Fix test and add comments

Author: astefan

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/optimizer/rules/physical/local/ReplaceSourceAttributes.java

@@ -43,13 +43,11 @@ protected PhysicalPlan rule(EsSourceExec plan) {
             if (attr instanceof MetadataAttribute ma) {
                 if (ma.name().equals(MetadataAttribute.SCORE)) {
                     score = attr;
-                } else if (isTimeSeries) {
-                    if (ma.name().equals(MetadataAttribute.TSID_FIELD)) {
-                        tsid = attr;
-                    } else if (ma.name().equals(MetadataAttribute.TIMESTAMP_FIELD)) {
-                        timestamp = attr;
-                    }
+                } else if (isTimeSeries && ma.name().equals(MetadataAttribute.TSID_FIELD)) {
+                    tsid = attr;
                 }
+            } else if (attr.name().equals(MetadataAttribute.TIMESTAMP_FIELD)) {
+                timestamp = attr;
             }
             keepIterating = score == null || (isTimeSeries && (tsid == null || timestamp == null));
         }

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/session/EsqlSession.java

@@ -718,11 +718,14 @@ private PhysicalPlan logicalPlanToPhysicalPlan(LogicalPlan optimizedPlan, EsqlQu
         final Holder<Boolean> hasScoring = new Holder<>(false);
 
         if (filter != null) {
+            // a PhysicalPlan completely transformed (no fragments) will have an EsQueryExec in it if the data comes from ES
             physicalPlan.forEachDown(EsQueryExec.class, esQueryExec -> {
                 if (hasScoring.get() == false && esQueryExec.hasScoring()) {
                     hasScoring.set(true);
                 }
             });
+            // if there is no EsQueryExec and still scoring is required, search for fragments as well where EsRelations should
+            // know if there is scoring needed or not
             if (hasScoring.get() == false) {
                 physicalPlan.forEachDown(FragmentExec.class, fragmentExec -> {
                     fragmentExec.fragment().forEachDown(EsRelation.class, esRelation -> {
@@ -744,8 +747,8 @@ private PhysicalPlan logicalPlanToPhysicalPlan(LogicalPlan optimizedPlan, EsqlQu
                 QueryBuilder newFilter;
                 if (fragmentFilter != null) {
                     newFilter = hasScoring.get()
-                        ? boolQuery().filter(fragmentFilter).must(filter)
-                        : boolQuery().filter(fragmentFilter).filter(filter);
+                        ? boolQuery().filter(fragmentFilter).must(filter)   // a "bool" "must" does influence scoring
+                        : boolQuery().filter(fragmentFilter).filter(filter);// no scoring? then "filter" to completely disable scoring
                 } else {
                     newFilter = hasScoring.get() ? filter : boolQuery().filter(filter);
                 }