fix(tools): warn once when tools.tool_search.defer is a scalar, then use the curated default

A non-list `defer` value (e.g. `defer: todo_list`) used to be silently ignored
- the user tried to shrink the eager tool surface and got nothing back. The
parser now logs a warning naming the expected shape (a YAML list of tool names;
[] keeps every tool eager) and falls back to the curated default set.

Why: config-key fixes must fail closed and loud; #116404 was only noticed
because the key was unregistered, and a scalar value would have failed the
same silent way. Tests collapsed into one invariant covering the registered
default, list/empty-list override, and the scalar warning path.

tests/tools/test_tool_search.py

@@ -46,21 +46,25 @@ class TestConfigParsing:
         assert cfg.enabled == "auto"
         assert cfg.threshold_pct == 5.0
 
-    def test_default_defer_set_is_shared_with_config_registry(self):
+    def test_defer_default_is_the_registered_list_and_a_user_list_replaces_it(self, caplog):
+        """#116404: the curated deferral set lives in DEFAULT_CONFIG (so ``hermes config set``
+        recognizes the key); a user list replaces it wholesale, [] keeps every tool eager, and a
+        scalar is warned about (naming the expected shape) before falling back to the default."""
         from hermes_cli.config_defaults import DEFAULT_CONFIG
         from tools.tool_search import ToolSearchConfig, _DEFAULT_DEFERRED_TOOLS
 
         configured = frozenset(DEFAULT_CONFIG["tools"]["tool_search"]["defer"])
-        assert configured
+        assert isinstance(DEFAULT_CONFIG["tools"]["tool_search"]["defer"], list) and configured
         assert _DEFAULT_DEFERRED_TOOLS == configured
         assert ToolSearchConfig.from_raw(None).effective_defer_tools == configured
-
-    def test_explicit_defer_list_and_empty_list_override_default(self):
-        from tools.tool_search import ToolSearchConfig
-
         assert ToolSearchConfig.from_raw({"defer": ["terminal"]}).effective_defer_tools == {"terminal"}
         assert ToolSearchConfig.from_raw({"defer": []}).effective_defer_tools == set()
 
+        with caplog.at_level("WARNING", logger="tools.tool_search"):
+            assert ToolSearchConfig.from_raw({"defer": "todo_list"}).effective_defer_tools == configured
+        assert any("tools.tool_search.defer" in r.getMessage() and "expected a YAML list" in r.getMessage()
+                   for r in caplog.records)
+
     def test_bool_true_maps_to_auto(self):
         from tools.tool_search import ToolSearchConfig
         cfg = ToolSearchConfig.from_raw(True)

tools/tool_search.py

@@ -62,6 +62,14 @@ class ToolSearchConfig:
             raw = {"enabled": "off" if raw is False else "auto"}
         max_search_limit = _clamped_int(raw.get("max_search_limit"), 25, 1, 50)
         defer_raw = raw.get("defer")
+        if defer_raw is not None and not isinstance(defer_raw, (list, tuple, set)):
+            # Loud, then the curated default: a scalar here means the user tried to shrink the
+            # tool surface and got nothing — never silently ignore it (#116404).
+            logger.warning(
+                "tools.tool_search.defer is %r, expected a YAML list of tool names "
+                "(e.g. [todo_list, computer_use]; [] keeps every tool eager) - "
+                "using the curated default set.", defer_raw)
+            defer_raw = None
         return cls(
             enabled=_tri_state(raw.get("enabled", "auto")),
             threshold_pct=max(0.0, min(100.0, _safe_float(raw.get("threshold_pct"), 5.0))),