T10 - client stateless lifecycle

[kubinio123]

Target branch: 2026-07-28-protocol-support

Requires:

• T1 - protocol version enum and ordering #239
• T4 - add request metadata, result type, cache hints, error codes, discover schemas types #242

Requests

• With a stateless version there is no initialize and no notifications/initialized
• Every request carries _meta with the protocol version, the client info and the client capabilities, the capabilities reflect the handlers the client was created with
• Over HTTP the MCP-Protocol-Version header always equals the version in _meta
• The protocol version is set once, on the client, transports do not carry their own version
• A logLevel option puts _meta.logLevel on every request, without it the client sends no log level and expects no notifications/message

Responses

• A result without resultType is complete. A result with an unknown resultType fails with McpProtocolException.
• On -32022 the client retries once with a version from supported that chimp also supports, with no common version the call fails with an error that names both version lists
• serverCapabilities and serverInfo come from server/discover, discover is available as an operation
• the capability checks that guard operations use the discover result, as they use the initialize result today.

Legacy-only operations

• ping, setLoggingLevel, subscribeResource, unsubscribeResource, sendProgress and sendRootsListChanged fail with McpProtocolException on the stateless wire, they keep working for legacy versions

Coverage

• The rules above hold for the sync and streaming clients, over HTTP and stdio, on ZIO, Ox and Pekko.
• The conformance client handles the request-metadata and json-schema-ref-no-deref scenarios.

Spec:

• Basic - _meta
• Basic - Result Responses
• Versioning - Protocol Version Negotiation
• Streamable HTTP - Sending Messages
• Streamable HTTP - Protocol Version Header
• Discover - When to Call
• Logging - Per-request log level

Conformance scenarios that must pass after this task:

• Client: request-metadata, tools_call, json-schema-ref-no-deref

Docs: yes.

• New page docs/client/protocol.md: the protocolVersion parameter, what a stateless client sends on every request, discover(), version negotiation on -32022, the operations that exist only for legacy versions, the logLevel option.