Why: the completion doc requires the client to recognize resultType,
treat input_required as a protocol-level result whose answer retries the
original tools/call, and expose tasks/get|update|cancel; today only a
content-block special case existed and the advertised version was never
checked against the server's.
Evidence: GOWORK=off go vet + go test -count=1 ./... green;
TestInputRequiredResultTypeRetriesOriginalCall (ask → tasks/update →
retry, call order and final content), TestNegotiatedVersionFallbackKeepsLegacyPath
(byte-level legacy behavior on 2024-11-05), TestTasksGetAndCancelRoundTrip,
TestRunEndCancelsSeenTasks, TestDefaultSchemaDeclares202012; the
acceptance-③ regression TestStdioSlowCancelThenEcho passes unchanged.
Impact: advertise 2026-07-28 and branch on the negotiated version
(older servers keep byte-identical behavior); synthesized default tool
schemas now declare JSON Schema 2020-12; runs cancel the MCP tasks they
saw via a per-run TaskTracker (other runs on the shared manager are
unaffected).
Refs: Agent-System-Documents#42 (N2 plan WP3)
weichen