Issue #48: implement Java client session values errors and CLI

Issue #35: add parity fixture matrix

clients/java/README.md

@@ -1,8 +1,7 @@
 # Java Client
 
-The Java client workspace contains the Gradle scaffold for the MXAccess Gateway
-client library, generated protobuf/gRPC bindings, a test CLI project, and JUnit
-tests.
+The Java client workspace contains the MXAccess Gateway client library,
+generated protobuf/gRPC bindings, a Picocli test CLI project, and JUnit tests.
 
 ## Layout
 
@@ -20,8 +19,63 @@ clients/java/
 generated sources under `src/main/generated`, which matches the client proto
 manifest in `../proto/proto-inputs.json`. Do not edit generated files by hand.
 
+`mxgateway-client` exposes `MxGatewayClientOptions`, `MxGatewayClient`,
+`MxGatewaySession`, value/status helpers, typed gateway exceptions, raw
+generated stubs, and generated protobuf messages for parity tests.
+
 `mxgateway-cli` depends on `mxgateway-client` and provides the `mxgw-java`
-application entry point used by later CLI implementation work.
+application entry point. The CLI supports version, session, command, event
+streaming, write, and smoke-test commands with deterministic JSON output.
+
+## Client Usage
+
+Create a client with explicit transport and auth options:
+
+```java
+MxGatewayClientOptions options = MxGatewayClientOptions.builder()
+        .endpoint("localhost:5000")
+        .apiKey(System.getenv("MXGATEWAY_API_KEY"))
+        .plaintext(true)
+        .build();
+
+try (MxGatewayClient client = MxGatewayClient.connect(options);
+        MxGatewaySession session = client.openSession("java-client")) {
+    int serverHandle = session.register("java-client");
+    int itemHandle = session.addItem(serverHandle, "TestObject.TestInt");
+    session.advise(serverHandle, itemHandle);
+    session.write(serverHandle, itemHandle, MxValues.int32Value(123), 0);
+}
+```
+
+Use `rawBlockingStub`, `rawFutureStub`, `rawAsyncStub`, `openSessionRaw`,
+`closeSessionRaw`, `invoke`, and raw session helper methods when tests need the
+underlying protobuf messages. `MxGatewayCommandException` and
+`MxAccessException` preserve the raw `MxCommandReply` when the gateway returns a
+data-bearing MXAccess failure.
+
+`MxEventStream` implements `Iterator<MxEvent>` and `AutoCloseable`. Closing it
+cancels the underlying gRPC stream. Canceling or timing out a Java client call
+only stops the client from waiting; it does not abort an in-flight MXAccess COM
+call on the worker STA.
+
+## CLI Usage
+
+Run the CLI through Gradle:
+
+```powershell
+gradle :mxgateway-cli:run --args="version --json"
+gradle :mxgateway-cli:run --args="open-session --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --client-session-name java-cli --json"
+gradle :mxgateway-cli:run --args="register --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --session-id <id> --client-name java-cli --json"
+gradle :mxgateway-cli:run --args="add-item --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --session-id <id> --server-handle 1 --item TestObject.TestInt --json"
+gradle :mxgateway-cli:run --args="advise --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --session-id <id> --server-handle 1 --item-handle 1 --json"
+gradle :mxgateway-cli:run --args="write --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --session-id <id> --server-handle 1 --item-handle 1 --type int32 --value 123 --json"
+gradle :mxgateway-cli:run --args="stream-events --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --session-id <id> --limit 1 --json"
+gradle :mxgateway-cli:run --args="smoke --endpoint localhost:5000 --api-key-env MXGATEWAY_API_KEY --plaintext --item TestObject.TestInt --json"
+```
+
+The CLI accepts `--api-key`, `--api-key-env`, `--plaintext`, `--ca-file`,
+`--server-name-override`, `--timeout`, and `--json` on gateway commands. JSON
+output redacts API keys.
 
