Notification on Capabilities

[m-paternostro]

Is your feature request related to a problem? Please describe.
Hi there 👋

I think it would be really valuable for developers to receive notifications from MCP Server instances when capabilities are added, removed, updated, or (most importantly) invoked — including the result of the invocation.

Right now, there’s no built-in way to observe what the server is doing in real time, which makes it hard to monitor, debug, or track performance effectively.

Describe the solution you'd like
I’ve opened a PR that adds support for this kind of notification: #334

It wires up the McpServer to emit detailed lifecycle events for capabilities. I think this can be a powerful addition for observability and tooling integration.

Describe alternatives you've considered
In my own project, I’ve subclassed McpServer and wrapped capability callbacks to emit 'invoked', 'completed', and 'error' events manually. That approach works to an extent, but it’s far less robust than having this behavior built into McpServer itself.

Additional context
Happy to expand on anything in the PR — let me know if I missed a use case or if there’s something worth clarifying!