fix(context): scale replay cap with context window

nanobot/agent/loop.py

@@ -57,7 +57,11 @@ from nanobot.session.goal_state import (
     sustained_goal_active,
 )
 from nanobot.session.keys import UNIFIED_SESSION_KEY, session_key_for_channel
-from nanobot.session.manager import DEFAULT_REPLAY_MAX_MESSAGES, Session, SessionManager
+from nanobot.session.manager import (
+    Session,
+    SessionManager,
+    replay_max_messages_for_context,
+)
 from nanobot.utils.document import extract_documents, reference_non_image_attachments
 from nanobot.utils.helpers import image_placeholder_text
 from nanobot.utils.helpers import truncate_text as truncate_text_fn
@@ -201,7 +205,7 @@ class AgentLoop:
         timezone: str | None = None,
         session_ttl_minutes: int = 0,
         consolidation_ratio: float = 0.5,
-        max_messages: int = DEFAULT_REPLAY_MAX_MESSAGES,
+        max_messages: int = 0,
         hooks: list[AgentHook] | None = None,
         unified_session: bool = False,
         disabled_skills: list[str] | None = None,
@@ -292,8 +296,11 @@ class AgentLoop:
             llm_wall_timeout_for_session=lambda sk: runner_wall_llm_timeout_s(self.sessions, sk),
         )
         self._unified_session = unified_session
+        self._explicit_max_messages = max_messages > 0
         self._max_messages = (
-            max_messages if max_messages > 0 else DEFAULT_REPLAY_MAX_MESSAGES
+            max_messages
+            if self._explicit_max_messages
+            else replay_max_messages_for_context(self.context_window_tokens)
         )
         self._running = False
         self._mcp_servers = mcp_servers or {}
@@ -422,6 +429,7 @@ class AgentLoop:
         self.runner.provider = provider
         self.subagents.set_provider(provider, model)
         self.consolidator.set_provider(provider, model, context_window_tokens)
+        self._sync_replay_max_messages()
         self._provider_signature = snapshot.signature
         if publish_update and self._runtime_model_publisher is not None:
             self._runtime_model_publisher(
@@ -435,6 +443,10 @@ class AgentLoop:
             )
         logger.info("Runtime model switched for next turn: {} -> {}", old_model, model)
 
+    def _sync_replay_max_messages(self) -> None:
+        if not self._explicit_max_messages:
+            self._max_messages = replay_max_messages_for_context(self.context_window_tokens)
+
     def _refresh_provider_snapshot(self) -> None:
         if self._provider_snapshot_loader is None:
             return

nanobot/agent/tools/self.py

@@ -438,6 +438,9 @@ class MyTool(Tool, ContextAware):
         setattr(self._runtime_state, key, value)
         if key == "model":
             self._runtime_state._active_preset = None
+        sync_replay = getattr(self._runtime_state, "_sync_replay_max_messages", None)
+        if key == "context_window_tokens" and callable(sync_replay):
+            sync_replay()
         if key == "max_iterations" and hasattr(self._runtime_state, "_sync_subagent_runtime_limits"):
             self._runtime_state._sync_subagent_runtime_limits()
         self._audit("modify", f"{key}: {old!r} -> {value!r}")

nanobot/session/manager.py

@@ -27,7 +27,9 @@ from nanobot.utils.helpers import (
 from nanobot.utils.subagent_channel_display import scrub_subagent_announce_body
 
 FILE_MAX_MESSAGES = 2000
-DEFAULT_REPLAY_MAX_MESSAGES = 500
+MIN_REPLAY_MAX_MESSAGES = 120
+REPLAY_TOKENS_PER_MESSAGE = 100
+DEFAULT_REPLAY_MAX_MESSAGES = FILE_MAX_MESSAGES
 _MESSAGE_TIME_PREFIX_RE = re.compile(r"^\[Message Time: [^\]]+\]\n?")
 _LOCAL_IMAGE_BREADCRUMB_RE = re.compile(r"^\[image: (?:/|~)[^\]]+\]\s*$")
 _TOOL_CALL_ECHO_RE = re.compile(r'^\s*(?:generate_image|message)\([^)]*\)\s*$')
@@ -44,6 +46,15 @@ _FORK_VOLATILE_METADATA_KEYS = {
 }
 
 
+def replay_max_messages_for_context(context_window_tokens: int | None) -> int:
+    if not context_window_tokens or context_window_tokens <= 0:
+        return DEFAULT_REPLAY_MAX_MESSAGES
+    return min(
+        FILE_MAX_MESSAGES,
+        max(MIN_REPLAY_MAX_MESSAGES, context_window_tokens // REPLAY_TOKENS_PER_MESSAGE),
+    )
+
+
 def _sanitize_assistant_replay_text(content: str) -> str:
     """Remove internal replay artifacts that the model may have copied before.
 

