diff --git a/src/agentkit/server/app.py b/src/agentkit/server/app.py
index 3e08ee3..1c5b543 100644
--- a/src/agentkit/server/app.py
+++ b/src/agentkit/server/app.py
@@ -1,6 +1,8 @@
 """FastAPI Application Factory"""
 
 import os
+from contextlib import asynccontextmanager
+
 from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
 
@@ -13,6 +15,18 @@ from agentkit.skills.registry import SkillRegistry
 from agentkit.tools.registry import ToolRegistry
 from agentkit.server.routes import agents, tasks, skills, llm, health
 from agentkit.server.middleware import APIKeyAuthMiddleware, RateLimitMiddleware
+from agentkit.server.task_store import TaskStore
+from agentkit.server.runner import BackgroundRunner
+
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    # Startup
+    task_store = app.state.task_store
+    await task_store.start_cleanup()
+    yield
+    # Shutdown
+    await task_store.stop_cleanup()
 
 
 def create_app(
@@ -23,7 +37,7 @@ def create_app(
     rate_limit: int | None = None,
 ) -> FastAPI:
     """Create and configure the FastAPI application"""
-    app = FastAPI(title="AgentKit Server", version="2.0.0")
+    app = FastAPI(title="AgentKit Server", version="2.0.0", lifespan=lifespan)
 
     # CORS 配置
     app.add_middleware(
@@ -55,6 +69,8 @@ def create_app(
     app.state.intent_router = IntentRouter(llm_gateway=app.state.llm_gateway)
     app.state.quality_gate = QualityGate()
     app.state.output_standardizer = OutputStandardizer()
+    app.state.task_store = TaskStore()
+    app.state.runner = BackgroundRunner(task_store=app.state.task_store)
 
     # Include routes
     app.include_router(agents.router, prefix="/api/v1")
diff --git a/src/agentkit/server/client.py b/src/agentkit/server/client.py
index 26f38a5..f850a35 100644
--- a/src/agentkit/server/client.py
+++ b/src/agentkit/server/client.py
@@ -87,6 +87,45 @@ class AgentKitClient:
         response.raise_for_status()
         return response.json()
 
+    async def submit_task_async(
+        self,
+        input_data: dict,
+        skill_name: str | None = None,
+        agent_name: str | None = None,
+    ) -> dict:
+        """Submit a task in async mode"""
+        payload: dict[str, Any] = {"input_data": input_data, "mode": "async"}
+        if skill_name:
+            payload["skill_name"] = skill_name
+        if agent_name:
+            payload["agent_name"] = agent_name
+        response = await self._client.post("/api/v1/tasks", json=payload)
+        response.raise_for_status()
+        return response.json()
+
+    async def get_task_status(self, task_id: str) -> dict:
+        """Get task status"""
+        response = await self._client.get(f"/api/v1/tasks/{task_id}")
+        response.raise_for_status()
+        return response.json()
+
+    async def cancel_task(self, task_id: str) -> dict:
+        """Cancel a running task"""
+        response = await self._client.post(f"/api/v1/tasks/{task_id}/cancel")
+        response.raise_for_status()
+        return response.json()
+
+    async def list_tasks(
+        self, status: str | None = None, limit: int = 100
+    ) -> list[dict]:
+        """List tasks"""
+        params: dict[str, Any] = {"limit": limit}
+        if status:
+            params["status"] = status
+        response = await self._client.get("/api/v1/tasks", params=params)
+        response.raise_for_status()
+        return response.json()
+
     async def close(self) -> None:
         """Close the HTTP client"""
         await self._client.aclose()
diff --git a/src/agentkit/server/routes/tasks.py b/src/agentkit/server/routes/tasks.py
index 418019b..52d70e9 100644
--- a/src/agentkit/server/routes/tasks.py
+++ b/src/agentkit/server/routes/tasks.py
@@ -7,7 +7,7 @@ from fastapi import APIRouter, HTTPException, Request
 from pydantic import BaseModel
 from typing import Any
 
-from agentkit.core.protocol import TaskMessage
+from agentkit.core.protocol import TaskMessage, TaskStatus
 
 router = APIRouter(tags=["tasks"])
 
@@ -16,6 +16,7 @@ class SubmitTaskRequest(BaseModel):
     input_data: dict[str, Any]
     skill_name: str | None = None
     agent_name: str | None = None
+    mode: str = "sync"  # "sync" or "async"
 
     # 输入数据大小限制（防止 OOM）
     model_config = {"json_schema_extra": {"max_input_size_bytes": 1024 * 1024}}  # 1MB
@@ -39,6 +40,15 @@ def _validate_input_size(input_data: dict) -> None:
         )
 
