feat(tools): introduce plugin-based tool discovery and runtime context protocol

This commit implements a progressive refactoring of the tool system to support
plugin discovery, scoped loading, and protocol-driven runtime context injection.

Key changes:
- Add Tool ABC metadata (tool_name, _scopes) and ToolContext dataclass for
dependency injection.
- Introduce ToolLoader with pkgutil-based builtin discovery and
entry_points-based third-party plugin loading.
- Add scope filtering (core/subagent/memory) so different contexts load
appropriate tool sets.
- Introduce ContextAware protocol and RequestContext dataclass to replace
hardcoded per-tool context injection in AgentLoop.
- Add RuntimeState / MutableRuntimeState protocols to decouple MyTool from
AgentLoop.
- Migrate all built-in tools to declare scopes and implement create()/enabled()
hooks.
- Migrate MessageTool, SpawnTool, CronTool, and MyTool to ContextAware.
- Refactor AgentLoop to use ToolLoader and protocol-driven context injection.
- Refactor SubagentManager to use ToolLoader(scope="subagent") with per-run
FileStates isolation.
- Register all built-in tools via pyproject.toml entry_points.
- Add comprehensive tests for loader scopes, entry_points, ContextAware,
subagent tools, and runtime state sync.

tests/agent/test_task_cancel.py

@@ -14,7 +14,7 @@ from nanobot.config.schema import AgentDefaults
 _MAX_TOOL_RESULT_CHARS = AgentDefaults().max_tool_result_chars
 
 
-def _make_loop(*, exec_config=None):
+def _make_loop(*, tools_config=None):
     """Create a minimal AgentLoop with mocked dependencies."""
     from nanobot.agent.loop import AgentLoop
     from nanobot.bus.queue import MessageBus
@@ -29,7 +29,7 @@ def _make_loop(*, exec_config=None):
          patch("nanobot.agent.loop.SessionManager"), \
          patch("nanobot.agent.loop.SubagentManager") as MockSubMgr:
         MockSubMgr.return_value.cancel_by_session = AsyncMock(return_value=0)
-        loop = AgentLoop(bus=bus, provider=provider, workspace=workspace, exec_config=exec_config)
+        loop = AgentLoop(bus=bus, provider=provider, workspace=workspace, tools_config=tools_config)
     return loop, bus
 
 
@@ -103,9 +103,10 @@ class TestHandleStop:
 
 class TestDispatch:
     def test_exec_tool_not_registered_when_disabled(self):
-        from nanobot.config.schema import ExecToolConfig
+        from nanobot.config.schema import ToolsConfig
+        from nanobot.agent.tools.shell import ExecToolConfig
 
-        loop, _bus = _make_loop(exec_config=ExecToolConfig(enable=False))
+        loop, _bus = _make_loop(tools_config=ToolsConfig(exec=ExecToolConfig(enable=False)))
 
         assert loop.tools.get("exec") is None
 
@@ -286,7 +287,8 @@ class TestSubagentCancellation:
     async def test_subagent_exec_tool_not_registered_when_disabled(self, tmp_path):
         from nanobot.agent.subagent import SubagentManager
         from nanobot.bus.queue import MessageBus
-        from nanobot.config.schema import ExecToolConfig
+        from nanobot.agent.tools.shell import ExecToolConfig
+        from nanobot.config.schema import ToolsConfig
 
         bus = MessageBus()
         provider = MagicMock()
@@ -296,7 +298,7 @@ class TestSubagentCancellation:
             workspace=tmp_path,
             bus=bus,
             max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
-            exec_config=ExecToolConfig(enable=False),
+            tools_config=ToolsConfig(exec=ExecToolConfig(enable=False)),
         )
         mgr._announce_result = AsyncMock()