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/common.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from collections.abc import Iterable
 from enum import StrEnum
 from typing import Literal, assert_never
 
@@ -197,3 +198,14 @@ class ToolOperationStep(ApiModel):
             actual_type = type(self.parameters).__name__
             raise ValueError(f"Parameters for tool {self.tool} must be {expected_type.__name__}, got {actual_type}.")
         return self
+
+
+def drop_unknown_tool_endpoints(value: Iterable[str | ToolEndpoint]) -> list[ToolEndpoint]:
+    """Coerce inbound endpoint identifiers into `ToolEndpoint` members, dropping unknowns.
+
+    Java sends the full set of endpoints it considers enabled. The engine and the Java
+    backend may have version drift in either direction, so we silently drop anything we
+    don't recognise rather than failing the request. Anything dropped simply doesn't
+    appear as a supported tool to the planner.
+    """
+    return [ToolEndpoint(item) for item in value if item in ToolEndpoint]