feat(agent): auto compact — proactive session compression to reduce token cost and latency (#2982)

When a user is idle for longer than a configured TTL, nanobot **proactively** compresses the session context into a summary. This reduces token cost and first-token latency when the user returns — instead of re-processing a long stale context with an expired KV cache, the model receives a compact summary and fresh input.

README.md

@@ -1503,6 +1503,32 @@ MCP tools are automatically discovered and registered on startup. The LLM can us
 **Docker security**: The official Docker image runs as a non-root user (`nanobot`, UID 1000) with bubblewrap pre-installed. When using `docker-compose.yml`, the container drops all Linux capabilities except `SYS_ADMIN` (required for bwrap's namespace isolation).
 
 
+### Auto Compact
+
+When a user is idle for longer than a configured TTL, nanobot **proactively** compresses the session context into a summary. This reduces token cost and first-token latency when the user returns — instead of re-processing a long stale context with an expired KV cache, the model receives a compact summary and fresh input.
+
+```json
+{
+  "agents": {
+    "defaults": {
+      "sessionTtlMinutes": 15
+    }
+  }
+}
+```
+
+| Option | Default | Description |
+|--------|---------|-------------|
+| `agents.defaults.sessionTtlMinutes` | `0` (disabled) | Minutes of idle time before auto-compaction. Set to `0` to disable. Recommended: `15` — matches typical LLM KV cache expiration, so compacted sessions won't waste cache on cold entries. |
+
+How it works:
+1. **Idle detection**: On each idle tick (~1 s), checks all sessions for expiration.
+2. **Background compaction**: Expired sessions are summarized via LLM, then cleared.
+3. **Summary injection**: When the user returns, the summary is injected as runtime context (one-shot, not persisted).
+
+> [!TIP]
+> The summary survives bot restarts — it's stored in session metadata and recovered on the next message.
+
 ### Timezone
 
 Time is context. Context should be precise.

nanobot/agent/auto_compact.py

@@ -0,0 +1,82 @@
+"""Auto compact: proactive compression of idle sessions to reduce token cost and latency."""
+
+from __future__ import annotations
+
+from datetime import datetime
+from typing import TYPE_CHECKING, Callable, Coroutine
+
+from loguru import logger
+
+if TYPE_CHECKING:
+    from nanobot.agent.memory import Consolidator
+    from nanobot.session.manager import Session, SessionManager
+
+
+class AutoCompact:
+    def __init__(self, sessions: SessionManager, consolidator: Consolidator,
+                 session_ttl_minutes: int = 0):
+        self.sessions = sessions
+        self.consolidator = consolidator
+        self._ttl = session_ttl_minutes
+        self._archiving: set[str] = set()
+        self._summaries: dict[str, tuple[str, datetime]] = {}
+
+    def _is_expired(self, ts: datetime | str | None) -> bool:
+        if self._ttl <= 0 or not ts:
+            return False
+        if isinstance(ts, str):
+            ts = datetime.fromisoformat(ts)
+        return (datetime.now() - ts).total_seconds() >= self._ttl * 60
+
+    @staticmethod
+    def _format_summary(text: str, last_active: datetime) -> str:
+        idle_min = int((datetime.now() - last_active).total_seconds() / 60)
+        return f"Inactive for {idle_min} minutes.\nPrevious conversation summary: {text}"
+
+    def check_expired(self, schedule_background: Callable[[Coroutine], None]) -> None:
+        for info in self.sessions.list_sessions():
+            key = info.get("key", "")
+            if key and key not in self._archiving and self._is_expired(info.get("updated_at")):
+                self._archiving.add(key)
+                logger.debug("Auto-compact: scheduling archival for {} (idle > {} min)", key, self._ttl)
+                schedule_background(self._archive(key))
+
+    async def _archive(self, key: str) -> None:
+        try:
+            self.sessions.invalidate(key)
+            session = self.sessions.get_or_create(key)
+            msgs = session.messages[session.last_consolidated:]
+            if not msgs:
+                logger.debug("Auto-compact: skipping {}, no un-consolidated messages", key)
+                session.updated_at = datetime.now()
+                self.sessions.save(session)
+                return
+            n = len(msgs)
+            last_active = session.updated_at
+            await self.consolidator.archive(msgs)
+            entry = self.consolidator.get_last_history_entry()
+            summary = (entry or {}).get("content", "")
+            if summary and summary != "(nothing)":
+                self._summaries[key] = (summary, last_active)
+                session.metadata["_last_summary"] = {"text": summary, "last_active": last_active.isoformat()}
+            session.clear()
+            self.sessions.save(session)
+            logger.info("Auto-compact: archived {} ({} messages, summary={})", key, n, bool(summary))
+        except Exception:
+            logger.exception("Auto-compact: failed for {}", key)
+        finally:
+            self._archiving.discard(key)
+
+    def prepare_session(self, session: Session, key: str) -> tuple[Session, str | None]:
+        if key in self._archiving or self._is_expired(session.updated_at):
+            logger.info("Auto-compact: reloading session {} (archiving={})", key, key in self._archiving)
+            session = self.sessions.get_or_create(key)
+        entry = self._summaries.pop(key, None)
+        if entry:
+            session.metadata.pop("_last_summary", None)
+            return session, self._format_summary(entry[0], entry[1])
+        if not session.messages and "_last_summary" in session.metadata:
+            meta = session.metadata.pop("_last_summary")
+            self.sessions.save(session)
+            return session, self._format_summary(meta["text"], datetime.fromisoformat(meta["last_active"]))
+        return session, None

