inter-hub-haskell/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.

---

## 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](contracts/core/widget-envelope-v1.md) — widget DOM
  protocol, required `data-*` attributes
- [append-only-events-v1](contracts/core/append-only-events-v1.md) — 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](contracts/functional/interaction-reporting-v1.md)

### Customization — Low rigidity, hub-specific adaptation

Hub-specific routing behaviour, policy configuration, and pattern adoption.
The manifest amendment workflow introduced in Phase 10 constitutes the formal
per-hub configuration contract: adopting a pattern or cloning a governance
template that introduces new types requires an explicit `HubCapabilityManifest`
draft amendment, reviewed and activated by the hub operator.

**Entities:** `HubRoutingRule`, `FederatedPolicyOverlay`, `PatternAdoption`,
`GovernanceTemplateClone`

**Mechanism:** Pattern adoption → manifest amendment draft → hub operator
activates → types registered in framework-wide registry. No type is in use
before it appears in an active manifest.

### 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`,
`ApiConsumer`, `ApiKey`, `WebhookSubscription`, `WebhookDelivery`, `ApiRequestLog`,
`WidgetPattern`, `WidgetPatternVersion`, `PatternAdoption`,
`GovernanceTemplate`, `GovernanceTemplateClone`

**Contract:** [hub-capability-manifest-v1](contracts/extensions/hub-capability-manifest-v1.md)

Phase 9 adds the external API surface to the Extensions layer: `ApiConsumer`
(with optional `HubCapabilityManifest` FK), `ApiKey` (Bearer + OAuth tokens),
`WebhookSubscription` (framework lifecycle events), `WebhookDelivery` (append-only
delivery log), `ApiRequestLog` (usage tracking). `ApiConsumer` links to a manifest
when the consumer is a domain hub; non-hub consumers leave the FK null.

Phase 10 adds the marketplace layer: `WidgetPattern` (reusable widget definitions,
`widget_type` FK to `widget_type_registry`), `WidgetPatternVersion` (explicit
version history), `PatternAdoption` (hub adoption records with pin/follow-latest),
`GovernanceTemplate` (reusable governance templates with category JSONB validated
at controller), `GovernanceTemplateClone` (adoption records for governance templates).

---

## 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**.

---

## GAAF-2026 Scorecard

*Last updated: 2026-04-01 (post IHUB-WP-0011 — Phase 10 Hub Registry and Widget Marketplace)*

| Layer | Score (0–5) | Weight | Weighted | Notes |
|---|---|---|---|---|
| Core | 3.8 | 30% | 1.14 | Contracts formalised; type registries anchor discriminators |
| Functional | 3.4 | 20% | 0.68 | API v2 covers hub registry + marketplace; OpenAPI spec updated |
| Customization | 3.2 | 15% | 0.48 | Manifest amendment workflow is formal per-hub config contract with migration |
| Configuration | 3.2 | 10% | 0.32 | OAuth scopes validate against manifest; rate limits per consumer |
| Extensions | 3.8 | 10% | 0.38 | Hub Registry UI + API; widget pattern marketplace operational |
| Cross-layer | 3.7 | 15% | 0.56 | Fitness functions in CI; contracts documented; layer map current |
| **Total** | | | **3.56** | Strong — Phase 10 exit criteria met |

**Interpretation:** 3.56 = Strong (≥3.5). Phase 10 exit target achieved.

*Customization layer improvement (2.5 → 3.2):* The `PatternAdoption` and
`CloneGovernanceTemplate` workflows require a manifest amendment draft when new
types are introduced, making the manifest a formal per-hub configuration contract
with an explicit activation gate. This is the specific GAAF-2026 Customization
criterion: formal, migration-backed per-hub configuration.

*Previous scorecard (Phase 9):* 3.41 (Usable but vulnerable)

*Next review date: 2026-09-30*

---

## 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 |

---

## 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.

---

## 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 |
| 2026-04-01 | No HubRegistry table — registry is a view over existing tables | HubCapabilityManifest + HubHealthSnapshot + Hub already contain all needed data; a separate table would duplicate state |
| 2026-04-01 | widget_patterns.widget_type is a true FK to widget_type_registry | GAAF rule: no bare TEXT type discriminators; FK ensures patterns only reference registered types |
| 2026-04-01 | governance_templates.categories validated at controller (JSONB array FK) | SQL cannot express array FK; controller validates each element against annotation_category_registry at write time |
| 2026-04-01 | Manifest amendment gate on pattern adoption and template cloning | Adopting a cross-type-boundary artifact must go through the manifest activation flow to maintain GAAF compliance |