fix(test): clear audit severe findings — rename test_callback + add explicit assertIsNone

- test_memory_pinned.py: rename two inner 'test_callback' helpers to
  '_dummy_callback' to avoid AST auditor picking them up as no-assert tests
- test_budget.py: add self.assertIsNone(result) to the zero-cost test
  that had mock+patch but no AST-countable assertion (self.fail() didn't
  start with 'assert', so the auditor didn't count it)

Constraint: no source file modifications, targeted test fixes
Tested: audit_test_quality.py --fail-on severe exits 0
Confidence: high

Author: johnteee

tests/test_budget.py

@@ -60,7 +60,8 @@ def test_zero_cost_budget_allows_zero_cost(self) -> None:
         """0 cap allows exactly zero cost."""
         budget = RunBudget(max_estimated_cost_cents=0)
         with patch('teaagent.budget.estimate_cost_preflight', return_value=0):
-            budget.check_cost_preflight('gpt', 'gpt-4o-mini', 100, 10)
+            result = budget.check_cost_preflight('gpt', 'gpt-4o-mini', 100, 10)
+        self.assertIsNone(result)
 
     def test_budget_is_frozen(self) -> None:
         budget = RunBudget()

tests/test_memory_pinned.py

@@ -329,7 +329,7 @@ def test_file_watcher_start_stop(self, temp_root: Path) -> None:
         """Test starting and stopping the file watcher."""
         from teaagent.memory.file_watcher import FileWatcher
 
-        def test_callback(file_path: str, event_type: str) -> None:
+        def _dummy_callback(file_path: str, event_type: str) -> None:
             pass
 
         class DummyObserver:
@@ -356,7 +356,7 @@ def join(self, timeout: float | None = None) -> None:
         with patch('teaagent.memory.file_watcher.Observer', DummyObserver):
             watcher = FileWatcher(
                 root=temp_root,
-                callback=test_callback,
+                callback=_dummy_callback,
             )
 
             # Start watcher
@@ -375,12 +375,12 @@ def test_update_watched_files(self, temp_root: Path) -> None:
         """Test updating the set of watched files."""
         from teaagent.memory.file_watcher import FileWatcher
 
-        def test_callback(file_path: str, event_type: str) -> None:
+        def _dummy_callback(file_path: str, event_type: str) -> None:
             pass
 
         watcher = FileWatcher(
             root=temp_root,
-            callback=test_callback,
+            callback=_dummy_callback,
         )
 
         # Update watched files