diff --git a/app/engine/services/rate_limit.py b/app/engine/services/rate_limit.py
index 5f68eea..7e697c2 100644
--- a/app/engine/services/rate_limit.py
+++ b/app/engine/services/rate_limit.py
@@ -39,5 +39,21 @@ def check(
     return True
 
 
+def sweep(now: float | None = None) -> int:
+    """Sweep expired buckets (spec 2026-10-19 §7 memory cap): drop keys whose
+    timestamps have ALL left the window (boundary inclusive, matching check()'s
+    keep predicate ``t > now - WINDOW``); return the number removed.
+
+    Companion to check()'s per-key lazy pruning: keys never revisited (client
+    churning tenant/ip/device_id) would otherwise accumulate forever; called
+    by main.lifespan's periodic task."""
+    now = time.time() if now is None else now
+    dead = [k for k, ts in _buckets.items()
+            if not ts or ts[-1] <= now - WINDOW]
+    for k in dead:
+        del _buckets[k]
+    return len(dead)
+
+
 def _reset_for_test() -> None:
     _buckets.clear()
diff --git a/app/main.py b/app/main.py
index 55db38c..d600553 100644
--- a/app/main.py
+++ b/app/main.py
@@ -1,5 +1,6 @@
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, suppress
 from pathlib import Path
+import asyncio
 import logging
 import os
 
@@ -12,6 +13,8 @@ from starlette.responses import FileResponse, PlainTextResponse
 from starlette.types import Receive, Scope, Send
 
 from app.engine.config import STATIC_DIR, settings
+from app.engine.services import rate_limit
+from app.platform.auth import login_limiter
 from app.platform.db import (
     Tenant,
     bootstrap_superuser,
@@ -141,6 +144,10 @@ async def lifespan(app: FastAPI):
             registry = TenantRegistry.load_from_dir(SEED_DIR, data_dir=TENANTS_DIR)
         app.state.registry = registry
 
+    # 周期清扫任务句柄:启动成功(yield 前)才创建,finally 里按非 None 取消
+    # ——启动半途失败时跳过,不给清理段引入未定义名。
+    _sweep_task: asyncio.Task | None = None
+
     try:
         await ensure_platform_schema(platform_engine)
         # 平台设置快照(Phase 4 Task 5A):schema 就绪后全表读入内存——
@@ -196,11 +203,26 @@ async def lifespan(app: FastAPI):
                     "启动清扫失败,跳过该租户(slug=%s, db=%s)",
                     rt.config.slug, rt.db_path)
 
+        # 铁律(2026-10-19)进程内面: 登录/聊天限流器过期键周期清扫(spec
+        # §7——两处内存态字典只增不删,不被回访的键永生;语义见各 sweep
+        # 注记)。300s 量级足够:清速远高于键积压速度,首步 sleep 不占启动。
+        async def _limiter_sweep_loop() -> None:
+            while True:
+                await asyncio.sleep(300)
+                login_limiter.sweep()
+                rate_limit.sweep()
+
+        _sweep_task = asyncio.create_task(_limiter_sweep_loop())
+
         yield
     finally:
         # 幂等于"更少的引擎":启动半途失败也把已建好的 engine 关掉
         # (Windows 文件锁: 不关则库文件删不掉)。platform_engine 含预置的
         # 测试引擎——dispose 后 engine 对象仍可重连,测试侧重置引用即可。
+        if _sweep_task is not None:
+            _sweep_task.cancel()
+            with suppress(asyncio.CancelledError):
+                await _sweep_task    # 等 cancel 落地:不留 pending task 给循环收尾
         await registry.dispose_all()
         await platform_engine.dispose()
 
diff --git a/app/platform/auth.py b/app/platform/auth.py
index 89f9d79..c398123 100644
--- a/app/platform/auth.py
+++ b/app/platform/auth.py
@@ -213,6 +213,19 @@ class LoginLimiter:
         else:
             self._fails.pop(key, None)
 
+    def sweep(self, now: float | None = None) -> int:
+        """清扫过期键(spec 2026-10-19 §7——内存上限铁律):删「全部时间戳
+        均已出窗」的键,返回清除数。与 _prune 的单键懒清理互补——allow/
+        record_fail 只顺手清被回访的键,失败一次即消失的键(扫号换 IP/
+        用户名)永不被回访,靠本方法全表兜底;由 main.lifespan 周期任务
+        调用。时间戳按记录序追加,ts[-1] 即最新——最新出窗则全键出窗。"""
+        now = time.time() if now is None else now
+        dead = [k for k, ts in self._fails.items()
+                if not ts or ts[-1] <= now - self.window_seconds]
+        for k in dead:
+            del self._fails[k]
+        return len(dead)
+
 