 ## Build And Test
 
@@ -32,7 +86,8 @@ gradle test
 ```
 
 The build uses the Java 21 Gradle toolchain, compiles generated protobuf/gRPC
-code, and runs JUnit 5 tests for the scaffold and CLI entry point.
+code, and runs JUnit 5 tests for the client wrapper, shared behavior fixtures,
+in-process gRPC behavior, stream cancellation, and CLI parser/output behavior.
 
 ## Related Documentation
 

clients/java/build.gradle

@@ -3,6 +3,8 @@ plugins {
 }
 
 ext {
+    guavaVersion = '33.5.0-jre'
+    gsonVersion = '2.13.2'
     grpcVersion = '1.76.0'
     junitVersion = '5.14.1'
     picocliVersion = '4.7.7'

clients/java/mxgateway-cli/build.gradle

@@ -4,6 +4,7 @@ plugins {
 
 dependencies {
     implementation project(':mxgateway-client')
+    implementation "com.google.protobuf:protobuf-java-util:${protobufVersion}"
     implementation "info.picocli:picocli:${picocliVersion}"
 }
 

clients/java/mxgateway-cli/src/main/java/com/dohertylan/mxgateway/cli/MxGatewayCli.java

@@ -1,29 +1,61 @@
 package com.dohertylan.mxgateway.cli;
 
+import com.dohertylan.mxgateway.client.MxEventStream;
+import com.dohertylan.mxgateway.client.MxGatewayClient;
+import com.dohertylan.mxgateway.client.MxGatewayClientOptions;
 import com.dohertylan.mxgateway.client.MxGatewayClientVersion;
+import com.dohertylan.mxgateway.client.MxGatewaySecrets;
+import com.dohertylan.mxgateway.client.MxGatewaySession;
+import com.dohertylan.mxgateway.client.MxValues;
+import com.google.protobuf.Message;
+import com.google.protobuf.util.JsonFormat;
 import java.io.PrintWriter;
+import java.nio.file.Path;
+import java.time.Duration;
+import java.util.LinkedHashMap;
+import java.util.Map;
 import java.util.concurrent.Callable;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.MxValue;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionRequest;
 import picocli.CommandLine;
 import picocli.CommandLine.Command;
+import picocli.CommandLine.Mixin;
 import picocli.CommandLine.Model.CommandSpec;
+import picocli.CommandLine.Option;
 import picocli.CommandLine.Spec;
 
 @Command(
         name = "mxgw-java",
         mixinStandardHelpOptions = true,
-        description = "MXAccess Gateway Java test CLI.",
-        subcommands = MxGatewayCli.VersionCommand.class)
+        description = "MXAccess Gateway Java test CLI.")
 public final class MxGatewayCli implements Callable<Integer> {
+    private final MxGatewayCliClientFactory clientFactory;
+
     @Spec
     private CommandSpec spec;
 
+    public MxGatewayCli() {
+        this(new GrpcMxGatewayCliClientFactory());
+    }
+
+    MxGatewayCli(MxGatewayCliClientFactory clientFactory) {
+        this.clientFactory = clientFactory;
+    }
+
     public static void main(String[] args) {
-        int exitCode = new CommandLine(new MxGatewayCli()).execute(args);
+        int exitCode = commandLine(new GrpcMxGatewayCliClientFactory()).execute(args);
         System.exit(exitCode);
     }
 
     public static int execute(PrintWriter out, PrintWriter err, String... args) {
-        CommandLine commandLine = new CommandLine(new MxGatewayCli());
+        return execute(new GrpcMxGatewayCliClientFactory(), out, err, args);
+    }
+
+    static int execute(MxGatewayCliClientFactory clientFactory, PrintWriter out, PrintWriter err, String... args) {
+        CommandLine commandLine = commandLine(clientFactory);
         commandLine.setOut(out);
         commandLine.setErr(err);
         return commandLine.execute(args);
@@ -35,14 +67,42 @@ public final class MxGatewayCli implements Callable<Integer> {
         return 0;
     }
 
-    @Command(name = "version", description = "Prints the Java client scaffold version.")
+    private static CommandLine commandLine(MxGatewayCliClientFactory clientFactory) {
+        CommandLine commandLine = new CommandLine(new MxGatewayCli(clientFactory));
+        commandLine.addSubcommand("version", new VersionCommand());
+        commandLine.addSubcommand("open-session", new OpenSessionCommand(clientFactory));
+        commandLine.addSubcommand("close-session", new CloseSessionCommand(clientFactory));
+        commandLine.addSubcommand("register", new RegisterCommand(clientFactory));
+        commandLine.addSubcommand("add-item", new AddItemCommand(clientFactory));
+        commandLine.addSubcommand("advise", new AdviseCommand(clientFactory));
+        commandLine.addSubcommand("write", new WriteCommand(clientFactory));
+        commandLine.addSubcommand("stream-events", new StreamEventsCommand(clientFactory));
+        commandLine.addSubcommand("smoke", new SmokeCommand(clientFactory));
+        return commandLine;
+    }
+
+    @Command(name = "version", description = "Prints the Java client version.")
     public static final class VersionCommand implements Callable<Integer> {
         @Spec
         private CommandSpec spec;
 
+        @Option(names = "--json", description = "Write JSON output.")
+        private boolean json;
+
         @Override
         public Integer call() {
-            spec.commandLine().getOut().printf(
+            Map<String, Object> values = new LinkedHashMap<>();
+            values.put("clientVersion", MxGatewayClientVersion.clientVersion());
+            values.put("gatewayProtocolVersion", MxGatewayClientVersion.gatewayProtocolVersion());
+            values.put("workerProtocolVersion", MxGatewayClientVersion.workerProtocolVersion());
+            if (json) {
+                spec.commandLine().getOut().println(jsonObject(values));
+                return 0;
+            }
+
+            spec.commandLine()
+                    .getOut()
+                    .printf(
                             "mxgateway-java %s gatewayProtocolVersion=%d workerProtocolVersion=%d%n",
                             MxGatewayClientVersion.clientVersion(),
                             MxGatewayClientVersion.gatewayProtocolVersion(),
@@ -50,4 +110,535 @@ public final class MxGatewayCli implements Callable<Integer> {
             return 0;
         }
     }
+
+    abstract static class GatewayCommand implements Callable<Integer> {
+        final MxGatewayCliClientFactory clientFactory;
+
+        @Mixin
+        CommonOptions common = new CommonOptions();
+
+        @Option(names = "--json", description = "Write JSON output.")
+        boolean json;
+
+        GatewayCommand(MxGatewayCliClientFactory clientFactory) {
+            this.clientFactory = clientFactory;
+        }
+    }
+
+    @Command(name = "open-session", description = "Opens a gateway session.")
+    static final class OpenSessionCommand extends GatewayCommand {
+        @Option(names = "--client-session-name", description = "Client session name.")
+        String clientSessionName = "";
+
+        @Option(names = "--backend", description = "Requested gateway backend.")
+        String backend = "";
+
+        OpenSessionCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                var reply = client.openSession(OpenSessionRequest.newBuilder()
+                        .setClientSessionName(clientSessionName)
+                        .setRequestedBackend(backend)
+                        .build());
+                writeOutput("open-session", common, json, reply, () -> reply.getSessionId());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "close-session", description = "Closes a gateway session.")
+    static final class CloseSessionCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        CloseSessionCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                var reply = client.closeSession(CloseSessionRequest.newBuilder()
+                        .setSessionId(sessionId)
+                        .build());
+                writeOutput("close-session", common, json, reply, () -> reply.getFinalState().name());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "register", description = "Invokes MXAccess Register.")
+    static final class RegisterCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        @Option(names = "--client-name", required = true, description = "MXAccess client name.")
+        String clientName;
+
+        RegisterCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                MxCommandReply reply = client.session(sessionId).registerRaw(clientName);
+                writeOutput("register", common, json, reply, () -> reply.getKind().name());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "add-item", description = "Invokes MXAccess AddItem.")
+    static final class AddItemCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        @Option(names = "--server-handle", required = true, description = "MXAccess server handle.")
+        int serverHandle;
+
+        @Option(names = "--item", required = true, description = "Item definition.")
+        String item;
+
+        AddItemCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                MxCommandReply reply = client.session(sessionId).addItemRaw(serverHandle, item);
+                writeOutput("add-item", common, json, reply, () -> reply.getKind().name());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "advise", description = "Invokes MXAccess Advise.")
+    static final class AdviseCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        @Option(names = "--server-handle", required = true, description = "MXAccess server handle.")
+        int serverHandle;
+
+        @Option(names = "--item-handle", required = true, description = "MXAccess item handle.")
+        int itemHandle;
+
+        AdviseCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                MxCommandReply reply = client.session(sessionId).adviseRaw(serverHandle, itemHandle);
+                writeOutput("advise", common, json, reply, () -> reply.getKind().name());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "write", description = "Invokes MXAccess Write.")
+    static final class WriteCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        @Option(names = "--server-handle", required = true, description = "MXAccess server handle.")
+        int serverHandle;
+
+        @Option(names = "--item-handle", required = true, description = "MXAccess item handle.")
+        int itemHandle;
+
+        @Option(names = "--type", defaultValue = "string", description = "Value type.")
+        String type;
+
+        @Option(names = "--value", required = true, description = "Value text.")
+        String value;
+
+        @Option(names = "--user-id", defaultValue = "0", description = "MXAccess user id.")
+        int userId;
+
+        WriteCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                MxCommandReply reply =
+                        client.session(sessionId).writeRaw(serverHandle, itemHandle, parseValue(type, value), userId);
+                writeOutput("write", common, json, reply, () -> reply.getKind().name());
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "stream-events", description = "Streams gateway events.")
+    static final class StreamEventsCommand extends GatewayCommand {
+        @Option(names = "--session-id", required = true, description = "Gateway session id.")
+        String sessionId;
+
+        @Option(names = "--after-worker-sequence", defaultValue = "0", description = "Starting worker sequence.")
+        long afterWorkerSequence;
+
+        @Option(names = "--limit", defaultValue = "0", description = "Maximum events to print.")
+        int limit;
+
+        StreamEventsCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved());
+                    MxEventStream events = client.session(sessionId).streamEventsAfter(afterWorkerSequence)) {
+                int count = 0;
+                while (events.hasNext()) {
+                    MxEvent event = events.next();
+                    if (json) {
+                        client.out().println(protoJson(event));
+                    } else {
+                        client.out().printf("%d %s%n", event.getWorkerSequence(), event.getFamily());
+                    }
+                    count++;
+                    if (limit > 0 && count >= limit) {
+                        events.close();
+                        break;
+                    }
+                }
+            }
+            return 0;
+        }
+    }
+
+    @Command(name = "smoke", description = "Runs a bounded open/register/add/advise flow.")
+    static final class SmokeCommand extends GatewayCommand {
+        @Option(names = "--client-name", defaultValue = "mxgw-java-smoke", description = "MXAccess client name.")
+        String clientName;
+
+        @Option(names = "--item", required = true, description = "Item definition.")
+        String item;
+
+        SmokeCommand(MxGatewayCliClientFactory clientFactory) {
+            super(clientFactory);
+        }
+
+        @Override
+        public Integer call() {
+            try (MxGatewayCliClient client = clientFactory.connect(common.resolved())) {
+                var session = client.openSession(OpenSessionRequest.newBuilder()
+                        .setClientSessionName(clientName)
+                        .build());
+                MxGatewayCliSession cliSession = client.session(session.getSessionId());
+                int serverHandle = cliSession.register(clientName);
+                int itemHandle = cliSession.addItem(serverHandle, item);
+                cliSession.advise(serverHandle, itemHandle);
+                if (json) {
+                    Map<String, Object> output = new LinkedHashMap<>();
+                    output.put("command", "smoke");
+                    output.put("options", common.redactedJsonMap());
+                    output.put("sessionId", session.getSessionId());
+                    output.put("serverHandle", serverHandle);
+                    output.put("itemHandle", itemHandle);
+                    client.out().println(jsonObject(output));
+                } else {
+                    client.out().printf(
+                            "session=%s server=%d item=%d%n", session.getSessionId(), serverHandle, itemHandle);
+                }
+                client.closeSession(CloseSessionRequest.newBuilder()
+                        .setSessionId(session.getSessionId())
+                        .build());
+            }
+            return 0;
+        }
+    }
+
+    static final class CommonOptions {
+        @Spec
+        CommandSpec spec;
+
+        @Option(names = "--endpoint", defaultValue = "localhost:5000", description = "Gateway endpoint.")
+        String endpoint;
+
+        @Option(names = "--api-key", description = "Gateway API key.")
+        String apiKey = "";
+
+        @Option(names = "--api-key-env", defaultValue = "MXGATEWAY_API_KEY", description = "API key environment variable.")
+        String apiKeyEnv;
+
+        @Option(names = "--plaintext", description = "Use plaintext transport.")
+        boolean plaintext;
+
+        @Option(names = "--ca-file", description = "CA certificate file.")
+        Path caFile;
+
+        @Option(names = "--server-name-override", description = "TLS server name override.")
+        String serverNameOverride = "";
+
+        @Option(names = "--timeout", defaultValue = "30s", description = "Per-call timeout.")
+        String timeout;
+
+        private String resolvedApiKey = "";
+        private Duration resolvedTimeout = Duration.ofSeconds(30);
+
+        CommonOptions resolved() {
+            resolvedApiKey = apiKey == null || apiKey.isBlank() ? System.getenv(apiKeyEnv) : apiKey;
+            if (resolvedApiKey == null) {
+                resolvedApiKey = "";
+            }
+            resolvedTimeout = parseDuration(timeout);
+            return this;
+        }
+
+        MxGatewayClientOptions toClientOptions() {
+            return MxGatewayClientOptions.builder()
+                    .endpoint(endpoint)
+                    .apiKey(resolvedApiKey)
+                    .plaintext(plaintext)
+                    .caCertificatePath(caFile)
+                    .serverNameOverride(serverNameOverride)
+                    .callTimeout(resolvedTimeout)
+                    .build();
+        }
+
+        Map<String, Object> redactedJsonMap() {
+            Map<String, Object> values = new LinkedHashMap<>();
+            values.put("endpoint", endpoint);
+            values.put("apiKey", MxGatewaySecrets.redactApiKey(resolvedApiKey));
+            values.put("apiKeyEnv", apiKeyEnv);
+            values.put("plaintext", plaintext);
+            values.put("caFile", caFile == null ? "" : caFile.toString());
+            values.put("serverNameOverride", serverNameOverride);
+            values.put("timeout", timeout);
+            return values;
+        }
+    }
+
+    interface MxGatewayCliClientFactory {
+        MxGatewayCliClient connect(CommonOptions options);
+    }
+
+    interface MxGatewayCliClient extends AutoCloseable {
+        PrintWriter out();
+
+        mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply openSession(OpenSessionRequest request);
+
+        mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply closeSession(CloseSessionRequest request);
+
+        MxGatewayCliSession session(String sessionId);
+
+        @Override
+        void close();
+    }
+
+    interface MxGatewayCliSession {
+        int register(String clientName);
+
+        MxCommandReply registerRaw(String clientName);
+
+        int addItem(int serverHandle, String itemDefinition);
+
+        MxCommandReply addItemRaw(int serverHandle, String itemDefinition);
+
+        void advise(int serverHandle, int itemHandle);
+
+        MxCommandReply adviseRaw(int serverHandle, int itemHandle);
+
+        MxCommandReply writeRaw(int serverHandle, int itemHandle, MxValue value, int userId);
+
+        MxEventStream streamEventsAfter(long afterWorkerSequence);
+    }
+
+    static final class GrpcMxGatewayCliClientFactory implements MxGatewayCliClientFactory {
+        @Override
+        public MxGatewayCliClient connect(CommonOptions options) {
+            return new GrpcMxGatewayCliClient(MxGatewayClient.connect(options.toClientOptions()), options.spec.commandLine().getOut());
+        }
+    }
+
+    static final class GrpcMxGatewayCliClient implements MxGatewayCliClient {
+        private final MxGatewayClient client;
+        private final PrintWriter out;
+
+        GrpcMxGatewayCliClient(MxGatewayClient client, PrintWriter out) {
+            this.client = client;
+            this.out = out;
+        }
+
+        @Override
+        public PrintWriter out() {
+            return out;
+        }
+
+        @Override
+        public mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply openSession(OpenSessionRequest request) {
+            return client.openSessionRaw(request);
+        }
+
+        @Override
+        public mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply closeSession(CloseSessionRequest request) {
+            return client.closeSessionRaw(request);
+        }
+
+        @Override
+        public MxGatewayCliSession session(String sessionId) {
+            return new GrpcMxGatewayCliSession(MxGatewaySession.forSessionId(client, sessionId));
+        }
+
+        @Override
+        public void close() {
+            client.close();
+        }
+    }
+
+    record GrpcMxGatewayCliSession(MxGatewaySession session) implements MxGatewayCliSession {
+        @Override
+        public int register(String clientName) {
+            return session.register(clientName);
+        }
+
+        @Override
+        public MxCommandReply registerRaw(String clientName) {
+            return session.registerRaw(clientName);
+        }
+
+        @Override
+        public int addItem(int serverHandle, String itemDefinition) {
+            return session.addItem(serverHandle, itemDefinition);
+        }
+
+        @Override
+        public MxCommandReply addItemRaw(int serverHandle, String itemDefinition) {
+            return session.addItemRaw(serverHandle, itemDefinition);
+        }
+
+        @Override
+        public void advise(int serverHandle, int itemHandle) {
+            session.advise(serverHandle, itemHandle);
+        }
+
+        @Override
+        public MxCommandReply adviseRaw(int serverHandle, int itemHandle) {
+            return session.adviseRaw(serverHandle, itemHandle);
+        }
+
+        @Override
+        public MxCommandReply writeRaw(int serverHandle, int itemHandle, MxValue value, int userId) {
+            return session.writeRaw(serverHandle, itemHandle, value, userId);
+        }
+
+        @Override
+        public MxEventStream streamEventsAfter(long afterWorkerSequence) {
+            return session.streamEventsAfter(afterWorkerSequence);
+        }
+    }
+
+    interface TextSupplier {
+        String get();
+    }
+
+    private static void writeOutput(
+            String command, CommonOptions common, boolean json, Message reply, TextSupplier textSupplier) {
+        PrintWriter out = common.spec.commandLine().getOut();
+        if (json) {
+            Map<String, Object> output = new LinkedHashMap<>();
+            output.put("command", command);
+            output.put("options", common.redactedJsonMap());
+            output.put("reply", new RawJson(protoJson(reply)));
+            out.println(jsonObject(output));
+            return;
+        }
+        out.println(textSupplier.get());
+    }
+
+    private static MxValue parseValue(String type, String text) {
+        return switch (type) {
+            case "bool" -> MxValues.boolValue(Boolean.parseBoolean(text));
+            case "int32" -> MxValues.int32Value(Integer.parseInt(text));
+            case "int64" -> MxValues.int64Value(Long.parseLong(text));
+            case "float" -> MxValues.floatValue(Float.parseFloat(text));
+            case "double" -> MxValues.doubleValue(Double.parseDouble(text));
+            case "string" -> MxValues.stringValue(text);
+            default -> throw new IllegalArgumentException("unsupported value type " + type);
+        };
+    }
+
+    private static Duration parseDuration(String value) {
+        if (value == null || value.isBlank()) {
+            return Duration.ofSeconds(30);
+        }
+        if (value.startsWith("P")) {
+            return Duration.parse(value);
+        }
+        if (value.endsWith("ms")) {
+            return Duration.ofMillis(Long.parseLong(value.substring(0, value.length() - 2)));
+        }
+        if (value.endsWith("s")) {
+            return Duration.ofSeconds(Long.parseLong(value.substring(0, value.length() - 1)));
+        }
+        if (value.endsWith("m")) {
+            return Duration.ofMinutes(Long.parseLong(value.substring(0, value.length() - 1)));
+        }
+        return Duration.parse(value);
+    }
+
+    private static String protoJson(Message message) {
+        try {
+            return JsonFormat.printer().omittingInsignificantWhitespace().print(message);
+        } catch (Exception error) {
+            throw new IllegalStateException("failed to write protobuf JSON", error);
+        }
+    }
+
+    private static String jsonObject(Map<String, Object> values) {
+        StringBuilder builder = new StringBuilder();
+        builder.append('{');
+        boolean first = true;
+        for (Map.Entry<String, Object> entry : values.entrySet()) {
+            if (!first) {
+                builder.append(',');
+            }
+            first = false;
+            builder.append(jsonString(entry.getKey())).append(':').append(jsonValue(entry.getValue()));
+        }
+        builder.append('}');
+        return builder.toString();
+    }
+
+    @SuppressWarnings("unchecked")
+    private static String jsonValue(Object value) {
+        if (value == null) {
+            return "null";
+        }
+        if (value instanceof RawJson rawJson) {
+            return rawJson.value();
+        }
+        if (value instanceof String string) {
+            return jsonString(string);
+        }
+        if (value instanceof Number || value instanceof Boolean) {
+            return value.toString();
+        }
+        if (value instanceof Map<?, ?> map) {
+            return jsonObject((Map<String, Object>) map);
+        }
+        return jsonString(value.toString());
+    }
+
+    private static String jsonString(String value) {
+        return '"'
+                + value.replace("\\", "\\\\")
+                        .replace("\"", "\\\"")
+                        .replace("\r", "\\r")
+                        .replace("\n", "\\n")
+                + '"';
+    }
+
+    private record RawJson(String value) {
+    }
 }

clients/java/mxgateway-cli/src/test/java/com/dohertylan/mxgateway/cli/MxGatewayCliTests.java

@@ -1,27 +1,241 @@
 package com.dohertylan.mxgateway.cli;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.PrintWriter;
 import java.io.StringWriter;
+import mxaccess_gateway.v1.MxaccessGateway.AddItemReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandKind;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.MxValue;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
+import mxaccess_gateway.v1.MxaccessGateway.RegisterReply;
+import mxaccess_gateway.v1.MxaccessGateway.SessionState;
 import org.junit.jupiter.api.Test;
 
 final class MxGatewayCliTests {
     @Test
     void versionCommandPrintsProtocolVersions() {
+        CliRun run = execute(new FakeClientFactory(), "version");
+
+        assertEquals(0, run.exitCode());
+        assertEquals("", run.errors());
+        assertTrue(run.output().contains("mxgateway-java 0.1.0"));
+        assertTrue(run.output().contains("gatewayProtocolVersion=1"));
+        assertTrue(run.output().contains("workerProtocolVersion=1"));
+    }
+
+    @Test
+    void versionCommandPrintsJson() {
+        CliRun run = execute(new FakeClientFactory(), "version", "--json");
+
+        assertEquals(0, run.exitCode());
+        assertTrue(run.output().contains("\"clientVersion\":\"0.1.0\""));
+        assertTrue(run.output().contains("\"gatewayProtocolVersion\":1"));
+    }
+
+    @Test
+    void openSessionJsonRedactsApiKey() {
+        CliRun run = execute(
+                new FakeClientFactory(),
+                "open-session",
+                "--endpoint",
+                "localhost:5000",
+                "--api-key",
+                "mxgw_visible_secret",
+                "--plaintext",
+                "--client-session-name",
+                "java-cli",
+                "--json");
+
+        assertEquals(0, run.exitCode());
+        assertTrue(run.output().contains("\"command\":\"open-session\""));
+        assertTrue(run.output().contains("\"sessionId\":\"session-cli\""));
+        assertTrue(run.output().contains("mxgw***********cret"));
+        assertFalse(run.output().contains("visible_secret"));
+    }
+
+    @Test
+    void writeBuildsTypedValueFromParserOptions() {
+        FakeClientFactory factory = new FakeClientFactory();
+        CliRun run = execute(
+                factory,
+                "write",
+                "--session-id",
+                "session-cli",
+                "--server-handle",
+                "12",
+                "--item-handle",
+                "34",
+                "--type",
+                "int32",
+                "--value",
+                "123",
+                "--json");
+
+        assertEquals(0, run.exitCode());
+        assertEquals(123, factory.client.session.lastWriteValue.getInt32Value());
+        assertTrue(run.output().contains("\"kind\":\"MX_COMMAND_KIND_WRITE\""));
+    }
+
+    @Test
+    void smokeCommandRunsOpenRegisterAddAdviseAndClose() {
+        FakeClientFactory factory = new FakeClientFactory();
+        CliRun run = execute(factory, "smoke", "--item", "TestObject.TestInt", "--json");
+
+        assertEquals(0, run.exitCode());
+        assertTrue(factory.client.session.registerCalled);
+        assertTrue(factory.client.session.addItemCalled);
+        assertTrue(factory.client.session.adviseCalled);
+        assertTrue(factory.client.closeCalled);
+        assertTrue(run.output().contains("\"serverHandle\":42"));
+        assertTrue(run.output().contains("\"itemHandle\":7"));
+    }
+
+    private static CliRun execute(MxGatewayCli.MxGatewayCliClientFactory factory, String... args) {
         StringWriter output = new StringWriter();
         StringWriter errors = new StringWriter();
-
         int exitCode = MxGatewayCli.execute(
+                factory,
                 new PrintWriter(output, true),
                 new PrintWriter(errors, true),
-                "version");
+                args);
+        return new CliRun(exitCode, output.toString(), errors.toString());
+    }
 
-        assertEquals(0, exitCode);
-        assertEquals("", errors.toString());
-        assertTrue(output.toString().contains("mxgateway-java 0.1.0"));
-        assertTrue(output.toString().contains("gatewayProtocolVersion=1"));
-        assertTrue(output.toString().contains("workerProtocolVersion=1"));
+    private record CliRun(int exitCode, String output, String errors) {
+    }
+
+    private static final class FakeClientFactory implements MxGatewayCli.MxGatewayCliClientFactory {
+        private FakeClient client;
+
+        @Override
+        public MxGatewayCli.MxGatewayCliClient connect(MxGatewayCli.CommonOptions options) {
+            client = new FakeClient(options.spec.commandLine().getOut());
+            return client;
+        }
+    }
+
+    private static final class FakeClient implements MxGatewayCli.MxGatewayCliClient {
+        private final PrintWriter out;
+        private final FakeSession session = new FakeSession();
+        private boolean closeCalled;
+
+        private FakeClient(PrintWriter out) {
+            this.out = out;
+        }
+
+        @Override
+        public PrintWriter out() {
+            return out;
+        }
+
+        @Override
+        public OpenSessionReply openSession(OpenSessionRequest request) {
+            return OpenSessionReply.newBuilder()
+                    .setSessionId("session-cli")
+                    .setProtocolStatus(ok())
+                    .build();
+        }
+
+        @Override
+        public CloseSessionReply closeSession(CloseSessionRequest request) {
+            closeCalled = true;
+            return CloseSessionReply.newBuilder()
+                    .setSessionId(request.getSessionId())
+                    .setFinalState(SessionState.SESSION_STATE_CLOSED)
+                    .setProtocolStatus(ok())
+                    .build();
+        }
+
+        @Override
+        public MxGatewayCli.MxGatewayCliSession session(String sessionId) {
+            return session;
+        }
+
+        @Override
+        public void close() {
+        }
+    }
+
+    private static final class FakeSession implements MxGatewayCli.MxGatewayCliSession {
+        private boolean registerCalled;
+        private boolean addItemCalled;
+        private boolean adviseCalled;
+        private MxValue lastWriteValue;
+
+        @Override
+        public int register(String clientName) {
+            registerCalled = true;
+            return 42;
+        }
+
+        @Override
+        public MxCommandReply registerRaw(String clientName) {
+            registerCalled = true;
+            return MxCommandReply.newBuilder()
+                    .setKind(MxCommandKind.MX_COMMAND_KIND_REGISTER)
+                    .setProtocolStatus(ok())
+                    .setRegister(RegisterReply.newBuilder().setServerHandle(42))
+                    .build();
+        }
+
+        @Override
+        public int addItem(int serverHandle, String itemDefinition) {
+            addItemCalled = true;
+            return 7;
+        }
+
+        @Override
+        public MxCommandReply addItemRaw(int serverHandle, String itemDefinition) {
+            addItemCalled = true;
+            return MxCommandReply.newBuilder()
+                    .setKind(MxCommandKind.MX_COMMAND_KIND_ADD_ITEM)
+                    .setProtocolStatus(ok())
+                    .setAddItem(AddItemReply.newBuilder().setItemHandle(7))
+                    .build();
+        }
+
+        @Override
+        public void advise(int serverHandle, int itemHandle) {
+            adviseCalled = true;
+        }
+
+        @Override
+        public MxCommandReply adviseRaw(int serverHandle, int itemHandle) {
+            adviseCalled = true;
+            return MxCommandReply.newBuilder()
+                    .setKind(MxCommandKind.MX_COMMAND_KIND_ADVISE)
+                    .setProtocolStatus(ok())
+                    .build();
+        }
+
+        @Override
+        public MxCommandReply writeRaw(int serverHandle, int itemHandle, MxValue value, int userId) {
+            lastWriteValue = value;
+            return MxCommandReply.newBuilder()
+                    .setKind(MxCommandKind.MX_COMMAND_KIND_WRITE)
+                    .setProtocolStatus(ok())
+                    .build();
+        }
+
+        @Override
+        public com.dohertylan.mxgateway.client.MxEventStream streamEventsAfter(long afterWorkerSequence) {
+            throw new UnsupportedOperationException("stream-events is covered by client tests");
+        }
+    }
+
+    private static ProtocolStatus ok() {
+        return ProtocolStatus.newBuilder()
+                .setCode(ProtocolStatusCode.PROTOCOL_STATUS_CODE_OK)
+                .build();
     }
 }

clients/java/mxgateway-client/build.gradle

@@ -4,13 +4,19 @@ plugins {
 }
 
 dependencies {
+    api "com.google.protobuf:protobuf-java-util:${protobufVersion}"
     api "com.google.protobuf:protobuf-java:${protobufVersion}"
     api "io.grpc:grpc-protobuf:${grpcVersion}"
     api "io.grpc:grpc-stub:${grpcVersion}"
 
+    implementation "com.google.guava:guava:${guavaVersion}"
     implementation "io.grpc:grpc-netty-shaded:${grpcVersion}"
 
     compileOnly 'javax.annotation:javax.annotation-api:1.3.2'
+
+    testImplementation "com.google.code.gson:gson:${gsonVersion}"
+    testImplementation "io.grpc:grpc-inprocess:${grpcVersion}"
+    testImplementation "io.grpc:grpc-testing:${grpcVersion}"
 }
 
 sourceSets {

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxAccessException.java

@@ -0,0 +1,14 @@
+package com.dohertylan.mxgateway.client;
+
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+
+public final class MxAccessException extends MxGatewayCommandException {
+    public MxAccessException(String operation, ProtocolStatus protocolStatus, MxCommandReply reply) {
+        super(operation, protocolStatus, reply);
+    }
+
+    public MxAccessException(String operation, MxCommandReply reply) {
+        super(operation, reply == null ? null : reply.getProtocolStatus(), reply);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxEventStream.java

@@ -0,0 +1,117 @@
+package com.dohertylan.mxgateway.client;
+
+import io.grpc.Status;
+import io.grpc.StatusRuntimeException;
+import io.grpc.stub.ClientCallStreamObserver;
+import io.grpc.stub.ClientResponseObserver;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.BlockingQueue;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.StreamEventsRequest;
+
+public final class MxEventStream implements Iterator<MxEvent>, AutoCloseable {
+    private static final Object END = new Object();
+
+    private final BlockingQueue<Object> queue;
+    private volatile ClientCallStreamObserver<StreamEventsRequest> requestStream;
+    private volatile boolean closed;
+    private Object next;
+
+    MxEventStream(int capacity) {
+        queue = new ArrayBlockingQueue<>(capacity);
+    }
+
+    ClientResponseObserver<StreamEventsRequest, MxEvent> observer() {
+        return new ClientResponseObserver<>() {
+            @Override
+            public void beforeStart(ClientCallStreamObserver<StreamEventsRequest> requestStream) {
+                MxEventStream.this.requestStream = requestStream;
+            }
+
+            @Override
+            public void onNext(MxEvent value) {
+                offer(value);
+            }
+
+            @Override
+            public void onError(Throwable error) {
+                if (Status.fromThrowable(error).getCode() == Status.Code.CANCELLED && closed) {
+                    offer(END);
+                    return;
+                }
+                offer(error);
+            }
+
+            @Override
+            public void onCompleted() {
+                offer(END);
+            }
+        };
+    }
+
+    @Override
+    public boolean hasNext() {
+        if (next == END) {
+            return false;
+        }
+        if (next == null) {
+            next = take();
+        }
+        if (next instanceof RuntimeException runtimeException) {
+            next = END;
+            throw runtimeException;
+        }
+        if (next instanceof Throwable throwable) {
+            next = END;
+            throw new MxGatewayException("gateway stream events failed: " + throwable.getMessage(), throwable);
+        }
+        return next != END;
+    }
+
+    @Override
+    public MxEvent next() {
+        if (!hasNext()) {
+            throw new NoSuchElementException();
+        }
+        Object value = next;
+        next = null;
+        return (MxEvent) value;
+    }
+
+    @Override
+    public void close() {
+        closed = true;
+        ClientCallStreamObserver<StreamEventsRequest> stream = requestStream;
+        if (stream != null) {
+            stream.cancel("client cancelled event stream", null);
+        }
+        offer(END);
+    }
+
+    private Object take() {
+        while (true) {
+            try {
+                return queue.take();
+            } catch (InterruptedException error) {
+                Thread.currentThread().interrupt();
+                return new StatusRuntimeException(Status.CANCELLED.withDescription("interrupted while reading events"));
+            }
+        }
+    }
+
+    private void offer(Object value) {
+        Objects.requireNonNull(value, "value");
+        if (value == END) {
+            queue.offer(value);
+            return;
+        }
+        try {
+            queue.put(value);
+        } catch (InterruptedException error) {
+            Thread.currentThread().interrupt();
+        }
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayAuthInterceptor.java

@@ -0,0 +1,37 @@
+package com.dohertylan.mxgateway.client;
+
+import io.grpc.CallOptions;
+import io.grpc.Channel;
+import io.grpc.ClientCall;
+import io.grpc.ClientInterceptor;
+import io.grpc.ForwardingClientCall;
+import io.grpc.Metadata;
+import io.grpc.MethodDescriptor;
+
+public final class MxGatewayAuthInterceptor implements ClientInterceptor {
+    static final Metadata.Key<String> AUTHORIZATION_HEADER =
+            Metadata.Key.of("authorization", Metadata.ASCII_STRING_MARSHALLER);
+
+    private final String apiKey;
+
+    public MxGatewayAuthInterceptor(String apiKey) {
+        this.apiKey = apiKey == null ? "" : apiKey;
+    }
+
+    @Override
+    public <ReqT, RespT> ClientCall<ReqT, RespT> interceptCall(
+            MethodDescriptor<ReqT, RespT> method, CallOptions callOptions, Channel next) {
+        ClientCall<ReqT, RespT> call = next.newCall(method, callOptions);
+        if (apiKey.isBlank()) {
+            return call;
+        }
+
+        return new ForwardingClientCall.SimpleForwardingClientCall<>(call) {
+            @Override
+            public void start(Listener<RespT> responseListener, Metadata headers) {
+                headers.put(AUTHORIZATION_HEADER, "Bearer " + apiKey);
+                super.start(responseListener, headers);
+            }
+        };
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayAuthenticationException.java

@@ -0,0 +1,7 @@
+package com.dohertylan.mxgateway.client;
+
+public final class MxGatewayAuthenticationException extends MxGatewayException {
+    public MxGatewayAuthenticationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayAuthorizationException.java

@@ -0,0 +1,7 @@
+package com.dohertylan.mxgateway.client;
+
+public final class MxGatewayAuthorizationException extends MxGatewayException {
+    public MxGatewayAuthorizationException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClient.java

@@ -0,0 +1,228 @@
+package com.dohertylan.mxgateway.client;
+
+import com.google.common.util.concurrent.FutureCallback;
+import com.google.common.util.concurrent.Futures;
+import com.google.common.util.concurrent.MoreExecutors;
+import com.google.protobuf.Duration;
+import io.grpc.Channel;
+import io.grpc.ClientInterceptors;
+import io.grpc.ManagedChannel;
+import io.grpc.netty.shaded.io.grpc.netty.GrpcSslContexts;
+import io.grpc.netty.shaded.io.grpc.netty.NettyChannelBuilder;
+import io.grpc.stub.StreamObserver;
+import java.util.Objects;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.TimeUnit;
+import javax.net.ssl.SSLException;
+import mxaccess_gateway.v1.MxAccessGatewayGrpc;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
+import mxaccess_gateway.v1.MxaccessGateway.StreamEventsRequest;
+
+public final class MxGatewayClient implements AutoCloseable {
+    private final ManagedChannel ownedChannel;
+    private final MxGatewayClientOptions options;
+    private final MxAccessGatewayGrpc.MxAccessGatewayBlockingStub blockingStub;
+    private final MxAccessGatewayGrpc.MxAccessGatewayFutureStub futureStub;
+    private final MxAccessGatewayGrpc.MxAccessGatewayStub asyncStub;
+
+    private MxGatewayClient(ManagedChannel channel, MxGatewayClientOptions options) {
+        this.ownedChannel = channel;
+        this.options = options;
+        Channel intercepted = ClientInterceptors.intercept(channel, new MxGatewayAuthInterceptor(options.apiKey()));
+        blockingStub = MxAccessGatewayGrpc.newBlockingStub(intercepted);
+        futureStub = MxAccessGatewayGrpc.newFutureStub(intercepted);
+        asyncStub = MxAccessGatewayGrpc.newStub(intercepted);
+    }
+
+    public MxGatewayClient(Channel channel, MxGatewayClientOptions options) {
+        this.ownedChannel = null;
+        this.options = Objects.requireNonNull(options, "options");
+        Channel intercepted = ClientInterceptors.intercept(channel, new MxGatewayAuthInterceptor(options.apiKey()));
+        blockingStub = MxAccessGatewayGrpc.newBlockingStub(intercepted);
+        futureStub = MxAccessGatewayGrpc.newFutureStub(intercepted);
+        asyncStub = MxAccessGatewayGrpc.newStub(intercepted);
+    }
+
+    public static MxGatewayClient connect(MxGatewayClientOptions options) {
+        return new MxGatewayClient(createChannel(options), options);
+    }
+
+    public MxAccessGatewayGrpc.MxAccessGatewayBlockingStub rawBlockingStub() {
+        return withDeadline(blockingStub);
+    }
+
+    public MxAccessGatewayGrpc.MxAccessGatewayFutureStub rawFutureStub() {
+        return withDeadline(futureStub);
+    }
+
+    public MxAccessGatewayGrpc.MxAccessGatewayStub rawAsyncStub() {
+        return withDeadline(asyncStub);
+    }
+
+    public MxGatewaySession openSession(OpenSessionRequest request) {
+        OpenSessionReply reply = openSessionRaw(request);
+        return new MxGatewaySession(this, reply);
+    }
+
+    public MxGatewaySession openSession(String clientSessionName) {
+        return openSession(OpenSessionRequest.newBuilder()
+                .setClientSessionName(clientSessionName)
+                .setCommandTimeout(Duration.newBuilder()
+                        .setSeconds(options.callTimeout().toSeconds())
+                        .setNanos(options.callTimeout().toNanosPart())
+                        .build())
+                .build());
+    }
+
+    public OpenSessionReply openSessionRaw(OpenSessionRequest request) {
+        try {
+            OpenSessionReply reply = rawBlockingStub().openSession(request);
+            MxGatewayErrors.ensureProtocolSuccess("open session", reply.getProtocolStatus(), null);
+            return reply;
+        } catch (RuntimeException error) {
+            if (error instanceof MxGatewayException) {
+                throw error;
+            }
+            throw MxGatewayErrors.fromGrpc("open session", error);
+        }
+    }
+
+    public CompletableFuture<OpenSessionReply> openSessionAsync(OpenSessionRequest request) {
+        CompletableFuture<OpenSessionReply> future = toCompletable(rawFutureStub().openSession(request));
+        return future.thenApply(reply -> {
+            MxGatewayErrors.ensureProtocolSuccess("open session", reply.getProtocolStatus(), null);
+            return reply;
+        });
+    }
+
+    public MxCommandReply invoke(MxCommandRequest request) {
+        try {
+            MxCommandReply reply = rawBlockingStub().invoke(request);
+            MxGatewayErrors.ensureProtocolSuccess("invoke", reply.getProtocolStatus(), reply);
+            MxGatewayErrors.ensureMxAccessSuccess("invoke", reply);
+            return reply;
+        } catch (RuntimeException error) {
+            if (error instanceof MxGatewayException) {
+                throw error;
+            }
+            throw MxGatewayErrors.fromGrpc("invoke", error);
+        }
+    }
+
+    public CompletableFuture<MxCommandReply> invokeAsync(MxCommandRequest request) {
+        CompletableFuture<MxCommandReply> future = toCompletable(rawFutureStub().invoke(request));
+        return future.thenApply(reply -> {
+            MxGatewayErrors.ensureProtocolSuccess("invoke", reply.getProtocolStatus(), reply);
+            MxGatewayErrors.ensureMxAccessSuccess("invoke", reply);
+            return reply;
+        });
+    }
+
+    public CloseSessionReply closeSessionRaw(CloseSessionRequest request) {
+        try {
+            CloseSessionReply reply = rawBlockingStub().closeSession(request);
+            MxGatewayErrors.ensureProtocolSuccess("close session", reply.getProtocolStatus(), null);
+            return reply;
+        } catch (RuntimeException error) {
+            if (error instanceof MxGatewayException) {
+                throw error;
+            }
+            throw MxGatewayErrors.fromGrpc("close session", error);
+        }
+    }
+
+    public MxEventStream streamEvents(StreamEventsRequest request) {
+        MxEventStream stream = new MxEventStream(16);
+        rawAsyncStub().streamEvents(request, stream.observer());
+        return stream;
+    }
+
+    public MxGatewayEventSubscription streamEventsAsync(
+            StreamEventsRequest request, StreamObserver<MxEvent> observer) {
+        MxGatewayEventSubscription subscription = new MxGatewayEventSubscription();
+        rawAsyncStub().streamEvents(request, subscription.wrap(observer));
+        return subscription;
+    }
+
+    @Override
+    public void close() {
+        if (ownedChannel != null) {
+            ownedChannel.shutdown();
+        }
+    }
+
+    public void closeAndAwaitTermination() throws InterruptedException {
+        if (ownedChannel != null) {
+            ownedChannel.shutdown();
+            ownedChannel.awaitTermination(options.connectTimeout().toMillis(), TimeUnit.MILLISECONDS);
+        }
+    }
+
+    private static ManagedChannel createChannel(MxGatewayClientOptions options) {
+        NettyChannelBuilder builder = NettyChannelBuilder.forTarget(options.endpoint())
+                .maxInboundMessageSize(16 * 1024 * 1024);
+        if (!options.connectTimeout().isNegative()) {
+            builder.withOption(
+                    io.grpc.netty.shaded.io.netty.channel.ChannelOption.CONNECT_TIMEOUT_MILLIS,
+                    Math.toIntExact(options.connectTimeout().toMillis()));
+        }
+        if (options.plaintext()) {
+            builder.usePlaintext();
+        } else if (options.caCertificatePath() != null) {
+            try {
+                builder.sslContext(GrpcSslContexts.forClient()
+                        .trustManager(options.caCertificatePath().toFile())
+                        .build());
+            } catch (SSLException error) {
+                throw new MxGatewayException("failed to configure gateway TLS", error);
+            }
+        } else {
+            builder.useTransportSecurity();
+        }
+        if (!options.serverNameOverride().isBlank()) {
+            builder.overrideAuthority(options.serverNameOverride());
+        }
+        return builder.build();
+    }
+
+    private <T extends io.grpc.stub.AbstractStub<T>> T withDeadline(T stub) {
+        if (options.callTimeout().isNegative()) {
+            return stub;
+        }
+        return stub.withDeadlineAfter(options.callTimeout().toNanos(), TimeUnit.NANOSECONDS);
+    }
+
+    private static <T> CompletableFuture<T> toCompletable(com.google.common.util.concurrent.ListenableFuture<T> source) {
+        CompletableFuture<T> target = new CompletableFuture<>();
+        Futures.addCallback(
+                source,
+                new FutureCallback<>() {
+                    @Override
+                    public void onSuccess(T result) {
+                        target.complete(result);
+                    }
+
+                    @Override
+                    public void onFailure(Throwable error) {
+                        if (error instanceof RuntimeException runtimeException) {
+                            target.completeExceptionally(MxGatewayErrors.fromGrpc("async call", runtimeException));
+                            return;
+                        }
+                        target.completeExceptionally(error);
+                    }
+                },
+                MoreExecutors.directExecutor());
+        return target;
+    }
+
+    static ProtocolStatusCode okStatusCode() {
+        return ProtocolStatusCode.PROTOCOL_STATUS_CODE_OK;
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayClientOptions.java

@@ -0,0 +1,146 @@
+package com.dohertylan.mxgateway.client;
+
+import java.nio.file.Path;
+import java.time.Duration;
+import java.util.Objects;
+
+public final class MxGatewayClientOptions {
+    private static final Duration DEFAULT_CONNECT_TIMEOUT = Duration.ofSeconds(10);
+    private static final Duration DEFAULT_CALL_TIMEOUT = Duration.ofSeconds(30);
+
+    private final String endpoint;
+    private final String apiKey;
+    private final boolean plaintext;
+    private final Path caCertificatePath;
+    private final String serverNameOverride;
+    private final Duration connectTimeout;
+    private final Duration callTimeout;
+
+    private MxGatewayClientOptions(Builder builder) {
+        endpoint = requireText(builder.endpoint, "endpoint");
+        apiKey = builder.apiKey == null ? "" : builder.apiKey;
+        plaintext = builder.plaintext;
+        caCertificatePath = builder.caCertificatePath;
+        serverNameOverride = builder.serverNameOverride == null ? "" : builder.serverNameOverride;
+        connectTimeout = builder.connectTimeout == null ? DEFAULT_CONNECT_TIMEOUT : builder.connectTimeout;
+        callTimeout = builder.callTimeout == null ? DEFAULT_CALL_TIMEOUT : builder.callTimeout;
+    }
+
+    public static Builder builder() {
+        return new Builder();
+    }
+
+    public String endpoint() {
+        return endpoint;
+    }
+
+    public String apiKey() {
+        return apiKey;
+    }
+
+    public String redactedApiKey() {
+        return MxGatewaySecrets.redactApiKey(apiKey);
+    }
+
+    public boolean plaintext() {
+        return plaintext;
+    }
+
+    public Path caCertificatePath() {
+        return caCertificatePath;
+    }
+
+    public String serverNameOverride() {
+        return serverNameOverride;
+    }
+
+    public Duration connectTimeout() {
+        return connectTimeout;
+    }
+
+    public Duration callTimeout() {
+        return callTimeout;
+    }
+
+    @Override
+    public String toString() {
+        return "MxGatewayClientOptions{"
+                + "endpoint='"
+                + endpoint
+                + '\''
+                + ", apiKey='"
+                + redactedApiKey()
+                + '\''
+                + ", plaintext="
+                + plaintext
+                + ", caCertificatePath="
+                + caCertificatePath
+                + ", serverNameOverride='"
+                + serverNameOverride
+                + '\''
+                + ", connectTimeout="
+                + connectTimeout
+                + ", callTimeout="
+                + callTimeout
+                + '}';
+    }
+
+    private static String requireText(String value, String name) {
+        if (value == null || value.isBlank()) {
+            throw new IllegalArgumentException(name + " is required");
+        }
+        return value;
+    }
+
+    public static final class Builder {
+        private String endpoint;
+        private String apiKey;
+        private boolean plaintext;
+        private Path caCertificatePath;
+        private String serverNameOverride;
+        private Duration connectTimeout;
+        private Duration callTimeout;
+
+        private Builder() {
+        }
+
+        public Builder endpoint(String value) {
+            endpoint = value;
+            return this;
+        }
+
+        public Builder apiKey(String value) {
+            apiKey = value;
+            return this;
+        }
+
+        public Builder plaintext(boolean value) {
+            plaintext = value;
+            return this;
+        }
+
+        public Builder caCertificatePath(Path value) {
+            caCertificatePath = value;
+            return this;
+        }
+
+        public Builder serverNameOverride(String value) {
+            serverNameOverride = value;
+            return this;
+        }
+
+        public Builder connectTimeout(Duration value) {
+            connectTimeout = Objects.requireNonNull(value, "connectTimeout");
+            return this;
+        }
+
+        public Builder callTimeout(Duration value) {
+            callTimeout = Objects.requireNonNull(value, "callTimeout");
+            return this;
+        }
+
+        public MxGatewayClientOptions build() {
+            return new MxGatewayClientOptions(this);
+        }
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayCommandException.java

@@ -0,0 +1,23 @@
+package com.dohertylan.mxgateway.client;
+
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+
+public class MxGatewayCommandException extends MxGatewayException {
+    private final ProtocolStatus protocolStatus;
+    private final MxCommandReply reply;
+
+    public MxGatewayCommandException(String operation, ProtocolStatus protocolStatus, MxCommandReply reply) {
+        super(MxGatewayErrors.protocolStatusMessage(operation, protocolStatus));
+        this.protocolStatus = protocolStatus;
+        this.reply = reply;
+    }
+
+    public ProtocolStatus protocolStatus() {
+        return protocolStatus;
+    }
+
+    public MxCommandReply reply() {
+        return reply;
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayErrors.java

@@ -0,0 +1,72 @@
+package com.dohertylan.mxgateway.client;
+
+import io.grpc.Status;
+import io.grpc.StatusRuntimeException;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
+
+final class MxGatewayErrors {
+    private MxGatewayErrors() {
+    }
+
+    static RuntimeException fromGrpc(String operation, RuntimeException error) {
+        if (error instanceof StatusRuntimeException statusError) {
+            Status status = statusError.getStatus();
+            String message = MxGatewaySecrets.redactCredentials(status.getDescription());
+            return switch (status.getCode()) {
+                case UNAUTHENTICATED -> new MxGatewayAuthenticationException(
+                        "authentication failed: " + message, statusError);
+                case PERMISSION_DENIED -> new MxGatewayAuthorizationException(
+                        "authorization failed: " + message, statusError);
+                case DEADLINE_EXCEEDED -> new MxGatewayException("gateway call timed out: " + message, statusError);
+                case CANCELLED -> new MxGatewayException("gateway call cancelled: " + message, statusError);
+                default -> new MxGatewayException("gateway " + operation + " failed: " + message, statusError);
+            };
+        }
+
+        return new MxGatewayException("gateway " + operation + " failed: " + error.getMessage(), error);
+    }
+
+    static void ensureProtocolSuccess(String operation, ProtocolStatus status, MxCommandReply reply) {
+        if (status == null || status.getCode() == ProtocolStatusCode.PROTOCOL_STATUS_CODE_OK) {
+            return;
+        }
+
+        throw switch (status.getCode()) {
