Add session/list, session/close, session/resume methods

Implement three stable ACP protocol methods across all SDK layers:

- session/list: enumerate sessions with optional cwd filter and pagination
- session/close: close a session and cancel in-flight work (request/response)
- session/resume: reconnect to session without replaying history

Each method follows the established pattern: AcpSchema types,
NegotiatedCapabilities, handler interfaces (sync + async), builder
methods, client methods, annotations, resolvers, and tests.

Also adds SessionCapabilities and SessionInfo types to the protocol
schema, and updates AgentCapabilities with sessionCapabilities field.

Author: Mark Pollack

acp-agent-support/src/main/java/com/agentclientprotocol/sdk/agent/support/AcpAgentSupport.java

@@ -27,19 +27,25 @@
 import com.agentclientprotocol.sdk.agent.support.resolver.ArgumentResolverComposite;
 import com.agentclientprotocol.sdk.agent.support.resolver.CancelNotificationResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.CapabilitiesResolver;
+import com.agentclientprotocol.sdk.agent.support.resolver.CloseSessionRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.InitializeRequestResolver;
+import com.agentclientprotocol.sdk.agent.support.resolver.ListSessionsRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.LoadSessionRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.NewSessionRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.PromptContextResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.PromptRequestResolver;
+import com.agentclientprotocol.sdk.agent.support.resolver.ResumeSessionRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.SessionIdResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.SetSessionModeRequestResolver;
 import com.agentclientprotocol.sdk.agent.support.resolver.SetSessionModelRequestResolver;
 import com.agentclientprotocol.sdk.annotation.Cancel;
+import com.agentclientprotocol.sdk.annotation.CloseSession;
 import com.agentclientprotocol.sdk.annotation.Initialize;
+import com.agentclientprotocol.sdk.annotation.ListSessions;
 import com.agentclientprotocol.sdk.annotation.LoadSession;
 import com.agentclientprotocol.sdk.annotation.NewSession;
 import com.agentclientprotocol.sdk.annotation.Prompt;
+import com.agentclientprotocol.sdk.annotation.ResumeSession;
 import com.agentclientprotocol.sdk.annotation.SetSessionMode;
 import com.agentclientprotocol.sdk.annotation.SetSessionModel;
 import com.agentclientprotocol.sdk.capabilities.NegotiatedCapabilities;
@@ -218,6 +224,26 @@ private void wireHandlers(AcpAgent.SyncAgentBuilder agentBuilder) {
 			agentBuilder.setSessionModelHandler(req -> invokeHandler(setModelHandler, req, req.sessionId(), null, null));
 		}
 
+		// ListSessions handler
+		AcpHandlerMethod listSessionsHandler = handlers.get("session/list");
+		if (listSessionsHandler != null) {
+			agentBuilder.listSessionsHandler(req -> invokeHandler(listSessionsHandler, req, null, null, null));
+		}
+
+		// CloseSession handler
+		AcpHandlerMethod closeSessionHandler = handlers.get("session/close");
+		if (closeSessionHandler != null) {
+			agentBuilder.closeSessionHandler(
+					req -> invokeHandler(closeSessionHandler, req, req.sessionId(), null, null));
+		}
+
+		// ResumeSession handler
+		AcpHandlerMethod resumeSessionHandler = handlers.get("session/resume");
+		if (resumeSessionHandler != null) {
+			agentBuilder.resumeSessionHandler(
+					req -> invokeHandler(resumeSessionHandler, req, req.sessionId(), null, null));
+		}
+
 		// Cancel handler
 		AcpHandlerMethod cancelHandler = handlers.get("session/cancel");
 		if (cancelHandler != null) {
@@ -441,6 +467,18 @@ private void discoverHandlers(Class<?> agentClass, Supplier<Object> beanSupplier
 					handlers.put("session/set_model", new AcpHandlerMethod(beanSupplier, method, "session/set_model"));
 					log.debug("Discovered @SetSessionModel handler: {}", method.getName());
 				}
+				if (method.isAnnotationPresent(ListSessions.class)) {
+					handlers.put("session/list", new AcpHandlerMethod(beanSupplier, method, "session/list"));
+					log.debug("Discovered @ListSessions handler: {}", method.getName());
+				}
+				if (method.isAnnotationPresent(CloseSession.class)) {
+					handlers.put("session/close", new AcpHandlerMethod(beanSupplier, method, "session/close"));
+					log.debug("Discovered @CloseSession handler: {}", method.getName());
+				}
+				if (method.isAnnotationPresent(ResumeSession.class)) {
+					handlers.put("session/resume", new AcpHandlerMethod(beanSupplier, method, "session/resume"));
+					log.debug("Discovered @ResumeSession handler: {}", method.getName());
+				}
 				if (method.isAnnotationPresent(Cancel.class)) {
 					handlers.put("session/cancel", new AcpHandlerMethod(beanSupplier, method, "session/cancel"));
 					log.debug("Discovered @Cancel handler: {}", method.getName());
@@ -457,6 +495,9 @@ private void addDefaultResolvers() {
 			argumentResolvers.addResolver(new PromptRequestResolver());
 			argumentResolvers.addResolver(new SetSessionModeRequestResolver());
 			argumentResolvers.addResolver(new SetSessionModelRequestResolver());
+			argumentResolvers.addResolver(new ListSessionsRequestResolver());
+			argumentResolvers.addResolver(new CloseSessionRequestResolver());
+			argumentResolvers.addResolver(new ResumeSessionRequestResolver());
 			argumentResolvers.addResolver(new CancelNotificationResolver());
 			argumentResolvers.addResolver(new PromptContextResolver());
 			argumentResolvers.addResolver(new SessionIdResolver());

