Simplify contextual entity grounding

internal/modules/dnd/locations/registry/grounding.go

@@ -36,7 +36,6 @@ type ContextUnit struct {
 // Its prompt input contains no durable IDs or source IDs.
 type Grounding struct {
 	promptInput         contracts.LLMInputMaterial
-	projectionDigest    string
 	locationsBySelector map[string]dnd.Location
 }
 
@@ -104,7 +103,6 @@ func NewGrounding(registry *Registry, doc *source.SourceDocument) (*Grounding, e
 	digest := semanticDigest(content)
 	return &Grounding{
 		promptInput:         contracts.NewLLMInputMaterial(ReferenceSlot, locationcodec.MediaType, content, digest, ""),
-		projectionDigest:    digest,
 		locationsBySelector: locationsBySelector,
 	}, nil
 }
@@ -118,14 +116,6 @@ func (g *Grounding) PromptInput() contracts.LLMInputMaterial {
 	return g.promptInput.Clone()
 }
 
-// ProjectionDigest returns the digest of the exact contextual prompt input.
-func (g *Grounding) ProjectionDigest() string {
-	if g == nil {
-		return ""
-	}
-	return g.projectionDigest
-}
-
 // Resolve maps a contextual selector to one canonical location.
 func (g *Grounding) Resolve(selector Selector) (dnd.Location, bool) {
 	if g == nil {