Add experimental WIP MCP support that serves the build commands as tools

src/main/java/rife/bld/BaseProject.java

@@ -393,6 +393,7 @@ public class BaseProject extends BuildExecutor {
     private final CompileOperation compileOperation_ = new CompileOperation();
     private final DependencyTreeOperation dependencyTreeOperation_ = new DependencyTreeOperation();
     private final DownloadOperation downloadOperation_ = new DownloadOperation();
+    private final McpOperation mcpOperation_ = new McpOperation();
     private final PurgeOperation purgeOperation_ = new PurgeOperation();
     private final PublishOperation publishOperation_ = new PublishOperation();
     private final RunOperation runOperation_ = new RunOperation();
@@ -440,6 +441,16 @@ public class BaseProject extends BuildExecutor {
         return downloadOperation_;
     }
 
+    /**
+     * Retrieves the project's default MCP operation.
+     *
+     * @return the default MCP operation instance
+     * @since 2.4.0
+     */
+    public McpOperation mcpOperation() {
+        return mcpOperation_;
+    }
+
     /**
      * Retrieves the project's default publish operation.
      *
@@ -544,6 +555,18 @@ public class BaseProject extends BuildExecutor {
         downloadOperation().executeOnce(() -> downloadOperation().fromProject(this));
     }
 
+    /**
+     * Standard build command, starts an MCP server that exposes the build
+     * commands as tools.
+     *
+     * @since 2.4.0
+     */
+    @BuildCommand(help = McpHelp.class)
+    public void mcp()
+    throws Exception {
+        mcpOperation().executeOnce(() -> mcpOperation().fromProject(this));
+    }
+
     /**
      * Standard build command, purges all unused artifacts from the project.
      *
@@ -2054,6 +2077,22 @@ public class BaseProject extends BuildExecutor {
         purge();
     }
 
+    /**
+     * Performs the automatic download and purge of the project
+     * dependencies when it's enabled through {@link #autoDownloadPurge()}
+     * and the project isn't offline.
+     * <p>
+     * The dependencies are only refreshed when the dependency cache is
+     * stale, so that repeated invocations are cheap.
+     *
+     * @since 2.4.0
+     */
+    public void performAutoDownloadPurgeIfEnabled() {
+        if (!offline() && autoDownloadPurge()) {
+            performAutoDownloadPurge();
+        }
+    }
+
     private void performAutoDownloadPurge() {
         var resolution = new VersionResolution(properties());
         var cache = new BldCache(libBldDirectory(), resolution);
@@ -2077,6 +2116,12 @@ public class BaseProject extends BuildExecutor {
         var remainingArguments = new ArrayList<>(List.of(arguments));
         var auto = remainingArguments.remove(AUTO_DOWNLOAD_PURGE_OPTION);
 
+        if (remainingArguments.contains(BuildExecutor.ARG_USE_STDERR)) {
+            // the build output is sent to standard error so that standard
+            // output stays free for the MCP protocol, done before the
+            // automatic download and purge produces any output
+            System.setOut(System.err);
+        }
         if (!offline() &&
             (autoDownloadPurge() || auto)) {
             performAutoDownloadPurge();

src/main/java/rife/bld/BuildExecutor.java

@@ -32,6 +32,8 @@ public class BuildExecutor {
     public static final String LOCAL_PROPERTIES = "local.properties";
 
     private static final String ARG_OFFLINE = "--offline";
+    static final String ARG_USE_STDERR = "--use-stderr";
+
     private static final String ARG_HELP1 = "--help";
     private static final String ARG_HELP2 = "-h";
     private static final String ARG_HELP3 = "-?";
@@ -41,7 +43,7 @@ public class BuildExecutor {
     private static final String ARG_VERBOSE2 = "-v";
 
     private final HierarchicalProperties properties_;
-    private List<String> arguments_ = Collections.emptyList();
+    private List<String> arguments_ = new ArrayList<>();
     private boolean offline_ = false;
     private boolean verbose_ = false;
     private Map<String, CommandDefinition> buildCommands_ = null;
@@ -138,6 +140,17 @@ public class BuildExecutor {
         return offline_;
     }
 
+    /**
+     * Changes whether the bld execution is intended to be offline.
+     *
+     * @param offline {@code true} if the execution is intended to be offline;
+     *                or {@code false} otherwise
+     * @since 2.4.0
+     */
+    public void offline(boolean offline) {
+        offline_ = offline;
+    }
+
     /**
      * Returns whether the bld execution should output detailed information
      * about the operations it performs.
@@ -150,6 +163,42 @@ public class BuildExecutor {
         return verbose_;
     }
 
+    /**
+     * Changes whether the bld execution should output detailed information
+     * about the operations it performs.
+     *
+     * @param verbose {@code true} if the execution is verbose;
+     *                or {@code false} otherwise
+     * @since 2.4.0
+     */
+    public void verbose(boolean verbose) {
+        verbose_ = verbose;
+    }
+
+    /**
+     * Returns whether the bld execution prints out the stacktrace for
+     * exceptions.
+     *
+     * @return {@code true} if the stacktrace is printed;
+     *         or {@code false} otherwise
+     * @since 2.4.0
+     */
+    public boolean showStacktrace() {
+        return showStacktrace;
+    }
+
+    /**
+     * Changes whether the bld execution prints out the stacktrace for
+     * exceptions.
+     *
+     * @param showStacktrace {@code true} if the stacktrace is printed;
+     *                       or {@code false} otherwise
+     * @since 2.4.0
+     */
+    public void showStacktrace(boolean showStacktrace) {
+        this.showStacktrace = showStacktrace;
+    }
+
     /**
      * Returns the properties uses for bld execution.
      *
@@ -243,12 +292,19 @@ public class BuildExecutor {
         show_help |= arguments_.removeAll(List.of(ARG_HELP1, ARG_HELP2, ARG_HELP3));
         showStacktrace = arguments_.removeAll(List.of(ARG_STACKTRACE1, ARG_STACKTRACE2));
         verbose_ = arguments_.removeAll(List.of(ARG_VERBOSE1, ARG_VERBOSE2));
+        if (arguments_.removeAll(List.of(ARG_USE_STDERR))) {
+            // the build output is sent to standard error so that standard
+            // output stays free for the MCP protocol, which the MCP server
+            // relies on to keep its protocol stream clean
+            System.setOut(System.err);
+        }
 
