diff --git a/nanobot/agent/subagent.py b/nanobot/agent/subagent.py
index db3c5125..b4f4cece 100644
--- a/nanobot/agent/subagent.py
+++ b/nanobot/agent/subagent.py
@@ -13,6 +13,7 @@ from loguru import logger
 
 from nanobot.agent.hook import AgentHook, AgentHookContext
 from nanobot.agent.runner import AgentRunner, AgentRunSpec
+from nanobot.agent.tools.base import ToolResult
 from nanobot.agent.tools.context import (
     RequestContext,
     ToolContext,
@@ -308,8 +309,8 @@ class SubagentManager:
         )
         self._task_statuses[task_id] = status
         logger.info("Running inline subagent [{}]: {}", task_id, display_label)
-        try:
-            return await self._run_subagent(
+        inline_task = asyncio.create_task(
+            self._run_subagent(
                 task_id,
                 task,
                 display_label,
@@ -320,8 +321,22 @@ class SubagentManager:
                 workspace_scope,
                 announce=False,
             )
+        )
+        self._running_tasks[task_id] = inline_task
+        if session_key:
+            self._session_tasks.setdefault(session_key, set()).add(task_id)
+        try:
+            result = await inline_task
+            if status.phase == "error" or status.stop_reason in {"error", "tool_error"}:
+                return ToolResult.error(result)
+            return result
         finally:
+            self._running_tasks.pop(task_id, None)
             self._task_statuses.pop(task_id, None)
+            if session_key and (ids := self._session_tasks.get(session_key)):
+                ids.discard(task_id)
+                if not ids:
+                    del self._session_tasks[session_key]
 
     async def _run_subagent(
         self,
diff --git a/tests/agent/tools/test_subagent_tools.py b/tests/agent/tools/test_subagent_tools.py
index befed85c..ec496325 100644
--- a/tests/agent/tools/test_subagent_tools.py
+++ b/tests/agent/tools/test_subagent_tools.py
@@ -47,7 +47,40 @@ async def test_run_inline_returns_result_without_announcement(tmp_path):
 
     assert result == "review result"
     manager._announce_result.assert_not_awaited()
+    assert manager._running_tasks == {}
     assert manager._task_statuses == {}
+    assert manager._session_tasks == {}
+
+
+@pytest.mark.asyncio
+async def test_run_inline_returns_structured_error(tmp_path):
+    """Inline subagent failures remain tool errors for the parent runner."""
+    from nanobot.agent.subagent import SubagentManager
+    from nanobot.agent.tools.registry import is_tool_error_result
+    from nanobot.bus.queue import MessageBus
+
+    manager = SubagentManager(
+        workspace=tmp_path,
+        bus=MessageBus(),
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+    )
+    manager.runner.run = AsyncMock(return_value=SimpleNamespace(
+        stop_reason="error",
+        final_content=None,
+        error="subagent failed",
+        tool_events=[],
+    ))
+
+    result = await manager.run_inline(
+        task="review this",
+        session_key="test:c1",
+        runtime=_runtime(MagicMock()),
+    )
+
+    assert result == "subagent failed"
+    assert is_tool_error_result("spawn", result)
+    assert manager._running_tasks == {}
+    assert manager._session_tasks == {}
 
 
 @pytest.mark.asyncio
@@ -265,6 +298,86 @@ async def test_spawn_tool_waits_for_inline_result():
     manager.spawn.assert_not_awaited()
 
 
+@pytest.mark.asyncio
+async def test_inline_spawn_counts_toward_concurrency_limit(tmp_path):
+    from nanobot.agent.subagent import SubagentManager
+    from nanobot.agent.tools.context import RequestContext, request_context
+    from nanobot.agent.tools.spawn import SpawnTool
+    from nanobot.bus.queue import MessageBus
+
+    manager = SubagentManager(
+        workspace=tmp_path,
+        bus=MessageBus(),
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+        max_concurrent_subagents=1,
+    )
+    release = asyncio.Event()
+    entered = asyncio.Event()
+
+    async def fake_run(spec):
+        entered.set()
+        await release.wait()
+        return SimpleNamespace(
+            stop_reason="done",
+            final_content="done",
+            error=None,
+            tool_events=[],
+        )
+
+    manager.runner.run = AsyncMock(side_effect=fake_run)
+    tool = SpawnTool(manager)
+    with request_context(RequestContext(
+        channel="test",
+        chat_id="c1",
+        session_key="test:c1",
+        runtime=_runtime(MagicMock()),
+    )):
+        first = asyncio.create_task(tool.execute(task="first", wait=True))
+        await asyncio.wait_for(entered.wait(), timeout=1.0)
+
+        second = await tool.execute(task="second", wait=True)
+
+        assert "concurrency limit reached" in second
+        assert manager.get_running_count() == 1
+        release.set()
+        assert await first == "done"
+
+    assert manager.get_running_count() == 0
+    assert manager._session_tasks == {}
+
+
+@pytest.mark.asyncio
+async def test_cancel_by_session_cancels_inline_subagent(tmp_path):
+    from nanobot.agent.subagent import SubagentManager
+    from nanobot.bus.queue import MessageBus
+
+    manager = SubagentManager(
+        workspace=tmp_path,
+        bus=MessageBus(),
+        max_tool_result_chars=_MAX_TOOL_RESULT_CHARS,
+    )
+    entered = asyncio.Event()
+
+    async def fake_run(spec):
+        entered.set()
+        await asyncio.Event().wait()
+
+    manager.runner.run = AsyncMock(side_effect=fake_run)
+    inline = asyncio.create_task(manager.run_inline(
+        task="wait",
+        session_key="test:c1",
+        runtime=_runtime(MagicMock()),
+    ))
+    await asyncio.wait_for(entered.wait(), timeout=1.0)
+
+    assert await manager.cancel_by_session("test:c1") == 1
+    with pytest.raises(asyncio.CancelledError):
+        await inline
+    assert manager._running_tasks == {}
+    assert manager._task_statuses == {}
+    assert manager._session_tasks == {}
+
+
 def test_subagent_default_max_concurrent_matches_agent_defaults(tmp_path):
     """Direct SubagentManager construction should use the agent default concurrency limit."""
     from nanobot.agent.subagent import SubagentManager