Add Implementation type with clientInfo/agentInfo fields

Add Implementation record (name, version, title) per stable ACP spec.
Add optional clientInfo to InitializeRequest and agentInfo to
InitializeResponse for client/agent identification.

Author: Mark Pollack

acp-core/src/main/java/com/agentclientprotocol/sdk/spec/AcpSchema.java

@@ -194,9 +194,10 @@ public sealed interface JSONRPCMessage permits JSONRPCRequest, JSONRPCNotificati
 	@JsonInclude(JsonInclude.Include.NON_NULL)
 	public record InitializeRequest(@JsonProperty("protocolVersion") Integer protocolVersion,
 			@JsonProperty("clientCapabilities") ClientCapabilities clientCapabilities,
+			@JsonProperty("clientInfo") Implementation clientInfo,
 			@JsonProperty("_meta") Map<String, Object> meta) {
 		public InitializeRequest(Integer protocolVersion, ClientCapabilities clientCapabilities) {
-			this(protocolVersion, clientCapabilities, null);
+			this(protocolVersion, clientCapabilities, null, null);
 		}
 	}
 
@@ -208,10 +209,11 @@ public InitializeRequest(Integer protocolVersion, ClientCapabilities clientCapab
 	public record InitializeResponse(@JsonProperty("protocolVersion") Integer protocolVersion,
 			@JsonProperty("agentCapabilities") AgentCapabilities agentCapabilities,
 			@JsonProperty("authMethods") List<AuthMethod> authMethods,
+			@JsonProperty("agentInfo") Implementation agentInfo,
 			@JsonProperty("_meta") Map<String, Object> meta) {
 		public InitializeResponse(Integer protocolVersion, AgentCapabilities agentCapabilities,
 				List<AuthMethod> authMethods) {
-			this(protocolVersion, agentCapabilities, authMethods, null);
+			this(protocolVersion, agentCapabilities, authMethods, null, null);
 		}
 
 		/**
@@ -1088,6 +1090,18 @@ public enum PlanEntryPriority {
 	// Supporting Types
 	// ---------------------------
 
+	/**
+	 * Metadata about an implementation (client or agent).
+	 */
+	@JsonIgnoreProperties(ignoreUnknown = true)
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record Implementation(@JsonProperty("name") String name, @JsonProperty("version") String version,
+			@JsonProperty("title") String title) {
+		public Implementation(String name, String version) {
+			this(name, version, null);
+		}
+	}
+
 	/**
 	 * MCP server configuration.
 	 * <p>

acp-core/src/test/java/com/agentclientprotocol/sdk/spec/AcpSchemaSerializationTest.java

@@ -292,7 +292,7 @@ void sessionModelStateSerialization() throws IOException {
 	void initializeRequestWithMetaSerialization() throws IOException {
 		Map<String, Object> meta = Map.of("zed.dev/debugMode", true, "custom/version", "1.0.0");
 		AcpSchema.InitializeRequest request = new AcpSchema.InitializeRequest(1,
-				new AcpSchema.ClientCapabilities(new AcpSchema.FileSystemCapability(true, true), true), meta);
+				new AcpSchema.ClientCapabilities(new AcpSchema.FileSystemCapability(true, true), true), null, meta);
 
 		String json = jsonMapper.writeValueAsString(request);
 		assertThat(json).contains("\"_meta\"");