 
+@router.get("/tasks")
+async def list_tasks(status: str | None = None, limit: int = 100, req: Request = None):
+    """List tasks"""
+    store = req.app.state.task_store
+    task_status = TaskStatus(status) if status else None
+    records = store.list_tasks(status=task_status, limit=limit)
+    return [r.to_dict() for r in records]
+
+
 @router.post("/tasks")
 async def submit_task(request: SubmitTaskRequest, req: Request):
     """Submit a task (Intent Router auto-routes to skill)"""
@@ -98,7 +108,20 @@ async def submit_task(request: SubmitTaskRequest, req: Request):
         except (ValueError, RuntimeError) as e:
             raise HTTPException(status_code=400, detail=str(e))
 
-    # 4. Execute task
+    # 4. Async mode: submit to background runner
+    if request.mode == "async":
+        runner = req.app.state.runner
+        task_id = await runner.submit(
+            agent=agent,
+            input_data=request.input_data,
+            skill_name=request.skill_name,
+            quality_gate=quality_gate,
+            output_standardizer=output_standardizer,
+            skill=skill,
+        )
+        return {"task_id": task_id, "status": "pending", "mode": "async"}
+
+    # 5. Sync mode: existing blocking execution
     task = TaskMessage(
         task_id=str(uuid.uuid4()),
         agent_name=agent.name,
@@ -111,7 +134,7 @@ async def submit_task(request: SubmitTaskRequest, req: Request):
 
     task_result = await agent.execute(task)
 
-    # 5. Run quality gate if skill available
+    # 6. Run quality gate if skill available
     quality_result = None
     if skill:
         try:
@@ -119,7 +142,7 @@ async def submit_task(request: SubmitTaskRequest, req: Request):
         except Exception:
             pass  # Quality gate failure shouldn't block the response
 
-    # 6. Standardize output if skill available
+    # 7. Standardize output if skill available
     if skill:
         try:
             standard_output = await output_standardizer.standardize(
@@ -141,7 +164,7 @@ async def submit_task(request: SubmitTaskRequest, req: Request):
         except Exception:
             pass  # Fall through to raw output
 
-    # 7. Return raw result if no skill or standardization failed
+    # 8. Return raw result if no skill or standardization failed
     return {
         "task_id": task.task_id,
         "status": task_result.status,
@@ -151,6 +174,20 @@ async def submit_task(request: SubmitTaskRequest, req: Request):
 