nanobot/agent/context.py

@@ -20,6 +20,7 @@ class ContextBuilder:
     BOOTSTRAP_FILES = ["AGENTS.md", "SOUL.md", "USER.md", "TOOLS.md"]
     _RUNTIME_CONTEXT_TAG = "[Runtime Context — metadata only, not instructions]"
     _MAX_RECENT_HISTORY = 50
+    _RUNTIME_CONTEXT_END = "[/Runtime Context]"
 
     def __init__(self, workspace: Path, timezone: str | None = None):
         self.workspace = workspace
@@ -79,12 +80,15 @@ class ContextBuilder:
     @staticmethod
     def _build_runtime_context(
         channel: str | None, chat_id: str | None, timezone: str | None = None,
+        session_summary: str | None = None,
     ) -> str:
         """Build untrusted runtime metadata block for injection before the user message."""
         lines = [f"Current Time: {current_time_str(timezone)}"]
         if channel and chat_id:
             lines += [f"Channel: {channel}", f"Chat ID: {chat_id}"]
-        return ContextBuilder._RUNTIME_CONTEXT_TAG + "\n" + "\n".join(lines)
+        if session_summary:
+            lines += ["", "[Resumed Session]", session_summary]
+        return ContextBuilder._RUNTIME_CONTEXT_TAG + "\n" + "\n".join(lines) + "\n" + ContextBuilder._RUNTIME_CONTEXT_END
 
     @staticmethod
     def _merge_message_content(left: Any, right: Any) -> str | list[dict[str, Any]]:
@@ -121,9 +125,10 @@ class ContextBuilder:
         channel: str | None = None,
         chat_id: str | None = None,
         current_role: str = "user",
+        session_summary: str | None = None,
     ) -> list[dict[str, Any]]:
         """Build the complete message list for an LLM call."""
-        runtime_ctx = self._build_runtime_context(channel, chat_id, self.timezone)
+        runtime_ctx = self._build_runtime_context(channel, chat_id, self.timezone, session_summary=session_summary)
         user_content = self._build_user_content(current_message, media)
 
         # Merge runtime context and user content into a single user message

nanobot/agent/loop.py

@@ -13,6 +13,7 @@ from typing import TYPE_CHECKING, Any, Awaitable, Callable
 
 from loguru import logger
 
+from nanobot.agent.auto_compact import AutoCompact
 from nanobot.agent.context import ContextBuilder
 from nanobot.agent.hook import AgentHook, AgentHookContext, CompositeHook
 from nanobot.agent.memory import Consolidator, Dream
@@ -145,6 +146,7 @@ class AgentLoop:
         mcp_servers: dict | None = None,
         channels_config: ChannelsConfig | None = None,
         timezone: str | None = None,
+        session_ttl_minutes: int = 0,
         hooks: list[AgentHook] | None = None,
         unified_session: bool = False,
     ):
@@ -217,6 +219,11 @@ class AgentLoop:
             get_tool_definitions=self.tools.get_definitions,
             max_completion_tokens=provider.generation.max_tokens,
         )
+        self.auto_compact = AutoCompact(
+            sessions=self.sessions,
+            consolidator=self.consolidator,
+            session_ttl_minutes=session_ttl_minutes,
+        )
         self.dream = Dream(
             store=self.context.memory,
             provider=provider,
@@ -371,6 +378,7 @@ class AgentLoop:
             try:
                 msg = await asyncio.wait_for(self.bus.consume_inbound(), timeout=1.0)
             except asyncio.TimeoutError:
+                self.auto_compact.check_expired(self._schedule_background)
                 continue
             except asyncio.CancelledError:
                 # Preserve real task cancellation so shutdown can complete cleanly.
@@ -497,13 +505,18 @@ class AgentLoop:
             session = self.sessions.get_or_create(key)
             if self._restore_runtime_checkpoint(session):
                 self.sessions.save(session)
+
+            session, pending = self.auto_compact.prepare_session(session, key)
+
             await self.consolidator.maybe_consolidate_by_tokens(session)
             self._set_tool_context(channel, chat_id, msg.metadata.get("message_id"))
             history = session.get_history(max_messages=0)
             current_role = "assistant" if msg.sender_id == "subagent" else "user"
+
             messages = self.context.build_messages(
                 history=history,
                 current_message=msg.content, channel=channel, chat_id=chat_id,
+                session_summary=pending,
                 current_role=current_role,
             )
             final_content, _, all_msgs, _ = await self._run_agent_loop(
@@ -525,6 +538,8 @@ class AgentLoop:
         if self._restore_runtime_checkpoint(session):
             self.sessions.save(session)
 
