Register shard-wiki capabilities (7 wiki.* registry entries)

Adds capability.wiki.{shard-orchestration, adapter-contract, page-model,
coordination-journal, overlay, federation-models, engine-typed-extensions}
with honest D/A/C/R maturity vectors, relations, and shard-wiki spec/test
evidence; updates registry/indexes/capabilities.yaml. reuse-surface validate: ok.
Source: shard-wiki SHARD-WP-0013 T1.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

registry/capabilities/capability.wiki.overlay.md

@@ -0,0 +1,102 @@
+---
+id: capability.wiki.overlay
+name: Overlay-Before-Mutation Write Path
+summary: Non-destructive edits (draft -> patch -> apply-under-drift) that let read-only, rate-limited, or lossy backends be edited safely without silent remote mutation.
+owner: shard-wiki
+status: draft
+domain: helix_forge
+tags: [wiki, overlay, patch, write-path, conflict, shard-wiki]
+
+maturity:
+  discovery:
+    current: D5
+    target: D6
+    confidence: high
+    rationale: >
+      Overlay lifecycle and apply-under-drift semantics are specified (ADR-05, blueprint
+      Section 8.6) and implemented as a single principled write path.
+  availability:
+    current: A2
+    target: A4
+    confidence: medium
+    rationale: >
+      OverlayEngine (draft/patch/apply), writable adapter, and InformationSpace.edit
+      exist as a source module; three-way merge is not (refuse-on-drift only).
+
+external_evidence:
+  completeness:
+    level: C2
+    name: Partial
+    confidence: medium
+    basis: scope_vs_intent_and_consumer_expectations
+    satisfied_expectations:
+      - draft -> patch -> apply with fast-forward / refuse-on-drift / keep-draft outcomes
+      - no silent remote mutation; overlay_state surfaced in provenance
+    broken_expectations:
+      - three-way / auto merge not implemented (refuse-on-conflict only)
+    out_of_scope_expectations:
+      - federation propagation of applied overlays
+  reliability:
+    level: R1
+    confidence: low
+    basis: consumer_quality_signals
+    known_reliability_risks:
+      - early implementation; conflict handling is detect-and-refuse only
+
+discovery:
+  intent: >
+    Make any sub-write-through backend editable safely: an edit is an overlay first, applied
+    only on explicit intent and only when the source has not drifted.
+  includes:
+    - overlay drafts recorded as coordination-canonical events
+    - patch rendering (unified diff)
+    - apply-under-drift (fast-forward / refuse / keep-draft)
+  excludes:
+    - destructive write without drift check
+  use_cases:
+    - "shard-wiki UseCaseCatalog UC-04, UC-26, UC-29 (remix primitives, overlay)"
+
+availability:
+  current_level: A2
+  target_level: A4
+  current_artifacts:
+    - "shard-wiki/src/shard_wiki/coordination/overlay.py"
+    - "shard-wiki/src/shard_wiki/coordination/patch.py"
+  consumption_modes:
+    - source module
+
+relations:
+  depends_on:
+    - capability.wiki.coordination-journal
+    - capability.wiki.adapter-contract
+
+evidence:
+  documentation:
+    - "shard-wiki/spec/FederationRequirements.md (ADR-05)"
+    - "shard-wiki/spec/CoreArchitectureBlueprint.md (Section 8.2, 8.6)"
+  tests:
+    - "shard-wiki/tests/test_apply.py"
+    - "shard-wiki/tests/test_write_path_integration.py"
+
+consumer_guidance:
+  recommended_for:
+    - safe editing over read-only / rate-limited / lossy backends
+  not_recommended_for:
+    - workflows needing automatic conflict resolution today
+  known_limitations:
+    - merge is detect-and-refuse; three-way merge is future work
+---
+
+# Overlay-Before-Mutation Write Path
+
+One principled write path: every edit drafts an overlay (a coordination-canonical event),
+renders as a patch, and applies under drift checks — fast-forwarding a writable target,
+keeping a local draft on a read-only target, and refusing (never clobbering) on external drift.
+
+## Assessment notes
+
+### Discovery
+Specified in FederationRequirements ADR-05 and CoreArchitectureBlueprint Section 8.2/8.6.
+
+### Availability
+`overlay.py` + `patch.py` + `InformationSpace.edit` ship the path; built in SHARD-WP-0008.