acp-agent-support/src/main/java/com/agentclientprotocol/sdk/agent/support/handler/DirectResponseHandler.java

@@ -6,10 +6,13 @@
 
 import com.agentclientprotocol.sdk.agent.support.AcpInvocationContext;
 import com.agentclientprotocol.sdk.agent.support.AcpMethodParameter;
+import com.agentclientprotocol.sdk.spec.AcpSchema.CloseSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.InitializeResponse;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ListSessionsResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.LoadSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.NewSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.PromptResponse;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ResumeSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.SetSessionModeResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.SetSessionModelResponse;
 
@@ -33,7 +36,10 @@ public boolean supportsReturnType(AcpMethodParameter returnType) {
 				|| LoadSessionResponse.class.isAssignableFrom(type)
 				|| PromptResponse.class.isAssignableFrom(type)
 				|| SetSessionModeResponse.class.isAssignableFrom(type)
-				|| SetSessionModelResponse.class.isAssignableFrom(type);
+				|| SetSessionModelResponse.class.isAssignableFrom(type)
+				|| ListSessionsResponse.class.isAssignableFrom(type)
+				|| CloseSessionResponse.class.isAssignableFrom(type)
+				|| ResumeSessionResponse.class.isAssignableFrom(type);
 	}
 
 	@Override

acp-agent-support/src/main/java/com/agentclientprotocol/sdk/agent/support/resolver/CloseSessionRequestResolver.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2025-2026 the original author or authors.
+ */
+
+package com.agentclientprotocol.sdk.agent.support.resolver;
+
+import com.agentclientprotocol.sdk.agent.support.AcpInvocationContext;
+import com.agentclientprotocol.sdk.agent.support.AcpMethodParameter;
+import com.agentclientprotocol.sdk.spec.AcpSchema.CloseSessionRequest;
+
+/**
+ * Resolves {@link CloseSessionRequest} parameters in close session handlers.
+ *
+ * @author Mark Pollack
+ * @since 1.0.0
+ */
+public class CloseSessionRequestResolver implements ArgumentResolver {
+
+	@Override
+	public boolean supportsParameter(AcpMethodParameter parameter) {
+		return CloseSessionRequest.class.isAssignableFrom(parameter.getParameterType());
+	}
+
+	@Override
+	public Object resolveArgument(AcpMethodParameter parameter, AcpInvocationContext context) {
+		Object request = context.getRequest();
+		if (request instanceof CloseSessionRequest) {
+			return request;
+		}
+		throw new ArgumentResolutionException(
+				"Expected CloseSessionRequest but got: " + (request != null ? request.getClass().getName() : "null"));
+	}
+
+}