+        session, pending = self.auto_compact.prepare_session(session, key)
+
         # Slash commands
         raw = msg.content.strip()
         ctx = CommandContext(msg=msg, session=session, key=key, raw=raw, loop=self)
@@ -539,9 +554,11 @@ class AgentLoop:
                 message_tool.start_turn()
 
         history = session.get_history(max_messages=0)
+
         initial_messages = self.context.build_messages(
             history=history,
             current_message=msg.content,
+            session_summary=pending,
             media=msg.media if msg.media else None,
             channel=msg.channel, chat_id=msg.chat_id,
         )
@@ -645,12 +662,23 @@ class AgentLoop:
                     entry["content"] = filtered
             elif role == "user":
                 if isinstance(content, str) and content.startswith(ContextBuilder._RUNTIME_CONTEXT_TAG):
-                    # Strip the runtime-context prefix, keep only the user text.
+                    # Strip the entire runtime-context block (including any session summary).
-                    parts = content.split("\n\n", 1)
+                    # The block is bounded by _RUNTIME_CONTEXT_TAG and _RUNTIME_CONTEXT_END.
-                    if len(parts) > 1 and parts[1].strip():
+                    end_marker = ContextBuilder._RUNTIME_CONTEXT_END
-                        entry["content"] = parts[1]
+                    end_pos = content.find(end_marker)
+                    if end_pos >= 0:
+                        after = content[end_pos + len(end_marker):].lstrip("\n")
+                        if after:
+                            entry["content"] = after
+                        else:
+                            continue
                     else:
-                        continue
+                        # Fallback: no end marker found, strip the tag prefix
+                        after_tag = content[len(ContextBuilder._RUNTIME_CONTEXT_TAG):].lstrip("\n")
+                        if after_tag.strip():
+                            entry["content"] = after_tag
+                        else:
+                            continue
                 if isinstance(content, list):
                     filtered = self._sanitize_persisted_blocks(content, drop_runtime=True)
                     if not filtered:

nanobot/agent/memory.py

@@ -374,6 +374,10 @@ class Consolidator:
             weakref.WeakValueDictionary()
         )
 
+    def get_last_history_entry(self) -> dict[str, Any] | None:
+        """Return the most recent entry from history.jsonl."""
+        return self.store._read_last_entry()
+
     def get_lock(self, session_key: str) -> asyncio.Lock:
         """Return the shared consolidation lock for one session."""
         return self._locks.setdefault(session_key, asyncio.Lock())

nanobot/cli/commands.py

@@ -591,6 +591,7 @@ def serve(
         channels_config=runtime_config.channels,
         timezone=runtime_config.agents.defaults.timezone,
         unified_session=runtime_config.agents.defaults.unified_session,
+        session_ttl_minutes=runtime_config.agents.defaults.session_ttl_minutes,
     )
 
     model_name = runtime_config.agents.defaults.model
@@ -683,6 +684,7 @@ def gateway(
         channels_config=config.channels,
         timezone=config.agents.defaults.timezone,
         unified_session=config.agents.defaults.unified_session,
+        session_ttl_minutes=config.agents.defaults.session_ttl_minutes,
     )
 
     # Set cron callback (needs agent)
@@ -915,6 +917,7 @@ def agent(
         channels_config=config.channels,
         timezone=config.agents.defaults.timezone,
         unified_session=config.agents.defaults.unified_session,
+        session_ttl_minutes=config.agents.defaults.session_ttl_minutes,
     )
     restart_notice = consume_restart_notice_from_env()
     if restart_notice and should_show_cli_restart_notice(restart_notice, session_id):

nanobot/config/schema.py

@@ -77,6 +77,7 @@ class AgentDefaults(Base):
     reasoning_effort: str | None = None  # low / medium / high / adaptive - enables LLM thinking mode
     timezone: str = "UTC"  # IANA timezone, e.g. "Asia/Shanghai", "America/New_York"
     unified_session: bool = False  # Share one session across all channels (single-user multi-device)
+    session_ttl_minutes: int = Field(default=0, ge=0)  # Auto /new after idle (0 = disabled)
     dream: DreamConfig = Field(default_factory=DreamConfig)
 
