The narrow waist is a small set of primitives, each specified hard (RFC 2119 — MUST / MUST NOT / SHOULD), so everything above plugs in with total freedom. Because We hold Ourselves to honesty, the table shows not just what each primitive is but how real it is today — including the one piece that is still a stand-in.

#	Primitive	Module	Core invariant	Status
1	UIR — Universal Identity Root	`x/uir`	One global identity; per-chain accounts derived deterministically; one signature authorizes	Real
2	UAC — Universal Asset Commitment	`x/uac`	Total-supply invariant `total == Σ perChain + lockedInTransit`; minimum security-class per asset	Real
3	XMP — XChain Messaging Protocol	`x/xmp`	Trust-minimized messaging; clean split of READ and WRITE	Real (anti-replay + containment)
4	PAI — Proof Aggregation Interface	`x/pai`	A parent verifies children without re-executing; recursive aggregation	Aggregation real · prover MOCK (§10)
5	DA Interface (tiered)	`fabric/da` + `tools/dasidecar`	Committed data stays retrievable / sampleable per the tier's policy	Real (Celestia mocha)
6	VLC — Verifiable Log Commitment	`x/vlc`	Append-only logs: tamper-evident + timestamped + inclusion-provable; value-free	Real (RFC 6962 Merkle)
7	SC — Settlement Contract	`x/settlement`	Minimal Global-Root logic: finalize cross-region value, consume aggregated proofs	Real (no blind commitments)

⚠️ Primitive #4 (PAI) uses a MOCK prover. The aggregation circuit (STC → Cell → Root) is real; the cryptographic proof underneath is a mock, and ProofSystem.MOCK is rejected on every non-testnet network. A real prover (SP1/Boojum) is open work — see §10. So We do not say "We use SP1."

The primitives compose in a strict dependency order: UIR → (UAC, XMP) ; DA → (VLC, PAI) ; (UAC, XMP, PAI, VLC) → SC.

Diagram

Figure 4 — Dependency graph of the seven primitives.

Takeaway: freeze a small, correct core and thousands of people can build wildly different things above it that still interoperate. The internet did this with TCP/IP; XChain does it for verifiable data.