fix: correct special tool detection for MCP-prefixed tools

[jankinf]

Features

• Fix _is_special_tool so that MCP-wrapped tools (named like mcp_{server_id}_{tool_name}) are correctly recognized as special tools.
• Ensure the terminate tool is treated as special even when invoked via MCP, e.g. mcp_server_id_terminate.
• Align _should_finish_execution logic with MCP naming conventions so that calls to MCP terminate tools correctly finish the agent execution.

Influence

• Without this change, MCP terminate tools are not recognized as special, so:

  • _handle_special_tool is never invoked for mcp_{server_id}_terminate.
  • The agent may continue executing instead of terminating after a tool-initiated stop signal.

• With the new detection logic:

  • MCP terminate tools behave consistently with non-MCP terminate tools.
  • Tool-initiated termination works reliably in both direct and MCP scenarios, reducing the chance of agents “running on” after a termination request.

Result

• _is_special_tool now correctly detects:
  • Plain terminate (and other special tools) by exact name.
  • MCP-wrapped variants like mcp_server_id_terminate by suffix match.
• _should_finish_execution now uses a lowercase name and supports both terminate and names ending in _terminate, aligning with the MCP naming scheme.
• Verified locally that:
  • Calling a non-MCP terminate tool still terminates the agent as before.
  • Calling an MCP terminate tool (e.g. mcp_test_terminate) correctly triggers special-tool handling and finishes execution.