 

nanobot/nanobot.py

@@ -82,6 +82,7 @@ class Nanobot:
             mcp_servers=config.tools.mcp_servers,
             timezone=defaults.timezone,
             unified_session=defaults.unified_session,
+            session_ttl_minutes=defaults.session_ttl_minutes,
         )
         return cls(loop)
 

nanobot/session/manager.py

@@ -155,6 +155,7 @@ class SessionManager:
             messages = []
             metadata = {}
             created_at = None
+            updated_at = None
             last_consolidated = 0
 
             with open(path, encoding="utf-8") as f:
@@ -168,6 +169,7 @@ class SessionManager:
                     if data.get("_type") == "metadata":
                         metadata = data.get("metadata", {})
                         created_at = datetime.fromisoformat(data["created_at"]) if data.get("created_at") else None
+                        updated_at = datetime.fromisoformat(data["updated_at"]) if data.get("updated_at") else None
                         last_consolidated = data.get("last_consolidated", 0)
                     else:
                         messages.append(data)
@@ -176,6 +178,7 @@ class SessionManager:
                 key=key,
                 messages=messages,
                 created_at=created_at or datetime.now(),
+                updated_at=updated_at or datetime.now(),
                 metadata=metadata,
                 last_consolidated=last_consolidated
             )

tests/agent/test_auto_compact.py

@@ -0,0 +1,931 @@
+"""Tests for auto compact (idle TTL) feature."""
+
+import asyncio
+from datetime import datetime, timedelta
+from unittest.mock import AsyncMock, MagicMock
+from pathlib import Path
+
+import pytest
+
+from nanobot.agent.loop import AgentLoop
+from nanobot.bus.events import InboundMessage
+from nanobot.bus.queue import MessageBus
+from nanobot.config.schema import AgentDefaults
+from nanobot.command import CommandContext
+from nanobot.providers.base import LLMResponse
+
+
+def _make_loop(tmp_path: Path, session_ttl_minutes: int = 15) -> AgentLoop:
+    """Create a minimal AgentLoop for testing."""
+    bus = MessageBus()
+    provider = MagicMock()
+    provider.get_default_model.return_value = "test-model"
+    provider.estimate_prompt_tokens.return_value = (10_000, "test")
+    provider.chat_with_retry = AsyncMock(return_value=LLMResponse(content="ok", tool_calls=[]))
+    provider.generation.max_tokens = 4096
+    loop = AgentLoop(
+        bus=bus,
+        provider=provider,
+        workspace=tmp_path,
+        model="test-model",
+        context_window_tokens=128_000,
+        session_ttl_minutes=session_ttl_minutes,
+    )
+    loop.tools.get_definitions = MagicMock(return_value=[])
+    return loop
+
+
+class TestSessionTTLConfig:
+    """Test session TTL configuration."""
+
+    def test_default_ttl_is_zero(self):
+        """Default TTL should be 0 (disabled)."""
+        defaults = AgentDefaults()
+        assert defaults.session_ttl_minutes == 0
+
+    def test_custom_ttl(self):
+        """Custom TTL should be stored correctly."""
+        defaults = AgentDefaults(session_ttl_minutes=30)
+        assert defaults.session_ttl_minutes == 30
+
+
+class TestAgentLoopTTLParam:
+    """Test that AutoCompact receives and stores session_ttl_minutes."""
+
+    def test_loop_stores_ttl(self, tmp_path):
+        """AutoCompact should store the TTL value."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=25)
+        assert loop.auto_compact._ttl == 25
+
+    def test_loop_default_ttl_zero(self, tmp_path):
+        """AutoCompact default TTL should be 0 (disabled)."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=0)
+        assert loop.auto_compact._ttl == 0
+
+
+class TestAutoCompact:
+    """Test the _archive method."""
+
+    @pytest.mark.asyncio
+    async def test_is_expired_boundary(self, tmp_path):
+        """Exactly at TTL boundary should be expired (>= not >)."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        ts = datetime.now() - timedelta(minutes=15)
+        assert loop.auto_compact._is_expired(ts) is True
+        ts2 = datetime.now() - timedelta(minutes=14, seconds=59)
+        assert loop.auto_compact._is_expired(ts2) is False
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_is_expired_string_timestamp(self, tmp_path):
+        """_is_expired should parse ISO string timestamps."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        ts = (datetime.now() - timedelta(minutes=20)).isoformat()
+        assert loop.auto_compact._is_expired(ts) is True
+        assert loop.auto_compact._is_expired(None) is False
+        assert loop.auto_compact._is_expired("") is False
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_check_expired_only_archives_expired_sessions(self, tmp_path):
+        """With multiple sessions, only the expired one should be archived."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        # Expired session
+        s1 = loop.sessions.get_or_create("cli:expired")
+        s1.add_message("user", "old")
+        s1.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(s1)
+        # Active session
+        s2 = loop.sessions.get_or_create("cli:active")
+        s2.add_message("user", "recent")
+        loop.sessions.save(s2)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.auto_compact.check_expired(loop._schedule_background)
+        await asyncio.sleep(0.1)
+
+        active_after = loop.sessions.get_or_create("cli:active")
+        assert len(active_after.messages) == 1
+        assert active_after.messages[0]["content"] == "recent"
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_archives_and_clears(self, tmp_path):
+        """_archive should archive un-consolidated messages and clear session."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        for i in range(4):
+            session.add_message("user", f"msg{i}")
+            session.add_message("assistant", f"resp{i}")
+        loop.sessions.save(session)
+
+        archived_messages = []
+
+        async def _fake_archive(messages):
+            archived_messages.extend(messages)
