Inform AI engine which endpoints are disabled on the backend (#6251)

# Description of Changes
Have the Java send a list of enabled endpoints to the AI engine so it
can intelligently respond to the user that the tool does exist but is
disabled on the server so it can't acutally run the operation, instead
of the current behaviour where it sends the API call back and then 503
errors because the execution fails when the URL is disabled.

<img width="380" height="208" alt="image"
src="https://github.com/user-attachments/assets/5842fb2e-2e55-45a5-8205-25515636daae"
/>

---------

Co-authored-by: EthanHealy01 <[email protected]>

engine/src/stirling/contracts/pdf_edit.py

@@ -2,9 +2,9 @@ from __future__ import annotations
 
 from typing import Annotated, Literal
 
-from pydantic import Field
+from pydantic import BeforeValidator, Field
 
-from stirling.models import ApiModel
+from stirling.models import ApiModel, ToolEndpoint
 
 from .common import (
     AiFile,
@@ -14,6 +14,7 @@ from .common import (
     SupportedCapability,
     ToolOperationStep,
     WorkflowOutcome,
+    drop_unknown_tool_endpoints,
 )
 
 
@@ -22,6 +23,13 @@ class PdfEditRequest(ApiModel):
     files: list[AiFile] = Field(default_factory=list)
     conversation_history: list[ConversationMessage] = Field(default_factory=list)
     page_text: list[ExtractedFileText] = Field(default_factory=list)
+    # The set of endpoints the Java backend considers usable. Unknown URLs are silently
+    # dropped so the engine and Java can drift in either direction without breaking
+    # validation. An empty list means no operations are available - the planner will
+    # return `cannot_do`.
+    enabled_endpoints: Annotated[list[ToolEndpoint], BeforeValidator(drop_unknown_tool_endpoints)] = Field(
+        default_factory=list
+    )
 
 
 class EditPlanResponse(ApiModel):