         if (show_help) {
             new HelpOperation(this, Collections.emptyList()).execute();
             return exitStatus_;
         }
-        else if (arguments_.isEmpty()) {
+
+        if (arguments_.isEmpty()) {
             showBldHelp();
             return exitStatus_;
         }
@@ -441,47 +497,14 @@ public class BuildExecutor {
      */
     public boolean executeCommand(String command)
     throws Throwable {
-        var matched_command = command;
-        var definition = buildCommands().get(command);
-
-        // try to find an alias
-        if (definition == null) {
-            var aliased_command = buildAliases().get(command);
-            if (aliased_command != null) {
-                matched_command = aliased_command;
-                definition = buildCommands().get(aliased_command);
-            }
-        }
-
-        // try to find a match for the provided command amongst
-        // the ones that are known
-        if (definition == null) {
-            // try to find starting matching options
-            var matches = new ArrayList<>(buildCommands().keySet().stream()
-                .filter(c -> c.toLowerCase().startsWith(command.toLowerCase()))
-                .toList());
-
-            if (matches.isEmpty()) {
-                // try to find fuzzy matching options
-                var fuzzy_regexp = new StringBuilder("^.*");
-                for (var ch : command.toCharArray()) {
-                    fuzzy_regexp.append("\\Q");
-                    fuzzy_regexp.append(ch);
-                    fuzzy_regexp.append("\\E.*");
-                }
-                fuzzy_regexp.append('$');
-                var fuzzy_pattern = Pattern.compile(fuzzy_regexp.toString());
-                matches.addAll(buildCommands().keySet().stream()
-                    .filter(c -> fuzzy_pattern.matcher(c.toLowerCase()).matches())
-                    .toList());
-            }
-
-            // only proceed if exactly one match was found
-            if (matches.size() == 1) {
-                matched_command = matches.get(0);
+        var matched_command = resolveCommand(command);
+        CommandDefinition definition = null;
+        if (matched_command != null) {
+            if (!matched_command.equals(command) &&
+                !matched_command.equals(buildAliases().get(command))) {
                 System.out.println("Executing matched command: " + matched_command);
-                definition = buildCommands().get(matched_command);
             }
+            definition = buildCommands().get(matched_command);
         }
 
         // execute the command if we found one
@@ -507,6 +530,54 @@ public class BuildExecutor {
         return true;
     }
 
+    /**
+     * Resolves a command name to the name of the build command that would
+     * be executed for it, taking the command aliases, unique name prefixes
+     * and unique fuzzy matches into account.
+     *
+     * @param command the command name to resolve
+     * @return the name of the build command that would be executed; or
+     * {@code null} when the name couldn't be resolved
+     * @since 2.4.0
+     */
+    public String resolveCommand(String command) {
+        if (buildCommands().containsKey(command)) {
+            return command;
+        }
+
+        // try to find an alias
+        var aliased_command = buildAliases().get(command);
+        if (aliased_command != null) {
+            return aliased_command;
+        }
+
+        // try to find starting matching options
+        var matches = new ArrayList<>(buildCommands().keySet().stream()
+            .filter(c -> c.toLowerCase().startsWith(command.toLowerCase()))
+            .toList());
+
+        if (matches.isEmpty()) {
+            // try to find fuzzy matching options
+            var fuzzy_regexp = new StringBuilder("^.*");
+            for (var ch : command.toCharArray()) {
+                fuzzy_regexp.append("\\Q");
+                fuzzy_regexp.append(ch);
+                fuzzy_regexp.append("\\E.*");
+            }
+            fuzzy_regexp.append('$');
+            var fuzzy_pattern = Pattern.compile(fuzzy_regexp.toString());
+            matches.addAll(buildCommands().keySet().stream()
+                .filter(c -> fuzzy_pattern.matcher(c.toLowerCase()).matches())
+                .toList());
+        }
+
+        // only resolve if exactly one match was found
+        if (matches.size() == 1) {
+            return matches.get(0);
+        }
+        return null;
+    }
+
     private void showBldHelp() {
         var help = new HelpOperation(this, arguments());
         help.executePrintWelcome();

src/main/java/rife/bld/help/McpHelp.java

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.help;
+
+import rife.bld.CommandHelp;
+import rife.tools.StringUtils;
+
+/**
+ * Provides help for the MCP command.
+ *
+ * @author Geert Bevin (gbevin[remove] at uwyn dot com)
+ * @since 2.4.0
+ */
+public class McpHelp implements CommandHelp {
+    public String getSummary() {
+        return "Starts an MCP server that exposes the build commands";
+    }
+
+    public String getDescription(String topic) {
+        return StringUtils.replace("""
+            Starts a Model Context Protocol (MCP) server that exposes the
+            build commands as tools, so that AI agents can drive the build.
+            This is an experimental feature and may still change.
+
+            The server communicates over standard input and output with the
+            MCP stdio transport and runs until its input stream ends. Launch
+            bld with the --use-stderr option to keep standard output free
+            for the protocol while the build starts up.
+
+            Usage : ${topic}""", "${topic}", topic);
+    }
+}

src/main/java/rife/bld/operations/HelpOperation.java

@@ -190,6 +190,7 @@ public class HelpOperation {
                 The following bld arguments are supported:
                 
                   --offline         Works without Internet (only as first argument)
+                  --use-stderr      Sends the build output to standard error
                   -?, -h, --help    Shows the help
                   -D<name>=<value>  Sets a JVM system property
                   -s, --stacktrace  Prints out the stacktrace for exceptions

src/main/java/rife/bld/operations/McpControl.java

@@ -0,0 +1,121 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.operations;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * The details that a single MCP tool call hands to the build process it
+ * launches.
+ * <p>
+ * The command, its arguments, the flags and the excluded commands are
+ * written to a control file instead of the command line, so they can never
+ * be mistaken for the command's own arguments. The values are escaped so
+ * that any character, including newlines, comes through intact. Only the
+ * MCP code uses this file, the build itself knows nothing about it.
+ *
+ * @author Geert Bevin (gbevin[remove] at uwyn dot com)
+ * @since 2.4.0
+ */
+final class McpControl {
+    final String command;
+    final List<String> arguments;
+    final boolean offline;
+    final boolean verbose;
+    final boolean stacktrace;
+    final Set<String> exclusions;
+
+    private McpControl(String command, List<String> arguments, boolean offline, boolean verbose, boolean stacktrace, Set<String> exclusions) {
+        this.command = command;
+        this.arguments = arguments;
+        this.offline = offline;
+        this.verbose = verbose;
+        this.stacktrace = stacktrace;
+        this.exclusions = exclusions;
+    }
+
+    static void write(File file, String command, List<String> arguments,
+                      boolean offline, boolean verbose, boolean stacktrace,
+                      Collection<String> exclusions)
+    throws IOException {
+        var lines = new ArrayList<String>();
+        lines.add("command " + escape(command));
+        for (var argument : arguments) {
+            lines.add("arg " + escape(argument));
+        }
+        if (offline) {
+            lines.add("offline");
+        }
+        if (verbose) {
+            lines.add("verbose");
+        }
+        if (stacktrace) {
+            lines.add("stacktrace");
+        }
+        for (var exclusion : exclusions) {
+            lines.add("exclude " + escape(exclusion));
+        }
+        Files.write(file.toPath(), lines);
+    }
+
+    static McpControl read(File file)
+    throws IOException {
+        String command = null;
+        var arguments = new ArrayList<String>();
+        var offline = false;
+        var verbose = false;
+        var stacktrace = false;
+        var exclusions = new LinkedHashSet<String>();
+        for (var line : Files.readAllLines(file.toPath())) {
+            if (line.equals("offline")) {
+                offline = true;
+            } else if (line.equals("verbose")) {
+                verbose = true;
+            } else if (line.equals("stacktrace")) {
+                stacktrace = true;
+            } else if (line.startsWith("command ")) {
+                command = unescape(line.substring("command ".length()));
+            } else if (line.startsWith("arg ")) {
+                arguments.add(unescape(line.substring("arg ".length())));
+            } else if (line.startsWith("exclude ")) {
+                exclusions.add(unescape(line.substring("exclude ".length())));
+            }
+        }
+        if (command == null) {
+            throw new IOException("the control file doesn't specify a command");
+        }
+        return new McpControl(command, arguments, offline, verbose, stacktrace, exclusions);
+    }
+
+    private static String escape(String value) {
+        return value.replace("\\", "\\\\").replace("\n", "\\n").replace("\r", "\\r");
+    }
+
+    private static String unescape(String value) {
+        var result = new StringBuilder();
+        for (var i = 0; i < value.length(); ++i) {
+            var c = value.charAt(i);
+            if (c == '\\' && i + 1 < value.length()) {
+                var next = value.charAt(++i);
+                switch (next) {
+                    case 'n' -> result.append('\n');
+                    case 'r' -> result.append('\r');
+                    case '\\' -> result.append('\\');
+                    default -> result.append(next);
+                }
+            } else {
+                result.append(c);
+            }
+        }
+        return result.toString();
+    }
+}