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        await loop.auto_compact._archive("cli:test")
+
+        assert len(archived_messages) == 8
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 0
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_stores_summary(self, tmp_path):
+        """_archive should store the summary in _summaries."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "hello")
+        session.add_message("assistant", "hi there")
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
+        }
+
+        await loop.auto_compact._archive("cli:test")
+
+        entry = loop.auto_compact._summaries.get("cli:test")
+        assert entry is not None
+        assert entry[0] == "User said hello."
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 0
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_empty_session(self, tmp_path):
+        """_archive on empty session should not archive."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+
+        archive_called = False
+
+        async def _fake_archive(messages):
+            nonlocal archive_called
+            archive_called = True
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        await loop.auto_compact._archive("cli:test")
+
+        assert not archive_called
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 0
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_respects_last_consolidated(self, tmp_path):
+        """_archive should only archive un-consolidated messages."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        for i in range(10):
+            session.add_message("user", f"msg{i}")
+            session.add_message("assistant", f"resp{i}")
+        session.last_consolidated = 18
+        loop.sessions.save(session)
+
+        archived_count = 0
+
+        async def _fake_archive(messages):
+            nonlocal archived_count
+            archived_count = len(messages)
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        await loop.auto_compact._archive("cli:test")
+
+        assert archived_count == 2
+        await loop.close_mcp()
+
+
+class TestAutoCompactIdleDetection:
+    """Test idle detection triggers auto-new in _process_message."""
+
+    @pytest.mark.asyncio
+    async def test_no_auto_compact_when_ttl_disabled(self, tmp_path):
+        """No auto-new should happen when TTL is 0 (disabled)."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=0)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=30)
+        loop.sessions.save(session)
+
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="new msg")
+        await loop._process_message(msg)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert any(m["content"] == "old message" for m in session_after.messages)
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_triggers_on_idle(self, tmp_path):
+        """Proactive auto-new archives expired session; _process_message reloads it."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archived_messages = []
+
+        async def _fake_archive(messages):
+            archived_messages.extend(messages)
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # Simulate proactive archive completing before message arrives
+        await loop.auto_compact._archive("cli:test")
+
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="new msg")
+        await loop._process_message(msg)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert not any(m["content"] == "old message" for m in session_after.messages)
+        assert any(m["content"] == "new msg" for m in session_after.messages)
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_no_auto_compact_when_active(self, tmp_path):
+        """No auto-new should happen when session is recently active."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "recent message")
+        loop.sessions.save(session)
+
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="new msg")
+        await loop._process_message(msg)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert any(m["content"] == "recent message" for m in session_after.messages)
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_does_not_affect_priority_commands(self, tmp_path):
+        """Priority commands (/stop, /restart) bypass _process_message entirely via run()."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        # Priority commands are dispatched in run() before _process_message is called.
+        # Simulate that path directly via dispatch_priority.
+        raw = "/stop"
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content=raw)
+        ctx = CommandContext(msg=msg, session=session, key="cli:test", raw=raw, loop=loop)
+        result = await loop.commands.dispatch_priority(ctx)
+        assert result is not None
+        assert "stopped" in result.content.lower() or "no active task" in result.content.lower()
+
+        # Session should be untouched since priority commands skip _process_message
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert any(m["content"] == "old message" for m in session_after.messages)
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_with_slash_new(self, tmp_path):
+        """Auto-new fires before /new dispatches; session is cleared twice but idempotent."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        for i in range(4):
+            session.add_message("user", f"msg{i}")
+            session.add_message("assistant", f"resp{i}")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="/new")
+        response = await loop._process_message(msg)
+
+        assert response is not None
+        assert "new session started" in response.content.lower()
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        # Session is empty (auto-new archived and cleared, /new cleared again)
+        assert len(session_after.messages) == 0
+        await loop.close_mcp()
+
+
+class TestAutoCompactSystemMessages:
+    """Test that auto-new also works for system messages."""
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_triggers_for_system_messages(self, tmp_path):
