Overview

Implement the create_document_results_and_metadata host service function, following the same pattern as create_id_lookup. Includes the C API declaration, host adapter implementation, and SDK wrapper. The DPL callback parameter is deferred to M2.

Background

During expand(), an extension calls this host service to construct a $_documentResultsAndMetadata AST node. The extension passes the source stage spec as BSON and the metadata variable name; the host parses it, builds a LiteParsedDocumentResultsAndMetadata, wraps it in a HostAggStageAstNodeAdapter, and returns an AST node handle.

Scope of Work

• api.h: add create_document_results_and_metadata to MongoExtensionHostServicesVTable:

  MongoExtensionStatus* (*create_document_results_and_metadata)(
      MongoExtensionByteView bsonSpec,
      MongoExtensionByteView metadataVarName,
      MongoExtensionAggStageAstNode** node);
  

• host_services_adapter.cpp: implement the function — parse bsonSpec into source stage, build LiteParsedDocumentResultsAndMetadata, wrap in HostAggStageAstNodeAdapter, return handle
• SDK (host_services.h): add createDocumentResultsAndMetadata(BSONObj sourceSpec, StringData varName) wrapper on HostServicesAPI
• Note: The DPL callback (MongoExtensionDocResultsDPLCallback) is not included here — it is part of M2.

Acceptance Criteria

• Extension can call createDocumentResultsAndMetadata during expand() and receive a valid AST node handle
• Host correctly builds LiteParsedDocumentResultsAndMetadata from the BSON spec
• Unit tests cover round-trip: extension calls service, host parses, AST node is valid