test(rules): locate the pre-tool arm by what it does, not by its name (#4633)

CI run 712 failed test_neither_rule_arm_logs_its_call_behind_a_results_guard
with "min() iterable argument is empty": the guard walked the function named
build_tool_rule_hint, which since fd2ebf4 is a wrapper that searches nothing
— the arm's body moved to _tool_rule_hint. The property it guards (the call
is logged before any early return) still held; the guard had pinned a name.

It now finds the async function that calls semantic_search_rules under the
pre_tool_rule source, so a later rename moves the guard with the arm instead
of emptying it (rule 167).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_rule_usage_wiring.py

@@ -908,9 +908,23 @@ def test_neither_rule_arm_logs_its_call_behind_a_results_guard():
     #
     # The property is positional: between the search and the first guard that
     # can return early, the call row has already been written.
+    # The arm's BODY, which since #4633 lives in `_tool_rule_hint`; the public
+    # `build_tool_rule_hint` is a wrapper that adds the via-lesson step and
+    # searches nothing itself. Located by what it does — the function that
+    # calls the rule search under the pre_tool_rule source — so the next
+    # rename moves the guard with it instead of emptying it.
     fn = next(
         n for n in ast.walk(ast.parse(pc_src))
-        if isinstance(n, ast.AsyncFunctionDef) and n.name == "build_tool_rule_hint"
+        if isinstance(n, ast.AsyncFunctionDef)
+        and any(
+            isinstance(c, ast.Call) and getattr(c.func, "id", None) == "semantic_search_rules"
+            for c in ast.walk(n)
+        )
+        and any(
+            isinstance(k, ast.keyword) and k.arg == "source"
+            and isinstance(k.value, ast.Constant) and k.value.value == "pre_tool_rule"
+            for k in ast.walk(n)
+        )
     )
     search_at = min(
         n.lineno for n in ast.walk(fn)
@@ -929,7 +943,7 @@ def test_neither_rule_arm_logs_its_call_behind_a_results_guard():
         and any(isinstance(b, ast.Return) for b in n.body)
     ]
     assert bailouts, (
-        "no early return found after the search in build_tool_rule_hint — the "
+        "no early return found after the search in the pre-tool arm — the "
         "guard has nothing left to protect, which means this test is now "
         "passing vacuously rather than the arm being correct"
     )