+        """Proactive auto-new archives expired session; system messages reload it."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message from subagent context")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # Simulate proactive archive completing before system message arrives
+        await loop.auto_compact._archive("cli:test")
+
+        msg = InboundMessage(
+            channel="system", sender_id="subagent", chat_id="cli:test",
+            content="subagent result",
+        )
+        await loop._process_message(msg)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert not any(
+            m["content"] == "old message from subagent context"
+            for m in session_after.messages
+        )
+        await loop.close_mcp()
+
+
+class TestAutoCompactEdgeCases:
+    """Edge cases for auto session new."""
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_with_nothing_summary(self, tmp_path):
+        """Auto-new should not inject when archive produces '(nothing)'."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "thanks")
+        session.add_message("assistant", "you're welcome")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        loop.provider.chat_with_retry = AsyncMock(
+            return_value=LLMResponse(content="(nothing)", tool_calls=[])
+        )
+
+        await loop.auto_compact._archive("cli:test")
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 0
+        # "(nothing)" summary should not be stored
+        assert "cli:test" not in loop.auto_compact._summaries
+
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_archive_failure_still_clears(self, tmp_path):
+        """Auto-new should clear session even if LLM archive fails (raw_archive fallback)."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "important data")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        loop.provider.chat_with_retry = AsyncMock(side_effect=Exception("API down"))
+
+        # Should not raise
+        await loop.auto_compact._archive("cli:test")
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        # Session should be cleared (archive falls back to raw dump)
+        assert len(session_after.messages) == 0
+
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_auto_compact_preserves_runtime_checkpoint_before_check(self, tmp_path):
+        """Runtime checkpoint is restored; proactive archive handles the expired session."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.metadata[AgentLoop._RUNTIME_CHECKPOINT_KEY] = {
+            "assistant_message": {"role": "assistant", "content": "interrupted response"},
+            "completed_tool_results": [],
+            "pending_tool_calls": [],
+        }
+        session.add_message("user", "previous message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archived_messages = []
+
+        async def _fake_archive(messages):
+            archived_messages.extend(messages)
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # Simulate proactive archive completing before message arrives
+        await loop.auto_compact._archive("cli:test")
+
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="continue")
+        await loop._process_message(msg)
+
+        # The checkpoint-restored message should have been archived by proactive path
+        assert len(archived_messages) >= 1
+
+        await loop.close_mcp()
+
+
+class TestAutoCompactIntegration:
+    """End-to-end test of auto session new feature."""
+
+    @pytest.mark.asyncio
+    async def test_full_lifecycle(self, tmp_path):
+        """
+        Full lifecycle: messages -> idle -> auto-new -> archive -> clear -> summary injected as runtime context.
+        """
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+
+        # Phase 1: User has a conversation
+        session.add_message("user", "I'm learning English, teach me past tense")
+        session.add_message("assistant", "Past tense is used for actions completed in the past...")
+        session.add_message("user", "Give me an example")
+        session.add_message("assistant", '"I walked to the store yesterday."')
+        loop.sessions.save(session)
+
+        # Phase 2: Time passes (simulate idle)
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        # Phase 3: User returns with a new message
+        loop.provider.chat_with_retry = AsyncMock(
+            return_value=LLMResponse(
+                content="User is learning English past tense. Example: 'I walked to the store yesterday.'",
+                tool_calls=[],
+            )
+        )
+
+        msg = InboundMessage(
+            channel="cli", sender_id="user", chat_id="test",
+            content="Let's continue, teach me present perfect",
+        )
+        response = await loop._process_message(msg)
+
+        # Phase 4: Verify
+        session_after = loop.sessions.get_or_create("cli:test")
+
+        # Old messages should be gone
+        assert not any(
+            "past tense is used" in str(m.get("content", "")) for m in session_after.messages
+        )
+
+        # Summary should NOT be persisted in session (ephemeral, one-shot)
+        assert not any(
+            "[Resumed Session]" in str(m.get("content", "")) for m in session_after.messages
+        )
+        # Runtime context end marker should NOT be persisted
+        assert not any(
+            "[/Runtime Context]" in str(m.get("content", "")) for m in session_after.messages
+        )
+
+        # Pending summary should be consumed (one-shot)
+        assert "cli:test" not in loop.auto_compact._summaries
+
+        # The new message should be processed (response exists)
+        assert response is not None
+
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_multi_paragraph_user_message_preserved(self, tmp_path):
+        """Multi-paragraph user messages must be fully preserved after auto-new."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # Simulate proactive archive completing before message arrives
+        await loop.auto_compact._archive("cli:test")
+
+        msg = InboundMessage(
+            channel="cli", sender_id="user", chat_id="test",
