Tools list behaviour when backend MCPs become unavailable

[maleck13]

What

Currently, the gateway will remove a set of tools and send a notification to clients of a tools/list change, if it cannot reach the associated MCP Backend. This may not always be the behaviour desired.

Other options include:

• Allowing a "grace period" where the tools are not removed until the MCP Backend has remained unreachable for a configurable period, in this circumstance the gateway would leave the tools in place and respond with a 503/504
• Only removing the tools in response to the removal of the MCP Server from the configuration. This would mean that if a MCP Backend became unavailable or unreachable, the tools would not be removed from the tools/list response until the MCP was removed from the Gateways configuration.