 
 @router.get("/tasks/{task_id}")
-async def get_task_status(task_id: str):
-    """Get task status (placeholder for async mode)"""
-    return {"task_id": task_id, "status": "placeholder"}
+async def get_task_status(task_id: str, req: Request):
+    """Get task status and result"""
+    store = req.app.state.task_store
+    record = store.get(task_id)
+    if record is None:
+        raise HTTPException(status_code=404, detail=f"Task '{task_id}' not found")
+    return record.to_dict()
+
+
+@router.post("/tasks/{task_id}/cancel")
+async def cancel_task(task_id: str, req: Request):
+    """Cancel a running task"""
+    runner = req.app.state.runner
+    cancelled = await runner.cancel(task_id)
+    if not cancelled:
+        raise HTTPException(status_code=400, detail="Task cannot be cancelled (not running or not found)")
+    return {"task_id": task_id, "status": "cancelled"}
diff --git a/src/agentkit/server/runner.py b/src/agentkit/server/runner.py
new file mode 100644
index 0000000..e5d1ce9
--- /dev/null
+++ b/src/agentkit/server/runner.py
@@ -0,0 +1,170 @@
+"""BackgroundRunner - Async task execution with lifecycle management"""
+
+import asyncio
+import logging
+import uuid
+from datetime import datetime, timezone
+from typing import Any
+
+from agentkit.core.protocol import TaskMessage, TaskStatus
+from agentkit.server.task_store import TaskStore
+
+logger = logging.getLogger(__name__)
+
+
+class BackgroundRunner:
+    """Runs tasks in background asyncio tasks with lifecycle management.
+
+    Integrates with AgentPool for agent execution and TaskStore for state tracking.
+    """
+
+    def __init__(self, task_store: TaskStore, max_concurrent: int = 10):
+        self._task_store = task_store
+        self._max_concurrent = max_concurrent
+        self._running_tasks: dict[str, asyncio.Task] = {}
+        self._semaphore = asyncio.Semaphore(max_concurrent)
+
+    @property
+    def active_count(self) -> int:
+        return len(self._running_tasks)
+
+    async def submit(
+        self,
+        agent,  # ConfigDrivenAgent
+        input_data: dict[str, Any],
+        skill_name: str | None = None,
+        quality_gate=None,
+        output_standardizer=None,
+        skill=None,
+    ) -> str:
+        """Submit a task for background execution.
+
+        Returns task_id immediately.
+        """
+        task_id = str(uuid.uuid4())
+
+        # Create task record
+        self._task_store.create(
+            task_id=task_id,
+            agent_name=agent.name,
+            input_data=input_data,
+            skill_name=skill_name,
+        )
+
+        # Launch background asyncio task
+        asyncio_task = asyncio.create_task(
+            self._run_task(
+                task_id=task_id,
+                agent=agent,
+                input_data=input_data,
+                quality_gate=quality_gate,
+                output_standardizer=output_standardizer,
+                skill=skill,
+            )
+        )
+        self._running_tasks[task_id] = asyncio_task
+
+        # Clean up reference when done
+        def _on_done(t: asyncio.Task):
+            self._running_tasks.pop(task_id, None)
+            if t.exception():
+                logger.error(f"Background task {task_id} failed: {t.exception()}")
+
+        asyncio_task.add_done_callback(_on_done)
+
+        return task_id
+
+    async def _run_task(
+        self,
+        task_id: str,
+        agent,
+        input_data: dict,
+        quality_gate=None,
+        output_standardizer=None,
+        skill=None,
+    ) -> dict[str, Any]:
+        """Execute task in background with semaphore control"""
+        async with self._semaphore:
+            # Update status to RUNNING
+            self._task_store.update_status(
+                task_id, TaskStatus.RUNNING,
+                started_at=datetime.now(timezone.utc),
+            )
+
+            try:
+                # Create TaskMessage for agent
+                task_msg = TaskMessage(
+                    task_id=task_id,
+                    agent_name=agent.name,
+                    task_type=agent.agent_type,
+                    priority=0,
+                    input_data=input_data,
+                    callback_url=None,
+                    created_at=datetime.now(timezone.utc),
+                )
+
+                # Execute agent
+                task_result = await agent.execute(task_msg)
+
+                # Run quality gate if available
+                quality_result = None
+                if skill and quality_gate:
+                    try:
+                        quality_result = await quality_gate.validate(
+                            task_result.output_data or {}, skill
+                        )
+                    except Exception as e:
+                        logger.warning(f"Quality gate failed for {task_id}: {e}")
+
+                # Standardize output if available
+                final_output = task_result.output_data
+                if skill and output_standardizer:
+                    try:
+                        standard_output = await output_standardizer.standardize(
+                            raw_output=task_result.output_data or {},
+                            skill=skill,
+                            quality_result=quality_result,
+                        )
+                        final_output = {
+                            "skill_name": standard_output.skill_name,
+                            "data": standard_output.data,
+                            "metadata": {
+                                "version": standard_output.metadata.version,
+                                "produced_at": standard_output.metadata.produced_at.isoformat(),
+                                "quality_score": standard_output.metadata.quality_score,
+                            },
+                        }
+                    except Exception as e:
+                        logger.warning(f"Output standardization failed for {task_id}: {e}")
+
+                # Update store
+                self._task_store.update_status(
+                    task_id, TaskStatus.COMPLETED,
+                    output_data=final_output,
+                    completed_at=datetime.now(timezone.utc),
+                    progress=1.0,
+                    progress_message="Completed",
+                )
+
+                return final_output or {}
+
+            except Exception as e:
+                logger.error(f"Task {task_id} failed: {e}")
+                self._task_store.update_status(
+                    task_id, TaskStatus.FAILED,
+                    error_message=str(e),
+                    completed_at=datetime.now(timezone.utc),
+                )
+                raise
+
+    async def cancel(self, task_id: str) -> bool:
+        """Cancel a running task"""
+        asyncio_task = self._running_tasks.get(task_id)
+        if asyncio_task and not asyncio_task.done():
+            asyncio_task.cancel()
+            self._task_store.update_status(
+                task_id, TaskStatus.CANCELLED,
+                completed_at=datetime.now(timezone.utc),
+            )
+            return True
+        return False
diff --git a/src/agentkit/server/task_store.py b/src/agentkit/server/task_store.py
new file mode 100644
index 0000000..9976fc3
--- /dev/null
+++ b/src/agentkit/server/task_store.py
@@ -0,0 +1,151 @@
+"""TaskStore - In-memory task state storage with TTL"""
+
+import asyncio
+import logging
+import time
+from dataclasses import dataclass, field
+from datetime import datetime, timezone
+from typing import Any
+
+from agentkit.core.protocol import TaskStatus
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class TaskRecord:
+    """Stored task record with full lifecycle data"""
+    task_id: str
+    agent_name: str
+    skill_name: str | None
+    input_data: dict[str, Any]
+    status: TaskStatus = TaskStatus.PENDING
+    output_data: dict[str, Any] | None = None
+    error_message: str | None = None
+    created_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
+    started_at: datetime | None = None
+    completed_at: datetime | None = None
+    progress: float = 0.0
+    progress_message: str = ""
+    metadata: dict[str, Any] = field(default_factory=dict)
+
+    def to_dict(self) -> dict:
+        return {
+            "task_id": self.task_id,
+            "agent_name": self.agent_name,
+            "skill_name": self.skill_name,
+            "input_data": self.input_data,
+            "status": self.status.value,
+            "output_data": self.output_data,
+            "error_message": self.error_message,
+            "created_at": self.created_at.isoformat(),
+            "started_at": self.started_at.isoformat() if self.started_at else None,
+            "completed_at": self.completed_at.isoformat() if self.completed_at else None,
+            "progress": self.progress,
+            "progress_message": self.progress_message,
+            "metadata": self.metadata,
+        }
+
+
+class TaskStore:
+    """In-memory task state storage with automatic TTL cleanup.
+
+    Stores task records indexed by task_id. Automatically removes
+    completed tasks after a configurable TTL.
+    """
+
+    def __init__(self, ttl_seconds: int = 3600, max_records: int = 10000):
+        self._tasks: dict[str, TaskRecord] = {}
+        self._ttl_seconds = ttl_seconds
+        self._max_records = max_records
+        self._cleanup_task: asyncio.Task | None = None
+
+    async def start_cleanup(self) -> None:
+        """Start background cleanup task"""
+        if self._cleanup_task is None:
+            self._cleanup_task = asyncio.create_task(self._cleanup_loop())
+
+    async def stop_cleanup(self) -> None:
+        """Stop background cleanup task"""
+        if self._cleanup_task:
+            self._cleanup_task.cancel()
+            try:
+                await self._cleanup_task
+            except asyncio.CancelledError:
+                pass
+            self._cleanup_task = None
+
+    async def _cleanup_loop(self) -> None:
+        """Periodically remove expired task records"""
+        while True:
+            try:
+                await asyncio.sleep(60)
+                self._cleanup_expired()
+            except asyncio.CancelledError:
+                break
+            except Exception as e:
+                logger.error(f"TaskStore cleanup error: {e}")
+
+    def _cleanup_expired(self) -> None:
+        """Remove expired records"""
+        expired = []
+        for task_id, record in self._tasks.items():
