## Motivation and Context
`instrumentation_callback` fires after request execution, making it impossible to wrap
requests with Application Performance Monitoring (APM) spans (e.g. Datadog tracing).
This adds `around_request`, which wraps request handling and allows executing code
before and after each request.
For example, to wrap requests with a Datadog trace:
```ruby
MCP.configure do |config|
config.around_request = ->(data, &request_handler) {
Datadog::Tracing.trace("mcp.#{data[:method]}") do
request_handler.call
end
}
end
```
`instrumentation_callback` is soft-deprecated in favor of `around_request`.
## How Has This Been Tested?
Added tests for `around_request` in configuration, instrumentation,
and server test files. All existing tests continue to pass.
## Breaking Changes
`around_request` itself is optional and defaults to a pass-through,
and `instrumentation_callback` continues to work as before.
However, `instrument_call` now accepts a `server_context:` keyword and its block is invoked
without arguments (previously `yield block` passed the block Proc as an argument).
This affects anyone mixing `MCP::Instrumentation` into their own classes,
though the public `Server` API is unchanged.
Resolves#302.
## Summary
Unlike applications, libraries provide value by remaining usable for a broad range of users,
even when that means supporting older Ruby versions beyond Ruby's own EOL timeline.
I maintain RuboCop, a Ruby linter. Because linters need to work across the ecosystem,
they often need to keep compatibility with older Ruby versions to some extent.
The trade-off is that the MCP Ruby SDK must remain compatible with Ruby 2.7.
However, given the ecosystem impact, supporting Ruby 2.7 is still worthwhile.
For example, bundled gems such as `csv` (Ruby >= 2.5), `bigdecimal` (Ruby >= 2.5), `json` (Ruby >= 2.7),
and `language_server-protocol` (Ruby >= 2.5) tend to keep compatibility with older Ruby versions.
Unlike dropping support, which imposes restrictions on users,
this change broadens compatibility and does not introduce breaking changes.
## Development Note
`rubocop-shopify` (2.18) supports Ruby 3.1+, and this PR does not change that.
Since RuboCop can configure the runtime Ruby version and the target Ruby version for analysis independently,
CI continues to run RuboCop on Ruby 4.0, while analyzing code with `TargetRubyVersion: 2.7`.
When setting `TargetRubyVersion: 2.7`, several RuboCop offenses were resolved.
Additionally, Sorbet-related libraries support Ruby 3.0+. Since these are not dependencies of the MCP Ruby SDK itself,
they are versioned and tested in the development Gemfile.
