P6: MCP Is Extensible¶

Each MCP is extensible with new skills by the T3 self-training loop.

MCP-bearing harnesses opt into receiving T3-added skills through explicit extension_points. A harness that cannot accept extensions safely records that choice by setting extension_points = None.

Why it matters¶

The MCP surface is where capability extension lands. If an MCP cannot accept new skills through a documented contract, the self-training loop has no path to expand the system — and "self-improving" becomes a claim with no mechanism behind it.

How it is enforced¶

C4: Extension points requires an extension_points declaration (or an explicit opt-out) for MCP-bearing harnesses, and the extension registry registers an extension's tools against the named harness only when extension_points is non-null. Customers use the same surface to extend G6 with their own components. Full self-training validation is tracked separately, so this principle is partially validated today.

Primary gate: C4: Extension points.