Construct every MCP client through one factory that declares capabilties - #2477
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…ties MCP clients were built in four places — tool listing, the connection pool, and both transports of the health check — with three different identities and no capability declaration on any of them. Capabilities have to be identical across all of them, and the file you would reach for is the wrong one: only the pooled client is alive while a tool runs, so a server-initiated request can only ever reach that one. A capability added to the listing client would look declared and never fire. Adds `createMcpClient`, the single construction point, and routes all four sites through it. The session and health identities stay distinct, since servers can see the difference. The declared set is deliberately empty, which is what the SDK already defaulted to, so nothing changes on the wire today. It exists so elicitation and sampling have one obvious place to be added — and a comment saying they must arrive with their handlers, because a capability declared without one makes servers issue a request the SDK can only answer with method-not-found.
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MCP clients were built in four places — tool listing, the connection pool, and both transports of the health check — with three different identities and no capability declaration on any of them. Capabilities have to be identical across all of them, and the file you would reach for is the wrong one: only the pooled client is alive while a tool runs, so a server-initiated request can only ever reach that one. A capability added to the listing client would look declared and never fire.
Adds
createMcpClient, the single construction point, and routes all four sites through it. The session and health identities stay distinct, since servers can see the difference.The declared set is deliberately empty, which is what the SDK already defaulted to, so nothing changes on the wire today. It exists so elicitation and sampling have one obvious place to be added — and a comment saying they must arrive with their handlers, because a capability declared without one makes servers issue a request the SDK can only answer with method-not-found.