src/main/java/rife/bld/operations/McpToolRunner.java

@@ -0,0 +1,180 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.operations;
+
+import rife.bld.BaseProject;
+import rife.bld.BuildExecutor;
+import rife.bld.operations.exceptions.ExitStatusException;
+import rife.tools.ExceptionUtils;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+/**
+ * The entry point that runs exactly one build command for an MCP tool
+ * call, in a separate build process.
+ * <p>
+ * It reads the command, its arguments, the flags and the excluded commands
+ * from the control file, creates the build executor, and runs the single
+ * command through its public API. All of this single command handling lives
+ * here in the MCP feature, the build itself stays unaware of it. The runner
+ * is launched with the build executor's class name as its last argument,
+ * any earlier arguments, like the wrapper's {@code --offline} option, are
+ * ignored.
+ *
+ * @author Geert Bevin (gbevin[remove] at uwyn dot com)
+ * @since 2.4.0
+ */
+public final class McpToolRunner {
+    /**
+     * The environment variable with the path of the control file that
+     * requests the execution of exactly one command.
+     * @since 2.4.0
+     */
+    public static final String ENV_CONTROL_FILE = "BLD_MCP_CONTROL_FILE";
+
+    /**
+     * The environment variable with the path of the file that the runner
+     * writes its result to.
+     * @since 2.4.0
+     */
+    public static final String ENV_STATUS_FILE = "BLD_MCP_STATUS_FILE";
+
+    /**
+     * The outcome that is written when the command couldn't be resolved.
+     * @since 2.4.0
+     */
+    public static final String STATUS_UNKNOWN_COMMAND = "unknown-command";
+
+    /**
+     * The outcome that is written when the command is excluded.
+     * @since 2.4.0
+     */
+    public static final String STATUS_EXCLUDED_COMMAND = "excluded-command";
+
+    /**
+     * The outcome that is written when the runner itself couldn't be set
+     * up, for instance when the build executor class couldn't be
+     * instantiated, this is a server failure rather than a tool failure.
+     * @since 2.4.0
+     */
+    public static final String STATUS_RUNNER_ERROR = "runner-error";
+
+    private McpToolRunner() {
+    }
+
+    /**
+     * Runs a single build command for an MCP tool call.
+     *
+     * @param arguments the build executor class name as the last argument
+     * @since 2.4.0
+     */
+    public static void main(String[] arguments) {
+        System.exit(run(arguments));
+    }
+
+    private static int run(String[] arguments) {
+        var control_path = System.getenv(ENV_CONTROL_FILE);
+        if (control_path == null) {
+            writeStatus(STATUS_RUNNER_ERROR);
+            System.err.println("ERROR: no MCP control file provided");
+            return ExitStatusException.EXIT_FAILURE;
+        }
+
+        var control_file = new File(control_path);
+        McpControl control;
+        try {
+            control = McpControl.read(control_file);
+        } catch (IOException e) {
+            writeStatus(STATUS_RUNNER_ERROR);
+            System.err.println("ERROR: the MCP control file couldn't be read");
+            return ExitStatusException.EXIT_FAILURE;
+        } finally {
+            // the control file is consumed immediately, so that nested
+            // processes that inherit the environment don't re-enter the
+            // single command execution and don't overwrite its status
+            control_file.delete();
+        }
+
+        if (arguments.length == 0) {
+            writeStatus(STATUS_RUNNER_ERROR);
+            System.err.println("ERROR: no build executor class provided");
+            return ExitStatusException.EXIT_FAILURE;
+        }
+        // the build executor class is instantiated directly through its
+        // no-arg constructor and driven through its public API, its main
+        // method is not invoked, so that a tool call runs exactly the
+        // requested command and nothing else
+        BuildExecutor executor;
+        try {
+            var executor_class = Class.forName(arguments[arguments.length - 1]);
+            executor = (BuildExecutor) executor_class.getDeclaredConstructor().newInstance();
+        } catch (ReflectiveOperationException | ClassCastException e) {
+            writeStatus(STATUS_RUNNER_ERROR);
+            System.err.println("ERROR: the build executor couldn't be instantiated: " + e);
+            return ExitStatusException.EXIT_FAILURE;
+        }
+
+        executor.offline(control.offline);
+        executor.verbose(control.verbose);
+        executor.showStacktrace(control.stacktrace);
+
+        var resolved = executor.resolveCommand(control.command);
+        if (resolved == null) {
+            // the result goes into the status file so that it can never be
+            // confused with a regular exit status of a build command
+            writeStatus(STATUS_UNKNOWN_COMMAND);
+            System.err.println("ERROR: Unknown command '" + control.command + "'");
+            return ExitStatusException.EXIT_FAILURE;
+        }
+        // the exclusions are enforced here, in the freshly compiled build,
+        // so that aliases or commands added to the build sources can't
+        // reach an excluded command either
+        if (control.exclusions.contains(control.command) || control.exclusions.contains(resolved)) {
+            writeStatus(STATUS_EXCLUDED_COMMAND);
+            System.err.println("ERROR: Command '" + control.command + "' is not available");
+            return ExitStatusException.EXIT_FAILURE;
+        }
+
+        // an automatic dependency download and purge that the project is
+        // configured for runs before the command, exactly like it would on
+        // the command line
+        if (executor instanceof BaseProject project) {
+            project.performAutoDownloadPurgeIfEnabled();
+        }
+
+        // the command's arguments come from the control file, they are
+        // never interpreted as additional commands or as global flags
+        executor.arguments().clear();
+        executor.arguments().addAll(control.arguments);
+        try {
+            executor.executeCommand(resolved);
+        } catch (Throwable e) {
+            executor.exitStatus(ExitStatusException.EXIT_FAILURE);
+            System.err.println();
+            if (control.stacktrace) {
+                System.err.println(ExceptionUtils.getExceptionStackTrace(e));
+            } else if (e.getMessage() != null) {
+                System.err.println(e.getMessage());
+            } else {
+                System.err.println(e.getClass().getName());
+            }
+        }
+        return executor.exitStatus();
+    }
+
+    private static void writeStatus(String status) {
+        var status_file = System.getenv(ENV_STATUS_FILE);
+        if (status_file != null) {
+            try {
+                Files.writeString(Path.of(status_file), status);
+            } catch (IOException e) {
+                // the caller falls back to the exit status
+            }
+        }
+    }
+}

