[Schema][Server] feat: support sampling with tools (#409)

* feat: support sampling with tools

* address sampling tools review feedback

* tighten sampling tools spec compliance

* drop SamplingStopReason enum in favor of open string

The spec leaves stopReason open for provider-specific values, so upcasting
the four known ones to enum cases makes every future enum addition a silent
BC break for string comparisons.

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Co-authored-by: Christopher Hertel <mail@christopher-hertel.de>
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wWzZb 2026-08-15 09:28:11 +08:00 • committed by GitHub
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@ -12,6 +12,7 @@ All notable changes to `mcp/sdk` will be documented in this file.
* Add `ClientGateway::supportsSampling()`, so a tool can check the client's advertised capabilities before issuing a `sampling/createMessage` request instead of asking and catching the refusal. Matches the existing `supportsRoots()` and `supportsElicitation()`.
* Add `Mcp\Schema\Content\ResourceLink` for the spec's `resource_link` content block (protocol revision 2025-06-18+), letting tool results and prompt messages reference a resource by URI/name without embedding its contents. Accepted anywhere `resource` (`EmbeddedResource`) content is (de)serialized: `CallToolResult::fromArray()`, `PromptMessage::fromArray()`, and `PromptResultFormatter`.
* Negotiate the protocol revision during the `initialize` handshake: the server echoes a revision it supports and counter-offers `ProtocolVersion::latestHandshake()` otherwise (`Builder::setProtocolVersion()` pins it to exactly one), and the client fails the handshake on a counter-offer it cannot speak rather than continuing on an unagreed revision. Adds `Client::getProtocolVersion()`, the `2026-07-28` revision, and the era helpers on `ProtocolVersion` — revisions from `2026-07-28` on have no `initialize`, so they are excluded from negotiation and from `ProtocolVersionMiddleware`'s default supported set.
* Add sampling with tools support: sampling requests now accept tools and tool-choice preferences, messages support tool-use/tool-result content blocks and multiple content blocks, and clients can advertise the `sampling.context` and `sampling.tools` capabilities.
0.7.0
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