## Motivation and Context
The `MCP::Client` currently only supports HTTP transport (`MCP::Client::HTTP`).
To achieve parity with other MCP SDKs (Python, TypeScript, C#) which provide
stdio client transports for spawning and communicating with server subprocesses,
the Ruby SDK needs a stdio client transport.
https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#stdio
This enables building MCP clients that launch server processes and communicate
via stdin/stdout using newline-delimited JSON-RPC 2.0 messages.
## How Has This Been Tested?
Added tests for process spawning, protocol initialization handshake,
notification handling, error handling, and transport close lifecycle.
## Additional context
Enabled the `Lint/IncompatibleIoSelectWithFiberScheduler` cop in `.rubocop.yml`
to detect accidental use of `IO.select` instead of `IO#wait_readable`.
## Summary
When using browser-based MCP clients such as MCP Inspector, connections to
the example HTTP server failed due to two issues:
1. CORS preflight (OPTIONS) requests returned 405 Method Not Allowed,
causing browsers to block all cross-origin requests.
2. `Accept: */*` (commonly sent by browsers and fetch API) returned 406 Not Acceptable
because the transport required the Accept header to explicitly list `application/json`
and `text/event-stream`.
Add `rack-cors` middleware to the example HTTP servers so that preflight requests are handled correctly
and `Mcp-Session-Id` is exposed to browser clients. Also fix `validate_accept_header` in `StreamableHTTPTransport`
to treat `*/*` as satisfying all required Accept types.
Fixes#141.
## Repro Steps
### 1. Start the example server (Terminal 1)
```console
$ bundle exec ruby examples/streamable_http_server.rb
```
### 2. Start MCP Inspector (Terminal 2)
```console
$ npx @modelcontextprotocol/inspector
```
### 3. Open the Inspector Web UI (http://localhost:6274) in a browser
- Set Transport Type to "Streamable HTTP"
- Set URL to http://localhost:9393
- Disable the Authorization header toggle (the example server does not require authentication)
- Click "Connect"
Before this change, the connection fails due to CORS or 406 errors.
After this change, the connection succeeds and tools are listed.
These steps have been added to examples/README.md.
Since the example files are not executable binaries, this PR removes the shebangs.
This ensures that all examples are consistently executed via `ruby` command.
It also removes the executable permission from `examples/stdio_server.rb` using `chmod 444`,
bringing it in line with the other example files.
This PR renamed the files related to the SSE example and fixed the README.md.
Because missing files were specified in README.md.
And also, I removed the word 'test' from the file names related to the SSE example.
Other examples file names do not contain the word `test`.
