Promote DomRange and Structural selector types for non-PDF anchoring

Define real DomRangeSelector, StructuralSelector, StructureMap, and
containerPath fields so evidence-anchor can implement HTML/Markdown
selector creation and resolution. Update SharedContracts.md with field
shapes and DomSelectionCapture payload.

wiki/SharedContracts.md

@@ -148,6 +148,38 @@ StructuralSelector        heading/section/AST path
 FragmentSelector          exported fragment / deep link (export-only)
 ```
 
+Field shapes (non-PDF selectors, EANCH-WP-0003):
+
+```ts
+type DomNodePath = readonly number[];  // child-index path from document root
+
+interface DomRangeSelector {
+  type: "DomRangeSelector";
+  startPath: DomNodePath;
+  startOffset: number;
+  endPath: DomNodePath;
+  endOffset: number;
+}
+
+interface StructuralPathSegment {
+  kind: "heading" | "section" | "block";
+  index: number;
+  level?: number;   // headings only
+  label?: string;
+}
+
+interface StructuralSelector {
+  type: "StructuralSelector";
+  path: readonly StructuralPathSegment[];
+  startOffset: number;
+  endOffset: number;
+}
+```
+
+`StructureMap` on `DocumentRepresentation` maps canonical-text spans to
+structural paths (sorted, non-overlapping). Ingest pipelines may omit it;
+viewer adapters populate it at selection time.
+
 **Selector redundancy rule:** when an annotation is created, the system stores
 *all selector types that are available* for that document representation, not
 just one. Resolution tries them in order of expected confidence and stops at
@@ -218,8 +250,32 @@ interface DocumentViewerAdapter {
 }
 ```
 
-MVP delivers a single `PDFViewerAdapter`. HTML and Markdown adapters are
-deferred.
+MVP delivers a single `PDFViewerAdapter`. HTML and Markdown adapters ship in
+`evidence-anchor/dom`.
+
+`SelectionCapture` is a discriminated union:
+
+```ts
+interface PdfSelectionCapture {
+  kind: "pdf";
+  text: string;
+  page: number;
+  rects: readonly NormalizedRect[];
+  boundingRect?: NormalizedRect;
+}
+
+interface DomSelectionCapture {
+  kind: "dom";
+  text: string;
+  startPath: DomNodePath;
+  startOffset: number;
+  endPath: DomNodePath;
+  endOffset: number;
+  structuralPath?: readonly StructuralPathSegment[];
+}
+
+type SelectionCapture = PdfSelectionCapture | DomSelectionCapture;
+```
 
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