feat: add TEST_EXPRESSION command with request-reply infrastructure

Adds CompletableFuture-based request-reply mechanism for commands that
need synchronous results. CommandReply record in core, pendingReplies
map in AgentRegistryService, test-expression endpoint on config controller
with 5s timeout. CommandAckRequest extended with optional data field.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-core/src/main/java/com/cameleer3/server/core/agent/AgentRegistryService.java

@@ -9,6 +9,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.UUID;
+import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.stream.Collectors;
@@ -30,6 +31,7 @@ public class AgentRegistryService {
 
     private final ConcurrentHashMap<String, AgentInfo> agents = new ConcurrentHashMap<>();
     private final ConcurrentHashMap<String, ConcurrentLinkedQueue<AgentCommand>> commands = new ConcurrentHashMap<>();
+    private final ConcurrentHashMap<String, CompletableFuture<CommandReply>> pendingReplies = new ConcurrentHashMap<>();
 
     private volatile AgentEventListener eventListener;
 
@@ -279,6 +281,31 @@ public class AgentRegistryService {
         }
     }
 
+    /**
+     * Register a command that expects a synchronous reply from the agent.
+     * Returns a CompletableFuture that will be completed when the agent ACKs the command.
+     * Auto-cleans up from the pending map on completion or timeout.
+     */
+    public CompletableFuture<CommandReply> addCommandWithReply(String agentId, CommandType type, String payload) {
+        AgentCommand command = addCommand(agentId, type, payload);
+        CompletableFuture<CommandReply> future = new CompletableFuture<>();
+        pendingReplies.put(command.id(), future);
+        future.whenComplete((result, ex) -> pendingReplies.remove(command.id()));
+        return future;
+    }
+
+    /**
+     * Complete a pending reply future for a command.
+     * Called when an agent ACKs a command that was registered via {@link #addCommandWithReply}.
+     * No-op if no pending future exists for the given command ID.
+     */
+    public void completeReply(String commandId, String status, String message, String data) {
+        CompletableFuture<CommandReply> future = pendingReplies.remove(commandId);
+        if (future != null) {
+            future.complete(new CommandReply(status, message, data));
+        }
+    }
+
     /**
      * Set the event listener for command notifications.
      * The SSE layer in the app module implements this interface.

cameleer3-server-core/src/main/java/com/cameleer3/server/core/agent/CommandReply.java

@@ -0,0 +1,11 @@
+package com.cameleer3.server.core.agent;
+
+/**
+ * Represents the reply data from an agent command acknowledgment.
+ * Used for synchronous request-reply command patterns (e.g. TEST_EXPRESSION).
+ *
+ * @param status  "SUCCESS" or "FAILURE"
+ * @param message human-readable description of the result
+ * @param data    optional structured JSON data returned by the agent
+ */
+public record CommandReply(String status, String message, String data) {}

cameleer3-server-core/src/main/java/com/cameleer3/server/core/agent/CommandType.java

@@ -7,5 +7,6 @@ public enum CommandType {
     CONFIG_UPDATE,
     DEEP_TRACE,
     REPLAY,
-    SET_TRACED_PROCESSORS
+    SET_TRACED_PROCESSORS,
+    TEST_EXPRESSION
 }