Improve edit agent's knowledge of tools (#6356)

# Description of Changes
Give Edit Agent access to descriptions of the request from the Java API.
This opens the door to us better documenting our Java APIs to give the
stirling engine better knowledge of what the various tools are and how
to use them.

Also improves the tool selection sub-agent to get the tool parameters
and descriptions so it can more intelligently decide which operations
should be used to fulfil the user's request. Also provides it more
encouragement to string together multiple operations if necessary.

engine/tests/test_pdf_edit_agent.py

@@ -136,6 +136,7 @@ async def test_pdf_edit_agent_passes_previous_steps_to_parameter_selector(runtim
         PdfEditPlanSelection(
             operations=[ToolEndpoint.ROTATE_PDF, ToolEndpoint.FLATTEN],
             summary="Rotate the PDF, then compress it.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -294,6 +295,7 @@ async def test_pdf_edit_agent_passes_page_text_to_parameter_selector(runtime: Ap
         PdfEditPlanSelection(
             operations=[ToolEndpoint.ROTATE_PDF],
             summary="Rotate the PDF.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -390,6 +392,7 @@ async def test_pdf_edit_agent_rejects_plan_referencing_unavailable_operations(
         PdfEditPlanSelection(
             operations=[ToolEndpoint.COMPRESS_PDF],
             summary="Compress.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -420,6 +423,7 @@ async def test_pdf_edit_agent_supports_literal_find_replace(runtime: AppRuntime)
         PdfEditPlanSelection(
             operations=[ToolEndpoint.EDIT_TEXT],
             summary="Replace 2025 with 2026 throughout the document.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -466,6 +470,7 @@ async def test_pdf_edit_agent_supports_copy_edit_using_page_text(runtime: AppRun
         PdfEditPlanSelection(
             operations=[ToolEndpoint.EDIT_TEXT],
             summary="Fix typos on page 3.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -515,6 +520,7 @@ async def test_pdf_edit_agent_supports_natural_language_directed_edit(runtime: A
         PdfEditPlanSelection(
             operations=[ToolEndpoint.EDIT_TEXT],
             summary="Update the company name to Acme Corp.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )
@@ -551,6 +557,7 @@ async def test_pdf_edit_agent_composes_edit_text_with_other_operations(runtime:
         PdfEditPlanSelection(
             operations=[ToolEndpoint.EDIT_TEXT, ToolEndpoint.ROTATE_PDF],
             summary="Remove DRAFT marker, then rotate.",
+            rationale="test rationale",
         ),
         parameter_selector=parameter_selector,
     )