fix(agent): preserve LoopHook error semantics when extra hooks are present

nanobot/agent/loop.py

@@ -102,6 +102,47 @@ class LoopHook(AgentHook):
         return self._loop._strip_think(content)
 
 
+class _LoopHookChain(AgentHook):
+    """Run the core loop hook first, then best-effort extra hooks.
+
+    This preserves the historical failure behavior of ``LoopHook`` while still
+    letting user-supplied hooks opt into ``CompositeHook`` isolation.
+    """
+
+    __slots__ = ("_primary", "_extras")
+
+    def __init__(self, primary: AgentHook, extra_hooks: list[AgentHook]) -> None:
+        self._primary = primary
+        self._extras = CompositeHook(extra_hooks)
+
+    def wants_streaming(self) -> bool:
+        return self._primary.wants_streaming() or self._extras.wants_streaming()
+
+    async def before_iteration(self, context: AgentHookContext) -> None:
+        await self._primary.before_iteration(context)
+        await self._extras.before_iteration(context)
+
+    async def on_stream(self, context: AgentHookContext, delta: str) -> None:
+        await self._primary.on_stream(context, delta)
+        await self._extras.on_stream(context, delta)
+
+    async def on_stream_end(self, context: AgentHookContext, *, resuming: bool) -> None:
+        await self._primary.on_stream_end(context, resuming=resuming)
+        await self._extras.on_stream_end(context, resuming=resuming)
+
+    async def before_execute_tools(self, context: AgentHookContext) -> None:
+        await self._primary.before_execute_tools(context)
+        await self._extras.before_execute_tools(context)
+
+    async def after_iteration(self, context: AgentHookContext) -> None:
+        await self._primary.after_iteration(context)
+        await self._extras.after_iteration(context)
+
+    def finalize_content(self, context: AgentHookContext, content: str | None) -> str | None:
+        content = self._primary.finalize_content(context, content)
+        return self._extras.finalize_content(context, content)
+
+
 class AgentLoop:
     """
     The agent loop is the core processing engine.
@@ -294,7 +335,7 @@ class AgentLoop:
             message_id=message_id,
         )
         hook: AgentHook = (
-            CompositeHook([loop_hook, *self._extra_hooks])
+            _LoopHookChain(loop_hook, self._extra_hooks)
             if self._extra_hooks
             else loop_hook
         )

tests/agent/test_hook_composite.py

@@ -308,6 +308,27 @@ async def test_agent_loop_extra_hook_error_isolation(tmp_path):
     assert content == "still works"
 
 
+@pytest.mark.asyncio
+async def test_agent_loop_extra_hooks_do_not_swallow_loop_hook_errors(tmp_path):
+    """Extra hooks must not change the core LoopHook failure behavior."""
+    from nanobot.providers.base import LLMResponse, ToolCallRequest
+
+    loop = _make_loop(tmp_path, hooks=[AgentHook()])
+    loop.provider.chat_with_retry = AsyncMock(return_value=LLMResponse(
+        content="working",
+        tool_calls=[ToolCallRequest(id="c1", name="list_dir", arguments={"path": "."})],
+        usage={},
+    ))
+    loop.tools.get_definitions = MagicMock(return_value=[])
+    loop.tools.execute = AsyncMock(return_value="ok")
+
+    async def bad_progress(*args, **kwargs):
+        raise RuntimeError("progress failed")
+
+    with pytest.raises(RuntimeError, match="progress failed"):
+        await loop._run_agent_loop([], on_progress=bad_progress)
+
+
 @pytest.mark.asyncio
 async def test_agent_loop_no_hooks_backward_compat(tmp_path):
     """Without hooks param, behavior is identical to before."""