inter-hub/ARCHITECTURE-LAYERS.md

ARCHITECTURE-LAYERS.md

Framework: GAAF-2026 v1.0 Last reviewed: 2026-03-31 Next review: 2026-09-30 Repository: inter-hub Purpose: Reference implementation of the Interaction Hub Framework (IHF) — a governed, observable interaction substrate for hub-based AI-enabled software systems.

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Layer Map

Core — High rigidity, frozen after v1

Domain-agnostic primitives and invariants. The substrate that all functional modules depend on.

Entities: Hub, Widget, WidgetVersion, InteractionEvent, Annotation, AnnotationThread

Traceability chain: Widget → InteractionEvent / Annotation → RequirementCandidate → Requirement → DecisionRecord → ImplementationChangeReference → DeploymentRecord → OutcomeSignal

Contracts:

• widget-envelope-v1 — widget DOM protocol, required data-* attributes
• append-only-events-v1 — immutability invariant on interaction_events and outcome_signals

Key invariants:

• interaction_events and outcome_signals are append-only (DB-trigger enforced)
• Widget identity (UUID) is stable across implementation changes
• Actor attribution is explicit on all interaction and decision artifacts

Functional — Medium rigidity, evolvable

Value-realisation modules. Each module has a declared maturity. See docs/functional-modules.md for the full maturity register.

Modules:

• RequirementCandidate lifecycle (triage, reviewer assignment) — Stable
• DecisionRecord + governance ledger — Stable
• Requirements (promoted from candidates) — Stable
• DeploymentRecord + OutcomeSignal — Stable
• AgentProposal + AgentReviewRecord + ConfidenceAnnotation — Beta
• Cross-framework adapter contracts (EnvelopeEmissionContract, InteractionReportingContract, WidgetAdapterSpec) — Stable
• FrictionScore + BottleneckRecord — Beta
• HubHealthSnapshot — Beta
• CrossHubPropagation — Experimental
• WidgetOwnership — Stable
• HubRoutingRule — Stable
• FederatedPolicyOverlay — Beta
• StewardshipRole — Stable
• ArchiveRecord + lineage inspector — Beta
• Type registries (WidgetTypeRegistry, EventTypeRegistry, AnnotationCategoryRegistry, PolicyScopeRegistry) — Beta
• HubCapabilityManifest — Beta

Contract: interaction-reporting-v1

Customization — Low rigidity, hub-specific adaptation

Hub-specific routing behaviour and policy configuration. These are Functional modules in implementation but serve the Customization purpose of adapting framework behaviour per-hub without forking code.

Entities: HubRoutingRule, FederatedPolicyOverlay

Note: A formal Customization layer manifest (per-hub configuration contract with migration support) is planned for IHF v1.0. Currently these are Functional modules with hub-scoped parameters.

Configuration — Very low rigidity, declarative state

User-controlled settings validated against known schemas.

Fields: hubs.hub_kind, hubs.domain, hubs.api_key, widgets.policy_scope (validated against policy_scope_registry)

Env vars: IHP_SESSION_SECRET, DATABASE_URL, IHP_BASEURL, IHP_ANTHROPIC_API_KEY

Note: Runtime-validated configuration schemas per hub are planned. Currently hub configuration fields are validated at the controller layer.

Extensions — Cross-cutting, externally supplied

Domain hub vocabulary registration. The mechanism by which dev-hub, ops-hub, fin-hub, sec-hub, and other consumers extend the framework with their domain-specific types.

Entities: HubCapabilityManifest, WidgetTypeRegistry, EventTypeRegistry, AnnotationCategoryRegistry, PolicyScopeRegistry

Contract: hub-capability-manifest-v1

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Dependency Rule

Core ← Functional ← Customization ← Configuration
Extensions plug into Core or Functional only via manifests and type registries.

Domain hubs (consumers) depend on Core and Functional.
They extend via Extensions (manifest registration).
They configure via Configuration (hub_kind, policy_scope, api_key).

Upward dependencies (Functional → Core) are permitted. Downward dependencies (Core → Functional) are forbidden.

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GAAF-2026 Scorecard

Initial assessment: 2026-03-31 (post IHUB-WP-0009)

Layer	Score (0–5)	Weight	Weighted	Notes
Core	3.8	30%	1.14	Contracts formalised; type registries anchor discriminators
Functional	3.2	20%	0.64	Maturity labels added; demand signals still informal
Customization	2.5	15%	0.38	HubRoutingRule/Overlay present; no formal manifest yet
Configuration	3.0	10%	0.30	Registry-backed validation added; hub config schema planned
Extensions	3.5	10%	0.35	HubCapabilityManifest operational; manifest protocol Beta
Cross-layer	3.5	15%	0.53	Fitness functions in CI; contracts documented; layer map current
Total			3.34	Usable but vulnerable — Phase 9 ready

Interpretation: 3.34 = Usable but vulnerable (2.5–3.4). Phase 9 may begin. Target for Phase 10 exit: ≥3.5 (Strong).

Score ≥3.5 target criteria for Phase 10:

• Customization layer manifest implemented (per-hub configuration contract)
• Functional module demand signals formalised
• Hub config schema runtime-validated

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Architectural Fitness Functions

Implemented in Test/Architecture/LayerBoundarySpec.hs. Run as part of the standard test command.

Test	What it checks	On failure
Test 1 — Core immutability	Schema contains all 4 append-only triggers	Hard failure
Test 2 — Contract artifacts	/contracts/ key files exist	Hard failure
Test 3 — Registry non-empty	All 4 type registries have ≥1 active entry	Hard failure
Test 4 — No bare TEXT discriminators	New columns after GAAF marker use registry refs	Hard failure
Test 5 — Domain hub manifest	Domain hubs have active manifests	Warning only

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GAAF Architectural Laws (Applied to inter-hub)

1. Type discriminator columns (widget_type, event_type, category, policy_scope) must reference a registry or carry a CHECK constraint. No new bare TEXT type discriminators after IHUB-WP-0009.

2. Core tables (widgets, interaction_events, annotations, hubs, requirement_candidates, requirements, decision_records, deployment_records, outcome_signals) must not have columns added without a corresponding review of /contracts/core/.

3. Append-only invariant on interaction_events and outcome_signals is permanent. No migration may remove or bypass the enforcement triggers.

4. Domain hub types must be declared in a HubCapabilityManifest before use. Unmanifested hub-owned types are flagged by fitness function Test 5.

5. Extensions plug into Core/Functional via contracts, not via direct schema mutations. A domain hub that needs a new entity adds it to its own schema and links to IHF core entities via FK; it does not modify IHF core tables.

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Decisions Log

Date	Decision	Rationale
2026-03-31	Adopted GAAF-2026 as architectural compliance framework	Post-Phase 8 review identified gaps in extension layer, type safety, and contract formalisation
2026-03-31	Type registries over CHECK constraints	Registries enable Phase 10 marketplace discovery; CHECK constraints are inflexible for domain extension
2026-03-31	HubCapabilityManifest in inter-hub (not hub-core)	hub-core not yet implemented; manifest provides DB-side registration contract immediately
2026-03-31	hub_kind 'framework' has unique index constraint	Prevents accidental creation of a second framework hub row