Fix fast-time-server modern wire shape for mcp SDK 2.0.0b2 interop - #12
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mcp_types 2.0.0b2 (v2026_07_28 wire models) marks serverInfo, cacheScope, and ttlMs as required top-level DiscoverResult fields, and cacheScope/ttlMs as required on every CacheableResult list response. The modern server/discover response now carries top-level serverInfo and cacheScope/ttlMs (the _meta serverInfo entry is kept per the spec text), and modern tools/list results include cacheScope "private" and ttlMs 0, matching the SDK's conservative defaults. Verified end-to-end with mcp==2.0.0b2: auto and pinned 2026-07-28 modes now complete list_tools and tools/call against a strict server; legacy mode fails cleanly with the intended strict -32602 rejection. Fixes #11. Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent) Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai> Signed-off-by: Jonathan Springer <jps@s390x.com>
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Summary
Fixes #11. The strict
2026-07-28mode was not interoperable withmcp==2.0.0b2(mcp_types/v2026_07_28wire models) in any negotiation mode, due to two wire-shape gaps in modern responses:server/discover:serverInfowas nested under_metaonly, butDiscoverResultrequires it as a top-level field. The unparseable discover result madeautomode fall back to legacyinitialize, which strict mode then rejected — soautocould not connect at all.tools/list:CacheableResultrequirescacheScopeandttlMson the wire (no defaults), and the server emitted neither, so pinned2026-07-28mode failed validation onlist_tools.Changes
server/discoverresult now includes top-level"serverInfo": {"name", "version"},"cacheScope": "private", and"ttlMs": 0. The_meta["io.modelcontextprotocol/serverInfo"]entry is kept, since the spec text marks it SHOULD.tools/listresults now include"cacheScope": "private"and"ttlMs": 0— the SDK's own conservative defaults (immediately stale, no shared caching).2025-11-25) responses are untouched;tools/callalready satisfiedCallToolResult(onlyresultType+contentrequired).Field requirements were confirmed against the installed
mcp-types 2.0.0b2models (v2026_07_28.DiscoverResult,.CacheableResult,.ListToolsResult), not just the issue text.Verification
cargo test: 36/36 passing (new assertions lock top-levelserverInfo/cacheScope/ttlMson discover andcacheScope/ttlMson moderntools/list)cargo clippy --all-targets: cleanmcp==2.0.0b2against a live--protocol 2026-07-28 --strictserver):autoserverInfovalidation → legacy fallback →-32602)echoround-trip2026-07-28pincacheScope/ttlMsrequired)echoround-triplegacyMCPError: Unsupported protocol version— the intended strict-mode rejection