src/main/java/rife/bld/wrapper/Wrapper.java

@@ -40,6 +40,7 @@ public class Wrapper {
 
     public static final String BUILD_ARGUMENT = "--build";
     public static final String OFFLINE_ARGUMENT = "--offline";
+    public static final String USE_STDERR_ARGUMENT = "--use-stderr";
 
     public static final String WRAPPER_PREFIX = "bld-wrapper";
     public static final String WRAPPER_PROPERTIES = WRAPPER_PREFIX + ".properties";
@@ -97,6 +98,11 @@ public class Wrapper {
      * @since 1.5
      */
     public static void main(String[] arguments) {
+        if (Arrays.asList(arguments).contains(USE_STDERR_ARGUMENT)) {
+            // the wrapper diagnostics are sent to standard error so that
+            // standard output stays free for the MCP protocol
+            System.setOut(System.err);
+        }
         System.exit(new Wrapper().installAndLaunch(new ArrayList<>(Arrays.asList(arguments))));
     }
 

src/test/java/rife/bld/operations/TestMcpOperation.java

@@ -0,0 +1,996 @@
+/*
+ * Copyright 2001-2026 Geert Bevin (gbevin[remove] at uwyn dot com)
+ * Licensed under the Apache License, Version 2.0 (the "License")
+ */
+package rife.bld.operations;
+
+import org.junit.jupiter.api.Test;
+import rife.bld.BuildCommand;
+import rife.bld.BuildExecutor;
+import rife.bld.Project;
+import rife.bld.dependencies.Bom;
+import rife.bld.dependencies.Dependency;
+import rife.bld.dependencies.Scope;
+import rife.bld.dependencies.VersionNumber;
+import rife.json.Json;
+import rife.json.JsonObject;
+import rife.tools.FileUtils;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.OutputStream;
+import java.io.PrintStream;
+import java.io.PrintWriter;
+import java.io.StringReader;
+import java.io.StringWriter;
+import java.nio.file.Files;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class TestMcpOperation {
+    public static class McpBuild extends BuildExecutor {
+        @BuildCommand(summary = "Greets the caller", alias = "hi")
+        public void hello() {
+            System.out.println("hello " + String.join(" ", arguments()));
+            arguments().clear();
+        }
+
+        @BuildCommand(summary = "Always fails")
+        public void trouble()
+        throws Exception {
+            throw new Exception("boom");
+        }
+
+        @BuildCommand(value = "custom-greet", summary = "Greets with a custom name", description = "Prints a custom greeting to the console.")
+        public void customGreet() {
+            System.out.println("custom hello");
+        }
+
+        private final OnceOperation onceOperation_ = new OnceOperation();
+
+        @BuildCommand(summary = "Runs a one-shot operation")
+        public void once()
+        throws Exception {
+            onceOperation_.executeOnce();
+        }
+
+        @BuildCommand(summary = "Prints the invocation state")
+        public void state() {
+            System.out.println("offline=" + offline() + " verbose=" + verbose());
+        }
+
+        @BuildCommand(summary = "Sleeps for a minute")
+        public void sleepy()
+        throws Exception {
+            System.out.println("sleeping");
+            Thread.sleep(60_000);
+        }
+
+        @BuildCommand(summary = "Prints a lot of output")
+        public void spam() {
+            for (var i = 0; i < 100; ++i) {
+                System.out.println("x".repeat(100));
+            }
+        }
+
+        @BuildCommand(summary = "Spawns a sleeping child process")
+        public void nested()
+        throws Exception {
+            System.out.println("nested start");
+            var child = new ProcessBuilder(
+                new File(new File(System.getProperty("java.home"), "bin"), "java").getAbsolutePath(),
+                "-cp", System.getProperty("java.class.path"),
+                SleepMain.class.getName())
+                .inheritIO()
+                .start();
+            child.waitFor();
+        }
+
+        public static void main(String[] args) {
+            new McpBuild().start(args);
+        }
+    }
+
+    public static class SleepMain {
+        public static void main(String[] args)
+        throws Exception {
+            Thread.sleep(60_000);
+        }
+    }
+
+    static class OnceOperation extends AbstractOperation<OnceOperation> {
+        public void execute() {
+            System.out.println("once executed");
+        }
+    }
+
+    // a build executor without a no-arg constructor can't be instantiated
+    // by the tool runner, which is a server error, not a tool failure
+    public static class NoDefaultConstructorBuild extends McpBuild {
+        public NoDefaultConstructorBuild(String ignored) {
+        }
+    }
+
+    @Test
+    void testRunnerSetupFailureIsAServerError() {
+        var operation = new McpOperation()
+            .executor(new NoDefaultConstructorBuild("x"));
+        initialize(operation);
+        // the runner can't instantiate the class through a no-arg
+        // constructor, this is reported as an internal server error
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello"}}""");
+        assertEquals(-32603, response.getObject("error").getInt("code"));
+    }
+
+    // commands inherited from parent classes are how bld extensions
+    // contribute commands, they're served like any other command
+    public static class ExtendedBuild extends McpBuild {
+        @BuildCommand(summary = "Provided by the extension")
+        public void extended() {
+            System.out.println("extended hello");
+        }
+
+        public static void main(String[] args) {
+            new ExtendedBuild().start(args);
+        }
+    }
+
+    private McpBuild createBuild() {
+        return new McpBuild();
+    }
+
+    private void initialize(McpOperation operation) {
+        operation.processMessage("""
+            {"jsonrpc":"2.0","id":0,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}""");
+        operation.processMessage("""
+            {"jsonrpc":"2.0","method":"notifications/initialized"}""");
+    }
+
+    private McpOperation createOperation() {
+        var operation = new McpOperation()
+            .executor(createBuild())
+            .serverTitle("mcp_test");
+        initialize(operation);
+        return operation;
+    }
+
+    private JsonObject process(McpOperation operation, String message) {
+        var response = operation.processMessage(message);
+        assertNotNull(response);
+        return Json.parseObject(response);
+    }
+
+    @Test
+    void testInitialize() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}""");
+
+        assertEquals("2.0", response.getString("jsonrpc"));
+        assertEquals(1, response.getInt("id"));
+        var result = response.getObject("result");
+        // a supported requested protocol version is echoed
+        assertEquals("2025-06-18", result.getString("protocolVersion"));
+        assertNotNull(result.getObject("capabilities").getObject("tools"));
+        assertEquals("bld", result.getObject("serverInfo").getString("name"));
+        assertEquals("mcp_test", result.getObject("serverInfo").getString("title"));
+        assertFalse(result.getObject("serverInfo").getString("version").isEmpty());
+        assertTrue(result.getString("instructions").contains("the bld project 'mcp_test'"));
+        // the instructions explain the nature of bld builds
+        assertTrue(result.getString("instructions").contains("src/bld/java"));
+        assertTrue(result.getString("instructions").contains("editing the build class"));
+
+        // an unsupported requested protocol version falls back to the
+        // most recent supported one
+        var fallback = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"initialize","params":{"protocolVersion":"1999-01-01","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}""");
+        assertEquals(McpOperation.PROTOCOL_VERSION, fallback.getObject("result").getString("protocolVersion"));
+    }
+
+    @Test
+    void testInitializeParamsAreValidated() {
+        var operation = createOperation();
+
+        // the params are required
+        var missing_params = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"initialize"}""");
+        assertEquals(-32602, missing_params.getObject("error").getInt("code"));
+
+        // the protocol version has to be a string
+        var invalid_version = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"initialize","params":{"protocolVersion":7,"capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}""");
+        assertEquals(-32602, invalid_version.getObject("error").getInt("code"));
+
+        // the capabilities and client info are required objects