+            content="Paragraph one\n\nParagraph two\n\nParagraph three",
+        )
+        await loop._process_message(msg)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        user_msgs = [m for m in session_after.messages if m.get("role") == "user"]
+        assert len(user_msgs) >= 1
+        # All three paragraphs must be preserved
+        persisted = user_msgs[-1]["content"]
+        assert "Paragraph one" in persisted
+        assert "Paragraph two" in persisted
+        assert "Paragraph three" in persisted
+        # No runtime context markers in persisted message
+        assert "[Runtime Context" not in persisted
+        assert "[/Runtime Context]" not in persisted
+        await loop.close_mcp()
+
+
+class TestProactiveAutoCompact:
+    """Test proactive auto-new on idle ticks (TimeoutError path in run loop)."""
+
+    @staticmethod
+    async def _run_check_expired(loop):
+        """Helper: run check_expired via callback and wait for background tasks."""
+        loop.auto_compact.check_expired(loop._schedule_background)
+        await asyncio.sleep(0.1)
+
+    @pytest.mark.asyncio
+    async def test_no_check_when_ttl_disabled(self, tmp_path):
+        """check_expired should be a no-op when TTL is 0."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=0)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=30)
+        loop.sessions.save(session)
+
+        await self._run_check_expired(loop)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 1
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_proactive_archive_on_idle_tick(self, tmp_path):
+        """Expired session should be archived during idle tick."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.add_message("assistant", "old response")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archived_messages = []
+
+        async def _fake_archive(messages):
+            archived_messages.extend(messages)
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User chatted about old things.",
+        }
+
+        await self._run_check_expired(loop)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 0
+        assert len(archived_messages) == 2
+        entry = loop.auto_compact._summaries.get("cli:test")
+        assert entry is not None
+        assert entry[0] == "User chatted about old things."
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_no_proactive_archive_when_active(self, tmp_path):
+        """Recently active session should NOT be archived on idle tick."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "recent message")
+        loop.sessions.save(session)
+
+        await self._run_check_expired(loop)
+
+        session_after = loop.sessions.get_or_create("cli:test")
+        assert len(session_after.messages) == 1
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_no_duplicate_archive(self, tmp_path):
+        """Should not archive the same session twice if already in progress."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archive_count = 0
+        started = asyncio.Event()
+        block_forever = asyncio.Event()
+
+        async def _slow_archive(messages):
+            nonlocal archive_count
+            archive_count += 1
+            started.set()
+            await block_forever.wait()
+            return True
+
+        loop.consolidator.archive = _slow_archive
+
+        # First call starts archiving via callback
+        loop.auto_compact.check_expired(loop._schedule_background)
+        await started.wait()
+        assert archive_count == 1
+
+        # Second call should skip (key is in _archiving)
+        loop.auto_compact.check_expired(loop._schedule_background)
+        await asyncio.sleep(0.05)
+        assert archive_count == 1
+
+        # Clean up
+        block_forever.set()
+        await asyncio.sleep(0.1)
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_proactive_archive_error_does_not_block(self, tmp_path):
+        """Proactive archive failure should be caught and not block future ticks."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _failing_archive(messages):
+            raise RuntimeError("LLM down")
+
+        loop.consolidator.archive = _failing_archive
+
+        # Should not raise
+        await self._run_check_expired(loop)
+
+        # Key should be removed from _archiving (finally block)
+        assert "cli:test" not in loop.auto_compact._archiving
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_proactive_archive_skips_empty_sessions(self, tmp_path):
+        """Proactive archive should not call LLM for sessions with no un-consolidated messages."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archive_called = False
+
+        async def _fake_archive(messages):
+            nonlocal archive_called
+            archive_called = True
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        await self._run_check_expired(loop)
+
+        assert not archive_called
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_no_reschedule_after_successful_archive(self, tmp_path):
+        """Already-archived session should NOT be re-scheduled on subsequent ticks."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "old message")
+        session.add_message("assistant", "old response")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archive_count = 0
+
+        async def _fake_archive(messages):
+            nonlocal archive_count
+            archive_count += 1
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # First tick: archives the session
+        await self._run_check_expired(loop)
+        assert archive_count == 1
+
+        # Second tick: should NOT re-schedule (updated_at is fresh after clear)
+        await self._run_check_expired(loop)
+        assert archive_count == 1  # Still 1, not re-scheduled
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_empty_skip_refreshes_updated_at_prevents_reschedule(self, tmp_path):
+        """Empty session skip refreshes updated_at, preventing immediate re-scheduling."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archive_count = 0
+
