Fix nodes returning empty when only __typename is requested (#1170)

* Fix nodes returning empty when only __typename is requested

When a query selects only `__typename` under `nodes` or `edges { node }`,
`requested_fields` ends up empty (because `__typename` is a dynamic field
and is stripped before populating `requested_fields`). This left
`individual_docs_needed: false`, causing `size: 0` in the datastore query
and returning no documents despite `total_edge_count > 0`.

Fix by additionally setting `individual_docs_needed: true` whenever
`nodes` or `edges.node` is selected at all — the client selecting that
part of the query is itself the signal that individual documents are needed.

Fixes #1055

Generated with Claude Code

* Add unit tests for individual_docs_needed when only __typename is requested

Covers the fix from the previous commit at the unit level, as requested
in code review.

Generated with Claude Code

Author: marcdaniels-toast

elasticgraph-graphql/lib/elastic_graph/graphql/query_adapter/requested_fields.rb

@@ -55,7 +55,7 @@ def query_attributes_for(field:, lookahead:)
                 .selection(@schema.element_names.highlights)
 
               {
-                individual_docs_needed: pagination_fields_need_individual_docs?(lookahead),
+                individual_docs_needed: pagination_fields_need_individual_docs?(lookahead) || relay_connection_node_from(lookahead).selected?,
                 requested_fields: requested_fields_under(relay_connection_node_from(lookahead), index_field_paths),
                 request_all_highlights: requesting_all_highlights?(lookahead),
                 requested_highlights: requested_fields_under(highlights, index_field_paths)

elasticgraph-graphql/spec/acceptance/search_spec.rb

@@ -913,6 +913,42 @@ module ElasticGraph
         ]
       end
 
+      it "returns nodes when querying only `__typename` with no other fields" do
+        index_records(
+          build(:address),
+          build(:address),
+          build(:electrical_part),
+          build(:mechanical_part)
+        )
+
+        # Concrete type: nodes { __typename }
+        address_nodes = call_graphql_query(<<~QUERY).dig("data", "addresses", "nodes")
+          query { addresses { nodes { __typename } } }
+        QUERY
+        expect(address_nodes).to contain_exactly(
+          {"__typename" => "Address"},
+          {"__typename" => "Address"}
+        )
+
+        # Concrete type: edges { node { __typename } }
+        address_edges = call_graphql_query(<<~QUERY).dig("data", "addresses", "edges")
+          query { addresses { edges { node { __typename } } } }
+        QUERY
+        expect(address_edges).to contain_exactly(
+          {"node" => {"__typename" => "Address"}},
+          {"node" => {"__typename" => "Address"}}
+        )
+
+        # Abstract type: nodes { __typename } (no type-specific fragments)
+        part_nodes = call_graphql_query(<<~QUERY).dig("data", "parts", "nodes")
+          query { parts { nodes { __typename } } }
+        QUERY
+        expect(part_nodes).to contain_exactly(
+          {"__typename" => "ElectricalPart"},
+          {"__typename" => "MechanicalPart"}
+        )
+      end
+
       describe "`list` filtering behavior" do
         it "supports filtering on scalar lists, nested object lists, and embedded object lists", :expect_index_exclusions do
           index_records(

elasticgraph-graphql/spec/unit/elastic_graph/graphql/query_adapter/requested_fields_spec.rb

@@ -669,6 +669,38 @@ class QueryAdapter
             expect(query.individual_docs_needed).to be true
           end
 
+          it "sets `individual_docs_needed = true` when only `__typename` is requested under `nodes`" do
+            query = datastore_query_for(:Query, :widgets, <<~QUERY)
+              query {
+                widgets {
+                  nodes {
+                    __typename
+                  }
+                }
+              }
+            QUERY
+
+            expect(query.individual_docs_needed).to be true
+            expect(query.requested_fields).to be_empty
+          end
+
+          it "sets `individual_docs_needed = true` when only `__typename` is requested under `edges.node`" do
+            query = datastore_query_for(:Query, :widgets, <<~QUERY)
+              query {
+                widgets {
+                  edges {
+                    node {
+                      __typename
+                    }
+                  }
+                }
+              }
+            QUERY
+
+            expect(query.individual_docs_needed).to be true
+            expect(query.requested_fields).to be_empty
+          end
+
           it "sets `individual_docs_needed = true` when an edge cursor is requested" do
             query = datastore_query_for(:Query, :widgets, <<~QUERY)
               query {