## Motivation and Context
PR #248 introduced server conformance testing using `@modelcontextprotocol/conformance`.
This extends coverage to the client side so that `MCP::Client` behavior can also be validated against
the MCP specification.
### Scope
Client conformance is driven by the conformance runner, which spawns test servers for each scenario
and invokes `conformance/client.rb` against them. The client script delegates the MCP initialize
handshake to `MCP::Client#connect` and executes scenario-specific operations (for example listing
tools or calling a tool).
### Usage
Run all conformance tests (server + client):
```console
bundle exec rake conformance
```
Run a single client scenario:
```console
bundle exec rake conformance SCENARIO=initialize
```
List available scenarios:
```console
bundle exec rake conformance_list
```
## How Has This Been Tested?
Ran `bundle exec rake conformance` locally.
- Server conformance: 40 passed, 0 failed.
- Client conformance: 3 passed, 54 failed (all 54 listed in `expected_failures.yml`).
## Breaking Change
No. This change only adds test infrastructure under `conformance/` and does not modify SDK behavior.
