mcp: add Cacheable fields to DiscoverResult (#1022)

This PR add the Cacheable fields to the DiscoverResult, as it was added
later
(modelcontextprotocol/modelcontextprotocol@8e4c232)

Author: guglielmo-san

docs/protocol.md

@@ -77,19 +77,13 @@ it is the client's responsibility to end the session.
 func Example_lifecycle() {
 	ctx := context.Background()
 
-	// Create a client and server.
-	// Wait for the client to initialize the session.
+	// Create a client and server. Under protocol version 2026-07-28, there
+	// is no dedicated initialize/initialized handshake: the session is
+	// implicitly live the moment the client issues its first request.
 	client := mcp.NewClient(&mcp.Implementation{Name: "client", Version: "v0.0.1"}, nil)
-	server := mcp.NewServer(&mcp.Implementation{Name: "server", Version: "v0.0.1"}, &mcp.ServerOptions{
-		InitializedHandler: func(context.Context, *mcp.InitializedRequest) {
-			fmt.Println("initialized!")
-		},
-	})
+	server := mcp.NewServer(&mcp.Implementation{Name: "server", Version: "v0.0.1"}, nil)
 
 	// Connect the server and client using in-memory transports.
-	//
-	// Connect the server first so that it's ready to receive initialization
-	// messages from the client.
 	t1, t2 := mcp.NewInMemoryTransports()
 	serverSession, err := server.Connect(ctx, t1, nil)
 	if err != nil {
@@ -108,7 +102,7 @@ func Example_lifecycle() {
 	if err := serverSession.Wait(); err != nil {
 		log.Fatal(err)
 	}
-	// Output: initialized!
+	// Output:
 }
 ```
 
@@ -213,7 +207,7 @@ func ExampleStreamableHTTPHandler() {
 	defer httpServer.Close()
 
 	// The SDK is currently permissive of some missing keys in "params".
-	resp := mustPostMessage(`{"jsonrpc": "2.0", "id": 1, "method":"initialize", "params": {}}`, httpServer.URL)
+	resp := mustPostMessage(`{"jsonrpc": "2.0", "id": 1, "method":"initialize", "params": {"protocolVersion":"2025-11-25"}}`, httpServer.URL)
 	fmt.Println(resp)
 	// Output:
 	// {"jsonrpc":"2.0","id":1,"result":{"capabilities":{"logging":{}},"protocolVersion":"2025-11-25","serverInfo":{"name":"server","version":"v0.1.0"}}}

docs/server.md

@@ -531,7 +531,7 @@ func Example_mrtr() {
 	// uses it to fulfil any input request the tool handler returns.
 	c := mcp.NewClient(&mcp.Implementation{Name: "client", Version: "v0.0.1"}, &mcp.ClientOptions{
 		ElicitationHandler: func(_ context.Context, _ *mcp.ElicitRequest) (*mcp.ElicitResult, error) {
-			return &mcp.ElicitResult{Action: "accept", Content: map[string]any{"name": "Ada"}}, nil
+			return &mcp.ElicitResult{Action: "accept", Content: map[string]any{"name": "MCP Go"}}, nil
 		},
 	})
 

docs/troubleshooting.md

@@ -50,9 +50,8 @@ func ExampleLoggingTransport() {
 	}
 
 	// Output:
-	// read: {"jsonrpc":"2.0","id":1,"result":{"capabilities":{"logging":{}},"protocolVersion":"2025-11-25","serverInfo":{"name":"server","version":"v0.0.1"}}}
-	// write: {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"clientInfo":{"name":"client","version":"v0.0.1"},"protocolVersion":"2025-11-25","capabilities":{"roots":{"listChanged":true}}}}
-	// write: {"jsonrpc":"2.0","method":"notifications/initialized","params":{}}
+	// read: {"jsonrpc":"2.0","id":1,"result":{"ttlMs":0,"cacheScope":"public","supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26","2024-11-05"],"capabilities":{"logging":{}},"serverInfo":{"name":"server","version":"v0.0.1"}}}
+	// write: {"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/clientCapabilities":{"roots":{"listChanged":true}},"io.modelcontextprotocol/clientInfo":{"name":"client","version":"v0.0.1"},"io.modelcontextprotocol/protocolVersion":"2026-07-28"}}}
 }
 ```
 

mcp/protocol.go

@@ -1129,6 +1129,7 @@ func (x *DiscoverParams) SetProgressToken(t any) { setProgressToken(x, t) }
 
 type DiscoverResult struct {
 	Meta `json:"_meta,omitempty"`
+	Cacheable
 	// The versions of the Model Context Protocol that the server supports.
 	SupportedVersions []string `json:"supportedVersions"`
 	// The server's capabilities.

mcp/server.go

@@ -869,12 +869,14 @@ func (s *Server) discover(_ context.Context, req *ServerRequest[*DiscoverParams]
 			ClientInfo:      req.ClientInfo(),
 		}
 	})
-	return &DiscoverResult{
+	res := &DiscoverResult{
 		SupportedVersions: versions,
 		Capabilities:      s.capabilities(),
 		ServerInfo:        s.impl,
 		Instructions:      s.opts.Instructions,
-	}, nil
+	}
+	res.setDefaultCacheableValues()
+	return res, nil
 }
 
 // filterSupportedVersions returns the subset of [supportedProtocolVersions]

mcp/testdata/conformance/server/discover.txtar

@@ -21,6 +21,8 @@ supports, its capabilities, and its identity.
 	"jsonrpc": "2.0",
 	"id": 1,
 	"result": {
+		"ttlMs": 0,
+		"cacheScope": "public",
 		"supportedVersions": [
 			"2026-07-28",
 			"2025-11-25",

mcp/transport_example_test.go

@@ -42,7 +42,7 @@ func ExampleLoggingTransport() {
 	}
 
 	// Output:
-	// read: {"jsonrpc":"2.0","id":1,"result":{"supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26","2024-11-05"],"capabilities":{"logging":{}},"serverInfo":{"name":"server","version":"v0.0.1"}}}
+	// read: {"jsonrpc":"2.0","id":1,"result":{"ttlMs":0,"cacheScope":"public","supportedVersions":["2026-07-28","2025-11-25","2025-06-18","2025-03-26","2024-11-05"],"capabilities":{"logging":{}},"serverInfo":{"name":"server","version":"v0.0.1"}}}
 	// write: {"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/clientCapabilities":{"roots":{"listChanged":true}},"io.modelcontextprotocol/clientInfo":{"name":"client","version":"v0.0.1"},"io.modelcontextprotocol/protocolVersion":"2026-07-28"}}}
 }