+        var missing_capabilities = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"initialize","params":{"protocolVersion":"2025-06-18","clientInfo":{"name":"test","version":"1.0"}}}""");
+        assertEquals(-32602, missing_capabilities.getObject("error").getInt("code"));
+        var missing_client_info = process(operation, """
+            {"jsonrpc":"2.0","id":4,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{}}}""");
+        assertEquals(-32602, missing_client_info.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testStrictSchemaValidation() {
+        var operation = createOperation();
+
+        // fractional ids are rejected
+        var fractional = process(operation, """
+            {"jsonrpc":"2.0","id":1.5,"method":"ping"}""");
+        assertEquals(-32600, fractional.getObject("error").getInt("code"));
+
+        // params, when present, have to be an object even for methods that
+        // ignore them
+        var array_params = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"ping","params":[]}""");
+        assertEquals(-32602, array_params.getObject("error").getInt("code"));
+
+        // an incomplete client info is rejected
+        var empty_client = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{}}}""");
+        assertEquals(-32602, empty_client.getObject("error").getInt("code"));
+
+        // a numeric tool name is rejected
+        var numeric_name = process(operation, """
+            {"jsonrpc":"2.0","id":4,"method":"tools/call","params":{"name":5}}""");
+        assertEquals(-32602, numeric_name.getObject("error").getInt("code"));
+
+        // an explicit null params is not the same as an omitted params
+        var null_params = process(operation, """
+            {"jsonrpc":"2.0","id":5,"method":"ping","params":null}""");
+        assertEquals(-32602, null_params.getObject("error").getInt("code"));
+
+        // a malformed envelope without an id gets an error with a null id,
+        // it isn't silently discarded as a notification
+        var empty_object = process(operation, "{}");
+        assertEquals(-32600, empty_object.getObject("error").getInt("code"));
+        assertNull(empty_object.get("id"));
+        var wrong_jsonrpc = process(operation, """
+            {"jsonrpc":"1.0","method":"ping"}""");
+        assertEquals(-32600, wrong_jsonrpc.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testRequestMethodsRequireAnId() {
+        var operation = createOperation();
+        // an id-less request method is a malformed notification, it must
+        // not execute and gets no response
+        assertNull(operation.processMessage("""
+            {"jsonrpc":"2.0","method":"tools/call","params":{"name":"hello"}}"""));
+    }
+
+    @Test
+    void testNotificationsAreNeverAnswered() {
+        var operation = createOperation();
+        // a notification with malformed params still gets no response, a
+        // notification is never answered
+        assertNull(operation.processMessage("""
+            {"jsonrpc":"2.0","method":"ping","params":[]}"""));
+        // a notification with an unknown method gets no response either
+        assertNull(operation.processMessage("""
+            {"jsonrpc":"2.0","method":"bogus"}"""));
+    }
+
+    @Test
+    void testUnsupportedProtocolVersionsAreNotAdvertised() {
+        var operation = createOperation();
+        // the 2025-03-26 revision, which mandates batch support, isn't
+        // offered, an unsupported request falls back to the newest
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-03-26","capabilities":{},"clientInfo":{"name":"t","version":"1"}}}""");
+        assertEquals(McpOperation.PROTOCOL_VERSION, response.getObject("result").getString("protocolVersion"));
+    }
+
+    @Test
+    void testInitializedNotificationIsSilent() {
+        var operation = createOperation();
+        assertNull(operation.processMessage("""
+            {"jsonrpc":"2.0","method":"notifications/initialized"}"""));
+    }
+
+    @Test
+    void testPing() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":"ping-1","method":"ping"}""");
+        assertEquals("ping-1", response.getString("id"));
+        assertTrue(response.getObject("result").isEmpty());
+    }
+
+    @Test
+    void testToolsList() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"tools/list"}""");
+
+        var tools = response.getObject("result").getArray("tools");
+        JsonObject hello = null;
+        for (var element : tools) {
+            if ("hello".equals(((JsonObject) element).getString("name"))) {
+                hello = (JsonObject) element;
+            }
+        }
+        assertNotNull(hello);
+        // the title qualifies the command with the server title for
+        // human-facing tool listings
+        assertEquals("hello (mcp_test)", hello.getString("title"));
+        assertEquals("Greets the caller", hello.getString("description"));
+        assertEquals("object", hello.getObject("inputSchema").getString("type"));
+        assertEquals("array", hello.getObject("inputSchema").getObject("properties").getObject("arguments").getString("type"));
+    }
+
+    @Test
+    void testInstructionsOverride() {
+        var operation = createOperation()
+            .instructions("Custom guidance");
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}""");
+        assertEquals("Custom guidance", response.getObject("result").getString("instructions"));
+    }
+
+    @Test
+    void testCustomAndInheritedCommands() {
+        var operation = new McpOperation().executor(new ExtendedBuild());
+        initialize(operation);
+
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/list"}""");
+        JsonObject custom = null;
+        var names = new StringBuilder();
+        for (var element : response.getObject("result").getArray("tools")) {
+            var tool = (JsonObject) element;
+            names.append(tool.getString("name")).append(' ');
+            if ("custom-greet".equals(tool.getString("name"))) {
+                custom = tool;
+            }
+        }
+        // custom command names are used as the tool names, and inherited
+        // commands are listed alongside the class's own
+        assertTrue(names.toString().contains("extended"));
+        assertTrue(names.toString().contains("hello"));
+        assertNotNull(custom);
+        // the tool description combines the summary and the full help text
+        assertTrue(custom.getString("description").startsWith("Greets with a custom name"));
+        assertTrue(custom.getString("description").contains("Prints a custom greeting to the console."));
+
+        // both custom-named and inherited commands are callable
+        var custom_call = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"custom-greet"}}""");
+        assertEquals("custom hello", custom_call.getObject("result").getArray("content").getObject(0).getString("text").trim());
+        var inherited_call = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"extended"}}""");
+        assertEquals("extended hello", inherited_call.getObject("result").getArray("content").getObject(0).getString("text").trim());
+    }
+
+    @Test
+    void testToolsListExcludesCommands() {
+        var operation = createOperation()
+            .excludeCommand("trouble");
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":4,"method":"tools/list"}""");
+
+        var names = new StringBuilder();
+        for (var element : response.getObject("result").getArray("tools")) {
+            names.append(((JsonObject) element).getString("name")).append(' ');
+        }
+        assertTrue(names.toString().contains("hello"));
+        assertFalse(names.toString().contains("trouble"));
+    }
+
+    @Test
+    void testToolsCall() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":5,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":["big","world"]}}}""");
+
+        var result = response.getObject("result");
+        assertFalse(result.getBoolean("isError"));
+        var content = result.getArray("content").getObject(0);
+        assertEquals("text", content.getString("type"));
+        assertEquals("hello big world", content.getString("text").trim());
+    }
+
+    @Test
+    void testToolsCallFailure() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":6,"method":"tools/call","params":{"name":"trouble"}}""");
+
+        var result = response.getObject("result");
+        assertTrue(result.getBoolean("isError"));
+        assertTrue(result.getArray("content").getObject(0).getString("text").contains("boom"));
+    }
+
+    @Test
+    void testToolsCallRepeatsOneShotOperations() {
