refine heartbeat session retention boundaries

nanobot/cli/commands.py

@@ -620,9 +620,10 @@ def gateway(
             on_progress=_silent,
         )
 
-        # Clear the heartbeat session to prevent token overflow from accumulated tasks
+        # Keep a small tail of heartbeat history so the loop stays bounded
+        # without losing all short-term context between runs.
         session = agent.sessions.get_or_create("heartbeat")
-        session.clear()
+        session.retain_recent_legal_suffix(hb_cfg.keep_recent_messages)
         agent.sessions.save(session)
 
         return resp.content if resp else ""

nanobot/config/schema.py

@@ -90,6 +90,7 @@ class HeartbeatConfig(Base):
 
     enabled: bool = True
     interval_s: int = 30 * 60  # 30 minutes
+    keep_recent_messages: int = 8
 
 
 class GatewayConfig(Base):

nanobot/session/manager.py

@@ -98,6 +98,32 @@ class Session:
         self.last_consolidated = 0
         self.updated_at = datetime.now()
 
+    def retain_recent_legal_suffix(self, max_messages: int) -> None:
+        """Keep a legal recent suffix, mirroring get_history boundary rules."""
+        if max_messages <= 0:
+            self.clear()
+            return
+        if len(self.messages) <= max_messages:
+            return
+
+        start_idx = max(0, len(self.messages) - max_messages)
+
+        # If the cutoff lands mid-turn, extend backward to the nearest user turn.
+        while start_idx > 0 and self.messages[start_idx].get("role") != "user":
+            start_idx -= 1
+
+        retained = self.messages[start_idx:]
+
+        # Mirror get_history(): avoid persisting orphan tool results at the front.
+        start = self._find_legal_start(retained)
+        if start:
+            retained = retained[start:]
+
+        dropped = len(self.messages) - len(retained)
+        self.messages = retained
+        self.last_consolidated = max(0, self.last_consolidated - dropped)
+        self.updated_at = datetime.now()
+
 
 class SessionManager:
     """

tests/test_commands.py

@@ -477,6 +477,12 @@ def test_agent_hints_about_deprecated_memory_window(mock_agent_runtime, tmp_path
     assert "no longer used" in result.stdout
 
 
+def test_heartbeat_retains_recent_messages_by_default():
+    config = Config()
+
+    assert config.gateway.heartbeat.keep_recent_messages == 8
+
+
 def test_gateway_uses_workspace_from_config_by_default(monkeypatch, tmp_path: Path) -> None:
     config_file = tmp_path / "instance" / "config.json"
     config_file.parent.mkdir(parents=True)

tests/test_session_manager_history.py

@@ -64,6 +64,58 @@ def test_legitimate_tool_pairs_preserved_after_trim():
     assert history[0]["role"] == "user"
 
 
+def test_retain_recent_legal_suffix_keeps_recent_messages():
+    session = Session(key="test:trim")
+    for i in range(10):
+        session.messages.append({"role": "user", "content": f"msg{i}"})
+
+    session.retain_recent_legal_suffix(4)
+
+    assert len(session.messages) == 4
+    assert session.messages[0]["content"] == "msg6"
+    assert session.messages[-1]["content"] == "msg9"
+
+
+def test_retain_recent_legal_suffix_adjusts_last_consolidated():
+    session = Session(key="test:trim-cons")
+    for i in range(10):
+        session.messages.append({"role": "user", "content": f"msg{i}"})
+    session.last_consolidated = 7
+
+    session.retain_recent_legal_suffix(4)
+
+    assert len(session.messages) == 4
+    assert session.last_consolidated == 1
+
+
+def test_retain_recent_legal_suffix_zero_clears_session():
+    session = Session(key="test:trim-zero")
+    for i in range(10):
+        session.messages.append({"role": "user", "content": f"msg{i}"})
+    session.last_consolidated = 5
+
+    session.retain_recent_legal_suffix(0)
+
+    assert session.messages == []
+    assert session.last_consolidated == 0
+
+
+def test_retain_recent_legal_suffix_keeps_legal_tool_boundary():
+    session = Session(key="test:trim-tools")
+    session.messages.append({"role": "user", "content": "old"})
+    session.messages.extend(_tool_turn("old", 0))
+    session.messages.append({"role": "user", "content": "keep"})
+    session.messages.extend(_tool_turn("keep", 0))
+    session.messages.append({"role": "assistant", "content": "done"})
+
+    session.retain_recent_legal_suffix(4)
+
+    history = session.get_history(max_messages=500)
+    _assert_no_orphans(history)
+    assert history[0]["role"] == "user"
+    assert history[0]["content"] == "keep"
+
+
 # --- last_consolidated > 0 ---
 
 def test_orphan_trim_with_last_consolidated():