Add Java orchestrator to connect to the AI engine (#6003)

# Description of Changes
Add Java orchestration layer which can connect and go back and forth
with the AI engine to get results for the user. It's expected that the
AI engine will not be publicly available and this Java layer will always
be in front of it, to manage sessions and auth etc.

engine/tests/test_stirling_contracts.py

@@ -9,17 +9,34 @@ from stirling.contracts import (
     AgentSpecStep,
     EditPlanResponse,
     ExecutionContext,
+    ExtractedFileText,
+    ExtractedTextArtifact,
     OrchestratorRequest,
     PdfQuestionAnswerResponse,
+    PdfTextSelection,
     ToolOperationStep,
 )
 from stirling.models.tool_models import OperationId, RotateParams
 
 
 def test_orchestrator_request_accepts_user_message() -> None:
-    request = OrchestratorRequest(user_message="Rotate the PDF")
+    request = OrchestratorRequest(
+        user_message="Rotate the PDF",
+        file_names=["test.pdf"],
+        artifacts=[
+            ExtractedTextArtifact(
+                files=[
+                    ExtractedFileText(
+                        file_name="test.pdf",
+                        pages=[PdfTextSelection(page_number=1, text="Hello")],
+                    )
+                ]
+            )
+        ],
+    )
 
     assert request.user_message == "Rotate the PDF"
+    assert len(request.artifacts) == 1
 
 
 def test_agent_execution_request_uses_typed_agent_spec() -> None: