[Server] Point a refused gateway request at InputRequiredResult

[chr-hertel]

On 2026-07-28 a handler calling ClientGateway::sample() or listRoots() is told that sampling and roots "were removed" and to take what it needs through tool arguments instead. That's not what the SDK does tho - InputRequiredResult carries both, the client's InputRequestResolver answers them and InputContext has samplingResult()/rootsResult(). The 0.9.0 changelog says the same.

The message now names the request and points at InputRequiredResult.

Ran into it with symfony/mcp-bundle's demo app, which took the message at face value and stopped testing sampling & roots on 2026-07-28.

[Copilot]

🟢 Approval recommended

The focused guidance correction matches existing SDK APIs and includes regression assertions, with no identified blocking issues.

No open issues 🎉

What changed in this PR

Corrects stateless gateway refusal guidance to point handlers to the SDK’s existing input-resolution flow.

Changes:

• Names the refused request and recommends InputRequiredResult and RequestContext::getInputContext().
• Adds assertions checking the request name and replacement guidance.

File	Description
tests/​Unit/​Server/​Stateless/​StatelessProtocolTest.php	Verifies the updated refusal message.
src/​Server/​Stateless/​StatelessProtocol.php	Corrects the exception message and explanatory comment.

_{Review effort: Balanced}