@@ -269,7 +269,11 @@ cdef _MemPool MP_from_allocation_handle(cls, alloc_handle):
     # Register it.
     if uuid is not None:
         registered = self.register(uuid)
-        assert registered is self
+        if registered is not self:
+            raise RuntimeError(
+                "Internal error: register() returned a different memory "
+                "resource than the one being registered"
+            )
 
     return self
 
@@ -292,7 +296,11 @@ cdef _MemPool MP_register(_MemPool self, uuid):
         return existing
     if not self.is_ipc_enabled:
         raise RuntimeError("Memory resource is not IPC-enabled")
-    assert self.uuid is None or self.uuid == uuid
+    if self.uuid is not None and self.uuid != uuid:
+        raise ValueError(
+            f"Cannot register memory resource with UUID {uuid}: "
+            f"the resource already has UUID {self.uuid}"
+        )
     registry[uuid] = self
     self._ipc_data._alloc_handle._uuid = uuid
     return self
 
@@ -72,6 +72,34 @@ def test_register_rejects_non_ipc_memory_resource(mempool_device):
         DeviceMemoryResource.from_registry(key)
 
 
+@pytest.mark.human_authored
+def test_register_rejects_mismatched_uuid(ipc_memory_resource):
+    """register() rejects a UUID that does not match the resource's own.
+
+    The check is an explicit ValueError (not a bare ``assert``) so it remains
+    enforced even when CPython runs with ``-O``, where assertions are removed
+    (see #2697). Registering under a foreign key would otherwise rewrite the
+    resource's UUID and silently corrupt the IPC registry.
+    """
+    mr = ipc_memory_resource
+    assert mr.is_ipc_enabled
+
+    # The resource must already carry its own UUID (assigned on creation).
+    assert mr.uuid is not None
+    other = uuid.uuid4()
+    while other == mr.uuid:
+        other = uuid.uuid4()
+
+    with pytest.raises(ValueError, match="already has UUID"):
+        mr.register(other)
+
+    # A rejected registration must not rewrite the resource's own UUID.
+    assert mr.uuid != other
+
+    # Registering under the resource's own UUID still succeeds.
+    assert mr.register(mr.uuid) is mr
+
+
 @pytest.mark.skipif(os.name == "nt", reason="IPC allocation handles are not supported on Windows")
 @pytest.mark.agent_authored(model="gpt-5.6")
 def test_ipc_allocation_handle_state_tracks_close():