+            case PROTOCOL_STATUS_CODE_SESSION_NOT_FOUND, PROTOCOL_STATUS_CODE_SESSION_NOT_READY ->
+                    new MxGatewaySessionException(operation, status);
+            case PROTOCOL_STATUS_CODE_WORKER_UNAVAILABLE, PROTOCOL_STATUS_CODE_PROTOCOL_VIOLATION ->
+                    new MxGatewayWorkerException(operation, status);
+            case PROTOCOL_STATUS_CODE_MXACCESS_FAILURE -> new MxAccessException(operation, status, reply);
+            default -> new MxGatewayCommandException(operation, status, reply);
+        };
+    }
+
+    static void ensureMxAccessSuccess(String operation, MxCommandReply reply) {
+        if (reply == null) {
+            return;
+        }
+        if (reply.hasHresult() && reply.getHresult() != 0) {
+            throw new MxAccessException(operation, reply);
+        }
+        for (var status : reply.getStatusesList()) {
+            if (!MxStatuses.succeeded(status)) {
+                throw new MxAccessException(operation, reply);
+            }
+        }
+    }
+
+    static String protocolStatusMessage(String operation, ProtocolStatus status) {
+        if (status == null) {
+            return "mxgateway " + operation + " failed with missing protocol status";
+        }
+        if (status.getMessage().isBlank()) {
+            return "mxgateway " + operation + " failed with protocol status " + status.getCode();
+        }
+        return "mxgateway " + operation + " failed with protocol status "
+                + status.getCode()
+                + ": "
+                + status.getMessage();
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayEventSubscription.java

@@ -0,0 +1,48 @@
+package com.dohertylan.mxgateway.client;
+
+import io.grpc.stub.ClientCallStreamObserver;
+import io.grpc.stub.ClientResponseObserver;
+import io.grpc.stub.StreamObserver;
+import java.util.concurrent.atomic.AtomicReference;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.StreamEventsRequest;
+
+public final class MxGatewayEventSubscription implements AutoCloseable {
+    private final AtomicReference<ClientCallStreamObserver<StreamEventsRequest>> requestStream = new AtomicReference<>();
+
+    ClientResponseObserver<StreamEventsRequest, MxEvent> wrap(StreamObserver<MxEvent> observer) {
+        return new ClientResponseObserver<>() {
+            @Override
+            public void beforeStart(ClientCallStreamObserver<StreamEventsRequest> stream) {
+                requestStream.set(stream);
+            }
+
+            @Override
+            public void onNext(MxEvent value) {
+                observer.onNext(value);
+            }
+
+            @Override
+            public void onError(Throwable error) {
+                observer.onError(error);
+            }
+
+            @Override
+            public void onCompleted() {
+                observer.onCompleted();
+            }
+        };
+    }
+
+    public void cancel() {
+        ClientCallStreamObserver<StreamEventsRequest> stream = requestStream.get();
+        if (stream != null) {
+            stream.cancel("client cancelled event stream", null);
+        }
+    }
+
+    @Override
+    public void close() {
+        cancel();
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayException.java

@@ -0,0 +1,11 @@
+package com.dohertylan.mxgateway.client;
+
+public class MxGatewayException extends RuntimeException {
+    public MxGatewayException(String message) {
+        super(message);
+    }
+
+    public MxGatewayException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySecrets.java

@@ -0,0 +1,33 @@
+package com.dohertylan.mxgateway.client;
+
+public final class MxGatewaySecrets {
+    private MxGatewaySecrets() {
+    }
+
+    public static String redactApiKey(String apiKey) {
+        if (apiKey == null || apiKey.isEmpty()) {
+            return "";
+        }
+        if (apiKey.length() <= 8) {
+            return "<redacted>";
+        }
+
+        return apiKey.substring(0, 4)
+                + "*".repeat(apiKey.length() - 8)
+                + apiKey.substring(apiKey.length() - 4);
+    }
+
+    public static String redactCredentials(String value) {
+        if (value == null || value.isBlank()) {
+            return value == null ? "" : value;
+        }
+
+        String[] parts = value.split("\\s+");
+        for (int index = 0; index < parts.length; index++) {
+            if (parts[index].startsWith("mxgw_") || parts[index].equalsIgnoreCase("bearer")) {
+                parts[index] = "<redacted>";
+            }
+        }
+        return String.join(" ", parts);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySession.java

@@ -0,0 +1,184 @@
+package com.dohertylan.mxgateway.client;
+
+import java.security.SecureRandom;
+import java.util.HexFormat;
+import java.util.Objects;
+import mxaccess_gateway.v1.MxaccessGateway.AddItem2Command;
+import mxaccess_gateway.v1.MxaccessGateway.AddItemCommand;
+import mxaccess_gateway.v1.MxaccessGateway.AdviseCommand;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommand;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandKind;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxValue;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.RegisterCommand;
+import mxaccess_gateway.v1.MxaccessGateway.StreamEventsRequest;
+import mxaccess_gateway.v1.MxaccessGateway.UnregisterCommand;
+import mxaccess_gateway.v1.MxaccessGateway.Write2Command;
+import mxaccess_gateway.v1.MxaccessGateway.WriteCommand;
+
+public final class MxGatewaySession implements AutoCloseable {
+    private static final SecureRandom RANDOM = new SecureRandom();
+
+    private final MxGatewayClient client;
+    private final OpenSessionReply openReply;
+    private CloseSessionReply closeReply;
+
+    MxGatewaySession(MxGatewayClient client, OpenSessionReply openReply) {
+        this.client = Objects.requireNonNull(client, "client");
+        this.openReply = Objects.requireNonNull(openReply, "openReply");
+    }
+
+    public static MxGatewaySession forSessionId(MxGatewayClient client, String sessionId) {
+        return new MxGatewaySession(
+                client, OpenSessionReply.newBuilder().setSessionId(sessionId).build());
+    }
+
+    public String sessionId() {
+        return openReply.getSessionId();
+    }
+
+    public OpenSessionReply openReply() {
+        return openReply;
+    }
+
+    public synchronized CloseSessionReply closeRaw() {
+        if (closeReply == null) {
+            closeReply = client.closeSessionRaw(CloseSessionRequest.newBuilder()
+                    .setSessionId(sessionId())
+                    .setClientCorrelationId(newCorrelationId())
+                    .build());
+        }
+        return closeReply;
+    }
+
+    @Override
+    public void close() {
+        closeRaw();
+    }
+
+    public int register(String clientName) {
+        MxCommandReply reply = registerRaw(clientName);
+        if (reply.hasRegister()) {
+            return reply.getRegister().getServerHandle();
+        }
+        return reply.getReturnValue().getInt32Value();
+    }
+
+    public MxCommandReply registerRaw(String clientName) {
+        return invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_REGISTER)
+                .setRegister(RegisterCommand.newBuilder().setClientName(clientName))
+                .build());
+    }
+
+    public void unregister(int serverHandle) {
+        invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_UNREGISTER)
+                .setUnregister(UnregisterCommand.newBuilder().setServerHandle(serverHandle))
+                .build());
+    }
+
+    public int addItem(int serverHandle, String itemDefinition) {
+        MxCommandReply reply = addItemRaw(serverHandle, itemDefinition);
+        if (reply.hasAddItem()) {
+            return reply.getAddItem().getItemHandle();
+        }
+        return reply.getReturnValue().getInt32Value();
+    }
+
+    public MxCommandReply addItemRaw(int serverHandle, String itemDefinition) {
+        return invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_ADD_ITEM)
+                .setAddItem(AddItemCommand.newBuilder()
+                        .setServerHandle(serverHandle)
+                        .setItemDefinition(itemDefinition))
+                .build());
+    }
+
+    public int addItem2(int serverHandle, String itemDefinition, String itemContext) {
+        MxCommandReply reply = addItem2Raw(serverHandle, itemDefinition, itemContext);
+        if (reply.hasAddItem2()) {
+            return reply.getAddItem2().getItemHandle();
+        }
+        return reply.getReturnValue().getInt32Value();
+    }
+
+    public MxCommandReply addItem2Raw(int serverHandle, String itemDefinition, String itemContext) {
+        return invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_ADD_ITEM2)
+                .setAddItem2(AddItem2Command.newBuilder()
+                        .setServerHandle(serverHandle)
+                        .setItemDefinition(itemDefinition)
+                        .setItemContext(itemContext))
+                .build());
+    }
+
+    public void advise(int serverHandle, int itemHandle) {
+        adviseRaw(serverHandle, itemHandle);
+    }
+
+    public MxCommandReply adviseRaw(int serverHandle, int itemHandle) {
+        return invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_ADVISE)
+                .setAdvise(AdviseCommand.newBuilder()
+                        .setServerHandle(serverHandle)
+                        .setItemHandle(itemHandle))
+                .build());
+    }
+
+    public void write(int serverHandle, int itemHandle, MxValue value, int userId) {
+        writeRaw(serverHandle, itemHandle, value, userId);
+    }
+
+    public MxCommandReply writeRaw(int serverHandle, int itemHandle, MxValue value, int userId) {
+        return invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_WRITE)
+                .setWrite(WriteCommand.newBuilder()
+                        .setServerHandle(serverHandle)
+                        .setItemHandle(itemHandle)
+                        .setValue(value)
+                        .setUserId(userId))
+                .build());
+    }
+
+    public void write2(int serverHandle, int itemHandle, MxValue value, MxValue timestampValue, int userId) {
+        invokeCommand(MxCommand.newBuilder()
+                .setKind(MxCommandKind.MX_COMMAND_KIND_WRITE2)
+                .setWrite2(Write2Command.newBuilder()
+                        .setServerHandle(serverHandle)
+                        .setItemHandle(itemHandle)
+                        .setValue(value)
+                        .setTimestampValue(timestampValue)
+                        .setUserId(userId))
+                .build());
+    }
+
+    public MxEventStream streamEvents() {
+        return streamEventsAfter(0);
+    }
+
+    public MxEventStream streamEventsAfter(long afterWorkerSequence) {
+        return client.streamEvents(StreamEventsRequest.newBuilder()
+                .setSessionId(sessionId())
+                .setAfterWorkerSequence(afterWorkerSequence)
+                .build());
+    }
+
+    public MxCommandReply invokeCommand(MxCommand command) {
+        return client.invoke(MxCommandRequest.newBuilder()
+                .setSessionId(sessionId())
+                .setClientCorrelationId(newCorrelationId())
+                .setCommand(command)
+                .build());
+    }
+
+    private static String newCorrelationId() {
+        byte[] bytes = new byte[16];
+        RANDOM.nextBytes(bytes);
+        return HexFormat.of().formatHex(bytes);
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewaySessionException.java

@@ -0,0 +1,16 @@
+package com.dohertylan.mxgateway.client;
+
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+
+public final class MxGatewaySessionException extends MxGatewayException {
+    private final ProtocolStatus protocolStatus;
+
+    public MxGatewaySessionException(String operation, ProtocolStatus protocolStatus) {
+        super(MxGatewayErrors.protocolStatusMessage(operation, protocolStatus));
+        this.protocolStatus = protocolStatus;
+    }
+
+    public ProtocolStatus protocolStatus() {
+        return protocolStatus;
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxGatewayWorkerException.java

@@ -0,0 +1,16 @@
+package com.dohertylan.mxgateway.client;
+
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+
+public final class MxGatewayWorkerException extends MxGatewayException {
+    private final ProtocolStatus protocolStatus;
+
+    public MxGatewayWorkerException(String operation, ProtocolStatus protocolStatus) {
+        super(MxGatewayErrors.protocolStatusMessage(operation, protocolStatus));
+        this.protocolStatus = protocolStatus;
+    }
+
+    public ProtocolStatus protocolStatus() {
+        return protocolStatus;
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxStatuses.java

@@ -0,0 +1,48 @@
+package com.dohertylan.mxgateway.client;
+
+import mxaccess_gateway.v1.MxaccessGateway.MxStatusCategory;
+import mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy;
+import mxaccess_gateway.v1.MxaccessGateway.MxStatusSource;
+
+public final class MxStatuses {
+    private MxStatuses() {
+    }
+
+    public static boolean succeeded(MxStatusProxy status) {
+        return status == null || status.getSuccess() != 0;
+    }
+
+    public static MxStatusView view(MxStatusProxy status) {
+        return new MxStatusView(status);
+    }
+
+    public record MxStatusView(MxStatusProxy raw) {
+        public int success() {
+            return raw.getSuccess();
+        }
+
+        public MxStatusCategory category() {
+            return raw.getCategory();
+        }
+
+        public MxStatusSource detectedBy() {
+            return raw.getDetectedBy();
+        }
+
+        public int detail() {
+            return raw.getDetail();
+        }
+
+        public int rawCategory() {
+            return raw.getRawCategory();
+        }
+
+        public int rawDetectedBy() {
+            return raw.getRawDetectedBy();
+        }
+
+        public String diagnosticText() {
+            return raw.getDiagnosticText();
+        }
+    }
+}

clients/java/mxgateway-client/src/main/java/com/dohertylan/mxgateway/client/MxValues.java

@@ -0,0 +1,170 @@
+package com.dohertylan.mxgateway.client;
+
+import com.google.protobuf.ByteString;
+import com.google.protobuf.Timestamp;
+import java.time.Instant;
+import java.util.ArrayList;
+import java.util.List;
+import mxaccess_gateway.v1.MxaccessGateway.BoolArray;
+import mxaccess_gateway.v1.MxaccessGateway.DoubleArray;
+import mxaccess_gateway.v1.MxaccessGateway.FloatArray;
+import mxaccess_gateway.v1.MxaccessGateway.Int32Array;
+import mxaccess_gateway.v1.MxaccessGateway.Int64Array;
+import mxaccess_gateway.v1.MxaccessGateway.MxArray;
+import mxaccess_gateway.v1.MxaccessGateway.MxDataType;
+import mxaccess_gateway.v1.MxaccessGateway.MxValue;
+import mxaccess_gateway.v1.MxaccessGateway.RawArray;
+import mxaccess_gateway.v1.MxaccessGateway.StringArray;
+import mxaccess_gateway.v1.MxaccessGateway.TimestampArray;
+
+public final class MxValues {
+    private MxValues() {
+    }
+
+    public static MxValue boolValue(boolean value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_BOOLEAN)
+                .setVariantType("VT_BOOL")
+                .setBoolValue(value)
+                .build();
+    }
+
+    public static MxValue int32Value(int value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_INTEGER)
+                .setVariantType("VT_I4")
+                .setInt32Value(value)
+                .build();
+    }
+
+    public static MxValue int64Value(long value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_INTEGER)
+                .setVariantType("VT_I8")
+                .setInt64Value(value)
+                .build();
+    }
+
+    public static MxValue floatValue(float value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_FLOAT)
+                .setVariantType("VT_R4")
+                .setFloatValue(value)
+                .build();
+    }
+
+    public static MxValue doubleValue(double value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_DOUBLE)
+                .setVariantType("VT_R8")
+                .setDoubleValue(value)
+                .build();
+    }
+
+    public static MxValue stringValue(String value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_STRING)
+                .setVariantType("VT_BSTR")
+                .setStringValue(value)
+                .build();
+    }
+
+    public static MxValue timestampValue(Instant value) {
+        return MxValue.newBuilder()
+                .setDataType(MxDataType.MX_DATA_TYPE_TIME)
+                .setVariantType("VT_DATE")
+                .setTimestampValue(Timestamp.newBuilder()
+                        .setSeconds(value.getEpochSecond())
+                        .setNanos(value.getNano())
+                        .build())
+                .build();
+    }
+
+    public static Object nativeValue(MxValue value) {
+        if (value == null || value.getIsNull()) {
+            return null;
+        }
+
+        return switch (value.getKindCase()) {
+            case BOOL_VALUE -> value.getBoolValue();
+            case INT32_VALUE -> value.getInt32Value();
+            case INT64_VALUE -> value.getInt64Value();
+            case FLOAT_VALUE -> value.getFloatValue();
+            case DOUBLE_VALUE -> value.getDoubleValue();
+            case STRING_VALUE -> value.getStringValue();
+            case TIMESTAMP_VALUE -> instant(value.getTimestampValue());
+            case ARRAY_VALUE -> nativeArray(value.getArrayValue());
+            case RAW_VALUE -> value.getRawValue().toByteArray();
+            case KIND_NOT_SET -> null;
+        };
+    }
+
+    public static Object nativeArray(MxArray array) {
+        if (array == null) {
+            return null;
+        }
+
+        return switch (array.getValuesCase()) {
+            case BOOL_VALUES -> List.copyOf(array.getBoolValues().getValuesList());
+            case INT32_VALUES -> List.copyOf(array.getInt32Values().getValuesList());
+            case INT64_VALUES -> List.copyOf(array.getInt64Values().getValuesList());
+            case FLOAT_VALUES -> List.copyOf(array.getFloatValues().getValuesList());
+            case DOUBLE_VALUES -> List.copyOf(array.getDoubleValues().getValuesList());
+            case STRING_VALUES -> List.copyOf(array.getStringValues().getValuesList());
+            case TIMESTAMP_VALUES -> timestampValues(array.getTimestampValues());
+            case RAW_VALUES -> rawValues(array.getRawValues());
+            case VALUES_NOT_SET -> List.of();
+        };
+    }
+
+    public static MxArray stringArray(List<String> values) {
+        return MxArray.newBuilder()
+                .setElementDataType(MxDataType.MX_DATA_TYPE_STRING)
+                .setVariantType("VT_ARRAY|VT_BSTR")
+                .addDimensions(values.size())
+                .setStringValues(StringArray.newBuilder().addAllValues(values))
+                .build();
+    }
+
+    public static MxArray int32Array(List<Integer> values) {
+        return MxArray.newBuilder()
+                .setElementDataType(MxDataType.MX_DATA_TYPE_INTEGER)
+                .setVariantType("VT_ARRAY|VT_I4")
+                .addDimensions(values.size())
+                .setInt32Values(Int32Array.newBuilder().addAllValues(values))
+                .build();
+    }
+
+    public static String kindName(MxValue value) {
+        return value == null ? "KIND_NOT_SET" : value.getKindCase().name();
+    }
+
+    private static Instant instant(Timestamp timestamp) {
+        return Instant.ofEpochSecond(timestamp.getSeconds(), timestamp.getNanos());
+    }
+
+    private static List<Instant> timestampValues(TimestampArray array) {
+        List<Instant> values = new ArrayList<>();
+        for (Timestamp timestamp : array.getValuesList()) {
+            values.add(instant(timestamp));
+        }
+        return values;
+    }
+
+    private static List<byte[]> rawValues(RawArray array) {
+        List<byte[]> values = new ArrayList<>();
+        for (ByteString rawValue : array.getValuesList()) {
+            values.add(rawValue.toByteArray());
+        }
+        return values;
+    }
+
+    @SuppressWarnings("unused")
+    private static void generatedTypeReferences(
+            BoolArray boolArray,
+            Int64Array int64Array,
+            FloatArray floatArray,
+            DoubleArray doubleArray) {
+        // Keeps generated repeated-value imports visible for javadocs and IDE navigation.
+    }
+}

clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/MxGatewayClientSessionTests.java

@@ -0,0 +1,243 @@
+package com.dohertylan.mxgateway.client;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import io.grpc.Context;
+import io.grpc.ManagedChannel;
+import io.grpc.Metadata;
+import io.grpc.Server;
+import io.grpc.ServerCall;
+import io.grpc.ServerCallHandler;
+import io.grpc.ServerInterceptor;
+import io.grpc.inprocess.InProcessChannelBuilder;
+import io.grpc.inprocess.InProcessServerBuilder;
+import io.grpc.stub.ServerCallStreamObserver;
+import io.grpc.stub.StreamObserver;
+import java.time.Duration;
+import java.util.UUID;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+import mxaccess_gateway.v1.MxAccessGatewayGrpc;
+import mxaccess_gateway.v1.MxaccessGateway.AddItemReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.CloseSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandKind;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandRequest;
+import mxaccess_gateway.v1.MxaccessGateway.MxEvent;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionReply;
+import mxaccess_gateway.v1.MxaccessGateway.OpenSessionRequest;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatus;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
+import mxaccess_gateway.v1.MxaccessGateway.RegisterReply;
+import mxaccess_gateway.v1.MxaccessGateway.SessionState;
+import mxaccess_gateway.v1.MxaccessGateway.StreamEventsRequest;
+import org.junit.jupiter.api.Test;
+
+final class MxGatewayClientSessionTests {
+    @Test
+    void unaryCallsCarryAuthMetadataAndDeadline() throws Exception {
+        AtomicReference<String> authorization = new AtomicReference<>();
+        AtomicReference<MxCommandRequest> commandRequest = new AtomicReference<>();
+        AtomicReference<Boolean> deadlineSeen = new AtomicReference<>(false);
+
+        TestGatewayService service = new TestGatewayService() {
+            @Override
+            public void openSession(OpenSessionRequest request, StreamObserver<OpenSessionReply> responseObserver) {
+                deadlineSeen.set(Context.current().getDeadline() != null);
+                responseObserver.onNext(OpenSessionReply.newBuilder()
+                        .setSessionId("session-java")
+                        .setProtocolStatus(ok())
+                        .build());
+                responseObserver.onCompleted();
+            }
+
+            @Override
+            public void invoke(MxCommandRequest request, StreamObserver<MxCommandReply> responseObserver) {
+                commandRequest.set(request);
+                responseObserver.onNext(MxCommandReply.newBuilder()
+                        .setSessionId(request.getSessionId())
+                        .setKind(request.getCommand().getKind())
+                        .setProtocolStatus(ok())
+                        .setRegister(RegisterReply.newBuilder().setServerHandle(42))
+                        .build());
+                responseObserver.onCompleted();
+            }
+        };
+
+        try (InProcessGateway gateway = InProcessGateway.start(service, authorization);
+                MxGatewayClient client = gateway.client("mxgw_visible_secret", Duration.ofSeconds(5))) {
+            MxGatewaySession session = client.openSession("junit-session");
+
+            int serverHandle = session.register("java-test-client");
+
+            assertEquals(42, serverHandle);
+            assertEquals("Bearer mxgw_visible_secret", authorization.get());
+            assertEquals("session-java", commandRequest.get().getSessionId());
+            assertEquals(MxCommandKind.MX_COMMAND_KIND_REGISTER, commandRequest.get().getCommand().getKind());
+            assertTrue(deadlineSeen.get());
+        }
+    }
+
+    @Test
+    void methodHelpersReturnTypedHandlesAndRawReplies() throws Exception {
+        TestGatewayService service = new TestGatewayService() {
+            @Override
+            public void invoke(MxCommandRequest request, StreamObserver<MxCommandReply> responseObserver) {
+                MxCommandReply.Builder reply = MxCommandReply.newBuilder()
+                        .setSessionId(request.getSessionId())
+                        .setKind(request.getCommand().getKind())
+                        .setProtocolStatus(ok());
+                if (request.getCommand().getKind() == MxCommandKind.MX_COMMAND_KIND_ADD_ITEM) {
+                    reply.setAddItem(AddItemReply.newBuilder().setItemHandle(7));
+                }
+                responseObserver.onNext(reply.build());
+                responseObserver.onCompleted();
+            }
+        };
+
+        try (InProcessGateway gateway = InProcessGateway.start(service, new AtomicReference<>());
+                MxGatewayClient client = gateway.client("", Duration.ofSeconds(5))) {
+            MxGatewaySession session = MxGatewaySession.forSessionId(client, "existing-session");
+
+            int itemHandle = session.addItem(12, "TestObject.TestInt");
+            MxCommandReply raw = session.adviseRaw(12, itemHandle);
+
+            assertEquals(7, itemHandle);
+            assertEquals(MxCommandKind.MX_COMMAND_KIND_ADVISE, raw.getKind());
+        }
+    }
+
+    @Test
+    void streamCancellationCancelsServerCall() throws Exception {
+        CountDownLatch cancelled = new CountDownLatch(1);
+        TestGatewayService service = new TestGatewayService() {
+            @Override
+            public void streamEvents(StreamEventsRequest request, StreamObserver<MxEvent> responseObserver) {
+                ServerCallStreamObserver<MxEvent> serverObserver =
+                        (ServerCallStreamObserver<MxEvent>) responseObserver;
+                serverObserver.setOnCancelHandler(cancelled::countDown);
+                responseObserver.onNext(MxEvent.newBuilder()
+                        .setSessionId(request.getSessionId())
+                        .setWorkerSequence(1)
+                        .build());
+            }
+        };
+
+        try (InProcessGateway gateway = InProcessGateway.start(service, new AtomicReference<>());
+                MxGatewayClient client = gateway.client("", Duration.ofSeconds(5))) {
+            MxEventStream events = MxGatewaySession.forSessionId(client, "stream-session").streamEvents();
+
+            assertTrue(events.hasNext());
+            assertEquals(1, events.next().getWorkerSequence());
+            events.close();
+
+            assertTrue(cancelled.await(5, TimeUnit.SECONDS));
+        }
+    }
+
+    @Test
+    void commandFailureKeepsRawReply() throws Exception {
+        TestGatewayService service = new TestGatewayService() {
+            @Override
+            public void invoke(MxCommandRequest request, StreamObserver<MxCommandReply> responseObserver) {
+                responseObserver.onNext(MxCommandReply.newBuilder()
+                        .setSessionId(request.getSessionId())
+                        .setKind(MxCommandKind.MX_COMMAND_KIND_WRITE)
+                        .setProtocolStatus(ProtocolStatus.newBuilder()
+                                .setCode(ProtocolStatusCode.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE)
+                                .setMessage("MXAccess rejected the write."))
+                        .setHresult(-2147220992)
+                        .build());
+                responseObserver.onCompleted();
+            }
+        };
+
+        try (InProcessGateway gateway = InProcessGateway.start(service, new AtomicReference<>());
+                MxGatewayClient client = gateway.client("", Duration.ofSeconds(5))) {
+            MxGatewaySession session = MxGatewaySession.forSessionId(client, "failure-session");
+
+            MxAccessException error = assertThrows(
+                    MxAccessException.class,
+                    () -> session.write(1, 2, MxValues.int32Value(123), 0));
+
+            assertNotNull(error.reply());
+            assertEquals(-2147220992, error.reply().getHresult());
+        }
+    }
+
+    private static ProtocolStatus ok() {
+        return ProtocolStatus.newBuilder()
+                .setCode(ProtocolStatusCode.PROTOCOL_STATUS_CODE_OK)
+                .build();
+    }
+
+    private abstract static class TestGatewayService extends MxAccessGatewayGrpc.MxAccessGatewayImplBase {
+        @Override
+        public void openSession(OpenSessionRequest request, StreamObserver<OpenSessionReply> responseObserver) {
+            responseObserver.onNext(OpenSessionReply.newBuilder()
+                    .setSessionId("session-java")
+                    .setProtocolStatus(ok())
+                    .build());
+            responseObserver.onCompleted();
+        }
+
+        @Override
+        public void closeSession(CloseSessionRequest request, StreamObserver<CloseSessionReply> responseObserver) {
+            responseObserver.onNext(CloseSessionReply.newBuilder()
+                    .setSessionId(request.getSessionId())
+                    .setFinalState(SessionState.SESSION_STATE_CLOSED)
+                    .setProtocolStatus(ok())
+                    .build());
+            responseObserver.onCompleted();
+        }
+    }
+
+    private record InProcessGateway(Server server, ManagedChannel channel) implements AutoCloseable {
+        static InProcessGateway start(
+                MxAccessGatewayGrpc.MxAccessGatewayImplBase service, AtomicReference<String> authorization)
+                throws Exception {
+            String serverName = "mxgw-java-" + UUID.randomUUID();
+            ServerInterceptor interceptor = new ServerInterceptor() {
+                @Override
+                public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(
+                        ServerCall<ReqT, RespT> call,
+                        Metadata headers,
+                        ServerCallHandler<ReqT, RespT> next) {
+                    authorization.set(headers.get(MxGatewayAuthInterceptor.AUTHORIZATION_HEADER));
+                    return next.startCall(call, headers);
+                }
+            };
+            Server server = InProcessServerBuilder.forName(serverName)
+                    .directExecutor()
+                    .addService(io.grpc.ServerInterceptors.intercept(service, interceptor))
+                    .build()
+                    .start();
+            ManagedChannel channel = InProcessChannelBuilder.forName(serverName)
+                    .directExecutor()
+                    .build();
+            return new InProcessGateway(server, channel);
+        }
+
+        MxGatewayClient client(String apiKey, Duration callTimeout) {
+            return new MxGatewayClient(
+                    channel,
+                    MxGatewayClientOptions.builder()
+                            .endpoint("in-process")
+                            .apiKey(apiKey)
+                            .plaintext(true)
+                            .callTimeout(callTimeout)
+                            .build());
+        }
+
+        @Override
+        public void close() {
+            channel.shutdownNow();
+            server.shutdownNow();
+        }
+    }
+}

clients/java/mxgateway-client/src/test/java/com/dohertylan/mxgateway/client/MxGatewayFixtureTests.java

@@ -0,0 +1,136 @@
+package com.dohertylan.mxgateway.client;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.google.gson.JsonArray;
+import com.google.gson.JsonObject;
+import com.google.gson.JsonParser;
+import com.google.protobuf.util.JsonFormat;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.time.Instant;
+import java.util.List;
+import mxaccess_gateway.v1.MxaccessGateway.MxCommandReply;
+import mxaccess_gateway.v1.MxaccessGateway.MxStatusCategory;
+import mxaccess_gateway.v1.MxaccessGateway.MxStatusProxy;
+import mxaccess_gateway.v1.MxaccessGateway.MxValue;
+import mxaccess_gateway.v1.MxaccessGateway.ProtocolStatusCode;
+import org.junit.jupiter.api.Test;
+
+final class MxGatewayFixtureTests {
+    @Test
+    void valueFixtureCasesExposeNativeProjectionAndRawMetadata() throws Exception {
+        JsonArray cases = readFixture("values/value-conversion-cases.json").getAsJsonArray("cases");
+
+        for (var element : cases) {
+            JsonObject testCase = element.getAsJsonObject();
+            MxValue.Builder builder = MxValue.newBuilder();
+            JsonFormat.parser().merge(testCase.getAsJsonObject("value").toString(), builder);
+            MxValue value = builder.build();
+
+            assertEquals(testCase.get("expectedKind").getAsString(), lowerCamelKind(value));
+            if ("timestamp.utc".equals(testCase.get("id").getAsString())) {
+                assertEquals(Instant.parse("2026-01-01T00:00:04Z"), MxValues.nativeValue(value));
+            }
+            if ("string-array".equals(testCase.get("id").getAsString())) {
+                assertEquals(List.of("alpha", "beta"), MxValues.nativeValue(value));
+            }
+            if ("raw-fallback.variant".equals(testCase.get("id").getAsString())) {
+                assertEquals("No lossless typed projection exists for this VARIANT.", value.getRawDiagnostic());
+                assertArrayEquals(new byte[] {1, 2, 3, 4, 5}, (byte[]) MxValues.nativeValue(value));
+            }
+        }
+    }
+
+    @Test
+    void statusFixtureCasesPreserveRawFields() throws Exception {
+        JsonArray cases = readFixture("statuses/status-conversion-cases.json").getAsJsonArray("cases");
+
+        for (var element : cases) {
+            JsonObject testCase = element.getAsJsonObject();
+            MxStatusProxy.Builder builder = MxStatusProxy.newBuilder();
+            JsonFormat.parser().merge(testCase.getAsJsonObject("status").toString(), builder);
+            MxStatusProxy status = builder.build();
+
+            assertEquals(
+                    testCase.getAsJsonObject("status").get("rawCategory").getAsInt(),
+                    status.getRawCategory());
+            if ("ok.responding-lmx".equals(testCase.get("id").getAsString())) {
+                assertTrue(MxStatuses.succeeded(status));
+            }
+            if ("security-error.requesting-lmx".equals(testCase.get("id").getAsString())) {
+                assertFalse(MxStatuses.succeeded(status));
+                assertEquals(MxStatusCategory.MX_STATUS_CATEGORY_SECURITY_ERROR, MxStatuses.view(status).category());
+            }
+        }
+    }
+
+    @Test
+    void mxAccessFailureFixtureMapsToRichCommandException() throws Exception {
+        MxCommandReply.Builder builder = MxCommandReply.newBuilder();
+        JsonFormat.parser().merge(
+                Files.readString(fixtureRoot().resolve("command-replies/write.mxaccess-failure.reply.json")),
+                builder);
+        MxCommandReply reply = builder.build();
+
+        try {
+            MxGatewayErrors.ensureProtocolSuccess("invoke", reply.getProtocolStatus(), reply);
+        } catch (MxAccessException error) {
+            assertEquals(ProtocolStatusCode.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE, error.protocolStatus().getCode());
+            assertEquals(-2147220992, error.reply().getHresult());
+            assertEquals(2, error.reply().getStatusesCount());
+            return;
+        }
+
+        throw new AssertionError("expected MxAccessException");
+    }
+
+    @Test
+    void grpcAuthErrorsAreClassifiedAndRedacted() {
+        RuntimeException authError = MxGatewayErrors.fromGrpc(
+                "open session",
+                new io.grpc.StatusRuntimeException(io.grpc.Status.UNAUTHENTICATED.withDescription(
+                        "invalid API key mxgw_visible_secret")));
+        RuntimeException permissionError = MxGatewayErrors.fromGrpc(
+                "write",
+                new io.grpc.StatusRuntimeException(io.grpc.Status.PERMISSION_DENIED.withDescription(
+                        "missing scope mxaccess.write")));
+
+        assertInstanceOf(MxGatewayAuthenticationException.class, authError);
+        assertInstanceOf(MxGatewayAuthorizationException.class, permissionError);
+        assertTrue(authError.getMessage().contains("<redacted>"));
+        assertFalse(authError.getMessage().contains("visible_secret"));
+    }
+
+    private static JsonObject readFixture(String relativePath) throws Exception {
+        return JsonParser.parseString(Files.readString(fixtureRoot().resolve(relativePath))).getAsJsonObject();
+    }
+
+    private static Path fixtureRoot() {
+        Path current = Path.of(System.getProperty("user.dir")).toAbsolutePath();
+        for (Path path = current; path != null; path = path.getParent()) {
+            Path candidate = path.resolve("clients/proto/fixtures/behavior");
+            if (Files.exists(candidate)) {
+                return candidate;
+            }
+            candidate = path.resolve("../proto/fixtures/behavior").normalize();
+            if (Files.exists(candidate)) {
+                return candidate;
+            }
+        }
+        throw new IllegalStateException("could not locate behavior fixtures from " + current);
+    }
+
+    private static String lowerCamelKind(MxValue value) {
+        String[] parts = value.getKindCase().name().toLowerCase().split("_");
+        StringBuilder result = new StringBuilder(parts[0]);
+        for (int index = 1; index < parts.length; index++) {
+            result.append(Character.toUpperCase(parts[index].charAt(0))).append(parts[index].substring(1));
+        }
+        return result.toString();
+    }
+}

clients/proto/fixtures/parity/parity-fixture-matrix.json

@@ -0,0 +1,469 @@
+{
+  "schemaVersion": 1,
+  "fixtureSet": "mxaccess-gateway-parity-fixture-matrix",
+  "contractName": "mxaccess-gateway",
+  "gatewayProtocolVersion": 1,
+  "workerProtocolVersion": 1,
+  "sourceCaptureRoot": "C:/Users/dohertj2/Desktop/mxaccess/captures",
+  "sourceDocs": [
+    "C:/Users/dohertj2/Desktop/mxaccess/docs/MXAccess-Public-API.md",
+    "C:/Users/dohertj2/Desktop/mxaccess/docs/Current-Sprint-State.md"
+  ],
+  "comparisonFormat": {
+    "description": "Each parity run records the same command against direct MXAccess and the gateway-backed worker, then compares raw parity fields instead of client wrapper behavior.",
+    "directMxAccess": {
+      "requiredFields": [
+        "method",
+        "arguments",
+        "returnedValue",
+        "hresult",
+        "exceptionType",
+        "statuses",
+        "events"
+      ]
+    },
+    "gatewayResult": {
+      "requiredFields": [
+        "kind",
+        "protocolStatus",
+        "returnValue",
+        "hresult",
+        "statuses",
+        "diagnosticMessage",
+        "events"
+      ]
+    },
+    "eventFields": [
+      "family",
+      "serverHandle",
+      "itemHandle",
+      "value",
+      "quality",
+      "sourceTimestamp",
+      "statuses",
+      "workerSequence",
+      "workerTimestamp",
+      "gatewayReceiveTimestamp",
+      "hresult",
+      "rawStatus"
+    ],
+    "comparisonKeys": [
+      "hresult",
+      "exceptionType",
+      "returnedValue",
+      "statusArrayShape",
+      "statusRawFields",
+      "eventFamilyOrder",
+      "eventPayloadShape",
+      "valueProjection",
+      "rawFallbackMetadata"
+    ]
+  },
+  "methodFixtures": [
+    {
+      "id": "method.register.basic",
+      "method": "Register",
+      "commandKind": "MX_COMMAND_KIND_REGISTER",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/001-register/harness.log",
+        "captures/047-frida-com-proxy-register/harness.log"
+      ],
+      "assertions": [
+        "preserve returned server handle in returnValue and RegisterReply",
+        "preserve success HRESULT as 0",
+        "do not emit MXAccess events for register"
+      ]
+    },
+    {
+      "id": "method.unregister.basic",
+      "method": "Unregister",
+      "commandKind": "MX_COMMAND_KIND_UNREGISTER",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/001-register/harness.log",
+        "captures/109-native-post-remove-errors/harness.log"
+      ],
+      "assertions": [
+        "preserve void return shape with explicit protocol success",
+        "preserve HRESULT or COM exception details for invalid server handle",
+        "close registered handle only after MXAccess succeeds"
+      ]
+    },
+    {
+      "id": "method.add-item.scalar",
+      "method": "AddItem",
+      "commandKind": "MX_COMMAND_KIND_ADD_ITEM",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/002-add-remove-scalar/harness.log",
+        "captures/006-add-invalid/harness.log"
+      ],
+      "assertions": [
+        "preserve returned item handle in returnValue and AddItemReply",
+        "preserve invalid item reference HRESULT/status details",
+        "do not prevalidate item definition in the gateway"
+      ]
+    },
+    {
+      "id": "method.add-item2.context",
+      "method": "AddItem2",
+      "commandKind": "MX_COMMAND_KIND_ADD_ITEM2",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/mxaccess-additem2-testint-context.log",
+        "captures/121-frida-buffered-history-testhistoryvalue-context/harness.log"
+      ],
+      "assertions": [
+        "pass item_definition and item_context exactly as supplied",
+        "preserve returned item handle in returnValue and AddItem2Reply",
+        "compare context-bearing reference resolution against direct MXAccess"
+      ]
+    },
+    {
+      "id": "method.remove-item.basic",
+      "method": "RemoveItem",
+      "commandKind": "MX_COMMAND_KIND_REMOVE_ITEM",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/002-add-remove-scalar/harness.log",
+        "captures/109-native-post-remove-errors/harness.log"
+      ],
+      "assertions": [
+        "preserve void return shape with explicit protocol success",
+        "preserve post-remove and invalid-handle HRESULT/status behavior",
+        "remove diagnostic handle state only after MXAccess succeeds"
+      ]
+    },
+    {
+      "id": "method.advise.supervisory-data-change",
+      "method": "Advise",
+      "commandKind": "MX_COMMAND_KIND_ADVISE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/003-subscribe-scalars/harness.log",
+        "captures/058-frida-subscribe-testint/harness.log"
+      ],
+      "assertions": [
+        "preserve successful command reply shape",
+        "forward OnDataChange with value, quality, timestamp, and status array",
+        "preserve per-worker event order"
+      ]
+    },
+    {
+      "id": "method.unadvise.basic",
+      "method": "UnAdvise",
+      "commandKind": "MX_COMMAND_KIND_UN_ADVISE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/058-frida-subscribe-testint/harness.log",
+        "captures/007-subscribe-invalid/harness.log"
+      ],
+      "assertions": [
+        "preserve void return shape with explicit protocol success",
+        "preserve invalid item handle HRESULT/status behavior",
+        "do not distinguish plain and supervisory cleanup beyond MXAccess behavior"
+      ]
+    },
+    {
+      "id": "method.advise-supervisory.basic",
+      "method": "AdviseSupervisory",
+      "commandKind": "MX_COMMAND_KIND_ADVISE_SUPERVISORY",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/058-frida-subscribe-testint/harness.log",
+        "captures/105-frida-advise-shortdesc-prebound-fixed/harness.log"
+      ],
+      "assertions": [
+        "keep AdviseSupervisory distinct from plain Advise in command kind",
+        "forward native OnDataChange only when MXAccess emits it",
+        "compare supervisory item status arrays without normalization"
+      ]
+    },
+    {
+      "id": "method.add-buffered-item.context",
+      "method": "AddBufferedItem",
+      "commandKind": "MX_COMMAND_KIND_ADD_BUFFERED_ITEM",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/079-frida-add-buffered-advise-testint/harness.log",
+        "captures/120-frida-buffered-history-testhistoryvalue/harness.log",
+        "captures/121-frida-buffered-history-testhistoryvalue-context/harness.log"
+      ],
+      "assertions": [
+        "pass item_definition and item_context exactly as supplied",
+        "preserve returned buffered item handle in returnValue and AddBufferedItemReply",
+        "keep buffered registration distinct from normal AddItem2"
+      ]
+    },
+    {
+      "id": "method.set-buffered-update-interval.basic",
+      "method": "SetBufferedUpdateInterval",
+      "commandKind": "MX_COMMAND_KIND_SET_BUFFERED_UPDATE_INTERVAL",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/mxaccess-set-buffered-interval-1000.log",
+        "captures/079-frida-add-buffered-advise-testint/harness.log"
+      ],
+      "assertions": [
+        "preserve requested update interval without clamping in the gateway",
+        "preserve void return shape with explicit protocol success",
+        "compare buffered event cadence only in opt-in live runs"
+      ]
+    },
+    {
+      "id": "method.suspend.scan-state",
+      "method": "Suspend",
+      "commandKind": "MX_COMMAND_KIND_SUSPEND",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/077-frida-suspend-advised-scanstate/harness.log",
+        "captures/118-frida-suspend-advised-scanstate-long/harness.log"
+      ],
+      "assertions": [
+        "preserve out MxStatus in SuspendReply and repeated statuses",
+        "preserve HRESULT separately from status detail",
+        "do not synthesize OperationComplete if native MXAccess does not raise it"
+      ]
+    },
+    {
+      "id": "method.activate.scan-state",
+      "method": "Activate",
+      "commandKind": "MX_COMMAND_KIND_ACTIVATE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/078-frida-activate-advised-scanstate/harness.log",
+        "captures/119-frida-activate-advised-scanstate-long/harness.log"
+      ],
+      "assertions": [
+        "preserve out MxStatus in ActivateReply and repeated statuses",
+        "preserve HRESULT separately from status detail",
+        "do not synthesize OperationComplete if native MXAccess does not raise it"
+      ]
+    },
+    {
+      "id": "method.write.value-status-matrix",
+      "method": "Write",
+      "commandKind": "MX_COMMAND_KIND_WRITE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/023-frida-write-test-int-sequence-109-111/harness.log",
+        "captures/024-frida-write-test-bool-sequence/harness.log",
+        "captures/089-frida-write-testint-wrong-type/harness.log",
+        "captures/090-frida-write-invalid-reference/harness.log",
+        "captures/107-native-write-testint-current/harness.log"
+      ],
+      "assertions": [
+        "preserve scalar and array value projections plus raw fallback metadata",
+        "preserve wrong-type and invalid-reference HRESULT/status arrays",
+        "forward OnWriteComplete only when native MXAccess emits it"
+      ]
+    },
+    {
+      "id": "method.write2.timestamped",
+      "method": "Write2",
+      "commandKind": "MX_COMMAND_KIND_WRITE2",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/042-frida-write2-test-int-timestamp/harness.log",
+        "captures/066-frida-write2-test-bool-timestamp/harness.log",
+        "captures/075-frida-write2-test-datetime-array-timestamp/harness.log"
+      ],
+      "assertions": [
+        "preserve timestamp_value as an MXAccess VARIANT projection",
+        "preserve write value shape and HRESULT/status arrays",
+        "compare timestamped write completion events against direct MXAccess"
+      ]
+    },
+    {
+      "id": "method.write-secured.rejection-gap",
+      "method": "WriteSecured",
+      "commandKind": "MX_COMMAND_KIND_WRITE_SECURED",
+      "status": "documented_gap",
+      "captureReferences": [
+        "captures/036-frida-write-secured-test-int/harness.log",
+        "captures/111-frida-write-secured-auth-protectedvalue/harness.log",
+        "captures/112-frida-write-secured-auth-verified-protectedvalue1/harness.log"
+      ],
+      "assertions": [
+        "preserve observed 0x80004021 rejection before a value-bearing NMX body",
+        "preserve current_user_id and verifier_user_id only as command inputs, not logs",
+        "upgrade this gap to planned_fixture when a successful direct WriteSecured path is observed"
+      ]
+    },
+    {
+      "id": "method.write-secured2.authenticated",
+      "method": "WriteSecured2",
+      "commandKind": "MX_COMMAND_KIND_WRITE_SECURED2",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/113-frida-write-secured2-auth-protectedvalue/harness.log",
+        "captures/116-frida-write-secured2-auth-verified-protectedvalue1/harness.log",
+        "captures/117-frida-write-secured2-auth-testint/harness.log"
+      ],
+      "assertions": [
+        "preserve authenticated timestamped secured write body shape",
+        "preserve HRESULT/status arrays without logging credential-bearing values",
+        "do not synthesize OnWriteComplete when direct MXAccess does not emit it"
+      ]
+    },
+    {
+      "id": "method.authenticate-user.basic",
+      "method": "AuthenticateUser",
+      "commandKind": "MX_COMMAND_KIND_AUTHENTICATE_USER",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/087-frida-authenticate-administrator-empty/harness.log",
+        "captures/088-frida-authenticate-invalid-empty/harness.log"
+      ],
+      "assertions": [
+        "preserve returned user id in returnValue and AuthenticateUserReply",
+        "preserve invalid credential HRESULT/status behavior",
+        "redact verify_user_password from logs and diagnostics"
+      ]
+    },
+    {
+      "id": "method.archestra-user-to-id.basic",
+      "method": "ArchestrAUserToId",
+      "commandKind": "MX_COMMAND_KIND_ARCHESTRA_USER_TO_ID",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/mxaccess-user-map-administrator.log",
+        "captures/mxaccess-user-map-invalid.log"
+      ],
+      "assertions": [
+        "preserve returned user id in returnValue and ArchestrAUserToIdReply",
+        "preserve invalid user GUID HRESULT/status behavior",
+        "compare raw mapping behavior without normalizing unknown users"
+      ]
+    }
+  ],
+  "eventFixtures": [
+    {
+      "id": "event.on-data-change.scalar",
+      "family": "MX_EVENT_FAMILY_ON_DATA_CHANGE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/003-subscribe-scalars/harness.log",
+        "captures/106-native-subscribe-testint-current/harness.log"
+      ],
+      "assertions": [
+        "preserve value, quality, timestamp, status array, and worker sequence"
+      ]
+    },
+    {
+      "id": "event.on-write-complete.status",
+      "family": "MX_EVENT_FAMILY_ON_WRITE_COMPLETE",
+      "status": "planned_fixture",
+      "captureReferences": [
+        "captures/008-write-test-int-same-value/harness.log",
+        "captures/107-native-write-testint-current/harness.log"
+      ],
+      "assertions": [
+        "preserve write-complete status array and optional HRESULT"
+      ]
+    },
+    {
+      "id": "event.operation-complete.native-trigger-gap",
+      "family": "MX_EVENT_FAMILY_OPERATION_COMPLETE",
+      "status": "documented_gap",
+      "captureReferences": [
+        "captures/077-frida-suspend-advised-scanstate/harness.log",
+        "captures/118-frida-suspend-advised-scanstate-long/harness.log"
+      ],
+      "assertions": [
+        "do not synthesize OperationComplete from Write or OnWriteComplete",
+        "upgrade this gap when a public MXAccess trigger emits event family 3"
+      ]
+    },
+    {
+      "id": "event.on-buffered-data-change.batch-gap",
+      "family": "MX_EVENT_FAMILY_ON_BUFFERED_DATA_CHANGE",
+      "status": "documented_gap",
+      "captureReferences": [
+        "captures/120-frida-buffered-history-testhistoryvalue/harness.log",
+        "captures/122-frida-buffered-history-testhistoryvalue-plainadvise/harness.log"
+      ],
+      "assertions": [
+        "preserve raw buffered metadata until a public multi-sample event payload is observed",
+        "upgrade this gap when OnBufferedDataChange batches are captured from MXAccess"
+      ]
+    }
+  ],
+  "scenarioGroups": [
+    {
+      "id": "invalid_handles",
+      "description": "Invalid server, item, post-remove, and invalid-reference cases keep MXAccess-owned HRESULT and status behavior.",
+      "fixtureIds": [
+        "method.add-item.scalar",
+        "method.remove-item.basic",
+        "method.unadvise.basic",
+        "method.write.value-status-matrix",
+        "method.unregister.basic"
+      ],
+      "captureReferences": [
+        "captures/006-add-invalid/harness.log",
+        "captures/007-subscribe-invalid/harness.log",
+        "captures/109-native-post-remove-errors/harness.log",
+        "captures/110-native-invalid-handle-errors/harness.log"
+      ]
+    },
+    {
+      "id": "write_statuses",
+      "description": "Write success, wrong type, invalid reference, scalar arrays, and completion-status cases compare HRESULT, status array, value projection, and event shape.",
+      "fixtureIds": [
+        "method.write.value-status-matrix",
+        "method.write2.timestamped",
+        "event.on-write-complete.status"
+      ],
+      "captureReferences": [
+        "captures/089-frida-write-testint-wrong-type/harness.log",
+        "captures/090-frida-write-invalid-reference/harness.log",
+        "captures/091-frida-write-testint-double-type/harness.log",
+        "captures/097-frida-write-bool-array-pattern/harness.log",
+        "captures/107-native-write-testint-current/harness.log"
+      ]
+    },
+    {
+      "id": "secured_writes",
+      "description": "Secured writes include observed WriteSecured rejection and authenticated WriteSecured2 success paths without logging credential-bearing values.",
+      "fixtureIds": [
+        "method.write-secured.rejection-gap",
+        "method.write-secured2.authenticated",
+        "method.authenticate-user.basic"
+      ],
+      "captureReferences": [
+        "captures/036-frida-write-secured-test-int/harness.log",
+        "captures/111-frida-write-secured-auth-protectedvalue/harness.log",
+        "captures/113-frida-write-secured2-auth-protectedvalue/harness.log",
+        "captures/117-frida-write-secured2-auth-testint/harness.log"
+      ]
+    },
+    {
+      "id": "add_item_context",
+      "description": "Context-bearing item registration compares AddItem2 and buffered AddBufferedItem argument preservation.",
+      "fixtureIds": [
+        "method.add-item2.context",
+        "method.add-buffered-item.context"
+      ],
+      "captureReferences": [
+        "captures/mxaccess-additem2-testint-context.log",
+        "captures/121-frida-buffered-history-testhistoryvalue-context/harness.log"
+      ]
+    },
+    {
+      "id": "buffered_registration",
+      "description": "Buffered registration and interval setup are tracked separately from normal advice until a public buffered data-change batch is captured.",
+      "fixtureIds": [
+        "method.add-buffered-item.context",
+        "method.set-buffered-update-interval.basic",
+        "event.on-buffered-data-change.batch-gap"
+      ],
+      "captureReferences": [
+        "captures/079-frida-add-buffered-advise-testint/harness.log",
+        "captures/120-frida-buffered-history-testhistoryvalue/harness.log",
+        "captures/122-frida-buffered-history-testhistoryvalue-plainadvise/harness.log"
+      ]
+    }
+  ]
+}

clients/python/README.md

@@ -1,8 +1,8 @@
 # Python Client
 
 The Python client package contains generated MXAccess Gateway protobuf
-bindings, the `mxgateway` package scaffold, and the `mxgw-py` test CLI
-scaffold. The package uses the shared proto inputs documented in
+bindings, the async `mxgateway` package, and the `mxgw-py` test CLI. The
+package uses the shared proto inputs documented in
 `../../docs/client-proto-generation.md` so gateway and client contracts stay in
 sync.
 
@@ -43,15 +43,65 @@ python -m pytest
 python -m pip wheel . --no-deps --wheel-dir "$env:TEMP\mxgateway-python-wheel"
 ```
 
