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.

nanobot/agent/tools/base.py

@@ -1,10 +1,17 @@
 """Base class for agent tools."""
+from __future__ import annotations
 
+import typing
 from abc import ABC, abstractmethod
 from collections.abc import Callable
 from copy import deepcopy
 from typing import Any, TypeVar
 
+if typing.TYPE_CHECKING:
+    from pydantic import BaseModel
+
+    from nanobot.agent.tools.context import ToolContext
+
 _ToolT = TypeVar("_ToolT", bound="Tool")
 
 # Matches :meth:`Tool._cast_value` / :meth:`Schema.validate_json_schema_value` behavior
@@ -117,14 +124,7 @@ class Schema(ABC):
 class Tool(ABC):
     """Agent capability: read files, run commands, etc."""
 
-    _TYPE_MAP = {
-        "string": str,
-        "integer": int,
-        "number": (int, float),
-        "boolean": bool,
-        "array": list,
-        "object": dict,
-    }
+    _TYPE_MAP = _JSON_TYPE_MAP
     _BOOL_TRUE = frozenset(("true", "1", "yes"))
     _BOOL_FALSE = frozenset(("false", "0", "no"))
 
@@ -166,6 +166,24 @@ class Tool(ABC):
         """Whether this tool should run alone even if concurrency is enabled."""
         return False
 
+    # --- Plugin metadata ---
+
+    config_key: str = ""
+    _plugin_discoverable: bool = True
+    _scopes: set[str] = {"core"}
+
+    @classmethod
+    def config_cls(cls) -> type[BaseModel] | None:
+        return None
+
+    @classmethod
+    def enabled(cls, ctx: ToolContext) -> bool:
+        return True
+
+    @classmethod
+    def create(cls, ctx: ToolContext) -> Tool:
+        return cls()
+
     @abstractmethod
     async def execute(self, **kwargs: Any) -> Any:
         """Run the tool; returns a string or list of content blocks."""