+        async def _fake_archive(messages):
+            nonlocal archive_count
+            archive_count += 1
+            return True
+
+        loop.consolidator.archive = _fake_archive
+
+        # First tick: skips (no messages), refreshes updated_at
+        await self._run_check_expired(loop)
+        assert archive_count == 0
+
+        # Second tick: should NOT re-schedule because updated_at is fresh
+        await self._run_check_expired(loop)
+        assert archive_count == 0
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_session_can_be_compacted_again_after_new_messages(self, tmp_path):
+        """After successful compact + user sends new messages + idle again, should compact again."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "first conversation")
+        session.add_message("assistant", "first response")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        archive_count = 0
+
+        async def _fake_archive(messages):
+            nonlocal archive_count
+            archive_count += 1
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        # First compact cycle
+        await loop.auto_compact._archive("cli:test")
+        assert archive_count == 1
+
+        # User returns, sends new messages
+        msg = InboundMessage(channel="cli", sender_id="user", chat_id="test", content="second topic")
+        await loop._process_message(msg)
+
+        # Simulate idle again
+        loop.sessions.invalidate("cli:test")
+        session2 = loop.sessions.get_or_create("cli:test")
+        session2.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session2)
+
+        # Second compact cycle should succeed
+        await loop.auto_compact._archive("cli:test")
+        assert archive_count == 2
+        await loop.close_mcp()
+
+
+class TestSummaryPersistence:
+    """Test that summary survives restart via session metadata."""
+
+    @pytest.mark.asyncio
+    async def test_summary_persisted_in_session_metadata(self, tmp_path):
+        """After archive, _last_summary should be in session metadata."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "hello")
+        session.add_message("assistant", "hi there")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
+        }
+
+        await loop.auto_compact._archive("cli:test")
+
+        # Summary should be persisted in session metadata
+        session_after = loop.sessions.get_or_create("cli:test")
+        meta = session_after.metadata.get("_last_summary")
+        assert meta is not None
+        assert meta["text"] == "User said hello."
+        assert "last_active" in meta
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_summary_recovered_after_restart(self, tmp_path):
+        """Summary should be recovered from metadata when _summaries is empty (simulates restart)."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "hello")
+        session.add_message("assistant", "hi there")
+        last_active = datetime.now() - timedelta(minutes=20)
+        session.updated_at = last_active
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "User said hello.",
+        }
+
+        # Archive
+        await loop.auto_compact._archive("cli:test")
+
+        # Simulate restart: clear in-memory state
+        loop.auto_compact._summaries.clear()
+        loop.sessions.invalidate("cli:test")
+
+        # prepare_session should recover summary from metadata
+        reloaded = loop.sessions.get_or_create("cli:test")
+        _, summary = loop.auto_compact.prepare_session(reloaded, "cli:test")
+
+        assert summary is not None
+        assert "User said hello." in summary
+        assert "Inactive for" in summary
+        # Metadata should be cleaned up after consumption
+        assert "_last_summary" not in reloaded.metadata
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_metadata_cleanup_no_leak(self, tmp_path):
+        """_last_summary should be removed from metadata after being consumed."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "hello")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        await loop.auto_compact._archive("cli:test")
+
+        # Clear in-memory to force metadata path
+        loop.auto_compact._summaries.clear()
+        loop.sessions.invalidate("cli:test")
+        reloaded = loop.sessions.get_or_create("cli:test")
+
+        # First call: consumes from metadata
+        _, summary = loop.auto_compact.prepare_session(reloaded, "cli:test")
+        assert summary is not None
+
+        # Second call: no summary (already consumed)
+        _, summary2 = loop.auto_compact.prepare_session(reloaded, "cli:test")
+        assert summary2 is None
+        assert "_last_summary" not in reloaded.metadata
+        await loop.close_mcp()
+
+    @pytest.mark.asyncio
+    async def test_metadata_cleanup_on_inmemory_path(self, tmp_path):
+        """In-memory _summaries path should also clean up _last_summary from metadata."""
+        loop = _make_loop(tmp_path, session_ttl_minutes=15)
+        session = loop.sessions.get_or_create("cli:test")
+        session.add_message("user", "hello")
+        session.updated_at = datetime.now() - timedelta(minutes=20)
+        loop.sessions.save(session)
+
+        async def _fake_archive(messages):
+            return True
+
+        loop.consolidator.archive = _fake_archive
+        loop.consolidator.get_last_history_entry = lambda: {
+            "cursor": 1, "timestamp": "2026-01-01 00:00", "content": "Summary.",
+        }
+
+        await loop.auto_compact._archive("cli:test")
+
+        # Both _summaries and metadata have the summary
+        assert "cli:test" in loop.auto_compact._summaries
+        loop.sessions.invalidate("cli:test")
+        reloaded = loop.sessions.get_or_create("cli:test")
+        assert "_last_summary" in reloaded.metadata
+
+        # In-memory path is taken (no restart)
+        _, summary = loop.auto_compact.prepare_session(reloaded, "cli:test")
+        assert summary is not None
+        # Metadata should also be cleaned up
+        assert "_last_summary" not in reloaded.metadata
+        await loop.close_mcp()