diff --git a/tests/test_counter.py b/tests/test_counter.py
new file mode 100644
index 0000000..bb3cc18
--- /dev/null
+++ b/tests/test_counter.py
@@ -0,0 +1,158 @@
+"""F10 ActiveAgentCounter 单元测试
+
+按 test-plan-v2.6.md §F10：
+- T1: 全局上限（P0）
+- T2: per-agent 串行（P0）
+- T3: release 恢复（P0）
+- T4: 并发竞争（P1）
+"""
+
+import asyncio
+import pytest
+
+from src.daemon.counter import ActiveAgentCounter
+
+
+@pytest.fixture
+def counter():
+    return ActiveAgentCounter(max_global=3, max_per_agent=1)
+
+
+# ---------------------------------------------------------------------------
+# T1: 全局上限
+# ---------------------------------------------------------------------------
+
+class TestGlobalLimit:
+    def test_acquire_within_limit(self, counter):
+        """全局未满 → 成功"""
+        result = asyncio.run(counter.acquire("agent-1"))
+        assert result is True
+        assert counter.global_active == 1
+
+    def test_acquire_fills_global(self, counter):
+        """填满全局"""
+        for i in range(3):
+            asyncio.run(counter.acquire(f"agent-{i}"))
+        assert counter.global_active == 3
+
+    def test_acquire_exceeds_global(self, counter):
+        """超出全局上限 → 失败"""
+        for i in range(3):
+            asyncio.run(counter.acquire(f"agent-{i}"))
+        result = asyncio.run(counter.acquire("agent-extra"))
+        assert result is False
+
+    def test_can_acquire_respects_limit(self, counter):
+        """can_acquire 检查全局上限"""
+        assert asyncio.run(counter.can_acquire("agent-1")) is True
+        for i in range(3):
+            asyncio.run(counter.acquire(f"agent-{i}"))
+        assert asyncio.run(counter.can_acquire("agent-extra")) is False
+
+
+# ---------------------------------------------------------------------------
+# T2: per-agent 串行
+# ---------------------------------------------------------------------------
+
+class TestPerAgentSerial:
+    def test_same_agent_blocked(self, counter):
+        """同一 Agent 第二个 acquire 失败"""
+        asyncio.run(counter.acquire("agent-1"))
+        result = asyncio.run(counter.acquire("agent-1"))
+        assert result is False
+
+    def test_different_agents_ok(self, counter):
+        """不同 Agent 可以同时 acquire"""
+        assert asyncio.run(counter.acquire("agent-1")) is True
+        assert asyncio.run(counter.acquire("agent-2")) is True
+
+    def test_per_agent_limit_2(self):
+        """max_per_agent=2 允许两个"""
+        c = ActiveAgentCounter(max_global=5, max_per_agent=2)
+        assert asyncio.run(c.acquire("a1")) is True
+        assert asyncio.run(c.acquire("a1")) is True
+        assert asyncio.run(c.acquire("a1")) is False  # 第三个失败
+
+
+# ---------------------------------------------------------------------------
+# T3: release 恢复
+# ---------------------------------------------------------------------------
+
+class TestRelease:
+    def test_release_allows_new_acquire(self, counter):
+        """release 后可以重新 acquire"""
+        asyncio.run(counter.acquire("agent-1"))
+        counter.release("agent-1")
+        result = asyncio.run(counter.acquire("agent-1"))
+        assert result is True
+
+    def test_release_updates_count(self, counter):
+        """release 后计数正确"""
+        asyncio.run(counter.acquire("agent-1"))
+        assert counter.global_active == 1
+        counter.release("agent-1")
+        assert counter.global_active == 0
+
+    def test_release_same_agent_twice(self, counter):
+        """release 后同一 Agent 可以再次 acquire"""
+        asyncio.run(counter.acquire("agent-1"))
+        counter.release("agent-1")
+        assert asyncio.run(counter.can_acquire("agent-1")) is True
+
+    def test_release_updates_active_agents(self, counter):
+        """active_agents 正确追踪"""
+        asyncio.run(counter.acquire("agent-1"))
+        assert counter.active_agents == {"agent-1": 1}
+        counter.release("agent-1")
+        assert "agent-1" not in counter.active_agents
+
+    def test_full_cycle(self, counter):
+        """完整获取-释放循环"""
+        # Fill
+        for i in range(3):
+            asyncio.run(counter.acquire(f"a{i}"))
+        assert counter.global_active == 3
+
+        # Full → can't acquire
+        assert asyncio.run(counter.can_acquire("extra")) is False
+
+        # Release one
+        counter.release("a1")
+        assert counter.global_active == 2
+
+        # Now can acquire
+        assert asyncio.run(counter.acquire("extra")) is True
+        assert counter.global_active == 3
+
+
+# ---------------------------------------------------------------------------
+# T4: 并发竞争（P1）
+# ---------------------------------------------------------------------------
+
+class TestConcurrency:
+    def test_concurrent_acquire_no_exceed(self):
+        """并发 acquire 不超过全局限制"""
+        counter = ActiveAgentCounter(max_global=3, max_per_agent=1)
+        results = []
+
+        async def try_acquire(agent_id):
+            r = await counter.acquire(agent_id)
+            results.append((agent_id, r))
+            if r:
+                await asyncio.sleep(0.01)
+                counter.release(agent_id)
+
+        async def run():
+            tasks = [try_acquire(f"agent-{i}") for i in range(10)]
+            await asyncio.gather(*tasks)
+
+        asyncio.run(run())
+
+        succeeded = sum(1 for _, r in results if r)
+        # 不超过 max_global 的倍数（因为 release 后可重用）
+        assert succeeded > 0
+
+    def test_no_negative_count(self, counter):
+        """release 不会导致负数计数"""
+        counter.release("nonexistent")  # 不应崩溃
+        assert counter.global_active >= 0