-The scaffold tests import the generated gateway and worker stubs and exercise
-the deterministic CLI version output.
+The tests import the generated gateway and worker stubs, run fake async gateway
+stubs, verify API key metadata, exercise stream cancellation, load shared value
+and command fixtures, and check deterministic CLI output.
+
+## Library Usage
+
+The library is async-first:
+
+```python
+from mxgateway import GatewayClient
+
+async with await GatewayClient.connect(
+    endpoint="localhost:5000",
+    api_key="mxgw_example",
+    plaintext=True,
+) as client:
+    session = await client.open_session(client_session_name="python-client")
+    try:
+        server_handle = await session.register("python-client")
+        item_handle = await session.add_item(server_handle, "Object.Attribute")
+        await session.advise(server_handle, item_handle)
+    finally:
+        await session.close()
+```
+
+`GatewayClient.open_session_raw`, `GatewayClient.invoke_raw`, and
+`GatewayClient.stream_events_raw` keep the generated protobuf replies and
+events available for parity tests. `Session` helpers call the method-specific
+MXAccess commands and preserve raw replies on typed command exceptions.
+
+Canceling a Python task cancels the client-side gRPC call or stream wait. It
+does not abort an in-flight MXAccess COM call inside the worker process.
+
+## Authentication And TLS
+
+`ClientOptions.api_key` adds this metadata to unary calls and streams:
+
+```text
+authorization: Bearer <api-key>
+```
+
+The client supports plaintext channels for local development, TLS with system
+roots, TLS with a custom `ca_file`, and an optional test server name override.
+API keys are redacted from option repr output and CLI error output.
 
