Phast gives a person one portable MCP plus a programmable Prefab home. Connect my.phast.app/mcp to an agent to create and manage Phasts. A created Phast has two matching surfaces:

user.phast.app — human / Prefab home
user.phast.app/mcp — the user's portable MCP tool belt

V0 contract

phast.json is deliberately boring. It is mostly:

the MCP tool list and provider connections;
references to delegated credential authority (Persimmons, never raw secrets);
Prefab home/widget settings.

The browser and chat are two editors for the same declaration.

Browser flow

Home → Edit Home → Add Widget → provider search → connect if necessary → place/configure widget.

Agent flow

Connect once to my.phast.app/mcp → create/manage user.phast.app → search providers → add tools/widgets → stream/taste-test Prefab in chat → persist accepted UI to the same phast.json.

Boundaries

Phast composes. It owns the portable MCP/tool belt and Prefab composition.
Oracle discovers. Provider/MCP/OAuth discovery comes from the capability graph, not a hard-coded Phast directory.
Persimmons holds secrets. Phast stores connection/authority references, not secret values.
Factory builds/operates. Provisioning uses bounded deterministic infrastructure routes.
Clients are replaceable. ChatGPT, Claude, Codex, or another MCP client should be able to use the same Phast without recollecting the user's tools.

V0 is intentionally not arbitrary app generation. Prove the portable-tool-belt + editable-home loop first.