W2-T08: lru_cache get_tool_output_limits to skip per-call config parse

tests/tools/test_tool_output_limits.py

@@ -22,6 +22,14 @@
 from tools import tool_output_limits as tol
 
 
+@pytest.fixture(autouse=True)
+def _clear_limits_cache():
+    """Ensure lru_cache is empty before every test so patches take effect."""
+    tol._invalidate_tool_output_limits_cache()
+    yield
+    tol._invalidate_tool_output_limits_cache()
+
+
 class TestDefaults:
     def test_defaults_match_previous_hardcoded_values(self):
         assert tol.DEFAULT_MAX_BYTES == 50_000
@@ -150,3 +158,22 @@ def test_pagination_default_when_config_missing(self):
         # Clamped to default MAX_LINES (2000).
         assert limit == tol.DEFAULT_MAX_LINES
         assert offset == 10
+
+
+class TestCaching:
+    """get_tool_output_limits must read config only once thanks to lru_cache."""
+
+    def test_get_tool_output_limits_cached(self):
+        """Calling get_tool_output_limits twice should invoke load_config once."""
+        with patch("hermes_cli.config.load_config", return_value={}) as mock_load:
+            tol.get_tool_output_limits()
+            tol.get_tool_output_limits()
+        mock_load.assert_called_once()
+
+    def test_invalidate_tool_output_limits_cache(self):
+        """After cache invalidation, the next call re-invokes load_config."""
+        with patch("hermes_cli.config.load_config", return_value={}) as mock_load:
+            tol.get_tool_output_limits()
+            tol._invalidate_tool_output_limits_cache()
+            tol.get_tool_output_limits()
+        assert mock_load.call_count == 2

tools/tool_output_limits.py

@@ -31,6 +31,7 @@
 
 from __future__ import annotations
 
+import functools
 from typing import Any, Dict
 
 # Hardcoded defaults — these match the pre-existing values, so adding
@@ -52,6 +53,7 @@ def _coerce_positive_int(value: Any, default: int) -> int:
     return iv
 
 
+@functools.lru_cache(maxsize=1)
 def get_tool_output_limits() -> Dict[str, int]:
     """Return resolved tool-output limits, reading ``tool_output`` from config.
 
@@ -77,6 +79,11 @@ def get_tool_output_limits() -> Dict[str, int]:
     }
 
 
+def _invalidate_tool_output_limits_cache() -> None:
+    """Clear the lru_cache on get_tool_output_limits. Intended for tests."""
+    get_tool_output_limits.cache_clear()
+
+
 def get_max_bytes() -> int:
     """Shortcut for terminal-tool callers that only need the byte cap."""
     return get_tool_output_limits()["max_bytes"]