Refuse server-to-client requests in the modern lifecycle per SEP-2575 - #503
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Refuse server-to-client requests in the modern lifecycle per SEP-2575#503koic wants to merge 1 commit into
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## Motivation and Context The modern lifecycle removes server-initiated JSON-RPC requests: a stateless server has no connection to send them on, and SEP-2322 multi round-trip `input_required` results replace what sampling and elicitation covered before. `StdioTransport#send_request` already says so, refusing outright when its session is modern. `StreamableHTTPTransport#send_request` says nothing, so a modern handler that reaches for elicitation or sampling falls through to the session lookup and is told `Session not found: <uuid>` against a session id it never chose. Failing is right, the explanation is not: `handle_modern` mints a session per request without ever registering it in `@sessions`, so that lookup cannot succeed for a modern request no matter what the handler does. `send_request` now refuses a modern-era session up front with the message `StdioTransport` uses, which turns an incidental registration detail into a stated rule and leaves the rest of the method a legacy-only path by construction. Callers see the same `RuntimeError` class as before, only with a message naming the actual constraint. ## How Has This Been Tested? A new test in `test/mcp/server/transports/streamable_http_transport_test.rb` sends `elicitation/create` from a session constructed with `era: :modern` and asserts the SEP-2575 message. It sits with the existing guard tests for stateless mode, a missing `session_id`, and an unknown session, which still pass unchanged. `bundle exec rake` is green, and both conformance legs pass their baseline check. ## Breaking Changes None. The call already failed; only the message changes.
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Motivation and Context
The modern lifecycle removes server-initiated JSON-RPC requests: a stateless server has no connection to send them on, and SEP-2322 multi round-trip
input_requiredresults replace what sampling and elicitation covered before.StdioTransport#send_requestalready says so, refusing outright when its session is modern.StreamableHTTPTransport#send_requestsays nothing, so a modern handler that reaches for elicitation or sampling falls through to the session lookup and is toldSession not found: <uuid>against a session id it never chose. Failing is right, the explanation is not:handle_modernmints a session per request without ever registering it in@sessions, so that lookup cannot succeed for a modern request no matter what the handler does.send_requestnow refuses a modern-era session up front with the messageStdioTransportuses, which turns an incidental registration detail into a stated rule and leaves the rest of the method a legacy-only path by construction. Callers see the sameRuntimeErrorclass as before, only with a message naming the actual constraint.How Has This Been Tested?
A new test in
test/mcp/server/transports/streamable_http_transport_test.rbsendselicitation/createfrom a session constructed withera: :modernand asserts the SEP-2575 message. It sits with the existing guard tests for stateless mode, a missingsession_id, and an unknown session, which still pass unchanged.bundle exec rakeis green, and both conformance legs pass their baseline check.Breaking Changes
None. The call already failed; only the message changes.
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