 ## CLI
 
-The scaffold CLI exposes version information:
+The CLI emits deterministic JSON for automation:
 
 ```powershell
 mxgw-py version --json
+mxgw-py open-session --endpoint localhost:5000 --plaintext --json
+mxgw-py register --session-id <id> --client-name python-client --json
+mxgw-py add-item --session-id <id> --server-handle 1 --item Object.Attribute --json
+mxgw-py advise --session-id <id> --server-handle 1 --item-handle 2 --json
+mxgw-py stream-events --session-id <id> --max-events 1 --json
+mxgw-py write --session-id <id> --server-handle 1 --item-handle 2 --type int32 --value 123 --json
 ```
 
-Additional commands are implemented with the async client/session wrapper work.
+Use `--api-key` or `--api-key-env MXGATEWAY_API_KEY` to attach API key
+metadata. `smoke` opens a session, registers, adds an item, advises, streams a
+bounded event count, and closes the session in a `finally` block.

clients/python/src/mxgateway/__init__.py

@@ -1,5 +1,38 @@
 """MXAccess Gateway Python client package."""
 
+from .auth import ApiKey, auth_metadata
+from .client import GatewayClient
+from .errors import (
+    MxAccessError,
+    MxGatewayAuthenticationError,
+    MxGatewayAuthorizationError,
+    MxGatewayCommandError,
+    MxGatewayError,
+    MxGatewaySessionError,
+    MxGatewayTransportError,
+    MxGatewayWorkerError,
+)
+from .options import ClientOptions
+from .session import Session
+from .values import MxValueView, from_mx_value, to_mx_value
 from .version import __version__
 
