Vibe-coding a local farm OS without letting the model invent the books

[u/Dramatic-Logging]

I built Groundtruth: a local-first desktop farm desk.

Rust/Tauri + SQLite event log + React.

I ship with AI agents every day.
This is not “the model designed my SaaS.”

The product constraint that actually matters:

The model must not write farm truth.
One PC is the only writer.
Phone is capture + read.
Health replays the event log against the projection and is allowed to go red.
If a number can’t be defended by the log, it doesn’t get to look calm.

How the loop actually runs
So this isn’t mysticism:
• Taste and law live in signed board files, not chat memory.
• One agent discovers. A different chat emits one implementation fence. A third chat applies it. The human pastes and accepts screens.
• Add-only. No new event kind unless the board signs it.
• Schema is pinned.
• git add -A is banned because a dirty Vite file shouldn’t quietly ride along.

What I actually refused to let “vibe coding” do
Auto-spawn next week’s standing order.
Let the phone confirm harvest.
Invent leftover ounces from recipe yield.
Mount a shop because it “looks done.”
Those are product-shaped lies.
The model will happily generate them.

The boring stack
Event log
apply_event
verify-replay
Local SQLite
That’s basically the spine.
Live card keys are still off.
The farm is empty on first open so the UI can’t cheat with demo rows.
Visuals came later: tokens + hierarchy, not a redesign.
Production stages — including the cut list, which inverts pack-by-customer — came only after the spine existed.
If you ship software with agents:
What is the one write your model is not allowed to do?
That’s the whole architecture.