A.5:4 - Solution

FPF’s modularity is declarative, not “callable”: pattern texts publish law‑governed declarations (vocabulary + laws + applicability) that can be reused and specialised.

To keep the Kernel open‑ended, use the following boundary rules:

1. Kernel minimality (C‑5). Domain knowledge stays outside the Kernel by default; it enters as extension vocabularies and laws.
2. Boundary packaging via U.Signature (A.6.0). For reusable declaration bundles admitted as signatures under A.6.0, expose actual declaration dependencies in an explicit SignatureManifest (imports, provides).
3. Dependency vs specialisation are separate relations. imports forms a dependency DAG constrained by E.5.3; refinement/extension (⊑, ⊑⁺) is expressed separately (for mechanism declarations, see A.6.1:4.8; use C.29 when a mathematical morphism is claimed) and should not be conflated with imports.
4. Registry references stay references. Bridge ids, policy‑ids, and edition‑ids (Part F) are registry identifiers: they are cited/pinned where needed, not treated as exported symbols in provides.