* [Client] Add client-side elicitation support
The SDK could send elicitation/create requests from a server tool via
ClientGateway::elicit(), but the client could not receive them: there was
no request handler, and ElicitRequest was not registered in MessageFactory,
so incoming elicitation/create messages failed to parse.
This adds the client half, mirroring the existing Sampling pattern:
- Register ElicitRequest in MessageFactory so elicitation/create parses.
- ElicitationRequestHandler wraps a user callback and returns an
ElicitResult (accept/decline/cancel) or an Error.
- ElicitationCallbackInterface defines the callback contract.
- ElicitationException forwards a specific message to the server; any
other throwable returns a generic error.
Includes unit tests, a runnable client example against the elicitation
demo server, and client docs/README updates.
* [Client] Simplify elicitation example labelFor() per review
Type the parameter as AbstractSchemaDefinition and read ->title directly
instead of matching on each concrete definition type. title is a required
non-null string on the base class, so the match and the $name fallback were
redundant.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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