I think I wired it all up." The part I actually care about is what it must NOT do. When mechanical gaps hit zero, a naive system says "architecture done." That's a lie. There's a hard difference between: a gap — a mechanical loose end, an arrow you forgot; the agent fixes it in seconds. an open question — an unresolved business decision (e.g. "if the restaurant rejects the order AFTER the card was charged, is that a void or a refund?"). You can't "fix" that by drawing an arrow, because nobody has decided which arrow. Painting it green means the agent silently made a product decision for you — the worst kind of tech debt. So those stay red and visible. The board passes validation but keeps the open questions listed. A green check means "the story is mechanically connected AND every unresolved fork is surfaced, not buried" — which is exactly the line between what the agent may build alone and where it must stop and ask a human. I ran this on a real seeded project: a 5-context food-delivery domain. Across the five boards — 17 mechanical gaps caught and closed, 15 business questions deliberately kept in the open. Same loop in every context. The generalizable pattern, minus my tooling: between an LLM/agent step and an expensive or irreversible downstream step, insert the cheapest artifact that has a checkable invariant, make the agent iterate against it, and hard-separate "mechanically incomplete" (agent fixes) from "undecided" (human decides). Never let the agent paint over the second with the first.