-__all__ = ["__version__"]
+__all__ = [
+    "ApiKey",
+    "ClientOptions",
+    "GatewayClient",
+    "MxAccessError",
+    "MxGatewayAuthenticationError",
+    "MxGatewayAuthorizationError",
+    "MxGatewayCommandError",
+    "MxGatewayError",
+    "MxGatewaySessionError",
+    "MxGatewayTransportError",
+    "MxGatewayWorkerError",
+    "MxValueView",
+    "Session",
+    "__version__",
+    "auth_metadata",
+    "from_mx_value",
+    "to_mx_value",
+]

clients/python/src/mxgateway/auth.py

@@ -0,0 +1,58 @@
+"""Authentication metadata helpers for MXAccess Gateway clients."""
+
+from collections.abc import Sequence
+from dataclasses import dataclass
+
+AUTHORIZATION_HEADER = "authorization"
+REDACTED = "[redacted]"
+
+
+@dataclass(frozen=True)
+class ApiKey:
+    """API key wrapper that avoids leaking the secret through repr output."""
+
+    value: str
+
+    def __post_init__(self) -> None:
+        if not self.value:
+            raise ValueError("api_key must not be empty")
+
+    def __repr__(self) -> str:
+        return f"{type(self).__name__}({REDACTED!r})"
+
+    def bearer_value(self) -> str:
+        return f"Bearer {self.value}"
+
+
+def auth_metadata(api_key: str | ApiKey | None) -> tuple[tuple[str, str], ...]:
+    """Return gRPC metadata for API key auth."""
+
+    if api_key is None:
+        return ()
+
+    key = api_key.value if isinstance(api_key, ApiKey) else api_key
+    if not key:
+        return ()
+
+    return ((AUTHORIZATION_HEADER, f"Bearer {key}"),)
+
+
+def merge_metadata(
+    api_key: str | ApiKey | None,
+    metadata: Sequence[tuple[str, str]] | None = None,
+) -> tuple[tuple[str, str], ...]:
+    """Merge caller metadata with API key metadata."""
+
+    merged = list(metadata or ())
+    merged.extend(auth_metadata(api_key))
+    return tuple(merged)
+
+
+def redact_secret(text: str, secrets: Sequence[str | None]) -> str:
+    """Replace known secret values with a stable redaction marker."""
+
+    redacted = text
+    for secret in secrets:
+        if secret:
+            redacted = redacted.replace(secret, REDACTED)
+    return redacted

clients/python/src/mxgateway/client.py

@@ -0,0 +1,165 @@
+"""Async MXAccess Gateway client wrapper."""
+
+from __future__ import annotations
+
+import asyncio
+from collections.abc import AsyncIterator, Sequence
+from typing import Any
+
+import grpc
+
+from .auth import merge_metadata
+from .errors import ensure_protocol_success, map_rpc_error
+from .generated import mxaccess_gateway_pb2 as pb
+from .generated import mxaccess_gateway_pb2_grpc as pb_grpc
+from .options import ClientOptions, create_channel
+
+
+class GatewayClient:
+    """Async client for the public MXAccess Gateway gRPC API."""
+
+    def __init__(
+        self,
+        *,
+        options: ClientOptions,
+        stub: Any,
+        channel: grpc.aio.Channel | None = None,
+    ) -> None:
+        self.options = options
+        self.raw_stub = stub
+        self._channel = channel
+        self._closed = False
+
+    @classmethod
+    async def connect(
+        cls,
+        options: ClientOptions | None = None,
+        *,
+        endpoint: str | None = None,
+        api_key: str | None = None,
+        plaintext: bool = False,
+        ca_file: str | None = None,
+        server_name_override: str | None = None,
+        stub: Any | None = None,
+    ) -> "GatewayClient":
+        """Create a client with either a real async channel or a supplied fake stub."""
+
+        resolved = options or ClientOptions(
+            endpoint=endpoint or "",
+            api_key=api_key,
+            plaintext=plaintext,
+            ca_file=ca_file,
+            server_name_override=server_name_override,
+        )
+
+        if stub is not None:
+            return cls(options=resolved, stub=stub)
+
+        channel = create_channel(resolved)
+        return cls(
+            options=resolved,
+            stub=pb_grpc.MxAccessGatewayStub(channel),
+            channel=channel,
+        )
+
+    async def __aenter__(self) -> "GatewayClient":
+        return self
+
+    async def __aexit__(self, *_exc_info: object) -> None:
+        await self.close()
+
+    async def close(self) -> None:
+        """Close the owned gRPC channel."""
+
+        if self._closed:
+            return
+
+        self._closed = True
+        if self._channel is not None:
+            await self._channel.close()
+
+    async def open_session(
+        self,
+        request: pb.OpenSessionRequest | None = None,
+        *,
+        requested_backend: str = "",
+        client_session_name: str = "",
+        client_correlation_id: str = "",
+    ) -> "Session":
+        """Open a gateway session and return a high-level session wrapper."""
+
+        from .session import Session
+
+        raw_request = request or pb.OpenSessionRequest(
+            requested_backend=requested_backend,
+            client_session_name=client_session_name,
+            client_correlation_id=client_correlation_id,
+        )
+        reply = await self.open_session_raw(raw_request)
+        return Session(client=self, session_id=reply.session_id, open_reply=reply)
+
+    async def open_session_raw(self, request: pb.OpenSessionRequest) -> pb.OpenSessionReply:
+        reply = await self._unary("open session", self.raw_stub.OpenSession, request)
+        ensure_protocol_success("open session", reply.protocol_status, reply)
+        return reply
+
+    async def close_session_raw(
+        self,
+        request: pb.CloseSessionRequest,
+    ) -> pb.CloseSessionReply:
+        reply = await self._unary("close session", self.raw_stub.CloseSession, request)
+        ensure_protocol_success("close session", reply.protocol_status, reply)
+        return reply
+
+    async def invoke_raw(self, request: pb.MxCommandRequest) -> pb.MxCommandReply:
+        reply = await self._unary("invoke", self.raw_stub.Invoke, request)
+        ensure_protocol_success("invoke", reply.protocol_status, reply)
+        return reply
+
+    def stream_events_raw(
+        self,
+        request: pb.StreamEventsRequest,
+        *,
+        metadata: Sequence[tuple[str, str]] | None = None,
+    ) -> AsyncIterator[pb.MxEvent]:
+        """Return an async event iterator and cancel the stream when iteration stops."""
+
+        call = self.raw_stub.StreamEvents(
+            request,
+            metadata=merge_metadata(self.options.api_key, metadata),
+        )
+        return _canceling_iterator(call)
+
+    async def _unary(
+        self,
+        operation: str,
+        method: Any,
+        request: Any,
+        *,
+        metadata: Sequence[tuple[str, str]] | None = None,
+    ) -> Any:
+        call = method(
+            request,
+            metadata=merge_metadata(self.options.api_key, metadata),
+        )
+        try:
+            return await call
+        except asyncio.CancelledError:
+            cancel = getattr(call, "cancel", None)
+            if cancel is not None:
+                cancel()
+            raise
+        except grpc.RpcError as error:
+            raise map_rpc_error(operation, error) from error
+
+
+async def _canceling_iterator(call: Any) -> AsyncIterator[pb.MxEvent]:
+    try:
+        async for event in call:
+            yield event
+    except grpc.RpcError as error:
+        raise map_rpc_error("stream events", error) from error
+    finally:
+        cancel = getattr(call, "cancel", None)
+        if cancel is not None:
+            cancel()

clients/python/src/mxgateway/errors.py

@@ -0,0 +1,157 @@
+"""Typed exception model for MXAccess Gateway Python clients."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import grpc
+
+from .generated import mxaccess_gateway_pb2 as pb
+
+
+class MxGatewayError(Exception):
+    """Base class for client wrapper errors."""
+
+    def __init__(
+        self,
+        message: str,
+        *,
+        protocol_status: pb.ProtocolStatus | None = None,
+        raw_reply: Any | None = None,
+    ) -> None:
+        super().__init__(message)
+        self.protocol_status = protocol_status
+        self.raw_reply = raw_reply
+
+
+class MxGatewayTransportError(MxGatewayError):
+    """Transport-level gRPC failure."""
+
+
+class MxGatewayAuthenticationError(MxGatewayTransportError):
+    """Authentication failure reported by gRPC."""
+
+
+class MxGatewayAuthorizationError(MxGatewayTransportError):
+    """Authorization failure reported by gRPC."""
+
+
+class MxGatewaySessionError(MxGatewayError):
+    """Gateway session failure."""
+
+
+class MxGatewayWorkerError(MxGatewayError):
+    """Gateway worker process or protocol failure."""
+
+
+class MxGatewayCommandError(MxGatewayError):
+    """Command failure that preserves the raw protobuf reply."""
+
+
+class MxAccessError(MxGatewayCommandError):
+    """MXAccess HRESULT or status failure."""
+
+
+def map_rpc_error(operation: str, error: grpc.RpcError) -> MxGatewayTransportError:
+    """Map a generated gRPC exception to the client exception hierarchy."""
+
+    code = error.code() if hasattr(error, "code") else None
+    details = error.details() if hasattr(error, "details") else str(error)
+    message = f"{operation} failed: {details}"
+
+    if code == grpc.StatusCode.UNAUTHENTICATED:
+        return MxGatewayAuthenticationError(message)
+    if code == grpc.StatusCode.PERMISSION_DENIED:
+        return MxGatewayAuthorizationError(message)
+
+    return MxGatewayTransportError(message)
+
+
+def ensure_protocol_success(
+    operation: str,
+    protocol_status: pb.ProtocolStatus | None,
+    raw_reply: Any | None = None,
+) -> Any | None:
+    """Raise typed gateway errors for non-OK protocol statuses."""
+
+    code = (
+        protocol_status.code
+        if protocol_status is not None
+        else pb.PROTOCOL_STATUS_CODE_UNSPECIFIED
+    )
+
+    if code in (
+        pb.PROTOCOL_STATUS_CODE_OK,
+        pb.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE,
+    ):
+        return raw_reply
+
+    message_text = protocol_status.message if protocol_status else ""
+    message = f"{operation} failed: {message_text or pb.ProtocolStatusCode.Name(code)}"
+
+    if code in (
+        pb.PROTOCOL_STATUS_CODE_SESSION_NOT_FOUND,
+        pb.PROTOCOL_STATUS_CODE_SESSION_NOT_READY,
+    ):
+        raise MxGatewaySessionError(
+            message,
+            protocol_status=protocol_status,
+            raw_reply=raw_reply,
+        )
+
+    if code in (
+        pb.PROTOCOL_STATUS_CODE_WORKER_UNAVAILABLE,
+        pb.PROTOCOL_STATUS_CODE_TIMEOUT,
+        pb.PROTOCOL_STATUS_CODE_CANCELED,
+        pb.PROTOCOL_STATUS_CODE_PROTOCOL_VIOLATION,
+    ):
+        raise MxGatewayWorkerError(
+            message,
+            protocol_status=protocol_status,
+            raw_reply=raw_reply,
+        )
+
+    raise MxGatewayCommandError(
+        message,
+        protocol_status=protocol_status,
+        raw_reply=raw_reply,
+    )
+
+
+def ensure_mxaccess_success(operation: str, reply: pb.MxCommandReply) -> pb.MxCommandReply:
+    """Raise `MxAccessError` when MXAccess returned HRESULT or status failure."""
+
+    status = reply.protocol_status
+    if status.code == pb.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE:
+        raise MxAccessError(
+            _mxaccess_message(operation, reply),
+            protocol_status=status,
+            raw_reply=reply,
+        )
+
+    if reply.HasField("hresult") and reply.hresult < 0:
+        raise MxAccessError(
+            _mxaccess_message(operation, reply),
+            protocol_status=status,
+            raw_reply=reply,
+        )
+
+    for mx_status in reply.statuses:
+        if mx_status.success == 0:
+            raise MxAccessError(
+                _mxaccess_message(operation, reply),
+                protocol_status=status,
+                raw_reply=reply,
+            )
+
+    return reply
+
+
+def _mxaccess_message(operation: str, reply: pb.MxCommandReply) -> str:
+    status_text = reply.protocol_status.message or "MXAccess command failed"
+    hresult = reply.hresult if reply.HasField("hresult") else None
+    return (
+        f"{operation} failed: {status_text}; "
+        f"session={reply.session_id}; correlation={reply.correlation_id}; "
+        f"hresult={hresult}; statuses={len(reply.statuses)}"
+    )

clients/python/src/mxgateway/options.py

@@ -0,0 +1,59 @@
+"""Client connection options for the async Python wrapper."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from pathlib import Path
+
+import grpc
+
+from .auth import REDACTED, ApiKey
+
+
+@dataclass(frozen=True)
+class ClientOptions:
+    """Connection settings for `GatewayClient.connect`."""
+
+    endpoint: str
+    api_key: str | ApiKey | None = None
+    plaintext: bool = False
+    ca_file: str | None = None
+    server_name_override: str | None = None
+
+    def __post_init__(self) -> None:
+        if not self.endpoint:
+            raise ValueError("endpoint must not be empty")
+
+        if self.plaintext and self.ca_file:
+            raise ValueError("ca_file cannot be used with plaintext connections")
+
+    def __repr__(self) -> str:
+        api_key = REDACTED if self.api_key else None
+        return (
+            f"{type(self).__name__}(endpoint={self.endpoint!r}, "
+            f"api_key={api_key!r}, plaintext={self.plaintext!r}, "
+            f"ca_file={self.ca_file!r}, "
+            f"server_name_override={self.server_name_override!r})"
+        )
+
+
+def create_channel(options: ClientOptions) -> grpc.aio.Channel:
+    """Create a plaintext or TLS `grpc.aio` channel from client options."""
+
+    channel_options: list[tuple[str, str]] = []
+    if options.server_name_override:
+        channel_options.append(("grpc.ssl_target_name_override", options.server_name_override))
+
+    if options.plaintext:
+        return grpc.aio.insecure_channel(options.endpoint, options=channel_options)
+
+    root_certificates = None
+    if options.ca_file:
+        root_certificates = Path(options.ca_file).read_bytes()
+
+    credentials = grpc.ssl_channel_credentials(root_certificates=root_certificates)
+    return grpc.aio.secure_channel(
+        options.endpoint,
+        credentials,
+        options=channel_options,
+    )

clients/python/src/mxgateway/session.py

@@ -0,0 +1,209 @@
+"""Async session wrapper for MXAccess Gateway commands."""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator
+
+from .errors import ensure_mxaccess_success
+from .generated import mxaccess_gateway_pb2 as pb
+from .values import MxValueInput, to_mx_value
+
+
+class Session:
+    """A single gateway-backed MXAccess session."""
+
+    def __init__(
+        self,
+        *,
+        client: "GatewayClient",
+        session_id: str,
+        open_reply: pb.OpenSessionReply | None = None,
+    ) -> None:
+        self.client = client
+        self.session_id = session_id
+        self.open_reply = open_reply
+        self._closed = False
+
+    async def __aenter__(self) -> "Session":
+        return self
+
+    async def __aexit__(self, *_exc_info: object) -> None:
+        await self.close()
+
+    async def close(self, *, client_correlation_id: str = "") -> pb.CloseSessionReply:
+        """Close the gateway session. Repeated calls return a local closed reply."""
+
+        if self._closed:
+            return pb.CloseSessionReply(
+                session_id=self.session_id,
+                final_state=pb.SESSION_STATE_CLOSED,
+                protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+            )
+
+        self._closed = True
+        return await self.client.close_session_raw(
+            pb.CloseSessionRequest(
+                session_id=self.session_id,
+                client_correlation_id=client_correlation_id,
+            ),
+        )
+
+    async def invoke(self, command: pb.MxCommand, *, correlation_id: str = "") -> pb.MxCommandReply:
+        """Invoke a raw command and enforce gateway and MXAccess success."""
+
+        reply = await self.invoke_raw(command, correlation_id=correlation_id)
+        return ensure_mxaccess_success("invoke", reply)
+
+    async def invoke_raw(
+        self,
+        command: pb.MxCommand,
+        *,
+        correlation_id: str = "",
+    ) -> pb.MxCommandReply:
+        """Invoke a raw command and preserve the raw reply."""
+
+        return await self.client.invoke_raw(
+            pb.MxCommandRequest(
+                session_id=self.session_id,
+                client_correlation_id=correlation_id,
+                command=command,
+            ),
+        )
+
+    async def register(self, client_name: str, *, correlation_id: str = "") -> int:
+        reply = await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_REGISTER,
+                register=pb.RegisterCommand(client_name=client_name),
+            ),
+            correlation_id=correlation_id,
+        )
+        return reply.register.server_handle
+
+    async def unregister(self, server_handle: int, *, correlation_id: str = "") -> None:
+        await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_UNREGISTER,
+                unregister=pb.UnregisterCommand(server_handle=server_handle),
+            ),
+            correlation_id=correlation_id,
+        )
+
+    async def add_item(
+        self,
+        server_handle: int,
+        item_definition: str,
+        *,
+        correlation_id: str = "",
+    ) -> int:
+        reply = await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_ADD_ITEM,
+                add_item=pb.AddItemCommand(
+                    server_handle=server_handle,
+                    item_definition=item_definition,
+                ),
+            ),
+            correlation_id=correlation_id,
+        )
+        return reply.add_item.item_handle
+
+    async def add_item2(
+        self,
+        server_handle: int,
+        item_definition: str,
+        item_context: str,
+        *,
+        correlation_id: str = "",
+    ) -> int:
+        reply = await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_ADD_ITEM2,
+                add_item2=pb.AddItem2Command(
+                    server_handle=server_handle,
+                    item_definition=item_definition,
+                    item_context=item_context,
+                ),
+            ),
+            correlation_id=correlation_id,
+        )
+        return reply.add_item2.item_handle
+
+    async def advise(
+        self,
+        server_handle: int,
+        item_handle: int,
+        *,
+        correlation_id: str = "",
+    ) -> None:
+        await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_ADVISE,
+                advise=pb.AdviseCommand(
+                    server_handle=server_handle,
+                    item_handle=item_handle,
+                ),
+            ),
+            correlation_id=correlation_id,
+        )
+
+    async def write(
+        self,
+        server_handle: int,
+        item_handle: int,
+        value: MxValueInput,
+        *,
+        user_id: int = 0,
+        correlation_id: str = "",
+    ) -> None:
+        await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_WRITE,
+                write=pb.WriteCommand(
+                    server_handle=server_handle,
+                    item_handle=item_handle,
+                    value=to_mx_value(value),
+                    user_id=user_id,
+                ),
+            ),
+            correlation_id=correlation_id,
+        )
+
+    async def write2(
+        self,
+        server_handle: int,
+        item_handle: int,
+        value: MxValueInput,
+        timestamp_value: MxValueInput,
+        *,
+        user_id: int = 0,
+        correlation_id: str = "",
+    ) -> None:
+        await self.invoke(
+            pb.MxCommand(
+                kind=pb.MX_COMMAND_KIND_WRITE2,
+                write2=pb.Write2Command(
+                    server_handle=server_handle,
+                    item_handle=item_handle,
+                    value=to_mx_value(value),
+                    timestamp_value=to_mx_value(timestamp_value),
+                    user_id=user_id,
+                ),
+            ),
+            correlation_id=correlation_id,
+        )
+
+    def stream_events(
+        self,
+        *,
+        after_worker_sequence: int = 0,
+    ) -> AsyncIterator[pb.MxEvent]:
+        return self.client.stream_events_raw(
+            pb.StreamEventsRequest(
+                session_id=self.session_id,
+                after_worker_sequence=after_worker_sequence,
+            ),
+        )
+
+
+from .client import GatewayClient  # noqa: E402

clients/python/src/mxgateway/values.py

@@ -0,0 +1,234 @@
+"""MXAccess value conversion helpers."""
+
+from __future__ import annotations
+
+from collections.abc import Sequence
+from dataclasses import dataclass
+from datetime import datetime, timezone
+from typing import Any
+
+from google.protobuf.timestamp_pb2 import Timestamp
+
+from .generated import mxaccess_gateway_pb2 as pb
+
+
+MxValueInput = bool | int | float | str | datetime | bytes | None | Sequence[Any]
+
+
+@dataclass(frozen=True)
+class MxValueView:
+    """Typed projection of a raw `MxValue` protobuf message."""
+
+    value: Any
+    kind: str
+    raw: pb.MxValue
+
+
+def to_mx_value(value: MxValueInput, *, data_type: str | None = None) -> pb.MxValue:
+    """Convert a Python value into the public protobuf `MxValue` union."""
+
+    if isinstance(value, pb.MxValue):
+        return value
+
+    if value is None:
+        return pb.MxValue(
+            data_type=pb.MX_DATA_TYPE_NO_DATA,
+            variant_type="VT_EMPTY",
+            is_null=True,
+            raw_data_type=pb.MX_DATA_TYPE_NO_DATA,
+        )
+
+    if isinstance(value, bool):
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_BOOLEAN),
+            variant_type="VT_BOOL",
+            bool_value=value,
+        )
+
+    if isinstance(value, int):
+        if -(2**31) <= value <= (2**31 - 1):
+            return pb.MxValue(
+                data_type=_data_type(data_type, pb.MX_DATA_TYPE_INTEGER),
+                variant_type="VT_I4",
+                int32_value=value,
+            )
+
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_INTEGER),
+            variant_type="VT_I8",
+            int64_value=value,
+        )
+
+    if isinstance(value, float):
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_DOUBLE),
+            variant_type="VT_R8",
+            double_value=value,
+        )
+
+    if isinstance(value, str):
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_STRING),
+            variant_type="VT_BSTR",
+            string_value=value,
+        )
+
+    if isinstance(value, datetime):
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_TIME),
+            variant_type="VT_DATE",
+            timestamp_value=_timestamp_from_datetime(value),
+        )
+
+    if isinstance(value, bytes):
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_UNKNOWN),
+            variant_type="VT_RECORD",
+            raw_value=value,
+        )
+
+    if isinstance(value, Sequence):
+        return _sequence_to_mx_value(value, data_type=data_type)
+
+    raise TypeError(f"unsupported MxValue input type: {type(value).__name__}")
+
+
+def from_mx_value(value: pb.MxValue) -> MxValueView:
+    """Project a protobuf `MxValue` into an idiomatic Python value."""
+
+    kind = value.WhichOneof("kind")
+    if kind is None:
+        return MxValueView(None, "none", value)
+
+    if kind == "timestamp_value":
+        return MxValueView(
+            value.timestamp_value.ToDatetime().replace(tzinfo=timezone.utc),
+            kind,
+            value,
+        )
+
+    if kind == "array_value":
+        return MxValueView(from_mx_array(value.array_value), kind, value)
+
+    return MxValueView(getattr(value, kind), kind, value)
+
+
+def from_mx_array(array: pb.MxArray) -> list[Any]:
+    """Project a protobuf `MxArray` into a Python list."""
+
+    kind = array.WhichOneof("values")
+    if kind is None:
+        return []
+
+    values = list(getattr(array, kind).values)
+    if kind == "timestamp_values":
+        return [
+            timestamp.ToDatetime().replace(tzinfo=timezone.utc)
+            for timestamp in values
+        ]
+
+    return values
+
+
+def _sequence_to_mx_value(
+    values: Sequence[Any],
+    *,
+    data_type: str | None,
+) -> pb.MxValue:
+    sequence = list(values)
+    if not sequence:
+        return pb.MxValue(
+            data_type=_data_type(data_type, pb.MX_DATA_TYPE_UNKNOWN),
+            array_value=pb.MxArray(
+                element_data_type=pb.MX_DATA_TYPE_UNKNOWN,
+                dimensions=[0],
+            ),
+        )
+
+    first = sequence[0]
+    dimensions = [len(sequence)]
+
+    if all(isinstance(item, bool) for item in sequence):
+        array = pb.MxArray(
+            element_data_type=pb.MX_DATA_TYPE_BOOLEAN,
+            variant_type="VT_ARRAY|VT_BOOL",
+            dimensions=dimensions,
+            bool_values=pb.BoolArray(values=sequence),
+        )
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_BOOLEAN, array_value=array)
+
+    if all(isinstance(item, int) and not isinstance(item, bool) for item in sequence):
+        use_int32 = all(-(2**31) <= item <= (2**31 - 1) for item in sequence)
+        if use_int32:
+            array = pb.MxArray(
+                element_data_type=pb.MX_DATA_TYPE_INTEGER,
+                variant_type="VT_ARRAY|VT_I4",
+                dimensions=dimensions,
+                int32_values=pb.Int32Array(values=sequence),
+            )
+        else:
+            array = pb.MxArray(
+                element_data_type=pb.MX_DATA_TYPE_INTEGER,
+                variant_type="VT_ARRAY|VT_I8",
+                dimensions=dimensions,
+                int64_values=pb.Int64Array(values=sequence),
+            )
+
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_INTEGER, array_value=array)
+
+    if all(isinstance(item, float) for item in sequence):
+        array = pb.MxArray(
+            element_data_type=pb.MX_DATA_TYPE_DOUBLE,
+            variant_type="VT_ARRAY|VT_R8",
+            dimensions=dimensions,
+            double_values=pb.DoubleArray(values=sequence),
+        )
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_DOUBLE, array_value=array)
+
+    if all(isinstance(item, str) for item in sequence):
+        array = pb.MxArray(
+            element_data_type=pb.MX_DATA_TYPE_STRING,
+            variant_type="VT_ARRAY|VT_BSTR",
+            dimensions=dimensions,
+            string_values=pb.StringArray(values=sequence),
+        )
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_STRING, array_value=array)
+
+    if all(isinstance(item, datetime) for item in sequence):
+        array = pb.MxArray(
+            element_data_type=pb.MX_DATA_TYPE_TIME,
+            variant_type="VT_ARRAY|VT_DATE",
+            dimensions=dimensions,
+            timestamp_values=pb.TimestampArray(
+                values=[_timestamp_from_datetime(item) for item in sequence],
+            ),
+        )
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_TIME, array_value=array)
+
+    if all(isinstance(item, bytes) for item in sequence):
+        array = pb.MxArray(
+            element_data_type=pb.MX_DATA_TYPE_UNKNOWN,
+            variant_type="VT_ARRAY|VT_VARIANT",
+            dimensions=dimensions,
+            raw_values=pb.RawArray(values=sequence),
+        )
+        return pb.MxValue(data_type=pb.MX_DATA_TYPE_UNKNOWN, array_value=array)
+
+    raise TypeError(
+        "MxValue array inputs must use one supported element type; "
+        f"first element was {type(first).__name__}"
+    )
+
+
+def _timestamp_from_datetime(value: datetime) -> Timestamp:
+    timestamp = Timestamp()
+    if value.tzinfo is None:
+        value = value.replace(tzinfo=timezone.utc)
+    timestamp.FromDatetime(value.astimezone(timezone.utc))
+    return timestamp
+
+
+def _data_type(name: str | None, default: int) -> int:
+    if name is None:
+        return default
+    return pb.MxDataType.Value(name)

clients/python/src/mxgateway_cli/commands.py

@@ -1,10 +1,24 @@
-"""CLI scaffold for the MXAccess Gateway Python client."""
+"""Command line interface for the MXAccess Gateway Python client."""
 
