Improve D&D validation reliability

internal/modules/dnd/shared/source_ref_coverage.go

@@ -0,0 +1,48 @@
+package shared
+
+import "gitea.maximumdirect.net/eric/notarius/internal/core/source"
+
+// ChunkCoverage is an immutable snapshot of the source units materialized in
+// one extraction chunk.
+type ChunkCoverage struct {
+	sourceID string
+	unitIDs  map[int]struct{}
+}
+
+// NewChunkCoverage snapshots chunk without retaining or mutating it.
+func NewChunkCoverage(chunk *source.Chunk) ChunkCoverage {
+	if chunk == nil {
+		return ChunkCoverage{}
+	}
+	coverage := ChunkCoverage{
+		sourceID: chunk.SourceID,
+		unitIDs:  make(map[int]struct{}, len(chunk.Units)),
+	}
+	for _, unit := range chunk.Units {
+		coverage.unitIDs[unit.ID] = struct{}{}
+	}
+	return coverage
+}
+
+// Contains reports whether ref identifies a valid inclusive span in index and
+// every unit in that document-ordered span is present in the chunk snapshot.
+func (c ChunkCoverage) Contains(index source.DocumentIndex, doc *source.SourceDocument, ref source.SourceRef) bool {
+	documentID, ok := index.DocumentID()
+	if !ok || doc == nil || doc.ID != documentID || c.sourceID == "" || ref.SourceID != c.sourceID || ref.SourceID != documentID {
+		return false
+	}
+	start, startOK := index.Position(ref.StartUnitID)
+	end, endOK := index.Position(ref.EndUnitID)
+	if !startOK || !endOK || start > end {
+		return false
+	}
+	for position := start; position <= end; position++ {
+		if position >= len(doc.Units) {
+			return false
+		}
+		if _, found := c.unitIDs[doc.Units[position].ID]; !found {
+			return false
+		}
+	}
+	return true
+}