+        var operation = createOperation();
+        // each tool call behaves like a separate command line invocation,
+        // one-shot operations run every time
+        for (var id = 1; id <= 2; ++id) {
+            var response = process(operation, """
+                {"jsonrpc":"2.0","id":%d,"method":"tools/call","params":{"name":"once"}}""".formatted(id));
+            var result = response.getObject("result");
+            assertFalse(result.getBoolean("isError"));
+            assertTrue(result.getArray("content").getObject(0).getString("text").contains("once executed"));
+        }
+    }
+
+    @Test
+    void testInvocationStateCarriesOver() {
+        var build = createBuild();
+        build.offline(true);
+        build.verbose(true);
+        var operation = new McpOperation().executor(build);
+        initialize(operation);
+
+        // the offline and verbose state of the original invocation
+        // carries over into the tool call processes
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"state"}}""");
+        assertEquals("offline=true verbose=true",
+            response.getObject("result").getArray("content").getObject(0).getString("text").trim());
+    }
+
+    @Test
+    void testInitializationGating() {
+        var operation = new McpOperation()
+            .executor(createBuild())
+            .serverTitle("mcp_test");
+
+        // pings are served before initialization, other requests are not
+        var ping = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"ping"}""");
+        assertNotNull(ping.getObject("result"));
+        var gated = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"tools/list"}""");
+        assertEquals(-32600, gated.getObject("error").getInt("code"));
+        assertTrue(gated.getObject("error").getString("message").contains("not initialized"));
+
+        // after initialization the same request is served
+        initialize(operation);
+        var listing = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"tools/list"}""");
+        assertNotNull(listing.getObject("result").getArray("tools"));
+    }
+
+    @Test
+    void testConfirmationCommands() {
+        var operation = createOperation()
+            .requireConfirmation("trouble");
+
+        // the publish command requires confirmation by default
+        assertTrue(operation.confirmationCommands().contains("publish"));
+
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/list"}""");
+        JsonObject trouble = null;
+        for (var element : response.getObject("result").getArray("tools")) {
+            if ("trouble".equals(((JsonObject) element).getString("name"))) {
+                trouble = (JsonObject) element;
+            }
+        }
+        assertNotNull(trouble);
+        // the description instructs agents to obtain confirmation and the
+        // annotations flag the command
+        assertTrue(trouble.getString("description").contains("explicit human confirmation"));
+        assertTrue(trouble.getObject("annotations").getBoolean("destructiveHint"));
+        assertTrue(trouble.getObject("annotations").getBoolean("openWorldHint"));
+    }
+
+    @Test
+    void testNonStringArgumentsAreRejected() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":[1,true]}}}""");
+        assertEquals(-32602, response.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testMalformedParamsDontTerminateTheServer() {
+        var operation = createOperation();
+        // an array where an object is expected is an invalid parameter,
+        // not a server crash
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":[]}""");
+        assertEquals(-32602, response.getObject("error").getInt("code"));
+
+        // the server keeps serving afterwards
+        var ping = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"ping"}""");
+        assertNotNull(ping.getObject("result"));
+    }
+
+    @Test
+    void testToolsCallUnknownTool() {
+        var operation = createOperation();
+
+        // unknown tools are delegated to the build process, which is the
+        // authority on the commands that exist, an unknown command is
+        // reported as a protocol error rather than a tool failure
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":7,"method":"tools/call","params":{"name":"nonexistent"}}""");
+        assertEquals(-32602, response.getObject("error").getInt("code"));
+
+        // excluded commands are rejected outright
+        operation.excludeCommand("hello");
+        var excluded = process(operation, """
+            {"jsonrpc":"2.0","id":8,"method":"tools/call","params":{"name":"hello"}}""");
+        assertEquals(-32602, excluded.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testArgumentsCannotChainCommands() {
+        var operation = createOperation()
+            .excludeCommand("state");
+        // passing an excluded command as an argument to another command
+        // must not execute it, only the called command runs
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":["state"]}}}""");
+        var text = response.getObject("result").getArray("content").getObject(0).getString("text");
+        assertTrue(text.contains("hello state"), text);
+        // the chained command's output is absent, it never executed
+        assertFalse(text.contains("offline="), text);
+    }
+
+    @Test
+    void testGlobalFlagArgumentsReachTheCommand() {
+        var operation = createOperation();
+        // a leading --offline is the command's own argument, it must reach
+        // the command and not be consumed as global bld state
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":["--offline","kept"]}}}""");
+        var text = response.getObject("result").getArray("content").getObject(0).getString("text");
+        assertTrue(text.contains("hello --offline kept"), text);
+    }
+
+    @Test
+    void testToolNameNewlineCannotInjectCommand() {
+        var operation = createOperation();
+        // a tool name containing a newline that would inject a second
+        // command record must not execute a different command, the escaped
+        // value stays a single unknown command
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"missing\\ncommand hello"}}""");
+        assertEquals(-32602, response.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testPropertyLikeArgumentsReachTheCommand() {
+        var operation = createOperation();
+        // a -D argument is the command's own argument, it must reach the
+        // command in both the direct and the wrapper mode, not be consumed
+        // as a JVM property
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":["-Dfoo=bar","kept"]}}}""");
+        var text = response.getObject("result").getArray("content").getObject(0).getString("text");
+        assertTrue(text.contains("hello -Dfoo=bar kept"), text);
+    }
+
+    @Test
+    void testToolArgumentsMustBeStructured() {
+        var operation = createOperation();
+        // an explicit null tool arguments is not the same as omitted
+        var null_args = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hello","arguments":null}}""");
+        assertEquals(-32602, null_args.getObject("error").getInt("code"));
+        // the inner arguments array must be an array
+        var bad_list = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":"nope"}}}""");
+        assertEquals(-32602, bad_list.getObject("error").getInt("code"));
+        // a numeric list cursor is rejected
+        var bad_cursor = process(operation, """
+            {"jsonrpc":"2.0","id":3,"method":"tools/list","params":{"cursor":5}}""");
+        assertEquals(-32602, bad_cursor.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testUnknownToolWithHelpArgumentStillFails() {
+        var operation = createOperation();
+        // a --help argument to an unknown tool must not be interpreted as
+        // global help, the unknown tool is still a protocol error
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"nonexistent","arguments":{"arguments":["--help"]}}}""");
+        assertEquals(-32602, response.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testChildProcessEnforcesExclusions() {
+        // the build process itself refuses an excluded command, this bypasses
+        // the server-side check and exercises the child enforcement, hi is
+        // an alias of the excluded hello and is refused there
+        var operation = createOperation()
+            .excludeCommand("hello");
+        assertThrows(RuntimeException.class,
+            () -> operation.executeToolCall("hi", List.of(), true));