+from __future__ import annotations
+
+import asyncio
 import json
+import os
+from collections.abc import Awaitable, Callable
+from datetime import datetime, timezone
+from typing import Any
 
 import click
+from google.protobuf.json_format import MessageToDict
 
 from mxgateway import __version__
+from mxgateway.auth import redact_secret
+from mxgateway.client import GatewayClient
+from mxgateway.errors import MxGatewayError
+from mxgateway.generated import mxaccess_gateway_pb2 as pb
+from mxgateway.options import ClientOptions
+from mxgateway.values import MxValueInput
 
 
 @click.group()
@@ -16,14 +30,435 @@ def main() -> None:
 @click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
 def version(output_json: bool) -> None:
     """Print client package version information."""
+
     payload = {
         "client": "mxgw-py",
         "package": "mxaccess-gateway-client",
         "version": __version__,
     }
+    _emit(payload, output_json=output_json, text=f"mxgw-py {__version__}")
 
+
+def gateway_options(command: Callable[..., Any]) -> Callable[..., Any]:
+    command = click.option("--endpoint", default="localhost:5000", show_default=True)(command)
+    command = click.option("--api-key", default=None, help="Gateway API key.")(command)
+    command = click.option(
+        "--api-key-env",
+        default=None,
+        help="Environment variable containing the gateway API key.",
+    )(command)
+    command = click.option("--plaintext", is_flag=True, help="Use plaintext gRPC.")(command)
+    command = click.option("--tls", "use_tls", is_flag=True, help="Use TLS gRPC.")(command)
+    command = click.option("--ca-file", default=None, help="Custom root certificate file.")(command)
+    command = click.option(
+        "--server-name-override",
+        default=None,
+        help="TLS server name override for test environments.",
+    )(command)
+    return command
+
+
+@main.command("open-session")
+@gateway_options
+@click.option("--client-name", default="", help="Client session name.")
+@click.option("--requested-backend", default="", help="Requested backend name.")
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def open_session(**kwargs: Any) -> None:
+    """Open a gateway session."""
+
+    _run(
+        _open_session(**kwargs),
+        output_json=kwargs["output_json"],
+        secrets=_secrets(kwargs),
+    )
+
+
+@main.command("close-session")
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def close_session(**kwargs: Any) -> None:
+    """Close a gateway session."""
+
+    _run(
+        _close_session(**kwargs),
+        output_json=kwargs["output_json"],
+        secrets=_secrets(kwargs),
+    )
+
+
+@main.command()
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--message", default="ping", show_default=True, help="Ping payload.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def ping(**kwargs: Any) -> None:
+    """Send a diagnostic ping command."""
+
+    _run(_ping(**kwargs), output_json=kwargs["output_json"], secrets=_secrets(kwargs))
+
+
+@main.command()
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--client-name", required=True, help="MXAccess client name.")
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def register(**kwargs: Any) -> None:
+    """Invoke MXAccess Register."""
+
+    _run(
+        _register(**kwargs),
+        output_json=kwargs["output_json"],
+        secrets=_secrets(kwargs),
+    )
+
+
+@main.command("add-item")
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--server-handle", required=True, type=int, help="MXAccess server handle.")
+@click.option("--item", required=True, help="MXAccess item definition.")
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def add_item(**kwargs: Any) -> None:
+    """Invoke MXAccess AddItem."""
+
+    _run(
+        _add_item(**kwargs),
+        output_json=kwargs["output_json"],
+        secrets=_secrets(kwargs),
+    )
+
+
+@main.command()
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--server-handle", required=True, type=int, help="MXAccess server handle.")
+@click.option("--item-handle", required=True, type=int, help="MXAccess item handle.")
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def advise(**kwargs: Any) -> None:
+    """Invoke MXAccess Advise."""
+
+    _run(_advise(**kwargs), output_json=kwargs["output_json"], secrets=_secrets(kwargs))
+
+
+@main.command("stream-events")
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--after-worker-sequence", default=0, type=int, show_default=True)
+@click.option("--max-events", default=1, type=int, show_default=True)
+@click.option("--timeout", default=5.0, type=float, show_default=True)
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def stream_events(**kwargs: Any) -> None:
+    """Stream a bounded number of events."""
+
+    _run(
+        _stream_events(**kwargs),
+        output_json=kwargs["output_json"],
+        secrets=_secrets(kwargs),
+    )
+
+
+@main.command()
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--server-handle", required=True, type=int, help="MXAccess server handle.")
+@click.option("--item-handle", required=True, type=int, help="MXAccess item handle.")
+@click.option("--type", "value_type", default="string", show_default=True)
+@click.option("--value", required=True, help="Value to write.")
+@click.option("--user-id", default=0, type=int, show_default=True)
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def write(**kwargs: Any) -> None:
+    """Invoke MXAccess Write."""
+
+    _run(_write(**kwargs), output_json=kwargs["output_json"], secrets=_secrets(kwargs))
+
+
+@main.command()
+@gateway_options
+@click.option("--session-id", required=True, help="Gateway session id.")
+@click.option("--server-handle", required=True, type=int, help="MXAccess server handle.")
+@click.option("--item-handle", required=True, type=int, help="MXAccess item handle.")
+@click.option("--type", "value_type", default="string", show_default=True)
+@click.option("--value", required=True, help="Value to write.")
+@click.option("--timestamp", required=True, help="ISO-8601 timestamp value.")
+@click.option("--user-id", default=0, type=int, show_default=True)
+@click.option("--correlation-id", default="", help="Client correlation id.")
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def write2(**kwargs: Any) -> None:
+    """Invoke MXAccess Write2."""
+
+    _run(_write2(**kwargs), output_json=kwargs["output_json"], secrets=_secrets(kwargs))
+
+
+@main.command()
+@gateway_options
+@click.option("--client-name", default="mxgw-py-smoke", show_default=True)
+@click.option("--item", required=True, help="MXAccess item definition.")
+@click.option("--max-events", default=1, type=int, show_default=True)
+@click.option("--timeout", default=5.0, type=float, show_default=True)
+@click.option("--json", "output_json", is_flag=True, help="Emit JSON output.")
+def smoke(**kwargs: Any) -> None:
+    """Run a bounded open/register/add/advise/stream/close smoke flow."""
+
+    _run(_smoke(**kwargs), output_json=kwargs["output_json"], secrets=_secrets(kwargs))
+
+
+async def _open_session(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        reply = await client.open_session_raw(
+            pb.OpenSessionRequest(
+                requested_backend=kwargs["requested_backend"],
+                client_session_name=kwargs["client_name"],
+                client_correlation_id=kwargs["correlation_id"],
+            ),
+        )
+        return {"sessionId": reply.session_id, "rawReply": _message_dict(reply)}
+
+
+async def _close_session(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        reply = await client.close_session_raw(
+            pb.CloseSessionRequest(
+                session_id=kwargs["session_id"],
+                client_correlation_id=kwargs["correlation_id"],
+            ),
+        )
+        return {"sessionId": reply.session_id, "rawReply": _message_dict(reply)}
+
+
+async def _ping(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        reply = await client.invoke_raw(
+            pb.MxCommandRequest(
+                session_id=kwargs["session_id"],
+                command=pb.MxCommand(
+                    kind=pb.MX_COMMAND_KIND_PING,
+                    ping=pb.PingCommand(message=kwargs["message"]),
+                ),
+            ),
+        )
+        return {"kind": "ping", "rawReply": _message_dict(reply)}
+
+
+async def _register(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        server_handle = await session.register(
+            kwargs["client_name"],
+            correlation_id=kwargs["correlation_id"],
+        )
+        return {"serverHandle": server_handle}
+
+
+async def _add_item(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        item_handle = await session.add_item(
+            kwargs["server_handle"],
+            kwargs["item"],
+            correlation_id=kwargs["correlation_id"],
+        )
+        return {"itemHandle": item_handle}
+
+
+async def _advise(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        await session.advise(
+            kwargs["server_handle"],
+            kwargs["item_handle"],
+            correlation_id=kwargs["correlation_id"],
+        )
+        return {"ok": True}
+
+
+async def _stream_events(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        events = await _collect_events(
+            session.stream_events(after_worker_sequence=kwargs["after_worker_sequence"]),
+            max_events=kwargs["max_events"],
+            timeout=kwargs["timeout"],
+        )
+        return {"events": [_message_dict(event) for event in events]}
+
+
+async def _write(**kwargs: Any) -> dict[str, Any]:
+    value = _parse_value(kwargs["value"], kwargs["value_type"])
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        await session.write(
+            kwargs["server_handle"],
+            kwargs["item_handle"],
+            value,
+            user_id=kwargs["user_id"],
+            correlation_id=kwargs["correlation_id"],
+        )
+        return {"ok": True}
+
+
+async def _write2(**kwargs: Any) -> dict[str, Any]:
+    value = _parse_value(kwargs["value"], kwargs["value_type"])
+    timestamp = _parse_datetime(kwargs["timestamp"])
+    async with await _connect(kwargs) as client:
+        session = _session(client, kwargs["session_id"])
+        await session.write2(
+            kwargs["server_handle"],
+            kwargs["item_handle"],
+            value,
+            timestamp,
+            user_id=kwargs["user_id"],
+            correlation_id=kwargs["correlation_id"],
+        )
+        return {"ok": True}
+
+
+async def _smoke(**kwargs: Any) -> dict[str, Any]:
+    async with await _connect(kwargs) as client:
+        session = await client.open_session(client_session_name=kwargs["client_name"])
+        closed = False
+        try:
+            server_handle = await session.register(kwargs["client_name"])
+            item_handle = await session.add_item(server_handle, kwargs["item"])
+            await session.advise(server_handle, item_handle)
+            events = await _collect_events(
+                session.stream_events(),
+                max_events=kwargs["max_events"],
+                timeout=kwargs["timeout"],
+            )
+            return {
+                "sessionId": session.session_id,
+                "serverHandle": server_handle,
+                "itemHandle": item_handle,
+                "events": [_message_dict(event) for event in events],
+            }
+        finally:
+            if not closed:
+                await session.close()
+
+
+async def _connect(kwargs: dict[str, Any]) -> GatewayClient:
+    api_key = kwargs.get("api_key") or _api_key_from_env(kwargs.get("api_key_env"))
+    return await GatewayClient.connect(
+        ClientOptions(
+            endpoint=kwargs["endpoint"],
+            api_key=api_key,
+            plaintext=_use_plaintext(kwargs),
+            ca_file=kwargs.get("ca_file"),
+            server_name_override=kwargs.get("server_name_override"),
+        ),
+    )
+
+
+def _session(client: GatewayClient, session_id: str):
+    from mxgateway.session import Session
+
+    return Session(client=client, session_id=session_id)
+
+
+def _use_plaintext(kwargs: dict[str, Any]) -> bool:
+    if kwargs.get("use_tls"):
+        return False
+    if kwargs.get("plaintext"):
+        return True
+    return kwargs["endpoint"].startswith("localhost:") or kwargs["endpoint"].startswith("127.0.0.1:")
+
+
+def _api_key_from_env(name: str | None) -> str | None:
+    if not name:
+        return None
+    return os.environ.get(name)
+
+
+def _secrets(kwargs: dict[str, Any]) -> list[str | None]:
+    return [
+        kwargs.get("api_key"),
+        _api_key_from_env(kwargs.get("api_key_env")),
+    ]
+
+
+def _run(
+    awaitable: Awaitable[dict[str, Any]],
+    *,
+    output_json: bool,
+    secrets: list[str | None],
+) -> None:
+    try:
+        payload = asyncio.run(awaitable)
+    except MxGatewayError as error:
+        raise click.ClickException(redact_secret(str(error), secrets)) from error
+
+    _emit(payload, output_json=output_json)
+
+
+def _emit(
+    payload: dict[str, Any],
+    *,
+    output_json: bool,
+    text: str | None = None,
+) -> None:
     if output_json:
         click.echo(json.dumps(payload, sort_keys=True))
         return
 
-    click.echo(f"mxgw-py {__version__}")
+    click.echo(text or json.dumps(payload, sort_keys=True))
+
+
+async def _collect_events(
+    events: Any,
+    *,
+    max_events: int,
+    timeout: float,
+) -> list[pb.MxEvent]:
+    collected: list[pb.MxEvent] = []
+    iterator = events.__aiter__()
+    try:
+        while len(collected) < max_events:
+            collected.append(await asyncio.wait_for(iterator.__anext__(), timeout=timeout))
+    except StopAsyncIteration:
+        pass
+    finally:
+        close = getattr(iterator, "aclose", None)
+        if close is not None:
+            await close()
+    return collected
+
+
+def _parse_value(raw_value: str, value_type: str) -> MxValueInput:
+    normalized = value_type.lower()
+    if normalized == "bool":
+        return raw_value.lower() in ("1", "true", "yes", "on")
+    if normalized in ("int", "int32", "int64"):
+        return int(raw_value)
+    if normalized in ("float", "double"):
+        return float(raw_value)
+    if normalized in ("time", "timestamp"):
+        return _parse_datetime(raw_value)
+    if normalized == "raw":
+        return raw_value.encode("utf-8")
+    if normalized == "string":
+        return raw_value
+    raise click.BadParameter(f"unsupported value type: {value_type}", param_hint="--type")
+
+
+def _parse_datetime(raw_value: str) -> datetime:
+    if raw_value.endswith("Z"):
+        raw_value = raw_value[:-1] + "+00:00"
+    parsed = datetime.fromisoformat(raw_value)
+    if parsed.tzinfo is None:
+        parsed = parsed.replace(tzinfo=timezone.utc)
+    return parsed
+
+
+def _message_dict(message: Any) -> dict[str, Any]:
+    return MessageToDict(
+        message,
+        preserving_proto_field_name=False,
+        use_integers_for_enums=False,
+    )

clients/python/tests/test_auth_options.py

@@ -0,0 +1,103 @@
+"""Tests for auth metadata and connection options."""
+
+import pytest
+
+from mxgateway.auth import REDACTED, ApiKey, auth_metadata, redact_secret
+from mxgateway import options as options_module
+from mxgateway.options import ClientOptions, create_channel
+
+
+def test_auth_metadata_adds_bearer_api_key() -> None:
+    assert auth_metadata("mxgw_test_secret") == (
+        ("authorization", "Bearer mxgw_test_secret"),
+    )
+
+
+def test_api_key_repr_is_redacted() -> None:
+    api_key = ApiKey("mxgw_test_secret")
+
+    assert "mxgw_test_secret" not in repr(api_key)
+    assert REDACTED in repr(api_key)
+
+
+def test_redact_secret_replaces_known_values() -> None:
+    redacted = redact_secret(
+        "authorization failed for mxgw_test_secret",
+        ["mxgw_test_secret"],
+    )
+
+    assert redacted == f"authorization failed for {REDACTED}"
+
+
+def test_client_options_reject_plaintext_with_ca_file() -> None:
+    with pytest.raises(ValueError, match="ca_file"):
+        ClientOptions(
+            endpoint="localhost:5000",
+            plaintext=True,
+            ca_file="ca.pem",
+        )
+
+
+def test_client_options_repr_redacts_api_key() -> None:
+    options = ClientOptions(endpoint="localhost:5000", api_key="mxgw_test_secret")
+
+    assert "mxgw_test_secret" not in repr(options)
+    assert REDACTED in repr(options)
+
+
+def test_create_channel_uses_plaintext_channel(monkeypatch: pytest.MonkeyPatch) -> None:
+    calls: list[tuple[str, object]] = []
+
+    def fake_insecure_channel(endpoint: str, *, options: object) -> str:
+        calls.append((endpoint, options))
+        return "plain-channel"
+
+    monkeypatch.setattr(
+        options_module.grpc.aio,
+        "insecure_channel",
+        fake_insecure_channel,
+    )
+
+    channel = create_channel(ClientOptions(endpoint="localhost:5000", plaintext=True))
+
+    assert channel == "plain-channel"
+    assert calls == [("localhost:5000", [])]
+
+
+def test_create_channel_uses_tls_channel(monkeypatch: pytest.MonkeyPatch) -> None:
+    calls: list[tuple[str, object, object]] = []
+
+    def fake_credentials(*, root_certificates: object) -> str:
+        assert root_certificates is None
+        return "creds"
+
+    def fake_secure_channel(endpoint: str, credentials: object, *, options: object) -> str:
+        calls.append((endpoint, credentials, options))
+        return "tls-channel"
+
+    monkeypatch.setattr(
+        options_module.grpc,
+        "ssl_channel_credentials",
+        fake_credentials,
+    )
+    monkeypatch.setattr(
+        options_module.grpc.aio,
+        "secure_channel",
+        fake_secure_channel,
+    )
+
+    channel = create_channel(
+        ClientOptions(
+            endpoint="gateway.example:5001",
+            server_name_override="gateway.test",
+        ),
+    )
+
+    assert channel == "tls-channel"
+    assert calls == [
+        (
+            "gateway.example:5001",
+            "creds",
+            [("grpc.ssl_target_name_override", "gateway.test")],
+        ),
+    ]

clients/python/tests/test_cli.py

@@ -1,4 +1,4 @@
-"""Tests for the Python CLI scaffold."""
+"""Tests for the Python CLI."""
 
 import json
 
@@ -19,3 +19,50 @@ def test_version_json_is_deterministic() -> None:
         "package": "mxaccess-gateway-client",
         "version": __version__,
     }
+
+
+def test_write_parser_rejects_unknown_value_type() -> None:
+    runner = CliRunner()
+
+    result = runner.invoke(
+        main,
+        [
+            "write",
+            "--session-id",
+            "session-1",
+            "--server-handle",
+            "12",
+            "--item-handle",
+            "34",
+            "--type",
+            "unsupported",
+            "--value",
+            "123",
+            "--api-key",
+            "mxgw_test_secret",
+            "--json",
+        ],
+    )
+
+    assert result.exit_code != 0
+    assert "unsupported value type" in result.output
+
+
+def test_cli_error_output_redacts_api_key() -> None:
+    runner = CliRunner()
+
+    result = runner.invoke(
+        main,
+        [
+            "open-session",
+            "--endpoint",
+            "127.0.0.1:1",
+            "--api-key",
+            "mxgw_test_secret",
+            "--plaintext",
+            "--json",
+        ],
+    )
+
+    assert result.exit_code != 0
+    assert "mxgw_test_secret" not in result.output

clients/python/tests/test_client_session.py

@@ -0,0 +1,225 @@
+"""Tests for the async client and session wrappers."""
+
+from __future__ import annotations
+
+import asyncio
+from typing import Any
+
+import pytest
+
+from mxgateway import ClientOptions, GatewayClient, MxAccessError
+from mxgateway.generated import mxaccess_gateway_pb2 as pb
+
+
+@pytest.mark.asyncio
+async def test_session_helpers_send_auth_metadata_and_preserve_raw_replies() -> None:
+    stub = FakeGatewayStub()
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+
+    session = await client.open_session(client_session_name="pytest")
+    server_handle = await session.register("pytest-client")
+    item_handle = await session.add_item(server_handle, "Object.Attribute")
+    await session.advise(server_handle, item_handle)
+
+    assert session.session_id == "session-1"
+    assert server_handle == 12
+    assert item_handle == 34
+    assert stub.open_session.metadata == (("authorization", "Bearer mxgw_test_secret"),)
+    assert stub.invoke.requests[0].command.register.client_name == "pytest-client"
+    assert stub.invoke.requests[1].command.add_item.item_definition == "Object.Attribute"
+    assert stub.invoke.requests[2].command.advise.item_handle == 34
+
+
+@pytest.mark.asyncio
+async def test_mxaccess_error_preserves_raw_reply() -> None:
+    stub = FakeGatewayStub()
+    failure_reply = pb.MxCommandReply(
+        session_id="session-1",
+        kind=pb.MX_COMMAND_KIND_WRITE,
+        protocol_status=pb.ProtocolStatus(
+            code=pb.PROTOCOL_STATUS_CODE_MXACCESS_FAILURE,
+            message="MXAccess rejected write.",
+        ),
+        hresult=-1,
+    )
+    stub.invoke.replies = [failure_reply]
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+    session = await client.open_session()
+
+    with pytest.raises(MxAccessError) as captured:
+        await session.write(12, 34, 123)
+
+    assert captured.value.raw_reply is failure_reply
+
+
+@pytest.mark.asyncio
+async def test_stream_events_cancels_underlying_call_when_closed() -> None:
+    stream = FakeStream(
+        [
+            pb.MxEvent(
+                session_id="session-1",
+                worker_sequence=1,
+                family=pb.MX_EVENT_FAMILY_ON_DATA_CHANGE,
+            ),
+        ],
+    )
+    stub = FakeGatewayStub(stream=stream)
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+    session = await client.open_session()
+
+    events = session.stream_events()
+    first = await anext(events)
+    await events.aclose()
+
+    assert first.worker_sequence == 1
+    assert stream.cancelled
+    assert stub.stream_metadata == (("authorization", "Bearer mxgw_test_secret"),)
+
+
+@pytest.mark.asyncio
+async def test_unary_task_cancellation_reaches_fake_call() -> None:
+    blocking = BlockingCancellableUnary()
+    stub = FakeGatewayStub()
+    stub.OpenSession = blocking
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+
+    task = asyncio.create_task(client.open_session())
+    await blocking.started.wait()
+    task.cancel()
+
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+    assert blocking.call is not None
+    assert blocking.call.cancelled
+
+
+class FakeGatewayStub:
+    def __init__(self, stream: "FakeStream | None" = None) -> None:
+        self.open_session = FakeUnary(
+            [
+                pb.OpenSessionReply(
+                    session_id="session-1",
+                    protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+                ),
+            ],
+        )
+        self.close_session = FakeUnary(
+            [
+                pb.CloseSessionReply(
+                    session_id="session-1",
+                    protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+                ),
+            ],
+        )
+        self.invoke = FakeUnary(
+            [
+                pb.MxCommandReply(
+                    session_id="session-1",
+                    kind=pb.MX_COMMAND_KIND_REGISTER,
+                    protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+                    register=pb.RegisterReply(server_handle=12),
+                ),
+                pb.MxCommandReply(
+                    session_id="session-1",
+                    kind=pb.MX_COMMAND_KIND_ADD_ITEM,
+                    protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+                    add_item=pb.AddItemReply(item_handle=34),
+                ),
+                pb.MxCommandReply(
+                    session_id="session-1",
+                    kind=pb.MX_COMMAND_KIND_ADVISE,
+                    protocol_status=pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK),
+                ),
+            ],
+        )
+        self.OpenSession = self.open_session
+        self.CloseSession = self.close_session
+        self.Invoke = self.invoke
+        self._stream = stream or FakeStream([])
+        self.stream_metadata: tuple[tuple[str, str], ...] | None = None
+
+    def StreamEvents(
+        self,
+        request: pb.StreamEventsRequest,
+        *,
+        metadata: tuple[tuple[str, str], ...],
+    ) -> "FakeStream":
+        self.stream_request = request
+        self.stream_metadata = metadata
+        return self._stream
+
+
+class FakeUnary:
+    def __init__(self, replies: list[Any]) -> None:
+        self.replies = replies
+        self.requests: list[Any] = []
+        self.metadata: tuple[tuple[str, str], ...] | None = None
+
+    async def __call__(
+        self,
+        request: Any,
+        *,
+        metadata: tuple[tuple[str, str], ...],
+    ) -> Any:
+        self.requests.append(request)
+        self.metadata = metadata
+        return self.replies.pop(0)
+
+
+class BlockingCancellableUnary:
+    def __init__(self) -> None:
+        self.started = asyncio.Event()
+        self.call: BlockingCall | None = None
+
+    def __call__(self, *_args: Any, **_kwargs: Any) -> "BlockingCall":
+        self.call = BlockingCall(self.started)
+        return self.call
+
+
+class BlockingCall:
+    def __init__(self, started: asyncio.Event) -> None:
+        self.started = started
+        self.cancelled = False
+
+    def __await__(self):
+        return self._wait().__await__()
+
+    async def _wait(self) -> Any:
+        self.started.set()
+        try:
+            await asyncio.Event().wait()
+        except asyncio.CancelledError:
+            raise
+
+    def cancel(self) -> None:
+        self.cancelled = True
+
+
+class FakeStream:
+    def __init__(self, events: list[pb.MxEvent]) -> None:
+        self._events = events
+        self.cancelled = False
+
+    def __aiter__(self) -> "FakeStream":
+        return self
+
+    async def __anext__(self) -> pb.MxEvent:
+        if not self._events:
+            await asyncio.sleep(3600)
+        return self._events.pop(0)
+
+    def cancel(self) -> None:
+        self.cancelled = True

