Write a stateless MCP client that carries protocol version and capabilities in per-request _meta instead of an initialize handshake

Documented steps

1. Read https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning — in 2026-07-28 there is no negotiation handshake; the server accepts or rejects each request independently.
2. Stop sending initialize and notifications/initialized. Build every request with a params._meta object instead.
3. Set params._meta['io.modelcontextprotocol/protocolVersion'] = '2026-07-28' on every request. This field is REQUIRED.
4. Set params._meta['io.modelcontextprotocol/clientCapabilities'] on every request. This field is REQUIRED; send {} if you support no optional client features.
5. Declare optional features inside clientCapabilities, e.g. {'elicitation': {'form': {}}} and {'extensions': {'io.modelcontextprotocol/tasks': {}}}.
6. Set params._meta['io.modelcontextprotocol/clientInfo'] = {name, version} on each request (spec: SHOULD).
7. To opt into server log messages for one request, add params._meta['io.modelcontextprotocol/logLevel']; the server MUST NOT emit notifications/message for a request that omits it.
8. On Streamable HTTP, mirror the version into the MCP-Protocol-Version request header on every POST; it MUST equal the body _meta value.
9. Send Mcp-Method (the method string) on every POST, and Mcp-Name (params.name, or params.uri for resources/read) on tools/call, resources/read and prompts/get.
10. Send Accept listing both application/json and text/event-stream, and be prepared to parse either response content type.
11. Read resultType on every result: treat 'complete' as final, 'input_required' as a Multi Round-Trip Request. Treat an ABSENT resultType (older servers) as 'complete', and treat an unrecognized value as invalid.
12. Read _meta['io.modelcontextprotocol/serverInfo'] from results for display or logging only.
13. Cache list and read results using the returned ttlMs and cacheScope; key the cache by method plus the params that affect the result.
14. Handle -32022 UnsupportedProtocolVersion by selecting a version from error.data.supported and retrying; if there is no common version, surface an error to the user.
15. Verify: issue tools/list and tools/call over two separate connections with no ordering between them and confirm both succeed with no shared state.