acp-agent-support/src/main/java/com/agentclientprotocol/sdk/agent/support/resolver/ListSessionsRequestResolver.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2025-2026 the original author or authors.
+ */
+
+package com.agentclientprotocol.sdk.agent.support.resolver;
+
+import com.agentclientprotocol.sdk.agent.support.AcpInvocationContext;
+import com.agentclientprotocol.sdk.agent.support.AcpMethodParameter;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ListSessionsRequest;
+
+/**
+ * Resolves {@link ListSessionsRequest} parameters in list sessions handlers.
+ *
+ * @author Mark Pollack
+ * @since 1.0.0
+ */
+public class ListSessionsRequestResolver implements ArgumentResolver {
+
+	@Override
+	public boolean supportsParameter(AcpMethodParameter parameter) {
+		return ListSessionsRequest.class.isAssignableFrom(parameter.getParameterType());
+	}
+
+	@Override
+	public Object resolveArgument(AcpMethodParameter parameter, AcpInvocationContext context) {
+		Object request = context.getRequest();
+		if (request instanceof ListSessionsRequest) {
+			return request;
+		}
+		throw new ArgumentResolutionException(
+				"Expected ListSessionsRequest but got: " + (request != null ? request.getClass().getName() : "null"));
+	}
+
+}

acp-agent-support/src/main/java/com/agentclientprotocol/sdk/agent/support/resolver/ResumeSessionRequestResolver.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2025-2026 the original author or authors.
+ */
+
+package com.agentclientprotocol.sdk.agent.support.resolver;
+
+import com.agentclientprotocol.sdk.agent.support.AcpInvocationContext;
+import com.agentclientprotocol.sdk.agent.support.AcpMethodParameter;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ResumeSessionRequest;
+
+/**
+ * Resolves {@link ResumeSessionRequest} parameters in resume session handlers.
+ *
+ * @author Mark Pollack
+ * @since 1.0.0
+ */
+public class ResumeSessionRequestResolver implements ArgumentResolver {
+
+	@Override
+	public boolean supportsParameter(AcpMethodParameter parameter) {
+		return ResumeSessionRequest.class.isAssignableFrom(parameter.getParameterType());
+	}
+
+	@Override
+	public Object resolveArgument(AcpMethodParameter parameter, AcpInvocationContext context) {
+		Object request = context.getRequest();
+		if (request instanceof ResumeSessionRequest) {
+			return request;
+		}
+		throw new ArgumentResolutionException(
+				"Expected ResumeSessionRequest but got: " + (request != null ? request.getClass().getName() : "null"));
+	}
+
+}

acp-agent-support/src/test/java/com/agentclientprotocol/sdk/agent/support/AcpAgentSupportTest.java

@@ -11,23 +11,33 @@
 import com.agentclientprotocol.sdk.agent.SyncPromptContext;
 import com.agentclientprotocol.sdk.annotation.AcpAgent;
 import com.agentclientprotocol.sdk.annotation.Cancel;
+import com.agentclientprotocol.sdk.annotation.CloseSession;
 import com.agentclientprotocol.sdk.annotation.Initialize;
+import com.agentclientprotocol.sdk.annotation.ListSessions;
 import com.agentclientprotocol.sdk.annotation.LoadSession;
 import com.agentclientprotocol.sdk.annotation.NewSession;
 import com.agentclientprotocol.sdk.annotation.Prompt;
+import com.agentclientprotocol.sdk.annotation.ResumeSession;
 import com.agentclientprotocol.sdk.annotation.SetSessionMode;
 import com.agentclientprotocol.sdk.annotation.SetSessionModel;
 import com.agentclientprotocol.sdk.client.AcpAsyncClient;
 import com.agentclientprotocol.sdk.client.AcpClient;
 import com.agentclientprotocol.sdk.spec.AcpSchema.CancelNotification;
+import com.agentclientprotocol.sdk.spec.AcpSchema.CloseSessionRequest;
+import com.agentclientprotocol.sdk.spec.AcpSchema.CloseSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.InitializeRequest;
 import com.agentclientprotocol.sdk.spec.AcpSchema.InitializeResponse;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ListSessionsRequest;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ListSessionsResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.LoadSessionRequest;
 import com.agentclientprotocol.sdk.spec.AcpSchema.LoadSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.NewSessionRequest;
 import com.agentclientprotocol.sdk.spec.AcpSchema.NewSessionResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.PromptRequest;
 import com.agentclientprotocol.sdk.spec.AcpSchema.PromptResponse;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ResumeSessionRequest;
+import com.agentclientprotocol.sdk.spec.AcpSchema.ResumeSessionResponse;
+import com.agentclientprotocol.sdk.spec.AcpSchema.SessionInfo;
 import com.agentclientprotocol.sdk.spec.AcpSchema.SetSessionModeRequest;
 import com.agentclientprotocol.sdk.spec.AcpSchema.SetSessionModeResponse;
 import com.agentclientprotocol.sdk.spec.AcpSchema.SetSessionModelRequest;
@@ -412,6 +422,130 @@ void onCancel(CancelNotification notification) {
 		assertThat(cancelledSessionId.get()).isEqualTo("cancel-session");
 	}
 