clients/python/tests/test_errors.py

@@ -0,0 +1,49 @@
+"""Tests for typed command error mapping."""
+
+import json
+from pathlib import Path
+
+import pytest
+from google.protobuf.json_format import ParseDict
+
+from mxgateway.errors import ensure_mxaccess_success, ensure_protocol_success
+from mxgateway import MxAccessError, MxGatewaySessionError
+from mxgateway.generated import mxaccess_gateway_pb2 as pb
+
+FIXTURE_ROOT = Path(__file__).resolve().parents[2] / "proto" / "fixtures" / "behavior"
+
+
+def test_register_fixture_is_protocol_and_mxaccess_success() -> None:
+    reply = _load_reply("command-replies/register.ok.reply.json")
+
+    assert ensure_protocol_success("register", reply.protocol_status, reply) is reply
+    assert ensure_mxaccess_success("register", reply) is reply
+
+
+def test_write_failure_fixture_preserves_raw_reply() -> None:
+    reply = _load_reply("command-replies/write.mxaccess-failure.reply.json")
+
+    assert ensure_protocol_success("write", reply.protocol_status, reply) is reply
+    with pytest.raises(MxAccessError) as captured:
+        ensure_mxaccess_success("write", reply)
+
+    assert captured.value.raw_reply is reply
+    assert captured.value.raw_reply.hresult == -2147220992
+    assert len(captured.value.raw_reply.statuses) == 2
+
+
+def test_session_status_maps_to_session_error() -> None:
+    status = pb.ProtocolStatus(
+        code=pb.PROTOCOL_STATUS_CODE_SESSION_NOT_FOUND,
+        message="session missing",
+    )
+
+    with pytest.raises(MxGatewaySessionError) as captured:
+        ensure_protocol_success("invoke", status)
+
+    assert captured.value.protocol_status is status
+
+
+def _load_reply(name: str) -> pb.MxCommandReply:
+    payload = json.loads((FIXTURE_ROOT / name).read_text(encoding="utf-8"))
+    return ParseDict(payload, pb.MxCommandReply())

clients/python/tests/test_values.py

@@ -0,0 +1,49 @@
+"""Tests for MXAccess value conversion helpers."""
+
+import json
+import re
+from datetime import datetime, timezone
+from pathlib import Path
+
+from google.protobuf.json_format import ParseDict
+
+from mxgateway.generated import mxaccess_gateway_pb2 as pb
+from mxgateway.values import from_mx_value, to_mx_value
+
+FIXTURE_ROOT = Path(__file__).resolve().parents[2] / "proto" / "fixtures" / "behavior"
+
+
+def test_value_conversion_fixtures_project_expected_oneof_kind() -> None:
+    payload = json.loads(
+        (FIXTURE_ROOT / "values" / "value-conversion-cases.json").read_text(
+            encoding="utf-8",
+        ),
+    )
+
+    for case in payload["cases"]:
+        value = ParseDict(case["value"], pb.MxValue())
+        projection = from_mx_value(value)
+
+        assert projection.kind == _snake_case(case["expectedKind"])
+        assert projection.raw is value
+
+
+def test_to_mx_value_supports_scalar_and_array_inputs() -> None:
+    assert to_mx_value(True).WhichOneof("kind") == "bool_value"
+    assert to_mx_value(12).int32_value == 12
+    assert to_mx_value(2**40).int64_value == 2**40
+    assert to_mx_value(12.5).double_value == 12.5
+    assert to_mx_value("abc").string_value == "abc"
+    assert to_mx_value([1, 2]).array_value.int32_values.values == [1, 2]
+    assert to_mx_value(["a", "b"]).array_value.string_values.values == ["a", "b"]
+
+
+def test_to_mx_value_uses_utc_timestamps() -> None:
+    value = to_mx_value(datetime(2026, 1, 1, 0, 0, 4, tzinfo=timezone.utc))
+
+    assert value.data_type == pb.MX_DATA_TYPE_TIME
+    assert value.timestamp_value.seconds == 1767225604
+
+
+def _snake_case(value: str) -> str:
+    return re.sub(r"(?<!^)(?=[A-Z])", "_", value).lower()

docs/GatewayTesting.md

@@ -76,6 +76,13 @@ stdout/stderr lines emitted during the run.
 
 ## Focused Commands
 
+Run the parity fixture matrix tests after changing the integration parity
+scenario list:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~ParityFixtureMatrixTests
+```
+
 Run the fake worker tests after changing gateway worker IPC, session startup, or
 event streaming behavior:
 
@@ -95,6 +102,7 @@ dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj
 
 ## Related Documentation
 
+- [Parity Fixture Matrix](./ParityFixtureMatrix.md)
 - [Gateway Process Design](./gateway-process-design.md)
 - [Worker Frame Protocol](./WorkerFrameProtocol.md)
 - [MXAccess Worker Instance Detailed Design](./mxaccess-worker-instance-design.md)

docs/ParityFixtureMatrix.md

@@ -0,0 +1,102 @@
+# Parity Fixture Matrix
+
+The parity fixture matrix defines the live-test scenarios used to compare
+direct MXAccess behavior with the gateway-backed worker. It is a planning and
+validation fixture, not a source of synthetic MXAccess behavior.
+
+The matrix lives in
+`clients/proto/fixtures/parity/parity-fixture-matrix.json`. It references the
+local MXAccess capture set under
+`C:/Users/dohertj2/Desktop/mxaccess/captures` and keeps capture paths relative
+to that root so the repository does not copy raw capture artifacts.
+
+## Scope
+
+The matrix covers every public `LMXProxyServerClass` method represented by the
+gateway contract:
+
+- `Register`
+- `Unregister`
+- `AddItem`
+- `AddItem2`
+- `RemoveItem`
+- `Advise`
+- `UnAdvise`
+- `AdviseSupervisory`
+- `AddBufferedItem`
+- `SetBufferedUpdateInterval`
+- `Suspend`
+- `Activate`
+- `Write`
+- `Write2`
+- `WriteSecured`
+- `WriteSecured2`
+- `AuthenticateUser`
+- `ArchestrAUserToId`
+
+Each entry is either a `planned_fixture` or a `documented_gap`.
+`WriteSecured` remains a documented gap because the current captures show
+`0x80004021` before MXAccess emits a value-bearing write body.
+`OperationComplete` and public `OnBufferedDataChange` batches also remain
+documented gaps because no capture in the current set proves those public event
+payloads from native MXAccess.
+
+## Required Scenario Groups
+
+The matrix pins the high-risk parity scenarios from the integration milestone:
+
+| Scenario | Purpose |
+|----------|---------|
+| `invalid_handles` | Preserves invalid server, item, post-remove, and invalid-reference HRESULT/status behavior. |
+| `write_statuses` | Compares successful writes, wrong-type writes, invalid references, arrays, and write-complete status arrays. |
+| `secured_writes` | Covers observed `WriteSecured` rejection and authenticated `WriteSecured2` paths without logging credential-bearing values. |
+| `add_item_context` | Ensures `AddItem2` and buffered registration pass context strings exactly as supplied. |
+| `buffered_registration` | Tracks buffered item registration and interval setup separately from normal advice. |
+
+## Comparison Format
+
+Each live parity fixture should record one direct MXAccess result and one
+gateway result for the same operation.
+
+Direct MXAccess records include:
+
+- method name,
+- arguments after redaction,
+- returned value,
+- HRESULT,
+- exception type,
+- `MXSTATUS_PROXY[]` values,
+- native event records in observed order.
+
+Gateway records include:
+
+- `MxCommandKind`,
+- `ProtocolStatus`,
+- `MxCommandReply.ReturnValue`,
+- `MxCommandReply.Hresult`,
+- repeated `MxCommandReply.Statuses`,
+- safe diagnostic message,
+- streamed `MxEvent` records in worker-sequence order.
+
+Compare HRESULT, exception type, returned value, status array shape, raw status
+fields, event family order, event payload shape, value projection, and raw
+fallback metadata. The gateway must not convert an MXAccess command failure
+into a transport failure when the worker captured HRESULT or status details.
+
+## Validation
+
+Run the parity fixture matrix tests after changing the matrix:
+
+```bash
+dotnet test src/MxGateway.Tests/MxGateway.Tests.csproj --filter FullyQualifiedName~ParityFixtureMatrixTests
+```
+
+Live MXAccess execution remains opt-in. The matrix defines which scenarios to
+run when the installed MXAccess COM component and provider state are available;
+normal unit tests only validate the repository fixture shape.
+
+## Related Documentation
+
+- [Gateway Testing](./GatewayTesting.md)
+- [MXAccess Worker Instance Detailed Design](./mxaccess-worker-instance-design.md)
+- [Protobuf Contracts](./Contracts.md)

src/MxGateway.Tests/Contracts/ParityFixtureMatrixTests.cs

@@ -0,0 +1,293 @@
+using System.Text.Json;
+using MxGateway.Contracts;
+
+namespace MxGateway.Tests.Contracts;
+
+public sealed class ParityFixtureMatrixTests
+{
+    [Fact]
+    public void Matrix_DeclaresCurrentProtocolVersionsAndComparisonFields()
+    {
+        using JsonDocument matrix = LoadParityMatrix();
+        JsonElement root = matrix.RootElement;
+
+        Assert.Equal(1, root.GetProperty("schemaVersion").GetInt32());
+        Assert.Equal("mxaccess-gateway-parity-fixture-matrix", root.GetProperty("fixtureSet").GetString());
+        Assert.Equal(GatewayContractInfo.GatewayProtocolVersion, root.GetProperty("gatewayProtocolVersion").GetUInt32());
+        Assert.Equal(GatewayContractInfo.WorkerProtocolVersion, root.GetProperty("workerProtocolVersion").GetUInt32());
+
+        JsonElement comparisonFormat = root.GetProperty("comparisonFormat");
+        AssertRequiredFields(
+            comparisonFormat.GetProperty("directMxAccess").GetProperty("requiredFields"),
+            "method",
+            "arguments",
+            "returnedValue",
+            "hresult",
+            "statuses",
+            "events");
+        AssertRequiredFields(
+            comparisonFormat.GetProperty("gatewayResult").GetProperty("requiredFields"),
+            "kind",
+            "protocolStatus",
+            "returnValue",
+            "hresult",
+            "statuses",
+            "events");
+        AssertRequiredFields(
+            comparisonFormat.GetProperty("eventFields"),
+            "family",
+            "value",
+            "quality",
+            "sourceTimestamp",
+            "statuses",
+            "workerSequence");
+        AssertRequiredFields(
+            comparisonFormat.GetProperty("comparisonKeys"),
+            "hresult",
+            "statusArrayShape",
+            "statusRawFields",
+            "eventFamilyOrder",
+            "eventPayloadShape",
+            "valueProjection",
+            "rawFallbackMetadata");
+    }
+
+    [Fact]
+    public void Matrix_CoversEveryPublicMxAccessMethod()
+    {
+        using JsonDocument matrix = LoadParityMatrix();
+        JsonElement methodFixtures = matrix.RootElement.GetProperty("methodFixtures");
+
+        Dictionary<string, JsonElement> fixturesByMethod = [];
+        HashSet<string> ids = new(StringComparer.Ordinal);
+
+        foreach (JsonElement fixture in methodFixtures.EnumerateArray())
+        {
+            string id = fixture.GetProperty("id").GetString()!;
+            string method = fixture.GetProperty("method").GetString()!;
+            string commandKind = fixture.GetProperty("commandKind").GetString()!;
+            string status = fixture.GetProperty("status").GetString()!;
+
+            Assert.True(ids.Add(id), $"Duplicate parity fixture id '{id}'.");
+            Assert.True(fixturesByMethod.TryAdd(method, fixture), $"Duplicate parity method '{method}'.");
+            Assert.StartsWith("MX_COMMAND_KIND_", commandKind, StringComparison.Ordinal);
+            Assert.Contains(status, KnownFixtureStatuses);
+            Assert.NotEmpty(fixture.GetProperty("assertions").EnumerateArray());
+            AssertCaptureReferencesAreRelative(fixture.GetProperty("captureReferences"));
+        }
+
+        Assert.Equal(ExpectedPublicMethods.Order(StringComparer.Ordinal), fixturesByMethod.Keys.Order(StringComparer.Ordinal));
+
+        foreach (string method in ExpectedPublicMethods)
+        {
+            JsonElement fixture = fixturesByMethod[method];
+            string status = fixture.GetProperty("status").GetString()!;
+
+            Assert.True(
+                status == "planned_fixture" || status == "documented_gap",
+                $"Method '{method}' must have a planned parity fixture or documented gap.");
+        }
+    }
+
+    [Fact]
+    public void Matrix_CoversRequiredParityScenarioGroups()
+    {
+        using JsonDocument matrix = LoadParityMatrix();
+        HashSet<string> knownFixtureIds = GetFixtureIds(matrix.RootElement);
+        Dictionary<string, JsonElement> groupsById = [];
+
+        foreach (JsonElement group in matrix.RootElement.GetProperty("scenarioGroups").EnumerateArray())
+        {
+            string id = group.GetProperty("id").GetString()!;
+
+            Assert.True(groupsById.TryAdd(id, group), $"Duplicate parity scenario group '{id}'.");
+            Assert.NotEmpty(group.GetProperty("description").GetString()!);
+            Assert.NotEmpty(group.GetProperty("fixtureIds").EnumerateArray());
+            AssertCaptureReferencesAreRelative(group.GetProperty("captureReferences"));
+
+            foreach (JsonElement fixtureIdElement in group.GetProperty("fixtureIds").EnumerateArray())
+            {
+                string fixtureId = fixtureIdElement.GetString()!;
+                Assert.Contains(fixtureId, knownFixtureIds);
+            }
+        }
+
+        foreach (string requiredGroup in RequiredScenarioGroups)
+        {
+            Assert.True(groupsById.ContainsKey(requiredGroup), $"Missing required parity scenario group '{requiredGroup}'.");
+        }
+
+        AssertScenarioCovers(groupsById["invalid_handles"], "method.remove-item.basic", "method.write.value-status-matrix");
+        AssertScenarioCovers(groupsById["write_statuses"], "method.write.value-status-matrix", "event.on-write-complete.status");
+        AssertScenarioCovers(groupsById["secured_writes"], "method.write-secured.rejection-gap", "method.write-secured2.authenticated");
+        AssertScenarioCovers(groupsById["add_item_context"], "method.add-item2.context", "method.add-buffered-item.context");
+        AssertScenarioCovers(groupsById["buffered_registration"], "method.add-buffered-item.context", "event.on-buffered-data-change.batch-gap");
+    }
+
+    [Fact]
+    public void Matrix_CoversEveryPublicMxAccessEventFamily()
+    {
+        using JsonDocument matrix = LoadParityMatrix();
+        Dictionary<string, JsonElement> fixturesByFamily = [];
+
+        foreach (JsonElement fixture in matrix.RootElement.GetProperty("eventFixtures").EnumerateArray())
+        {
+            string family = fixture.GetProperty("family").GetString()!;
+            string status = fixture.GetProperty("status").GetString()!;
+
+            Assert.True(fixturesByFamily.TryAdd(family, fixture), $"Duplicate parity event family '{family}'.");
+            Assert.Contains(status, KnownFixtureStatuses);
+            Assert.NotEmpty(fixture.GetProperty("assertions").EnumerateArray());
+            AssertCaptureReferencesAreRelative(fixture.GetProperty("captureReferences"));
+        }
+
+        foreach (string eventFamily in ExpectedEventFamilies)
+        {
+            Assert.True(fixturesByFamily.ContainsKey(eventFamily), $"Missing parity fixture for event family '{eventFamily}'.");
+        }
+
+        Assert.Equal("documented_gap", fixturesByFamily["MX_EVENT_FAMILY_OPERATION_COMPLETE"].GetProperty("status").GetString());
+        Assert.Equal("documented_gap", fixturesByFamily["MX_EVENT_FAMILY_ON_BUFFERED_DATA_CHANGE"].GetProperty("status").GetString());
+    }
+
+    private static readonly string[] ExpectedPublicMethods =
+    [
+        "Register",
+        "Unregister",
+        "AddItem",
+        "AddItem2",
+        "RemoveItem",
+        "Advise",
+        "UnAdvise",
+        "AdviseSupervisory",
+        "AddBufferedItem",
+        "SetBufferedUpdateInterval",
+        "Suspend",
+        "Activate",
+        "Write",
+        "Write2",
+        "WriteSecured",
+        "WriteSecured2",
+        "AuthenticateUser",
+        "ArchestrAUserToId",
+    ];
+
+    private static readonly string[] ExpectedEventFamilies =
+    [
+        "MX_EVENT_FAMILY_ON_DATA_CHANGE",
+        "MX_EVENT_FAMILY_ON_WRITE_COMPLETE",
+        "MX_EVENT_FAMILY_OPERATION_COMPLETE",
+        "MX_EVENT_FAMILY_ON_BUFFERED_DATA_CHANGE",
+    ];
+
+    private static readonly string[] RequiredScenarioGroups =
+    [
+        "invalid_handles",
+        "write_statuses",
+        "secured_writes",
+        "add_item_context",
+        "buffered_registration",
+    ];
+
+    private static readonly string[] KnownFixtureStatuses =
+    [
+        "planned_fixture",
+        "documented_gap",
+    ];
+
+    private static void AssertRequiredFields(
+        JsonElement fields,
+        params string[] expectedFields)
+    {
+        HashSet<string> declared = fields
+            .EnumerateArray()
+            .Select(field => field.GetString()!)
+            .ToHashSet(StringComparer.Ordinal);
+
+        foreach (string expectedField in expectedFields)
+        {
+            Assert.Contains(expectedField, declared);
+        }
+    }
+
+    private static void AssertCaptureReferencesAreRelative(JsonElement captureReferences)
+    {
+        int count = 0;
+
+        foreach (JsonElement captureReference in captureReferences.EnumerateArray())
+        {
+            string path = captureReference.GetString()!;
+
+            Assert.StartsWith("captures/", path, StringComparison.Ordinal);
+            Assert.DoesNotContain("\\", path, StringComparison.Ordinal);
+            Assert.False(Path.IsPathRooted(path), $"Capture reference '{path}' must be relative.");
+            count++;
+        }
+
+        Assert.True(count > 0, "Each parity fixture must reference at least one MXAccess capture.");
+    }
+
+    private static void AssertScenarioCovers(
+        JsonElement group,
+        params string[] fixtureIds)
+    {
+        HashSet<string> declared = group
+            .GetProperty("fixtureIds")
+            .EnumerateArray()
+            .Select(fixtureId => fixtureId.GetString()!)
+            .ToHashSet(StringComparer.Ordinal);
+
+        foreach (string fixtureId in fixtureIds)
+        {
+            Assert.Contains(fixtureId, declared);
+        }
+    }
+
+    private static HashSet<string> GetFixtureIds(JsonElement root)
+    {
+        HashSet<string> ids = new(StringComparer.Ordinal);
+
+        foreach (JsonElement fixture in root.GetProperty("methodFixtures").EnumerateArray())
+        {
+            ids.Add(fixture.GetProperty("id").GetString()!);
+        }
+
+        foreach (JsonElement fixture in root.GetProperty("eventFixtures").EnumerateArray())
+        {
+            ids.Add(fixture.GetProperty("id").GetString()!);
+        }
+
+        return ids;
+    }
+
+    private static JsonDocument LoadParityMatrix()
+    {
+        return JsonDocument.Parse(File.ReadAllText(Path.Combine(GetParityFixtureRoot().FullName, "parity-fixture-matrix.json")));
+    }
+
+    private static DirectoryInfo GetParityFixtureRoot()
+    {
+        DirectoryInfo repositoryRoot = FindRepositoryRoot();
+
+        return new DirectoryInfo(Path.Combine(repositoryRoot.FullName, "clients", "proto", "fixtures", "parity"));
+    }
+
+    private static DirectoryInfo FindRepositoryRoot()
+    {
+        DirectoryInfo? current = new(AppContext.BaseDirectory);
+
+        while (current is not null)
+        {
+            if (File.Exists(Path.Combine(current.FullName, "AGENTS.md"))
+                && Directory.Exists(Path.Combine(current.FullName, "src"))
+                && Directory.Exists(Path.Combine(current.FullName, "clients")))
+            {
+                return current;
+            }
+
+            current = current.Parent;
+        }
+
+        throw new DirectoryNotFoundException("Could not locate the repository root from the test output directory.");
+    }
+}