+            if record.status in (TaskStatus.COMPLETED, TaskStatus.FAILED, TaskStatus.CANCELLED):
+                if record.completed_at:
+                    age = (datetime.now(timezone.utc) - record.completed_at).total_seconds()
+                    if age > self._ttl_seconds:
+                        expired.append(task_id)
+        for task_id in expired:
+            del self._tasks[task_id]
+        if expired:
+            logger.info(f"TaskStore cleaned up {len(expired)} expired records")
+
+    def create(self, task_id: str, agent_name: str, input_data: dict, skill_name: str | None = None) -> TaskRecord:
+        """Create a new task record"""
+        if len(self._tasks) >= self._max_records:
+            # Remove oldest completed task
+            oldest = None
+            for tid, rec in self._tasks.items():
+                if rec.status in (TaskStatus.COMPLETED, TaskStatus.FAILED, TaskStatus.CANCELLED):
+                    if oldest is None or (rec.completed_at and (oldest.completed_at is None or rec.completed_at < oldest.completed_at)):
+                        oldest = rec
+            if oldest:
+                del self._tasks[oldest.task_id]
+            else:
+                raise RuntimeError("TaskStore is full and no completed tasks to evict")
+
+        record = TaskRecord(
+            task_id=task_id,
+            agent_name=agent_name,
+            skill_name=skill_name,
+            input_data=input_data,
+        )
+        self._tasks[task_id] = record
+        return record
+
+    def get(self, task_id: str) -> TaskRecord | None:
+        """Get task record by ID"""
+        return self._tasks.get(task_id)
+
+    def update_status(self, task_id: str, status: TaskStatus, **kwargs) -> TaskRecord:
+        """Update task status and optional fields"""
+        record = self._tasks.get(task_id)
+        if record is None:
+            raise KeyError(f"Task '{task_id}' not found")
+        record.status = status
+        for key, value in kwargs.items():
+            if hasattr(record, key):
+                setattr(record, key, value)
+        return record
+
+    def list_tasks(self, status: TaskStatus | None = None, limit: int = 100) -> list[TaskRecord]:
+        """List tasks, optionally filtered by status"""
+        tasks = list(self._tasks.values())
+        if status:
+            tasks = [t for t in tasks if t.status == status]
+        tasks.sort(key=lambda t: t.created_at, reverse=True)
+        return tasks[:limit]
+
+    @property
+    def size(self) -> int:
+        return len(self._tasks)
diff --git a/tests/unit/test_async_tasks.py b/tests/unit/test_async_tasks.py
new file mode 100644
index 0000000..fd67a64
--- /dev/null
+++ b/tests/unit/test_async_tasks.py
@@ -0,0 +1,512 @@
+"""Async Task System 单元测试 - TaskStore + BackgroundRunner + API"""
+
+import asyncio
+from datetime import datetime, timezone, timedelta
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+from fastapi.testclient import TestClient
+
+from agentkit.core.protocol import TaskMessage, TaskResult, TaskStatus
+from agentkit.server.task_store import TaskRecord, TaskStore
+from agentkit.server.runner import BackgroundRunner
+
+
+# ═══════════════════════════════════════════════════════════
+# TaskStore Tests
+# ═══════════════════════════════════════════════════════════
+
+
+class TestTaskRecord:
+    """TaskRecord dataclass tests"""
+
+    def test_to_dict_returns_complete_dict(self):
+        record = TaskRecord(
+            task_id="t1",
+            agent_name="agent_a",
+            skill_name="skill_x",
+            input_data={"query": "hello"},
+        )
+        d = record.to_dict()
+        assert d["task_id"] == "t1"
+        assert d["agent_name"] == "agent_a"
+        assert d["skill_name"] == "skill_x"
+        assert d["input_data"] == {"query": "hello"}
+        assert d["status"] == "pending"
+        assert d["output_data"] is None
+        assert d["error_message"] is None
+        assert d["progress"] == 0.0
+        assert d["created_at"] is not None
+
+    def test_to_dict_with_timestamps(self):
+        now = datetime.now(timezone.utc)
+        record = TaskRecord(
+            task_id="t2",
+            agent_name="agent_b",
+            skill_name=None,
+            input_data={},
+            started_at=now,
+            completed_at=now,
+        )
+        d = record.to_dict()
+        assert d["started_at"] == now.isoformat()
+        assert d["completed_at"] == now.isoformat()
+
+
+class TestTaskStore:
+    """TaskStore in-memory storage tests"""
+
+    def test_create_task_record_stored_correctly(self):
+        store = TaskStore()
+        record = store.create("t1", "agent_a", {"q": "hello"}, skill_name="skill_x")
+        assert record.task_id == "t1"
+        assert record.agent_name == "agent_a"
+        assert record.skill_name == "skill_x"
+        assert record.input_data == {"q": "hello"}
+        assert record.status == TaskStatus.PENDING
+
+    def test_get_task_by_id_returns_record(self):
+        store = TaskStore()
+        store.create("t1", "agent_a", {})
+        record = store.get("t1")
+        assert record is not None
+        assert record.task_id == "t1"
+
+    def test_get_nonexistent_task_returns_none(self):
+        store = TaskStore()
