fix(tools): isolate plugin runtime state

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/agent/test_subagent.py

@@ -28,3 +28,27 @@ async def test_subagent_uses_tool_loader():
     assert tools.has("glob")
     assert not tools.has("message")
     assert not tools.has("spawn")
+
+
+@pytest.mark.asyncio
+async def test_subagent_build_tools_isolates_file_read_state(tmp_path):
+    """Each spawned subagent needs a fresh file-state cache."""
+    (tmp_path / "note.txt").write_text("hello\n", encoding="utf-8")
+    provider = MagicMock(spec=LLMProvider)
+    provider.get_default_model.return_value = "test"
+    sm = SubagentManager(
+        provider=provider,
+        workspace=tmp_path,
+        bus=MessageBus(),
+        model="test",
+        max_tool_result_chars=16_000,
+    )
+
+    first_read = sm._build_tools().get("read_file")
+    second_read = sm._build_tools().get("read_file")
+
+    assert first_read is not second_read
+    assert (await first_read.execute(path="note.txt")).startswith("1| hello")
+    second_result = await second_read.execute(path="note.txt")
+    assert second_result.startswith("1| hello")
+    assert "File unchanged" not in second_result

tests/tools/test_message_tool.py

@@ -91,6 +91,29 @@ async def test_message_tool_inherits_metadata_for_same_target() -> None:
     assert sent[0].metadata == slack_meta
 
 
+@pytest.mark.asyncio
+async def test_message_tool_clears_metadata_when_context_has_none() -> None:
+    sent: list[OutboundMessage] = []
+
+    async def _send(msg: OutboundMessage) -> None:
+        sent.append(msg)
+
+    tool = MessageTool(send_callback=_send)
+    from nanobot.agent.tools.context import RequestContext
+    tool.set_context(
+        RequestContext(
+            channel="slack",
+            chat_id="C123",
+            metadata={"slack": {"thread_ts": "111.222", "channel_type": "channel"}},
+        ),
+    )
+    tool.set_context(RequestContext(channel="slack", chat_id="C123", metadata={}))
+
+    await tool.execute(content="plain reply")
+
+    assert sent[0].metadata == {}
+
+
 @pytest.mark.asyncio
 async def test_message_tool_does_not_inherit_metadata_for_cross_target() -> None:
     sent: list[OutboundMessage] = []