One canonical model

There is exactly one canonical model: the Engineering Intermediate Representation. The kernel graph is its live realization. Everything else is a lowering of it, a projection of it or an interchange encoding of it. That covers a netlist, a view, a SPICE deck and a KiCad file.

No feature may introduce a second persisted representation of the same facts.

Why it is stated as a prohibition

Most hardware toolchains fail in the same place. The schematic, the BOM and the simulation deck each hold their own copy of the same facts, and each copy was true when it was written. Reconciling them becomes the work. The invariant removes that work by leaving nothing to reconcile.

The cost is real. A downstream tool that wants its own store cannot have one. It gets a generated Projection and recomputes, which is slower. A cache that can go stale is a second representation.

How it is enforced

ConstraintRegistry enforces it literally. Constructing a second registry for a project raises ELAB-0012:

ConstraintRegistry(project)   # fine
ConstraintRegistry(project)   # ELAB-0012: a second constraint registry was created

There is no flag to allow it.

What the model holds

Sixteen entity kinds, each a frozen dataclass carrying identity, parameters, provenance and a source location:

Group	Kinds
Structure	Component, Net, Rail, Connection, Domain
Interfaces	Interface, Port, Bus, Pin
Rationale	Requirement, Decision, Evidence, Calculation, Verification, Assumption
Analysis	Model

Every entity answers two questions. references() drives referential integrity, diff impact and topology adjacency. as_dict() drives canonical serialization. A new entity kind that does not answer both cannot participate in the graph.

Identity

An identifier is a UUIDv5 over (project namespace, "<kind>:<canonical semantic path>"), rendered as a prefix plus twelve hex digits. Two consequences matter in practice.

Re-derivation is stable. The same design gives the same identifiers, in this process or another one. Identifiers are not allocated from a counter, so there is no allocation order to preserve.

Collisions lengthen rather than renumber. An identifier is extended four digits at a time, only against the identifiers already in that revision, so lengthening is itself reproducible.

Three origins exist and are distinguished: derive() for a fact the kernel computed, authored() for one a person wrote and imported() for one that came from CAD.

Determinism

Identical inputs give byte-identical snapshots. This is verified across processes with differing PYTHONHASHSEED, not merely within one run.

Two rules make that hold. Magnitudes are Decimal strings under a fixed Context(prec=34), never binary floats, so no value depends on rounding mode. And canonical serialization sorts by Unicode code point, except for the collections in serialization.ORDERED_COLLECTIONS, whose order carries meaning and is preserved.