feat: discover and register BaseTool subclasses from plugin tools/ dirs

Plugins can now contribute Python tools by placing BaseTool subclasses
in their tools/ directory. The loader scans for .py files, imports them
via importlib, instantiates any BaseTool subclasses found, and registers
them in the tool registry at runtime.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on Keep a Changelog, and this project currently tracks chang
 
 ### Added
 
+- Plugin tool discovery: plugins can now provide `BaseTool` subclasses in a `<plugin>/tools/` directory and they are auto-discovered, instantiated, and registered in the tool registry at runtime. Add `tools_dir` to `plugin.json` (defaults to `"tools"`).
 - `oh --dry-run` safe preview mode for inspecting resolved runtime settings, auth state, prompt assembly, commands, skills, tools, and configured MCP servers without executing the model or tools.
 - Built-in `minimax` provider profile so `oh setup` offers MiniMax as a first-class provider choice, with `MINIMAX_API_KEY` auth source, `MiniMax-M2.7` as the default model, and `MiniMax-M2.7-highspeed` in the model picker.
 - Docker as an alternative sandbox backend (`sandbox.backend = "docker"`) for stronger execution isolation with configurable resource limits, network isolation, and automatic image management.

src/openharness/plugins/loader.py

@@ -2,9 +2,12 @@
 
 from __future__ import annotations
 
+import importlib
+import importlib.util
 import json
 import logging
 import os
+import sys
 from pathlib import Path
 from typing import Any, Iterable
 
@@ -135,6 +138,7 @@ def load_plugin(path: Path, enabled_plugins: dict[str, bool]) -> LoadedPlugin |
     skills = _load_plugin_skills(path / manifest.skills_dir)
     commands = _load_plugin_commands(path, manifest)
     agents = _load_plugin_agents(path, manifest)
+    tools = _load_plugin_tools(path, manifest)
     hooks = _load_plugin_hooks(path / manifest.hooks_file)
     hooks_dir_file = path / "hooks" / "hooks.json"
     if not hooks and hooks_dir_file.exists():
@@ -154,6 +158,7 @@ def load_plugin(path: Path, enabled_plugins: dict[str, bool]) -> LoadedPlugin |
         agents=agents,
         hooks=hooks,
         mcp_servers=mcp,
+        tools=tools,
     )
 
 
@@ -661,3 +666,45 @@ def _load_plugin_mcp(path: Path) -> dict[str, object]:
     raw = json.loads(path.read_text(encoding="utf-8"))
     parsed = McpJsonConfig.model_validate(raw)
     return parsed.mcpServers
+
+
+def _load_plugin_tools(path: Path, manifest: PluginManifest) -> list:
+    """Discover and instantiate BaseTool subclasses from a plugin's tools/ directory."""
+    from openharness.tools.base import BaseTool
+
+    tools_dir = path / manifest.tools_dir
+    if not tools_dir.is_dir():
+        return []
+
+    tools: list[BaseTool] = []
+    for py_file in sorted(tools_dir.glob("*.py")):
+        if py_file.name.startswith("_"):
+            continue
+        module_name = f"_plugin_tools_{manifest.name}_{py_file.stem}"
+        try:
+            spec = importlib.util.spec_from_file_location(module_name, py_file)
+            if spec is None or spec.loader is None:
+                continue
+            module = importlib.util.module_from_spec(spec)
+            sys.modules[module_name] = module
+            spec.loader.exec_module(module)
+        except Exception:
+            logger.debug("Failed to load plugin tool module %s", py_file, exc_info=True)
+            continue
+
+        for attr_name in dir(module):
+            attr = getattr(module, attr_name, None)
+            if (
+                isinstance(attr, type)
+                and issubclass(attr, BaseTool)
+                and attr is not BaseTool
+                and hasattr(attr, "name")
+                and hasattr(attr, "description")
+            ):
+                try:
+                    instance = attr()
+                    tools.append(instance)
+                    logger.debug("Loaded plugin tool: %s from %s", instance.name, py_file)
+                except Exception:
+                    logger.debug("Failed to instantiate tool %s from %s", attr_name, py_file, exc_info=True)
+    return tools

src/openharness/plugins/schemas.py

@@ -13,6 +13,7 @@ class PluginManifest(BaseModel):
     description: str = ""
     enabled_by_default: bool = True
     skills_dir: str = "skills"
+    tools_dir: str = "tools"
     hooks_file: str = "hooks.json"
     mcp_file: str = "mcp.json"
     # Extended fields: optional author, commands, agents, etc.

src/openharness/plugins/types.py

@@ -42,6 +42,7 @@ class LoadedPlugin:
     skills: list[SkillDefinition] = field(default_factory=list)
     commands: list[PluginCommandDefinition] = field(default_factory=list)
     agents: list[AgentDefinition] = field(default_factory=list)
+    tools: list = field(default_factory=list)
     hooks: dict[str, list] = field(default_factory=dict)
     mcp_servers: dict[str, McpServerConfig] = field(default_factory=dict)
 

src/openharness/ui/runtime.py

@@ -212,6 +212,11 @@ async def build_runtime(
     mcp_manager = McpClientManager(load_mcp_server_configs(settings, plugins))
     await mcp_manager.connect_all()
     tool_registry = create_default_tool_registry(mcp_manager)
+    # Register plugin-provided tools
+    for plugin in plugins:
+        if plugin.enabled and plugin.tools:
+            for tool in plugin.tools:
+                tool_registry.register(tool)
     provider = detect_provider(settings)
     bridge_manager = get_bridge_manager()
     app_state = AppStateStore(