+    }
+
+    @Test
+    void testExclusionsCoverAliasesAndMatches() {
+        var operation = createOperation()
+            .excludeCommand("hello");
+
+        // aliases of excluded commands are rejected
+        var alias = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"hi"}}""");
+        assertEquals(-32602, alias.getObject("error").getInt("code"));
+
+        // unique prefixes that resolve to excluded commands are rejected
+        var prefix = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"hell"}}""");
+        assertEquals(-32602, prefix.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testToolCallTimeoutTerminatesDescendants() {
+        var operation = createOperation()
+            .toolCallTimeout(2);
+        var start = System.currentTimeMillis();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"nested"}}""");
+        var elapsed = System.currentTimeMillis() - start;
+
+        var result = response.getObject("result");
+        assertTrue(result.getBoolean("isError"));
+        assertTrue(result.getArray("content").getObject(0).getString("text").contains("timed out"));
+        // the wrapper-style child process is terminated too, the call
+        // doesn't wait for it to end on its own
+        assertTrue(elapsed < 20_000, String.valueOf(elapsed));
+    }
+
+    @Test
+    void testToolCallTimeout() {
+        var operation = createOperation()
+            .toolCallTimeout(1);
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"sleepy"}}""");
+        var result = response.getObject("result");
+        assertTrue(result.getBoolean("isError"));
+        assertTrue(result.getArray("content").getObject(0).getString("text").contains("timed out after 1 seconds"));
+    }
+
+    @Test
+    void testOutputLimit() {
+        var operation = createOperation()
+            .outputLimit(150);
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"spam"}}""");
+        var text = response.getObject("result").getArray("content").getObject(0).getString("text");
+        assertTrue(text.contains("truncated after 150 characters"), text);
+        assertTrue(text.length() < 300, String.valueOf(text.length()));
+    }
+
+    @Test
+    void testJvmPropertiesCarryOver() {
+        var operation = createOperation();
+        var command_line = operation.toolCallCommand("hello", List.of());
+
+        // the JVM properties of the original invocation are part of the
+        // tool call command lines
+        ProcessHandle.current().info().arguments().ifPresent(process_arguments -> {
+            for (var argument : process_arguments) {
+                if (argument.startsWith("-D")) {
+                    assertTrue(command_line.contains(argument), argument);
+                }
+            }
+        });
+        // the encoding is forced to UTF-8
+        assertTrue(command_line.contains("-Dfile.encoding=UTF-8"), command_line.toString());
+        // the command name goes through the control file, not the command
+        // line, so that arguments can never be interpreted as commands
+        assertFalse(command_line.contains("hello"), command_line.toString());
+    }
+
+    @Test
+    void testUnknownMethod() {
+        var operation = createOperation();
+        var response = process(operation, """
+            {"jsonrpc":"2.0","id":8,"method":"bogus/method"}""");
+        assertEquals(-32601, response.getObject("error").getInt("code"));
+
+        // unknown notifications don't warrant a response
+        assertNull(operation.processMessage("""
+            {"jsonrpc":"2.0","method":"bogus/notification"}"""));
+    }
+
+    @Test
+    void testInvalidRequestEnvelopes() {
+        var operation = createOperation();
+
+        // syntactically valid JSON that isn't a request object
+        var array = process(operation, "[1,2]");
+        assertEquals(-32600, array.getObject("error").getInt("code"));
+        assertNull(array.get("id"));
+
+        // the jsonrpc version is required
+        var missing_version = process(operation, """
+            {"id":1,"method":"ping"}""");
+        assertEquals(-32600, missing_version.getObject("error").getInt("code"));
+        var wrong_version = process(operation, """
+            {"jsonrpc":"1.0","id":1,"method":"ping"}""");
+        assertEquals(-32600, wrong_version.getObject("error").getInt("code"));
+        assertEquals(1, wrong_version.getInt("id"));
+
+        // the method has to be a string
+        var invalid_method = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":5}""");
+        assertEquals(-32600, invalid_method.getObject("error").getInt("code"));
+
+        // the id has to be a string or a number
+        var invalid_id = process(operation, """
+            {"jsonrpc":"2.0","id":{},"method":"ping"}""");
+        assertEquals(-32600, invalid_id.getObject("error").getInt("code"));
+        assertNull(invalid_id.get("id"));
+
+        // an explicitly null id is invalid, it's not a notification
+        var null_id = process(operation, """
+            {"jsonrpc":"2.0","id":null,"method":"ping"}""");
+        assertEquals(-32600, null_id.getObject("error").getInt("code"));
+        assertNull(null_id.get("id"));
+    }
+
+    @Test
+    void testParseError() {
+        var operation = createOperation();
+        var response = process(operation, "this is not json");
+        assertEquals(-32700, response.getObject("error").getInt("code"));
+        assertNull(response.get("id"));
+    }
+
+    public static class McpProject extends Project {
+        public McpProject() {
+            this(new File(System.getProperty("user.dir")));
+        }
+
+        McpProject(File tmp) {
+            workDirectory = tmp;
+            pkg = "test.pkg";
+            name = "mcp_project";
+            version = new VersionNumber(1, 0, 0);
+            repositories = List.of();
+        }
+
+        public static void main(String[] args) {
+            new McpProject().start(args);
+        }
+    }
+
+    public static class FailingTreeProject extends McpProject {
+        public FailingTreeProject() {
+        }
+
+        FailingTreeProject(File tmp) {
+            super(tmp);
+        }
+
+        {
+            // a dependency without any repository to resolve it in
+            dependencies().scope(Scope.compile)
+                .include(new Dependency("com.example", "missing", new VersionNumber(1, 0, 0)));
+        }
+
+        public static void main(String[] args) {
+            new FailingTreeProject().start(args);
+        }
+    }
+
+    @Test
+    void testResourcesWithoutProject() {
+        var operation = createOperation();
+        initialize(operation);
+        var listing = process(operation, """
+            {"jsonrpc":"2.0","id":1,"method":"resources/list"}""");
+        assertTrue(listing.getObject("result").getArray("resources").isEmpty());
+
+        var read = process(operation, """
+            {"jsonrpc":"2.0","id":2,"method":"resources/read","params":{"uri":"bld://project"}}""");
+        assertEquals(-32002, read.getObject("error").getInt("code"));
+    }
+
+    @Test
+    void testResources()
+    throws Exception {
+        var tmp = Files.createTempDirectory("mcpresources").toFile();
+        try {
+            var project = new McpProject(tmp);
+            project.dependencies().scope(Scope.compile)
+                .include(new Bom("com.example", "bom1", new VersionNumber(1, 0, 0)))
+                .include(new Dependency("com.example", "a"));
+            project.dependencies().scope(Scope.test)
+                .include(new Dependency("com.example", "t", new VersionNumber(2, 0, 0)));
+            var operation = new McpOperation().fromProject(project);
+            initialize(operation);
+
+            // the three project resources are listed
+            var listing = process(operation, """
+                {"jsonrpc":"2.0","id":1,"method":"resources/list"}""");
+            var uris = new StringBuilder();
+            for (var element : listing.getObject("result").getArray("resources")) {
+                uris.append(((JsonObject) element).getString("uri")).append(' ');
+            }
+            assertTrue(uris.toString().contains("bld://project"));
+            assertTrue(uris.toString().contains("bld://dependencies"));
+            assertTrue(uris.toString().contains("bld://dependency-tree"));
+
+            // the project resource describes the identification and layout
+            var read_project = process(operation, """
+                {"jsonrpc":"2.0","id":2,"method":"resources/read","params":{"uri":"bld://project"}}""");