+	@Test
+	void listSessionsHandlerInvoked() throws Exception {
+		AtomicReference<String> requestedCwd = new AtomicReference<>();
+
+		@AcpAgent
+		class ListSessionsAgent {
+
+			@Initialize
+			InitializeResponse init() {
+				return InitializeResponse.ok();
+			}
+
+			@ListSessions
+			ListSessionsResponse listSessions(ListSessionsRequest req) {
+				requestedCwd.set(req.cwd());
+				return new ListSessionsResponse(
+						List.of(new SessionInfo("session-1", "/workspace")));
+			}
+
+		}
+
+		agentSupport = AcpAgentSupport.create(new ListSessionsAgent())
+				.transport(transportPair.agentTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		agentSupport.start();
+		Thread.sleep(100);
+
+		client = AcpClient.async(transportPair.clientTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		client.initialize(new InitializeRequest(1, null)).block(TIMEOUT);
+		ListSessionsResponse resp = client.listSessions(new ListSessionsRequest("/workspace"))
+				.block(TIMEOUT);
+
+		assertThat(requestedCwd.get()).isEqualTo("/workspace");
+		assertThat(resp).isNotNull();
+		assertThat(resp.sessions()).hasSize(1);
+		assertThat(resp.sessions().get(0).sessionId()).isEqualTo("session-1");
+	}
+
+	@Test
+	void closeSessionHandlerInvoked() throws Exception {
+		AtomicReference<String> closedSessionId = new AtomicReference<>();
+
+		@AcpAgent
+		class CloseSessionAgent {
+
+			@Initialize
+			InitializeResponse init() {
+				return InitializeResponse.ok();
+			}
+
+			@CloseSession
+			CloseSessionResponse closeSession(CloseSessionRequest req) {
+				closedSessionId.set(req.sessionId());
+				return new CloseSessionResponse();
+			}
+
+		}
+
+		agentSupport = AcpAgentSupport.create(new CloseSessionAgent())
+				.transport(transportPair.agentTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		agentSupport.start();
+		Thread.sleep(100);
+
+		client = AcpClient.async(transportPair.clientTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		client.initialize(new InitializeRequest(1, null)).block(TIMEOUT);
+		CloseSessionResponse resp = client.closeSession(new CloseSessionRequest("session-to-close"))
+				.block(TIMEOUT);
+
+		assertThat(closedSessionId.get()).isEqualTo("session-to-close");
+		assertThat(resp).isNotNull();
+	}
+
+	@Test
+	void resumeSessionHandlerInvoked() throws Exception {
+		AtomicReference<String> resumedSessionId = new AtomicReference<>();
+
+		@AcpAgent
+		class ResumeSessionAgent {
+
+			@Initialize
+			InitializeResponse init() {
+				return InitializeResponse.ok();
+			}
+
+			@ResumeSession
+			ResumeSessionResponse resumeSession(ResumeSessionRequest req) {
+				resumedSessionId.set(req.sessionId());
+				return new ResumeSessionResponse(null, null);
+			}
+
+		}
+
+		agentSupport = AcpAgentSupport.create(new ResumeSessionAgent())
+				.transport(transportPair.agentTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		agentSupport.start();
+		Thread.sleep(100);
+
+		client = AcpClient.async(transportPair.clientTransport())
+				.requestTimeout(TIMEOUT)
+				.build();
+
+		client.initialize(new InitializeRequest(1, null)).block(TIMEOUT);
+		ResumeSessionResponse resp = client
+				.resumeSession(new ResumeSessionRequest("existing-session", "/workspace", List.of()))
+				.block(TIMEOUT);
+
+		assertThat(resumedSessionId.get()).isEqualTo("existing-session");
+		assertThat(resp).isNotNull();
+	}
+
 	// Simple test agent
 	@AcpAgent(name = "simple-agent", version = "1.0")
 	static class SimpleAgent {