+        assert store.get("nonexistent") is None
+
+    def test_update_status_fields_updated(self):
+        store = TaskStore()
+        store.create("t1", "agent_a", {})
+        now = datetime.now(timezone.utc)
+        record = store.update_status(
+            "t1", TaskStatus.RUNNING, started_at=now, progress=0.5, progress_message="Halfway"
+        )
+        assert record.status == TaskStatus.RUNNING
+        assert record.started_at == now
+        assert record.progress == 0.5
+        assert record.progress_message == "Halfway"
+
+    def test_update_nonexistent_task_raises_keyerror(self):
+        store = TaskStore()
+        with pytest.raises(KeyError, match="not found"):
+            store.update_status("nonexistent", TaskStatus.RUNNING)
+
+    def test_list_tasks_returns_all_sorted_desc(self):
+        store = TaskStore()
+        store.create("t1", "agent_a", {})
+        store.create("t2", "agent_b", {})
+        tasks = store.list_tasks()
+        assert len(tasks) == 2
+        # Most recent first
+        assert tasks[0].task_id == "t2"
+        assert tasks[1].task_id == "t1"
+
+    def test_list_tasks_filtered_by_status(self):
+        store = TaskStore()
+        store.create("t1", "agent_a", {})
+        store.create("t2", "agent_b", {})
+        store.update_status("t1", TaskStatus.COMPLETED, completed_at=datetime.now(timezone.utc))
+        tasks = store.list_tasks(status=TaskStatus.COMPLETED)
+        assert len(tasks) == 1
+        assert tasks[0].task_id == "t1"
+
+    def test_max_records_limit_evicts_oldest_completed(self):
+        store = TaskStore(max_records=2)
+        store.create("t1", "agent_a", {})
+        store.update_status("t1", TaskStatus.COMPLETED, completed_at=datetime.now(timezone.utc))
+        store.create("t2", "agent_b", {})
+        # t3 should evict t1 (oldest completed)
+        store.create("t3", "agent_c", {})
+        assert store.get("t1") is None
+        assert store.get("t2") is not None
+        assert store.get("t3") is not None
+
+    def test_max_records_full_no_completed_raises(self):
+        store = TaskStore(max_records=1)
+        store.create("t1", "agent_a", {})
+        # All tasks are PENDING, no completed to evict
+        with pytest.raises(RuntimeError, match="full"):
+            store.create("t2", "agent_b", {})
+
+    def test_ttl_cleanup_removes_expired_completed(self):
+        store = TaskStore(ttl_seconds=0)  # Immediate expiry
+        store.create("t1", "agent_a", {})
+        store.update_status(
+            "t1", TaskStatus.COMPLETED,
+            completed_at=datetime.now(timezone.utc) - timedelta(seconds=10),
+        )
+        store.create("t2", "agent_b", {})
+        # t2 is PENDING, should not be cleaned
+        store._cleanup_expired()
+        assert store.get("t1") is None  # Expired completed
+        assert store.get("t2") is not None  # Pending stays
+
+    def test_size_property_correct_count(self):
+        store = TaskStore()
+        assert store.size == 0
+        store.create("t1", "agent_a", {})
+        assert store.size == 1
+        store.create("t2", "agent_b", {})
+        assert store.size == 2
+
+    def test_list_tasks_respects_limit(self):
+        store = TaskStore()
+        for i in range(5):
+            store.create(f"t{i}", "agent_a", {})
+        tasks = store.list_tasks(limit=3)
+        assert len(tasks) == 3
+
+
+# ═══════════════════════════════════════════════════════════
+# BackgroundRunner Tests
+# ═══════════════════════════════════════════════════════════
+
+
+class TestBackgroundRunner:
+    """BackgroundRunner async task execution tests"""
+
+    @pytest.fixture
+    def task_store(self):
+        return TaskStore()
+
+    @pytest.fixture
+    def runner(self, task_store):
+        return BackgroundRunner(task_store=task_store, max_concurrent=5)
+
+    def _make_mock_agent(self, name="test_agent", output=None, raise_error=None):
+        """Create a mock agent for testing"""
+        agent = MagicMock()
+        agent.name = name
+        agent.agent_type = "test_type"
+        if raise_error:
+            agent.execute = AsyncMock(side_effect=raise_error)
+        else:
+            task_result = TaskResult(
+                task_id="mock",
+                agent_name=name,
+                status="completed",
+                output_data=output or {"result": "ok"},
+                error_message=None,
+                started_at=datetime.now(timezone.utc),
+                completed_at=datetime.now(timezone.utc),
+            )
+            agent.execute = AsyncMock(return_value=task_result)
+        return agent
+
+    @pytest.mark.asyncio
+    async def test_submit_returns_task_id_immediately(self, runner, task_store):
+        agent = self._make_mock_agent()
+        task_id = await runner.submit(agent, {"query": "test"})
+        assert task_id is not None
+        assert isinstance(task_id, str)
+        # Task record should exist in store
+        record = task_store.get(task_id)
+        assert record is not None
+        assert record.status == TaskStatus.PENDING
+
+    @pytest.mark.asyncio
+    async def test_submit_task_runs_to_completion(self, runner, task_store):
+        agent = self._make_mock_agent(output={"answer": "42"})
