feat(session): enforce replay/file-cap invariants for history lifecycle

nanobot/agent/loop.py

@@ -192,6 +192,9 @@ class AgentLoop:
         timezone: str | None = None,
         session_ttl_minutes: int = 0,
         consolidation_ratio: float = 0.5,
+        session_history_max_messages: int | None = None,
+        session_history_max_tokens: int | None = None,
+        session_file_max_messages: int | None = None,
         hooks: list[AgentHook] | None = None,
         unified_session: bool = False,
         disabled_skills: list[str] | None = None,
@@ -224,6 +227,21 @@ class AgentLoop:
             if max_tool_result_chars is not None
             else defaults.max_tool_result_chars
         )
+        self.session_history_max_messages = (
+            session_history_max_messages
+            if session_history_max_messages is not None
+            else defaults.session_history_max_messages
+        )
+        self.session_history_max_tokens = (
+            session_history_max_tokens
+            if session_history_max_tokens is not None
+            else defaults.session_history_max_tokens
+        )
+        self.session_file_max_messages = (
+            session_file_max_messages
+            if session_file_max_messages is not None
+            else defaults.session_file_max_messages
+        )
         self.provider_retry_mode = provider_retry_mode
         self.web_config = web_config or WebToolsConfig()
         self.exec_config = exec_config or ExecToolConfig()
@@ -452,6 +470,49 @@ class AgentLoop:
             return UNIFIED_SESSION_KEY
         return msg.session_key
 
+    def _history_token_budget(self) -> int:
+        """Resolve token budget for session history replay."""
+        if self.session_history_max_tokens > 0:
+            return self.session_history_max_tokens
+        if self.context_window_tokens <= 0:
+            return 0
+        max_output = getattr(getattr(self.provider, "generation", None), "max_tokens", 4096)
+        try:
+            reserved_output = int(max_output)
+        except (TypeError, ValueError):
+            reserved_output = 4096
+        budget = self.context_window_tokens - max(1, reserved_output) - 1024
+        if budget > 0:
+            return budget
+        return max(128, self.context_window_tokens // 2)
+
+    def _enforce_session_file_cap(self, session: Session) -> None:
+        """Bound session.jsonl growth by archiving and trimming old prefixes."""
+        limit = self.session_file_max_messages
+        if limit <= 0 or len(session.messages) <= limit:
+            return
+
+        before = list(session.messages)
+        before_last_consolidated = session.last_consolidated
+        before_count = len(before)
+        session.retain_recent_legal_suffix(limit)
+        dropped_count = before_count - len(session.messages)
+        if dropped_count <= 0:
+            return
+
+        dropped = before[:dropped_count]
+        already_consolidated = min(before_last_consolidated, dropped_count)
+        archive_chunk = dropped[already_consolidated:]
+        if archive_chunk:
+            self.context.memory.raw_archive(archive_chunk)
+        logger.info(
+            "Session file cap hit for {}: dropped {}, raw-archived {}, kept {}",
+            session.key,
+            dropped_count,
+            len(archive_chunk),
+            len(session.messages),
+        )
+
     async def _run_agent_loop(
         self,
         initial_messages: list[dict],
@@ -832,7 +893,10 @@ class AgentLoop:
             if is_subagent and self._persist_subagent_followup(session, msg):
                 self.sessions.save(session)
             self._set_tool_context(channel, chat_id, msg.metadata.get("message_id"))
-            history = session.get_history(max_messages=0)
+            history = session.get_history(
+                max_messages=self.session_history_max_messages,
+                max_tokens=self._history_token_budget(),
+            )
             current_role = "assistant" if is_subagent else "user"
 
             # Subagent content is already in `history` above; passing it again
@@ -851,6 +915,7 @@ class AgentLoop:
                 pending_queue=pending_queue,
             )
             self._save_turn(session, all_msgs, 1 + len(history))
+            self._enforce_session_file_cap(session)
             self._clear_runtime_checkpoint(session)
             self.sessions.save(session)
             self._schedule_background(self.consolidator.maybe_consolidate_by_tokens(session))
@@ -901,7 +966,10 @@ class AgentLoop:
             if isinstance(message_tool, MessageTool):
                 message_tool.start_turn()
 
-        history = session.get_history(max_messages=0)
+        history = session.get_history(
+            max_messages=self.session_history_max_messages,
+            max_tokens=self._history_token_budget(),
+        )
 
         pending_ask_id = pending_ask_user_id(history)
         if pending_ask_id:
@@ -987,6 +1055,7 @@ class AgentLoop:
         # Skip the already-persisted user message when saving the turn
         save_skip = 1 + len(history) + (1 if user_persisted_early else 0)
         self._save_turn(session, all_msgs, save_skip)
+        self._enforce_session_file_cap(session)
         self._clear_pending_user_turn(session)
         self._clear_runtime_checkpoint(session)
         self.sessions.save(session)