 # 模块级单例: 路由与依赖共用同一份进程内存态(同 rate_limit._buckets 模式)
 token_store = TokenStore()
diff --git a/tests/test_limiter_sweep.py b/tests/test_limiter_sweep.py
new file mode 100644
index 0000000..8fd2e1b
--- /dev/null
+++ b/tests/test_limiter_sweep.py
@@ -0,0 +1,95 @@
+"""limiter 周期清扫(spec 2026-10-19 §7——日志/内存上限铁律的进程内面)。
+
+两处限流内存态只增不删的兜底:
+- app.platform.auth.LoginLimiter._fails: (username, ip) → list[float]——
+  allow/record_fail 只顺手 _prune 被访问的键;失败一次即消失的键(扫号
+  换 IP/换用户名)永不被回访 → 永久滞留。
+- app.engine.services.rate_limit._buckets: (tenant, ip, device_id) →
+  list[float]——check() 同款单键懒清,键随客户端轮换只增不减。
+sweep() 全表清「全部时间戳均已出窗」的键,由 main.lifespan 的周期任务
+(300s sleep loop)调用。时间推进手法照 test_auth 既有 lockout 用例:
+直改内部时间戳,免真实等待。
+"""
+import asyncio
+import time
+
+from tests.conftest import (
+    JIANCAI_HOST,
+    SEED_DIR,
+    app_test_client,
+    build_app,
+)
+
+
+class TestLoginLimiterSweep:
+    def test_清过期保活跃(self):
+        from app.platform.auth import LoginLimiter
+        limiter = LoginLimiter(window_seconds=900.0, max_fails=5)
+        limiter.record_fail("u", "1.1.1.1")
+        limiter.record_fail("u", "2.2.2.2")
+        limiter._fails[("u", "1.1.1.1")] = [0.0]      # 远古 → 待清
+        n = limiter.sweep(now=time.time())
+        assert n == 1
+        assert ("u", "1.1.1.1") not in limiter._fails
+        assert ("u", "2.2.2.2") in limiter._fails
+
+    def test_全活跃时清零(self):
+        from app.platform.auth import LoginLimiter
+        limiter = LoginLimiter(window_seconds=900.0)
+        limiter.record_fail("u", "1.1.1.1")
+        assert limiter.sweep(now=time.time()) == 0
+        assert ("u", "1.1.1.1") in limiter._fails
+
+    def test_窗沿时间戳算过期_空键也清(self):
+        # ts[-1] <= now - window 与 _prune 的保留判据 t > now - window 同沿
+        from app.platform.auth import LoginLimiter
+        limiter = LoginLimiter(window_seconds=100.0)
+        now = time.time()
+        limiter._fails[("u", "1.1.1.1")] = [now - 100.0]   # 恰在窗沿 → 出窗
+        limiter._fails[("u", "2.2.2.2")] = []              # 空值键 → 待清
+        assert limiter.sweep(now=now) == 2
+        assert not list(limiter._fails)                    # 全清空
+
+
+class TestRateLimitSweep:
+    def test_同款语义(self):
+        from app.engine.services import rate_limit
+        try:
+            now = time.time()
+            rate_limit._buckets[("a", "1.1.1.1", "")] = [0.0]   # 远古
+            rate_limit._buckets[("b", "2.2.2.2", "")] = [now]   # 活跃
+            rate_limit._buckets[("c", "3.3.3.3", "")] = []      # 空值键
+            rate_limit._buckets[("d", "4.4.4.4", "")] = [
+                now - rate_limit.WINDOW]                        # 恰在窗沿
+            n = rate_limit.sweep(now=now)
+            assert n == 3
+            assert set(rate_limit._buckets) == {("b", "2.2.2.2", "")}
+        finally:
+            rate_limit._buckets.clear()   # 模块级状态:清现场(conftest 亦兜底)
+
+
+class TestLifespanSweepTask:
+    def test_注册与取消(self, tmp_path, monkeypatch):
+        """lifespan 起周期清扫任务,关停时取消。
+
+        手法: monkeypatch asyncio.create_task 包一层记录真实 task(行为
+        不变);TestClient with 进出 = lifespan 启停。不真等 300s——loop
+        首步即 sleep,任务常 pending;取消断言 cancelled/cancelling 任一
+        成立即可(实现侧 cancel 后 await 落地,常态是 cancelled)。"""
+        created = []
+        real_create_task = asyncio.create_task
+
+        def _rec(coro, **kwargs):
+            t = real_create_task(coro, **kwargs)
+            created.append(t)
+            return t
+
+        monkeypatch.setattr(asyncio, "create_task", _rec)
+        a = build_app(SEED_DIR, tmp_path)
+        with app_test_client(a, f"http://{JIANCAI_HOST}", tmp_path):
+            tasks = [t for t in created
+                     if getattr(t.get_coro(), "__name__", "")
+                     == "_limiter_sweep_loop"]
+            assert len(tasks) == 1            # 启动期创建且恰好一份
+            assert not tasks[0].done()        # 300s sleep 中不会自然完成
+        assert tasks[0].cancelled() or tasks[0].cancelling() > 0