diff --git a/repository/sandbox_lock.py b/repository/sandbox_lock.py
index b13cd65..ffa0e35 100644
--- a/repository/sandbox_lock.py
+++ b/repository/sandbox_lock.py
@@ -1,4 +1,5 @@
 import threading
+from dataclasses import dataclass
 from types import TracebackType
 from typing import Protocol
 from uuid import UUID
@@ -12,12 +13,25 @@ class _SyncLock(Protocol):
     def release(self) -> None: ...
 
 
+@dataclass(slots=True)
+class _LockEntry:
+    lock: _SyncLock
+    users: int = 0
+
+
 class _ChatLock(LockContext):
-    def __init__(self, lock: _SyncLock) -> None:
-        self._lock = lock
+    def __init__(
+        self,
+        locker: 'ProcessLocalSandboxLifecycleLocker',
+        chat_id: UUID,
+        entry: _LockEntry,
+    ) -> None:
+        self._locker = locker
+        self._chat_id = chat_id
+        self._entry = entry
 
     def __enter__(self) -> None:
-        self._lock.acquire()
+        self._entry.lock.acquire()
 
     def __exit__(
         self,
@@ -25,20 +39,32 @@ class _ChatLock(LockContext):
         exc: BaseException | None,
         traceback: TracebackType | None,
     ) -> bool | None:
-        self._lock.release()
+        self._entry.lock.release()
+        self._locker._release(self._chat_id, self._entry)
         return None
 
 
 class ProcessLocalSandboxLifecycleLocker(SandboxLifecycleLocker):
     def __init__(self) -> None:
         self._registry_lock = threading.Lock()
-        self._locks_by_chat_id: dict[UUID, _SyncLock] = {}
+        self._locks_by_chat_id: dict[UUID, _LockEntry] = {}
 
     def lock(self, chat_id: UUID) -> LockContext:
         with self._registry_lock:
-            lock = self._locks_by_chat_id.get(chat_id)
-            if lock is None:
-                lock = threading.Lock()
-                self._locks_by_chat_id[chat_id] = lock
+            entry = self._locks_by_chat_id.get(chat_id)
+            if entry is None:
+                entry = _LockEntry(lock=threading.Lock())
+                self._locks_by_chat_id[chat_id] = entry
+            entry.users += 1
 
-        return _ChatLock(lock)
+        return _ChatLock(self, chat_id, entry)
+
+    def _release(self, chat_id: UUID, entry: _LockEntry) -> None:
+        with self._registry_lock:
+            entry.users -= 1
+            if entry.users != 0:
+                return
+
+            current_entry = self._locks_by_chat_id.get(chat_id)
+            if current_entry is entry:
+                del self._locks_by_chat_id[chat_id]
diff --git a/tasks.md b/tasks.md
index 1101e17..494c655 100644
--- a/tasks.md
+++ b/tasks.md
@@ -209,7 +209,7 @@
 ### M17. Управление жизненным циклом per-chat locks
 
 - Субагент: `feature-developer`
-- Статус: pending
+- Статус: completed
 - Зависимости: `M13`
 - Commit required: no
 - Scope: ограничить неограниченный рост registry locks по числу когда-либо увиденных `chat_id`
diff --git a/test/test_sandbox_lock.py b/test/test_sandbox_lock.py
new file mode 100644
index 0000000..1177cec
--- /dev/null
+++ b/test/test_sandbox_lock.py
@@ -0,0 +1,93 @@
+import threading
+from uuid import UUID
+
+from repository.sandbox_lock import ProcessLocalSandboxLifecycleLocker
+
+CHAT_ID = UUID('77777777-7777-7777-7777-777777777777')
+
+
+class LockRace:
+    def __init__(self, locker: ProcessLocalSandboxLifecycleLocker) -> None:
+        self.locker = locker
+        self.entered_first = threading.Event()
+        self.second_requested = threading.Event()
+        self.second_entered = threading.Event()
+        self.release_first = threading.Event()
+        self.release_second = threading.Event()
+        self.errors: list[Exception] = []
+        self.order: list[str] = []
+        self.first_entry: object | None = None
+
+    def run_first(self) -> None:
+        try:
+            with self.locker.lock(CHAT_ID):
+                self.first_entry = self.locker._locks_by_chat_id[CHAT_ID]
+                self.order.append('first_entered')
+                self.entered_first.set()
+                assert self.release_first.wait(timeout=1)
+                self.order.append('first_releasing')
+        except Exception as exc:
+            self.errors.append(exc)
+
+    def run_second(self) -> None:
+        try:
+            assert self.entered_first.wait(timeout=1)
+            context = self.locker.lock(CHAT_ID)
+            self.second_requested.set()
+
+            with context:
+                self.order.append('second_entered')
+                self.second_entered.set()
+                assert self.release_second.wait(timeout=1)
+                self.order.append('second_releasing')
+        except Exception as exc:
+            self.errors.append(exc)
+
+
+def test_process_local_sandbox_lifecycle_locker_evicts_idle_lock() -> None:
+    locker = ProcessLocalSandboxLifecycleLocker()
+
+    with locker.lock(CHAT_ID):
+        assert CHAT_ID in locker._locks_by_chat_id
+        assert len(locker._locks_by_chat_id) == 1
+
+    assert CHAT_ID not in locker._locks_by_chat_id
+    assert len(locker._locks_by_chat_id) == 0
+
+
+def test_process_local_sandbox_lifecycle_locker_keeps_shared_lock_for_waiters() -> None:
+    locker = ProcessLocalSandboxLifecycleLocker()
+    race = LockRace(locker)
+    first_thread = threading.Thread(target=race.run_first)
+    second_thread = threading.Thread(target=race.run_second)
+
+    first_thread.start()
+    assert race.entered_first.wait(timeout=1)
+
+    second_thread.start()
+    assert race.second_requested.wait(timeout=1)
+    assert len(locker._locks_by_chat_id) == 1
+    assert locker._locks_by_chat_id[CHAT_ID] is race.first_entry
+    assert not race.second_entered.wait(timeout=0.1)
+
+    race.release_first.set()
+    assert race.second_entered.wait(timeout=1)
+    assert len(locker._locks_by_chat_id) == 1
+    assert locker._locks_by_chat_id[CHAT_ID] is race.first_entry
+
+    race.release_second.set()
+
+    first_thread.join(timeout=1)
+    second_thread.join(timeout=1)
+
+    assert not first_thread.is_alive()
+    assert not second_thread.is_alive()
+    assert race.errors == []
+    assert race.order == [
+        'first_entered',
+        'first_releasing',
+        'second_entered',
+        'second_releasing',
+    ]
+    assert CHAT_ID not in locker._locks_by_chat_id
+    assert len(locker._locks_by_chat_id) == 0