tests/agent/test_max_messages_config.py

@@ -11,20 +11,31 @@ from nanobot.agent.loop import AgentLoop
 from nanobot.bus.events import InboundMessage
 from nanobot.bus.queue import MessageBus
 from nanobot.providers.base import LLMResponse
-from nanobot.session.manager import DEFAULT_REPLAY_MAX_MESSAGES, Session
+from nanobot.providers.factory import ProviderSnapshot
+from nanobot.session.manager import (
+    DEFAULT_REPLAY_MAX_MESSAGES,
+    Session,
+    replay_max_messages_for_context,
+)
 
 DEFAULT_MAX_MESSAGES = DEFAULT_REPLAY_MAX_MESSAGES
 
 
-def _make_loop(tmp_path: Path, max_messages: int = DEFAULT_MAX_MESSAGES) -> AgentLoop:
+def _make_loop(
+    tmp_path: Path,
+    max_messages: int = 0,
+    context_window_tokens: int = 200_000,
+) -> AgentLoop:
     provider = MagicMock()
     provider.get_default_model.return_value = "test-model"
+    provider.generation.max_tokens = 4096
     return AgentLoop(
         bus=MessageBus(),
         provider=provider,
         workspace=tmp_path,
         model="test-model",
         max_messages=max_messages,
+        context_window_tokens=context_window_tokens,
     )
 
 
@@ -51,17 +62,26 @@ def _tool_round(call_id: str) -> list[dict]:
 
 
 class TestMaxMessagesInit:
-    """Verify AgentLoop stores the config value correctly."""
+    """Verify AgentLoop derives the internal replay cap correctly."""
 
-    def test_default_is_builtin_limit(self, tmp_path: Path) -> None:
+    def test_context_formula(self) -> None:
+        assert replay_max_messages_for_context(8_000) == 120
+        assert replay_max_messages_for_context(32_768) == 327
+        assert replay_max_messages_for_context(200_000) == DEFAULT_MAX_MESSAGES
+
+    def test_default_for_200k_context_reaches_file_cap(self, tmp_path: Path) -> None:
         loop = _make_loop(tmp_path)
         assert loop._max_messages == DEFAULT_MAX_MESSAGES
 
+    def test_default_scales_with_context_window(self, tmp_path: Path) -> None:
+        loop = _make_loop(tmp_path, context_window_tokens=32_768)
+        assert loop._max_messages == 327
+
     def test_positive_value_stored(self, tmp_path: Path) -> None:
         loop = _make_loop(tmp_path, max_messages=25)
         assert loop._max_messages == 25
 
-    def test_zero_uses_builtin_limit(self, tmp_path: Path) -> None:
+    def test_zero_uses_context_derived_limit(self, tmp_path: Path) -> None:
         loop = _make_loop(tmp_path, max_messages=0)
         assert loop._max_messages == DEFAULT_MAX_MESSAGES
 
@@ -70,6 +90,30 @@ class TestMaxMessagesInit:
         loop = _make_loop(tmp_path, max_messages=-5)
         assert loop._max_messages == DEFAULT_MAX_MESSAGES
 
+    def test_provider_refresh_resyncs_context_derived_limit(self, tmp_path: Path) -> None:
+        old_provider = MagicMock()
+        old_provider.get_default_model.return_value = "old-model"
+        old_provider.generation.max_tokens = 4096
+        new_provider = MagicMock()
+        new_provider.generation.max_tokens = 4096
+        loop = AgentLoop(
+            bus=MessageBus(),
+            provider=old_provider,
+            workspace=tmp_path,
+            model="old-model",
+            context_window_tokens=32_768,
+            provider_snapshot_loader=lambda: ProviderSnapshot(
+                provider=new_provider,
+                model="new-model",
+                context_window_tokens=200_000,
+                signature=("new-model",),
+            ),
+        )
+
+        assert loop._max_messages == 327
+        loop._refresh_provider_snapshot()
+        assert loop._max_messages == DEFAULT_MAX_MESSAGES
+
 
 class TestGetHistoryWithMaxMessages:
     """Verify get_history respects max_messages parameter."""

tests/agent/tools/test_self_tool.py

@@ -236,10 +236,12 @@ class TestModifyRestricted:
 
     @pytest.mark.asyncio
     async def test_modify_context_window_valid(self):
-        tool = _make_tool()
+        loop = _make_mock_loop(_sync_replay_max_messages=MagicMock())
+        tool = _make_tool(runtime_state=loop)
         result = await tool.execute(action="set", key="context_window_tokens", value=131072)
         assert "Set context_window_tokens" in result
-        assert tool._runtime_state.context_window_tokens == 131072
+        assert loop.context_window_tokens == 131072
+        loop._sync_replay_max_messages.assert_called_once_with()
 
     @pytest.mark.asyncio
     async def test_modify_none_value_for_restricted_int(self):