Add memory facade (mem) including onboarding

Introduce MemoryApi, exposing the memory operations list_memories, read_memory, write_memory,
edit_memory, rename_memory and delete_memory (the latter four marked as editing operations) as well
as onboarding, which provides the onboarding instructions. list_memories returns a MemoryList, which
exposes the (writable and read-only) memory names to code and renders as JSON.

The memory tools and the onboarding tool delegate to the API via MemoryApiMixin; the onboarding tool
retains its check for the availability of the memory writing tool. The mem facade is always part of
the REPL.

The modes no-onboarding, no-memories and benchmark exclude the corresponding APIs (mem.onboarding,
or the mem facade as a whole), mirroring their tool exclusions.

test/serena/test_mem_api.py

@@ -0,0 +1,68 @@
+"""
+Tests for the memory facade API.
+"""
+
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+from serena.config.serena_config import SerenaConfig
+from serena.project import Project
+from serena.repl.api.mem_api import MemoryApi
+from serena.repl.facade import ApiScope, Facade
+
+
+@pytest.fixture
+def api(tmp_path: Path) -> MemoryApi:
+    project = Project.load(str(tmp_path), serena_config=SerenaConfig(gui_log_window=False, web_dashboard=False))
+    agent = MagicMock()
+    agent.get_active_project_or_raise.return_value = project
+    agent.serena_config.default_max_tool_answer_chars = 10000
+    return MemoryApi(agent)
+
+
+def test_facade_exposes_memory_operations(api: MemoryApi) -> None:
+    facade = Facade.from_api(api, ApiScope())
+    assert facade.name == "mem"
+    assert set(facade.enabled_method_names) == {
+        "list_memories",
+        "read_memory",
+        "write_memory",
+        "edit_memory",
+        "rename_memory",
+        "delete_memory",
+        "onboarding",
+    }
+    assert {name for name in facade.enabled_method_names if facade.get_method(name).info.can_edit} == {
+        "write_memory",
+        "edit_memory",
+        "rename_memory",
+        "delete_memory",
+    }
+
+
+def test_memory_lifecycle(api: MemoryApi) -> None:
+    api.write_memory("topic/first", "# First\nhello")
+    api.write_memory("second", "see `mem:topic/first`")
+
+    # listing exposes the names to code and renders as JSON (global memories of the machine may be present, too)
+    memory_list = api.list_memories()
+    assert {"second", "topic/first"} <= set(memory_list.memories)
+    assert api.list_memories("topic").memories == ["topic/first"]
+    assert '"memories"' in memory_list.represent()
+
+    # reading, editing, renaming (with reference propagation) and deleting
+    assert api.read_memory("topic/first") == "# First\nhello"
+    api.edit_memory("topic/first", "hello", "world", mode="literal")
+    assert api.read_memory("topic/first") == "# First\nworld"
+    api.rename_memory("topic/first", "topic/renamed")
+    assert "mem:topic/renamed" in api.read_memory("second")
+    api.delete_memory("second")
+    assert "second" not in api.list_memories().memories
+    assert api.list_memories("topic").memories == ["topic/renamed"]
+
+
+def test_write_memory_rejects_overlong_content(api: MemoryApi) -> None:
+    with pytest.raises(ValueError, match="too long"):
+        api.write_memory("big", "x" * 100, max_chars=10)