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/cron/test_cron_tool_list.py

@@ -4,6 +4,7 @@ from datetime import datetime, timezone
 
 import pytest
 
+from nanobot.agent.tools.context import RequestContext
 from nanobot.agent.tools.cron import CronTool
 from nanobot.cron.service import CronService
 from nanobot.cron.types import CronJob, CronJobState, CronPayload, CronSchedule
@@ -302,7 +303,7 @@ def test_remove_protected_dream_job_returns_clear_feedback(tmp_path) -> None:
 
 def test_add_cron_job_defaults_to_tool_timezone(tmp_path) -> None:
     tool = _make_tool_with_tz(tmp_path, "Asia/Shanghai")
-    tool.set_context("telegram", "chat-1")
+    tool.set_context(RequestContext(channel="telegram", chat_id="chat-1"))
 
     result = tool._add_job(None, "Morning standup", None, "0 8 * * *", None, None)
 
@@ -313,7 +314,7 @@ def test_add_cron_job_defaults_to_tool_timezone(tmp_path) -> None:
 
 def test_add_at_job_uses_default_timezone_for_naive_datetime(tmp_path) -> None:
     tool = _make_tool_with_tz(tmp_path, "Asia/Shanghai")
-    tool.set_context("telegram", "chat-1")
+    tool.set_context(RequestContext(channel="telegram", chat_id="chat-1"))
 
     result = tool._add_job(None, "Morning reminder", None, None, None, "2026-03-25T08:00:00")
 
@@ -325,7 +326,7 @@ def test_add_at_job_uses_default_timezone_for_naive_datetime(tmp_path) -> None:
 
 def test_add_job_delivers_by_default(tmp_path) -> None:
     tool = _make_tool(tmp_path)
-    tool.set_context("telegram", "chat-1")
+    tool.set_context(RequestContext(channel="telegram", chat_id="chat-1"))
 
     result = tool._add_job(None, "Morning standup", 60, None, None, None)
 
@@ -336,7 +337,7 @@ def test_add_job_delivers_by_default(tmp_path) -> None:
 
 def test_add_job_can_disable_delivery(tmp_path) -> None:
     tool = _make_tool(tmp_path)
-    tool.set_context("telegram", "chat-1")
+    tool.set_context(RequestContext(channel="telegram", chat_id="chat-1"))
 
     result = tool._add_job(None, "Background refresh", 60, None, None, None, deliver=False)
 
@@ -374,7 +375,7 @@ def test_validate_params_requires_message_only_for_add(tmp_path) -> None:
 
 def test_add_job_empty_message_returns_actionable_error(tmp_path) -> None:
     tool = _make_tool(tmp_path)
-    tool.set_context("telegram", "chat-1")
+    tool.set_context(RequestContext(channel="telegram", chat_id="chat-1"))
 
     result = tool._add_job(None, "", 60, None, None, None)
 
@@ -386,7 +387,9 @@ def test_add_job_captures_metadata_and_session_key(tmp_path) -> None:
     """CronTool stores channel metadata and session_key when adding a job."""
     tool = _make_tool(tmp_path)
     meta = {"slack": {"thread_ts": "111.222", "channel_type": "channel"}}
-    tool.set_context("slack", "C99", metadata=meta, session_key="slack:C99:111.222")
+    tool.set_context(RequestContext(
+        channel="slack", chat_id="C99", metadata=meta, session_key="slack:C99:111.222"
+    ))
 
     result = tool._add_job("test", "say hi", 60, None, None, None)
     assert "Created job" in result