Complete architectural overview of the Vocabulary Hub v0.2.1 specification implementation (alexandria-server, alexandria-client, and alexandriac).

Vocabulary Hub (`vhub`) — Specification v0.2.1

Alexandria includes the complete reference implementation of the Vocabulary Hub System v0.2.1 (F2–F8, Appendices A and B) and the eunomia.profiles/v1 YAML profile compiler.

It is engineered around two strict architectural guarantees:

Deterministic Convergence (REQ-SYS-001): Any two alexandria-client instances that have synchronized the same signed listing (eunomia.versions/v1) and evaluate the same DSP message at the same instant t produce the exact same classification, HTTP action, and VHub-Verdict header.
Zero Hub Contact on the Hot Path (REQ-SYS-002): The edge validation sidecar (alexandria-client) never contacts alexandria-server or resolves did:web while processing a Connector's DSP traffic. All cryptographic verification (S1–S13) happens asynchronously in the background.

System Topology

  ┌─────────────────────────────────────────────────────────────────────────┐
  │                       alexandria-server (C-HUB)                               │
  │                                                                         │
  │  ┌─────────────────────┐  ┌─────────────────────┐  ┌─────────────────┐  │
  │  │ /v1 Governance API  │  │  /pub Distribution  │  │ /.well-known/   │  │
  │  │ Draft -> Candidate  │  │  Immutable Blobs &  │  │ did.json        │  │
  │  │ -> Release / Revoke │  │  303 Head Redirects │  │ (Ed25519 JWK)   │  │
  │  └──────────┬──────────┘  └──────────▲──────────┘  └────────▲────────┘  │
  │             │                        │                      │           │
  │             ▼                        │                      │           │
  │  ┌───────────────────────────────────┴──────────────────────┴────────┐  │
  │  │ compiler_dsl (eunomia.profiles/v1) · SQLite (immutable triggers)  │  │
  │  │ JCS + EdDSA Signer · TransparencyLog (SCITT) · Listing Scheduler  │  │
  │  └───────────────────────────────────────────────────────────────────┘  │
  └───────────────────────────▲──────────────────────▲──────────────────────┘
                              │                      │
             Background Sync  │ GET /v1/versions     │ GET /.well-known/did.json
             (S1–S13, V1–V4)  │ GET /pub/packages/.. │ (cached by did_ttl)
                              │                      │
  ┌───────────────────────────┴──────────────────────┴──────────────────────┐
  │                       alexandria-client (C-CLI Sidecar)                       │
  │                                                                         │
  │  ┌────────────────────────────────────┐  ┌───────────────────────────┐  │
  │  │ Background Sync & Atomic Store     │  │ Admin & Telemetry (:9900) │  │
  │  │ Continuity · PVP Digest Verify     │  │ /status · /versions       │  │
  │  │ Retained Packages · Agreements     │  │ /agreements · /metrics    │  │
  │  └─────────────────┬──────────────────┘  └───────────────────────────┘  │
  │                    │ In-Memory Snapshot (app.Cell)                      │
  │                    ▼                                                    │
  │  ┌───────────────────────────────────────────────────────────────────┐  │
  │  │ Hot-Path L7 DSP Proxy (dsp-ingress :8443 / dsp-egress :3128)      │  │
  │  │ 16 Default DSP Routes · 4 Gates (dsp_message, policy_intake,      │  │
  │  │ catalog_entry, agreement_admission) · VHub-Verdict RFC 9651       │  │
  │  └─────────────────────────────────┬─────────────────────────────────┘  │
  └────────────────────────────────────┼────────────────────────────────────┘
                                       │ Byte-for-byte HTTP Forward
                                       ▼
                        ┌──────────────────────────────┐
                        │  Dataspace Connector (DSP)   │
                        └──────────────────────────────┘

Pure Shared Core (`internal/core`)

Both alexandria-server and alexandria-client share a zero-network, deterministic core (internal/core):

Package	Responsibility
`internal/core/timex`	Injectable `Clock` interface and ISO 8601 duration parser (`P30D`, `PT24H`, `PT10S`).
`internal/core/semver`	Strict SemVer 2.0 parsing, ordering, and bump classification (`initial`, `compatible`, `breaking`).
`internal/core/canon`	RFC 8785 JSON Canonicalization Scheme (JCS) for deterministic signing payloads.
`internal/core/ni`	RFC 6920 Named Information (`ni:///sha-256;<base64url>`) digest calculation and verification.
`internal/core/did`	`did:web` parsing, URL transformation (`%3A` port decoding), and W3C DID Document verification (`V1`–`V4`).
`internal/core/sign`	Normative `{signed, signature: {kid, alg: "EdDSA", sig}}` envelope signing and verification over `JCS(signed)`.
`internal/core/lifecycle`	9-row release date calculator (`REQ-HUB-005`), date invariants (`DATE-1`, `DATE-2`), revocation invariants (`REV-1`..`REV-4`), state machine (`Announced`, `Effective`, `Enforced`, `Transition`, `Retired`, `Revoked`), and effective version set `V_t`.
`internal/core/pkgv`	Profile Vocabulary Package (PVP) verifier (`manifest.json`, `space-lock.json`, file digest completeness).
`internal/core/codes`	Closed catalog of 64 normative error and verdict codes (`catalog.tsv`).
`internal/core/problem`	RFC 9457 `application/problem+json` serializer for HTTP errors.
`internal/core/schemas`	Embedded JSON Schema Draft 2020-12 validators for Appendix A.1 (`versions`), A.2 (`version`), A.3 (`config`), and A.4 (`verdict-event`).