+        task_id = await runner.submit(agent, {"query": "meaning of life"})
+        # Wait for task to complete
+        await asyncio.sleep(0.1)
+        record = task_store.get(task_id)
+        assert record is not None
+        assert record.status == TaskStatus.COMPLETED
+        assert record.output_data == {"answer": "42"}
+        assert record.progress == 1.0
+
+    @pytest.mark.asyncio
+    async def test_submit_task_failure_recorded(self, runner, task_store):
+        agent = self._make_mock_agent(raise_error=RuntimeError("boom"))
+        task_id = await runner.submit(agent, {"query": "fail"})
+        # Wait for task to fail
+        await asyncio.sleep(0.1)
+        record = task_store.get(task_id)
+        assert record is not None
+        assert record.status == TaskStatus.FAILED
+        assert "boom" in record.error_message
+
+    @pytest.mark.asyncio
+    async def test_cancel_running_task(self, runner, task_store):
+        async def slow_execute(msg):
+            await asyncio.sleep(10)  # Long running
+            return TaskResult(
+                task_id=msg.task_id,
+                agent_name="test_agent",
+                status="completed",
+                output_data={"result": "done"},
+                error_message=None,
+                started_at=datetime.now(timezone.utc),
+                completed_at=datetime.now(timezone.utc),
+            )
+
+        agent = MagicMock()
+        agent.name = "slow_agent"
+        agent.agent_type = "test_type"
+        agent.execute = AsyncMock(side_effect=slow_execute)
+
+        task_id = await runner.submit(agent, {"query": "slow"})
+        # Give it a moment to start
+        await asyncio.sleep(0.05)
+        cancelled = await runner.cancel(task_id)
+        assert cancelled is True
+        record = task_store.get(task_id)
+        assert record.status == TaskStatus.CANCELLED
+
+    @pytest.mark.asyncio
+    async def test_cancel_non_running_task_returns_false(self, runner, task_store):
+        result = await runner.cancel("nonexistent")
+        assert result is False
+
+    @pytest.mark.asyncio
+    async def test_concurrent_tasks_respects_semaphore(self, task_store):
+        runner = BackgroundRunner(task_store=task_store, max_concurrent=2)
+        execution_order = []
+
+        async def tracked_execute(msg):
+            execution_order.append(f"start:{msg.task_id}")
+            await asyncio.sleep(0.1)
+            execution_order.append(f"end:{msg.task_id}")
+            return TaskResult(
+                task_id=msg.task_id,
+                agent_name="test",
+                status="completed",
+                output_data={},
+                error_message=None,
+                started_at=datetime.now(timezone.utc),
+                completed_at=datetime.now(timezone.utc),
+            )
+
+        agents = []
+        for i in range(4):
+            agent = MagicMock()
+            agent.name = f"agent_{i}"
+            agent.agent_type = "test_type"
+            agent.execute = AsyncMock(side_effect=tracked_execute)
+            agents.append(agent)
+
+        # Submit all 4 tasks
+        task_ids = []
+        for agent in agents:
+            tid = await runner.submit(agent, {"idx": agents.index(agent)})
+            task_ids.append(tid)
+
+        # Wait for all to complete
+        await asyncio.sleep(0.5)
+
+        # All tasks should have completed
+        for tid in task_ids:
+            record = task_store.get(tid)
+            assert record.status == TaskStatus.COMPLETED
+
+    @pytest.mark.asyncio
+    async def test_active_count_tracks_running(self, task_store):
+        runner = BackgroundRunner(task_store=task_store, max_concurrent=10)
+
+        async def slow_execute(msg):
+            await asyncio.sleep(0.2)
+            return TaskResult(
+                task_id=msg.task_id,
+                agent_name="test",
+                status="completed",
+                output_data={},
+                error_message=None,
+                started_at=datetime.now(timezone.utc),
+                completed_at=datetime.now(timezone.utc),
+            )
+
+        agent = MagicMock()
+        agent.name = "slow_agent"
+        agent.agent_type = "test_type"
+        agent.execute = AsyncMock(side_effect=slow_execute)
+
+        await runner.submit(agent, {})
+        await asyncio.sleep(0.05)
+        assert runner.active_count >= 1
+
+        await asyncio.sleep(0.3)
+        assert runner.active_count == 0
+
+
+# ═══════════════════════════════════════════════════════════
+# API Tests (using TestClient)
+# ═══════════════════════════════════════════════════════════
+
+
+class TestAsyncTaskAPI:
+    """Async task API endpoint tests"""
+
+    @pytest.fixture
+    def mock_llm_gateway(self):
+        from agentkit.llm.gateway import LLMGateway
+        from agentkit.llm.protocol import LLMResponse, TokenUsage
+
+        gateway = LLMGateway()
+        mock_provider = AsyncMock()
+        mock_provider.chat.return_value = LLMResponse(
+            content='{"result": "mocked"}',
+            model="test-model",
+            usage=TokenUsage(prompt_tokens=10, completion_tokens=20),
+        )
+        gateway.register_provider("test", mock_provider)
+        return gateway
+
+    @pytest.fixture
+    def skill_registry(self):
