Default MCP tab tools to the active tab

Requiring an explicit tab_id forced every navigate or close through a
preceding tabs_list call, which costs an MCP client a full round trip just to
learn the ID the browser already considers current.

navigate and tabs_close now resolve the active tab when tab_id is omitted,
matching the screenshot tool. Resolution is explicit rather than forwarding
None into the SDK, so the acting tool knows which tab it touched; tabs_close
reports it, since closing the wrong tab is not recoverable.

This stays in the MCP layer: the SDK and CLI signatures are unchanged.

tests/test_mcp.py

@@ -26,6 +26,7 @@ class FakeClient:
       list=self.tabs_list,
       open=self.tabs_open,
       close=self.tabs_close,
+      active=self.tabs_active,
       status=self.tabs_status,
       screenshot=self.tabs_screenshot,
     )
@@ -46,6 +47,10 @@ class FakeClient:
     self.calls.append(("close", tab_id))
     return 1
 
+  def tabs_active(self):
+    self.calls.append(("active",))
+    return SimpleNamespace(id=7)
+
   def tabs_status(self, tab_id):
     self.calls.append(("status", tab_id))
     return {"id": tab_id, "title": "Navigated", "url": "https://example.com/next"}
@@ -178,6 +183,18 @@ async def test_mutating_tools_use_sdk_and_return_fresh_state(client):
     ("navigate", 8, "https://example.com/next"), ("status", 8)
   ]
 
+@pytest.mark.anyio
+async def test_tab_tools_default_to_the_active_tab(client):
+  navigated = await client.call_tool("browser_navigate", {"url": "https://example.com/next"})
+  closed = await client.call_tool("browser_tabs_close", {})
+
+  assert navigated.structured_content["id"] == 7
+  assert closed.structured_content == {"closed": 1, "tab_id": 7}
+  assert FakeClient.instances[0].calls == [
+    ("active",), ("navigate", 7, "https://example.com/next"), ("status", 7)
+  ]
+  assert FakeClient.instances[1].calls == [("active",), ("close", 7)]
+
 @pytest.mark.anyio
 async def test_screenshot_returns_image_content(client):
   result = await client.call_tool("browser_screenshot", {"tab_id": 7, "format": "png"})

tests/test_remote_pool.py

@@ -43,6 +43,39 @@ def test_checkin_caps_pool_size():
     b.close()
   pool.close_all()
 
+def test_checkin_caps_endpoint_buckets():
+  pool.close_all()
+  peers = []
+  try:
+    for i in range(pool._MAX_ENDPOINTS + 5):
+      a, b = _socketpair()
+      peers.append(b)
+      pool.checkin(f"host-{i}:443", pool.PooledConnection(a, b"secret"))
+    assert len(pool._POOL) <= pool._MAX_ENDPOINTS
+  finally:
+    for peer in peers:
+      peer.close()
+    pool.close_all()
+
+def test_checkin_prunes_stale_endpoint_buckets():
+  pool.close_all()
+  old_a, old_b = _socketpair()
+  old = pool.PooledConnection(old_a, b"secret")
+  pool.checkin("old:443", old)
+  old.last_used -= pool._MAX_IDLE_SECONDS + 1
+  peers = [old_b]
+  try:
+    for i in range(pool._MAX_ENDPOINTS):
+      a, b = _socketpair()
+      peers.append(b)
+      pool.checkin(f"new-{i}:443", pool.PooledConnection(a, b"secret"))
+    assert "old:443" not in pool._POOL
+    assert len(pool._POOL) <= pool._MAX_ENDPOINTS
+  finally:
+    for peer in peers:
+      peer.close()
+    pool.close_all()
+
 def test_session_inner_message_strips_auth_fields():
   msg = {
     "id": "1", "command": "tabs.list", "args": {}, "user_agent": "browser-cli/1",

tests/test_serve_security.py

@@ -181,6 +181,23 @@ def test_rate_limiter_is_per_key():
   assert limiter.allow("a") is False
   assert limiter.allow("b") is False
 
+def test_rate_limiter_caps_identity_buckets():
+  limiter = RateLimiter(rate=0.0001, burst=1, max_buckets=3)
+  for i in range(10):
+    assert limiter.allow(f"key-{i}") is True
+  assert len(limiter._buckets) <= 3
+
+def test_rate_limiter_prunes_refilled_idle_buckets(monkeypatch):
+  current = 1000.0
+  monkeypatch.setattr("browser_cli.serve.security.time.monotonic", lambda: current)
+  limiter = RateLimiter(rate=1, burst=2, max_buckets=2)
+  assert limiter.allow("old") is True
+  current += 120.0
+  assert limiter.allow("a") is True
+  assert limiter.allow("b") is True
+  assert "old" not in limiter._buckets
+  assert len(limiter._buckets) <= 2
+
 # ── ServeSecurity ────────────────────────────────────────────────────────────────
 
 def test_effective_policy_prefers_per_key_override():