Thirteen pieces. Folding them.
Two axes
"How is that different" was two questions.
To a platform that runs apps inside a device — who owns the business. There, the one that owns the device makes the business, and growth is counted in units. Here, the people who own domains each make their own, and growth is counted in domains. And the two are not a place to fight — go in as one app and that screen becomes the place from which outside devices are handled.
To a window a model opens — who owns the window. MCP Apps is the window a model shows a person; this is the window where a person handles a machine. Remove the model and the first disappears; the second runs without one. And the two can sit on the same screen.
Different layers, so neither answer cuts the other. This volume was ordered that way to avoid diminishing either.
Where it started
This work did not begin by looking at MCP.
A runtime where an app runs from declaration alone had been in build before that — with its own sandbox, state isolation, resource management and execution engine. After MCP was published, a connection layer went on top.
The public record reads like this.
| Date | |
|---|---|
| MCP protocol published | 2024-11-05 |
mcp_client · mcp_server 0.1.0 | 2025-03-25 |
mcp_llm 0.1.0 | 2025-04-06 |
mcp_server 1.0.0 — "supports embedded systems" in the description | 2025-06-06 |
flutter_mcp_ui_runtime 0.1.0 | 2025-06-16 |
| MCP-UI · Apps SDK appear | 2025-11 |
| SEP-1865 created | 2025-11-21 |
The UI runtime today implements the 1.4 specification. 158 widgets, Material 3 theming, design-token round trips, multi-server orchestration. There are six form factors and one of them is embedded — the one a host pins, for kiosks and industrial equipment and vehicle consoles.
This is not about putting the dates first. That the previous thirteen pieces never raised a date is the point. State the difference first; give the dates when asked.
What the table says is one thing — someone else was solving the same problem. They started from a web host; we started from devices. We simply did not know about each other.
From Here, the Domain Does It
What the structure opens and who fills it are two different things.
A different grade of screen per channel. That one server hands out a different screen depending on where the client attached is confirmed on screen in this volume. How many grades there are, and what each seat may open, is set by the people who know the equipment — and that decision never leaves them. That is the point of the structure.
Field transports. An industrial bus, a classification protocol — the place that takes it is the device side. When the device offers its functions the screen follows as it is; a change of transport does not mean writing the screen again.
A domain's verification regime. The party being verified stays the party that built the equipment, because the screen never duplicates the function. That was one of this volume's two axes.
All three seats are filled by whoever built the equipment. The structure does not stand in for them; it fixes where each one attaches.
The proposal
MCP has opened a path for extensions and is moving toward a working-group model. The seats that exist are transports, authorization, registry, security, multimodality, compliance.
There is no seat yet for constrained environments and physical devices.
We propose starting that discussion. Not writing a new specification — putting together, with a running implementation, what does and does not work on embedded targets. There are things you only learn by getting it onto the hardware, and the thirteen pieces of this volume are part of that list.
We would like to talk with people solving the same problem from the other side.
Finally
This volume never wrote "we are better". It did not need to.
When the ownership differs, what is possible and what is not separate on their own. We wrote that separation thirteen times, and confirmed on screen whatever could be confirmed.
And this structure stands on a written document. What a declaration guarantees is set down there, and the screen comes out as written. Everything this volume rests on came from there.
makemind.dev "Horizon" — Every measurement in this volume came from the samples and probes published with it.