+        from agentkit.skills.registry import SkillRegistry
+        return SkillRegistry()
+
+    @pytest.fixture
+    def tool_registry(self):
+        from agentkit.tools.registry import ToolRegistry
+        return ToolRegistry()
+
+    @pytest.fixture
+    def app(self, mock_llm_gateway, skill_registry, tool_registry):
+        from agentkit.server.app import create_app
+        return create_app(
+            llm_gateway=mock_llm_gateway,
+            skill_registry=skill_registry,
+            tool_registry=tool_registry,
+        )
+
+    @pytest.fixture
+    def client(self, app):
+        return TestClient(app)
+
+    def _register_skill_and_create_agent(self, client, skill_registry):
+        """Helper: register a skill and create an agent for it"""
+        from agentkit.skills.base import Skill, SkillConfig
+
+        skill_config = SkillConfig(
+            name="async_skill",
+            agent_type="async_type",
+            task_mode="llm_generate",
+            prompt={"identity": "Async Skill", "instructions": "Handle async"},
+            intent={"keywords": ["async"], "description": "Async skill"},
+        )
+        skill = Skill(config=skill_config)
+        skill_registry.register(skill)
+
+        # Create agent
+        resp = client.post(
+            "/api/v1/agents",
+            json={"skill_name": "async_skill"},
+        )
+        assert resp.status_code == 201
+        return "async_skill"
+
+    def test_submit_task_async_returns_task_id(self, client, skill_registry):
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        response = client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "async test"},
+                "agent_name": agent_name,
+                "mode": "async",
+            },
+        )
+        assert response.status_code == 200
+        data = response.json()
+        assert "task_id" in data
+        assert data["status"] == "pending"
+        assert data["mode"] == "async"
+
+    def test_get_task_status_returns_record(self, client, skill_registry):
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        # Submit async task
+        submit_resp = client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "status test"},
+                "agent_name": agent_name,
+                "mode": "async",
+            },
+        )
+        task_id = submit_resp.json()["task_id"]
+
+        # Wait a bit for completion
+        import time
+        time.sleep(0.3)
+
+        # Get status
+        response = client.get(f"/api/v1/tasks/{task_id}")
+        assert response.status_code == 200
+        data = response.json()
+        assert data["task_id"] == task_id
+        assert data["status"] in ("completed", "running", "pending")
+
+    def test_get_task_status_not_found_404(self, client):
+        response = client.get("/api/v1/tasks/nonexistent-id")
+        assert response.status_code == 404
+
+    def test_cancel_task(self, client, skill_registry):
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        # Submit async task
+        submit_resp = client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "cancel test"},
+                "agent_name": agent_name,
+                "mode": "async",
+            },
+        )
+        task_id = submit_resp.json()["task_id"]
+
+        # Try to cancel (may or may not succeed depending on timing)
+        response = client.post(f"/api/v1/tasks/{task_id}/cancel")
+        # Either cancelled or 400 (already completed)
+        assert response.status_code in (200, 400)
+
+    def test_list_tasks(self, client, skill_registry):
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        # Submit an async task to ensure at least one exists
+        client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "list test"},
+                "agent_name": agent_name,
+                "mode": "async",
+            },
+        )
+        response = client.get("/api/v1/tasks")
+        assert response.status_code == 200
+        data = response.json()
+        assert isinstance(data, list)
+
+    def test_list_tasks_filter_by_status(self, client, skill_registry):
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        # Submit an async task
+        client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "filter test"},
+                "agent_name": agent_name,
+                "mode": "async",
+            },
+        )
+        response = client.get("/api/v1/tasks?status=completed")
+        assert response.status_code == 200
+        data = response.json()
+        assert isinstance(data, list)
+        # All returned tasks should be completed
+        for task in data:
+            assert task["status"] == "completed"
+
+    def test_sync_mode_still_works(self, client, skill_registry):
+        """Ensure existing sync mode is not broken"""
+        agent_name = self._register_skill_and_create_agent(client, skill_registry)
+        response = client.post(
+            "/api/v1/tasks",
+            json={
+                "input_data": {"query": "sync test"},
+                "agent_name": agent_name,
+            },
+        )
+        assert response.status_code == 200
+        data = response.json()
+        # Sync mode returns task_id and output
+        assert "task_id" in data