+            var project_content = read_project.getObject("result").getArray("contents").getObject(0);
+            assertEquals("application/json", project_content.getString("mimeType"));
+            var description = Json.parseObject(project_content.getString("text"));
+            assertEquals("mcp_project", description.getString("name"));
+            assertEquals("1.0.0", description.getString("version"));
+            assertEquals("test.pkg", description.getString("package"));
+            assertNotNull(description.getObject("directories").getString("srcMainJava"));
+
+            // the dependencies resource describes the scopes
+            var read_dependencies = process(operation, """
+                {"jsonrpc":"2.0","id":3,"method":"resources/read","params":{"uri":"bld://dependencies"}}""");
+            var dependencies = Json.parseObject(read_dependencies.getObject("result").getArray("contents").getObject(0).getString("text"));
+            assertEquals("com.example:bom1:1.0.0@bom", dependencies.getObject("compile").getArray("boms").getString(0));
+            assertEquals("com.example:a", dependencies.getObject("compile").getArray("dependencies").getString(0));
+            assertEquals("com.example:t:2.0.0", dependencies.getObject("test").getArray("dependencies").getString(0));
+
+            // unknown resources report the dedicated error
+            var unknown = process(operation, """
+                {"jsonrpc":"2.0","id":4,"method":"resources/read","params":{"uri":"bld://bogus"}}""");
+            assertEquals(-32002, unknown.getObject("error").getInt("code"));
+
+            // a missing URI is an invalid parameter
+            var missing = process(operation, """
+                {"jsonrpc":"2.0","id":5,"method":"resources/read","params":{}}""");
+            assertEquals(-32602, missing.getObject("error").getInt("code"));
+        } finally {
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testResourceDependencyTree()
+    throws Exception {
+        var tmp = Files.createTempDirectory("mcptree").toFile();
+        try {
+            var operation = new McpOperation().fromProject(new McpProject(tmp));
+            initialize(operation);
+            var response = process(operation, """
+                {"jsonrpc":"2.0","id":1,"method":"resources/read","params":{"uri":"bld://dependency-tree"}}""");
+            var content = response.getObject("result").getArray("contents").getObject(0);
+            assertEquals("text/plain", content.getString("mimeType"));
+            assertTrue(content.getString("text").contains("no dependencies"), content.getString("text"));
+        } finally {
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testExcludedToolDoesNotBreakResource()
+    throws Exception {
+        var tmp = Files.createTempDirectory("mcptreeexcl").toFile();
+        try {
+            var operation = new McpOperation()
+                .fromProject(new McpProject(tmp))
+                .excludeCommand("dependency-tree");
+            initialize(operation);
+
+            // excluding the dependency-tree tool doesn't break the still
+            // advertised dependency-tree resource, its generation doesn't
+            // enforce the tool exclusions
+            var response = process(operation, """
+                {"jsonrpc":"2.0","id":1,"method":"resources/read","params":{"uri":"bld://dependency-tree"}}""");
+            var content = response.getObject("result").getArray("contents").getObject(0);
+            assertTrue(content.getString("text").contains("no dependencies"), content.getString("text"));
+        } finally {
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testResourceDependencyTreeReportsFailures()
+    throws Exception {
+        var tmp = Files.createTempDirectory("mcptreefail").toFile();
+        try {
+            var operation = new McpOperation().fromProject(new FailingTreeProject(tmp));
+            initialize(operation);
+            var response = process(operation, """
+                {"jsonrpc":"2.0","id":1,"method":"resources/read","params":{"uri":"bld://dependency-tree"}}""");
+            var error = response.getObject("error");
+            assertEquals(-32603, error.getInt("code"));
+            assertTrue(error.getString("message").contains("dependency tree"), error.getString("message"));
+        } finally {
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    public static class E2eProject extends Project {
+        public E2eProject() {
+            this(new File(System.getProperty("user.dir")));
+        }
+
+        E2eProject(File work) {
+            workDirectory = work;
+            pkg = "test.pkg";
+            name = "myapp";
+            version = new VersionNumber(0, 0, 1);
+        }
+
+        public static void main(String[] args) {
+            new E2eProject().start(args);
+        }
+    }
+
+    @Test
+    void testMcpEndToEndWithRealProject()
+    throws Exception {
+        var tmp = Files.createTempDirectory("mcpe2e").toFile();
+        try {
+            var create_operation = new CreateAppOperation()
+                .workDirectory(tmp)
+                .packageName("test.pkg")
+                .projectName("myapp")
+                .downloadDependencies(true);
+            create_operation.execute();
+            var project_dir = new File(tmp, "myapp");
+            // the generated wrapper would require a published bld
+            // distribution, remove it so that the tool calls launch the
+            // build class directly with the class path of this test
+            new File(project_dir, "lib/bld/bld-wrapper.jar").delete();
+            var project = new E2eProject(project_dir);
+
+            var operation = new McpOperation().fromProject(project);
+            var input = """
+                {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}
+                {"jsonrpc":"2.0","method":"notifications/initialized"}
+                {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"compile"}}
+                {"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"compile"}}
+                {"jsonrpc":"2.0","id":4,"method":"resources/read","params":{"uri":"bld://project"}}
+                """;
+            var output = new StringWriter();
+            operation.executeServerLoop(new BufferedReader(new StringReader(input)), new PrintWriter(output));
+
+            var responses = output.toString().trim().split("\n");
+            assertEquals(4, responses.length);
+
+            // both compile tool calls executed and reported their output,
+            // repeated calls behave like separate command line invocations
+            for (var i = 1; i <= 2; ++i) {
+                var compile = Json.parseObject(responses[i]);
+                var compile_result = compile.getObject("result");
+                assertFalse(compile_result.getBoolean("isError"));
+                assertTrue(compile_result.getArray("content").getObject(0).getString("text").contains("Compilation finished successfully"));
+            }
+
+            // the compiled classes are actually there
+            var listing = FileUtils.generateDirectoryListing(project.buildMainDirectory());
+            assertTrue(listing.contains(".class"), listing);
+
+            // the project resource reflects the created project
+            var read_project = Json.parseObject(responses[3]);
+            var description = Json.parseObject(read_project.getObject("result").getArray("contents").getObject(0).getString("text"));
+            assertEquals("myapp", description.getString("name"));
+        } finally {
+            FileUtils.deleteDirectory(tmp);
+        }
+    }
+
+    @Test
+    void testServerLoop()
+    throws Exception {
+        var operation = createOperation();
+        var input = """
+            {"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"test","version":"1.0"}}}
+            {"jsonrpc":"2.0","method":"notifications/initialized"}
+
+            {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"hello","arguments":{"arguments":["loop"]}}}
+            """;
+        var output = new StringWriter();
+        operation.executeServerLoop(new BufferedReader(new StringReader(input)), new PrintWriter(output));
+
+        var responses = output.toString().trim().split("\n");
+        assertEquals(2, responses.length);
+        assertEquals(1, Json.parseObject(responses[0]).getInt("id"));
+        var call = Json.parseObject(responses[1]);
+        assertEquals(2, call.getInt("id"));
+        assertEquals("hello loop", call.getObject("result").getArray("content").getObject(0).getString("text").trim());
+    }
+}