fix(context): reject tool-output byte ceilings below the notice size

A configured tool_output_max_bytes smaller than the truncation notice
itself can't fit a bounded preview, so a persisted result could exceed the
ceiling. Enforce a config floor (ge=1024) so nonsensical values are
rejected at load time instead of being worked around at runtime.

tests/test_config_loader.py

@@ -6,10 +6,11 @@ import json
 from typing import TYPE_CHECKING
 
 import pytest
-from pydantic import AliasChoices, Field
+from pydantic import AliasChoices, Field, ValidationError
 from pydantic.fields import FieldInfo
 
 from strix.config import loader
+from strix.config.settings import ContextSettings
 
 
 if TYPE_CHECKING:
@@ -120,6 +121,22 @@ def test_read_json_overrides_uses_json_when_no_alias_in_environ(tmp_path: Path)
     assert loader._read_json_overrides(path) == {"llm": {"api_key": "sk-file"}}
 
 
+# --------------------------------------------------------------------------- #
+# ContextSettings validation
+# --------------------------------------------------------------------------- #
+
+
+def test_tool_output_max_bytes_rejects_sub_notice_values() -> None:
+    # A ceiling below the truncation notice can't fit a bounded preview, so it
+    # is rejected at load time rather than producing over-cap persisted output.
+    with pytest.raises(ValidationError):
+        ContextSettings(STRIX_TOOL_OUTPUT_MAX_BYTES=64)
+
+
+def test_tool_output_max_bytes_accepts_floor() -> None:
+    assert ContextSettings(STRIX_TOOL_OUTPUT_MAX_BYTES=1024).tool_output_max_bytes == 1024
+
+
 # --------------------------------------------------------------------------- #
 # _aliases_for
 # --------------------------------------------------------------------------- #