// Tell the agent what we support: set on the client builder, not on initialize(). As of 0.80.0,
// a client without this call would advertise what its handlers serve instead (Module 02); setting
// it explicitly here means it's sent exactly as given, which is this module's lesson.
var clientCaps = ClientCapabilities.builder()
    .readTextFile()
    .writeTextFile()  // no .terminal(): no terminal handlers here (see Module 18)
    .build();

AcpSyncClient client = AcpClient.sync(transport)
    .clientCapabilities(clientCaps)
    // A handler for each advertised capability, and only those: build() fails naming any
    // advertised capability with no handler, and warns about a handler for one not advertised.
    .readTextFileHandler(req -> new ReadTextFileResponse(Files.readString(Path.of(req.path()))))
    .writeTextFileHandler(req -> {
        Files.writeString(Path.of(req.path()), req.content());
        return new WriteTextFileResponse();
    })
    .build();

client.initialize();

// Check what the agent supports
NegotiatedCapabilities agentCaps = client.getAgentCapabilities();
System.out.println("loadSession: " + agentCaps.supportsLoadSession());
System.out.println("mcpHttp: " + agentCaps.supportsMcpHttp());
System.out.println("mcpSse: " + agentCaps.supportsMcpSse());

.initializeHandler(req -> {
    // Read what the client supports
    var clientCaps = req.clientCapabilities();

    // Advertise our own capabilities
    var agentCaps = AgentCapabilities.builder()
        .loadSession()            // we support session resume
        .promptEmbeddedContext()  // only embeddedContext; no MCP, image or audio
        .build();

    return InitializeResponse.ok(agentCaps);
})

.promptHandler((req, context) -> {
    // Check capabilities before attempting operations
    NegotiatedCapabilities caps = context.getClientCapabilities();

    if (caps.supportsReadTextFile()) {
        String content = context.readFile("/etc/hostname");
    } else {
        // Graceful degradation
        context.sendMessage("File read not supported by client");
    }

    return PromptResponse.endTurn();
})

./mvnw package -pl module-17-capability-negotiation -q
./mvnw exec:java -pl module-17-capability-negotiation