Add support for elicitation

[ptitjes]

Fixes #137

In this PR, I add:

• the request and result objects for the elicitation mechanism
• adds the client capabilities and capability checking on the client and server sides
• adds tests to ClientTest

Motivation and Context

To support the new elicitation feature of the 2025-06-18 protocol version.

How Has This Been Tested?

I added two tests in ClientTest. The tests are not extensive yet as I only check:

• that the server throws when the client doesn't support elicitation
• that the client correctly handles a simple elicitation request

Maybe should I add some more tests? Please advise me.

Breaking Changes

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

1. I was not sure whether to add the tests to ClientTest or ServerTest. (It seems to me that the tests should be divided by feature and not by client/server side, as most features involve both client and server, but I respected how it is done today.)

2. I was not sure whether to add a method to Client to register an elicitation handler (i.e. wrap the setRequestHandler(...) call). Please advise me on what you think is best. (If that is best to add a wrapper method, maybe this can be implemented as a follow-up?)

3. The CreateElicitationRequest.RequestedSchema class I introduced is duplicated from Tool.Input. Maybe that should be factored-out in a JsonSchema top-level class in types.kt. I was not sure you would approve that, so I did not factor it out. Please tell me if you'd prefer I factor that out. (The support for the new Tool output schema in the latest protocol version will also need the same type.)

[Copilot]

Pull Request Overview

Adds initial support for the new “elicitation” feature in the MCP protocol, including data types, capability checks, client/server handling, and basic tests.

• Introduces CreateElicitationRequest and CreateElicitationResult types and updates Method.Defined
• Adds client/server capability checks and a Server.createElicitation helper
• Adds two new tests in ClientTest for reject and success paths

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/jvmTest/kotlin/client/ClientTest.kt	New tests for server-initiated elicitation accept/reject paths
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt	Added elicitation types and client capability field
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt	Added createElicitation and server-side capability assertion
src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/client/Client.kt	Added client-side capability assertion for elicitation requests
api/kotlin-sdk.api	Updated public API signature dump to include elicitation types

Comments suppressed due to low confidence (1)

src/jvmTest/kotlin/client/ClientTest.kt:846

• [nitpick] Consider adding tests for the decline and cancel branches of CreateElicitationResult.Action to ensure all response paths are handled correctly.

    fun `should handle server elicitation`() = runTest {

[Copilot]

The exception message is inconsistent with the server-side text and the test expectation. Consider matching it to "Client does not support elicitation (required for elicitation/create)" and use method.value rather than $method for clarity.

Suggested change

	"Client does not support elicitation capability (required for $method)"
	"Client does not support elicitation (required for elicitation/create)"