pool: decode blocks tracked without parent lineage (from prefill)

Author: RishabhSaini

pkg/kvevents/pool.go

@@ -282,11 +282,15 @@ func (p *Pool) digestEvents(ctx context.Context, podIdentifier, modelName string
 
 				key, err := p.index.GetRequestKey(ctx, parentEngineKey)
 				if err != nil {
-					debugLogger.Error(err, "Failed to get request key for parent block",
+					// Parent block not found - expected in P/D disaggregation where blocks
+					// are transferred between pods. Continue with empty parent to track this block.
+					debugLogger.V(1).Info("Parent block key not found in index, tracking block with model init hash",
 						"parentEngineKey", parentEngineKey, "effectiveModelName", effectiveModelName)
-					continue
+					// Use empty parent - TokensToKVBlockKeys will use model init hash
+					parentRequestKey = kvblock.EmptyBlockHash
+				} else {
+					parentRequestKey = key
 				}
-				parentRequestKey = key
 			}
 
 			requestKeys := p.tokenProcessor.TokensToKVBlockKeys(parentRequestKey, ev.TokenIds, effectiveModelName)