Add capability registry scaffold and seed entries from reuse-surface

Bootstrap registry/indexes/capabilities.yaml and migrate helix_forge
capability entries owned by this repository for federation publishing.

registry/capabilities/capability.wiki.engine-typed-extensions.md

@@ -0,0 +1,115 @@
+---
+id: capability.wiki.engine-typed-extensions
+name: Wiki Engine with Typed Extensions
+summary: A small-core wiki engine realizing a stringent typed-extension framework that addresses all wiki use cases and lets each shard activate only the features it needs.
+owner: shard-wiki
+status: draft
+domain: helix_forge
+tags: [wiki, engine, typed-extensions, feature-activation, shard-wiki]
+
+maturity:
+  discovery:
+    current: D3
+    target: D5
+    confidence: medium
+    rationale: >
+      Architecture authored (shard-wiki/spec/WikiEngineCoreArchitecture.md): small page-store
+      kernel + typed-extension framework, per-shard activation, engine-as-canonical-mode-shard,
+      and a conflict-mediation realization are explored. Detailed extension SDK/ABI and the API
+      protocol remain (so D3 Explored, not yet D4/D5).
+  availability:
+    current: A0
+    target: A4
+    confidence: low
+    rationale: >
+      Planned. No engine kernel or extensions exist yet; informational/planning reuse only.
+
+external_evidence:
+  completeness:
+    level: C0
+    name: Absent
+    confidence: low
+    basis: scope_vs_intent_and_consumer_expectations
+    satisfied_expectations: []
+    broken_expectations:
+      - engine core and typed-extension mechanism not yet designed in detail
+    out_of_scope_expectations:
+      - replacing other wiki engines or mandating one implementation
+  reliability:
+    level: R0
+    confidence: low
+    basis: consumer_quality_signals
+    known_reliability_risks:
+      - planning-stage capability
+
+discovery:
+  intent: >
+    Provide shard-wiki's reference first-party shard backend: a small core + a stringent
+    typed-extension framework covering all collected use cases, mediating conflicting
+    requirements into an integrated whole, with per-shard activation (only what you need).
+  includes:
+    - a minimal engine kernel (page lifecycle, storage via the adapter contract, the typing mechanism)
+    - typed extensions that declare contracts and compose
+    - per-shard feature activation
+  excludes:
+    - replacing or mandating other wiki engines (it is one shard type among many)
+    - a single canonical implementation for all wikis
+  use_cases:
+    - "shard-wiki UseCaseCatalog UC-08..UC-25 and the full catalog (the engine must cover all)"
+
+availability:
+  current_level: A0
+  target_level: A4
+  current_artifacts:
+    - "shard-wiki/workplans/SHARD-WP-0013-wiki-engine-prep.md"
+    - "shard-wiki/spec/WikiEngineCoreArchitecture.md"
+  consumption_modes:
+    - informational
+
+relations:
+  depends_on:
+    - capability.wiki.adapter-contract
+    - capability.wiki.page-model
+  related_to:
+    - capability.feature-control.evaluate
+    - capability.authorization.policy-evaluate
+
+evidence:
+  documentation:
+    - "shard-wiki/workplans/SHARD-WP-0013-wiki-engine-prep.md"
+
+consumer_guidance:
+  recommended_for:
+    - planning a composable, feature-activatable native wiki engine
+  not_recommended_for:
+    - implementation reuse today (planning-stage)
+  known_limitations:
+    - architecture authored; extension SDK/ABI + API protocol still to design; not yet built
+
+promotion_history:
+  - date: "2026-06-15"
+    dimension: discovery
+    from: D2
+    to: D3
+    rationale: WikiEngineCoreArchitecture.md authored (kernel + typed-extension framework explored); INTENT amendment ratified.
+    author: shard-wiki
+---
+
+# Wiki Engine with Typed Extensions
+
+shard-wiki's planned reference first-party shard backend — a *canonical-mode shard* it
+implements natively: a small core plus a stringent typed-extension framework addressing all
+collected use cases, mediating conflicting requirements into a consistent whole, with per-shard
+activation (activate only what you need). It is one shard type among many — not a replacement
+for other engines. Per-shard activation is a candidate consumer of
+`capability.feature-control.evaluate`.
+
+## Assessment notes
+
+### Discovery
+Architecture authored: `shard-wiki/spec/WikiEngineCoreArchitecture.md` (small kernel +
+typed-extension framework; engine = canonical-mode shard). INTENT amendment ratified
+(2026-06-15, decision 84ffdb48). Extension SDK/ABI + API protocol are the next deliverables.
+
+### Availability
+Planning-stage; informational reuse only.