Add subagent mode via agent-as-tool pattern

Each AgentProfile defines a model and a subset of tools. Profiles are
registered as callable tools in the main harness so the orchestrator LLM
can delegate tasks to specialized subagents. Each invocation runs an
isolated Harness with fresh history; only the final answer is returned,
keeping the orchestrator context clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CMakeLists.txt

@@ -13,6 +13,7 @@ add_library(drharness_lib
     src/ollama_client.cpp
     src/harness.cpp
     tools/shell_tool.cpp
+    tools/agent_tool.cpp
 )
 target_include_directories(drharness_lib PUBLIC include tools)
 target_link_libraries(drharness_lib

include/agent_profile.hpp

@@ -0,0 +1,10 @@
+#pragma once
+#include <string>
+#include <vector>
+
+struct AgentProfile {
+    std::string name;
+    std::string description;
+    std::string model;
+    std::vector<std::string> tool_names;
+};

src/main.cpp

@@ -1,10 +1,24 @@
 #include "harness.hpp"
 #include "ollama_client.hpp"
 #include "tool_registry.hpp"
+#include "agent_profile.hpp"
 #include "shell_tool.hpp"
+#include "agent_tool.hpp"
 #include <cstdlib>
 #include <iostream>
 #include <string>
+#include <vector>
+
+static const std::vector<AgentProfile> profiles = {
+    {
+        .name        = "shell_expert",
+        .description = "An agent that can run shell commands to inspect the system, "
+                       "files, and processes. Delegate multi-step shell tasks here.",
+        .model       = "gemma4:26b",
+        .tool_names  = {"run_shell"}
+    },
+    // Add more agent profiles here
+};
 
 int main() {
     OllamaConfig cfg;
@@ -13,9 +27,12 @@ int main() {
 
     ToolRegistry registry;
     registry.register_tool(make_shell_tool());
-    // Add more tools here:
+    // Add more base tools here:
     // registry.register_tool(make_file_read_tool());
 
+    for (const auto& profile : profiles)
+        registry.register_tool(make_agent_tool(profile, registry, cfg.base_url));
+
     Harness harness(OllamaClient(cfg), registry, {.max_tool_iterations = 16, .verbose = true});
 
     std::cout << "drharness | model: " << cfg.model

tools/agent_tool.cpp

@@ -0,0 +1,50 @@
+#include "agent_tool.hpp"
+#include "harness.hpp"
+#include "ollama_client.hpp"
+
+Tool make_agent_tool(const AgentProfile& profile,
+                     const ToolRegistry& registry,
+                     const std::string& base_url) {
+    return Tool{
+        .name        = "agent_" + profile.name,
+        .description = profile.description,
+        .parameters_schema = {
+            {"type", "object"},
+            {"properties", {
+                {"task", {
+                    {"type", "string"},
+                    {"description", "The task to assign to this agent."}
+                }}
+            }},
+            {"required", {"task"}}
+        },
+        .execute = [profile, &registry, base_url](const nlohmann::json& args) -> std::string {
+            if (!args.contains("task") || !args["task"].is_string())
+                return "Error: missing required parameter 'task'";
+
+            ToolRegistry sub_registry;
+            for (const auto& tool_name : profile.tool_names) {
+                auto found = registry.find(tool_name);
+                if (found)
+                    sub_registry.register_tool(**found);
+            }
+
+            OllamaClient client(OllamaConfig{
+                .base_url  = base_url,
+                .model     = profile.model,
+                .timeout_s = 120
+            });
+
+            Harness harness(std::move(client), sub_registry, {
+                .max_tool_iterations = 16,
+                .verbose             = false
+            });
+
+            try {
+                return harness.chat(args["task"].get<std::string>());
+            } catch (const std::exception& e) {
+                return std::string("Agent error: ") + e.what();
+            }
+        }
+    };
+}

tools/agent_tool.hpp

@@ -0,0 +1,9 @@
+#pragma once
+#include "agent_profile.hpp"
+#include "tool.hpp"
+#include "tool_registry.hpp"
+#include <string>
+
+Tool make_agent_tool(const AgentProfile& profile,
+                     const ToolRegistry& registry,
+                     const std::string& base_url);