Can a harness evolve on the fly?

The answer is in the first chapter of the paper. Agents depend on a harness. And a future harness could generate and deploy modifications to its own pieces while still serving requests. Every one of those modifications is, by definition, composition at runtime.

Because they would happen continuously and with little supervision, composability stops being a convenience.

• Without the temporal dimension Every change forces a restart And that throws away everything accumulated. At that frequency the downtime adds up and work in progress is interrupted again and again. The paper adds the awkward case: a faulty modification can disable the very process needed to fix it.
• Without the spatial dimension Every piece improvises It has to detect on its own the changes in the pieces it depends on. A naive replacement can silently break dependants or create cycles that only show up on reload.

Where the circle closes

In the product this already has a name: Creator mode, which lets you look inside the running system and mount and unmount pieces without restarting.

That mode is the first practical application of what the 88 pages spend their time proving.

What exists today and what does not

• Exists Mounting and unmounting at runtime Creator mode does it today, and hot reload works without marking anything by hand.
• Proposed by the architecture That the substrate holds The five theorems say a system that never stops recomposing ends up where it would have ended up assembled in one go.
• Could merely allow An agent that rewrites itself Nothing we have read claims that behaviour exists. It is what the architecture makes possible, not what the repository ships.