log: clear handlers on setup by default

CHANGELOG.md

@@ -19,6 +19,11 @@ and this project adheres to
 - build: Make `authors` optional in setup converter (omit `author` and
   `author_email` when not specified).
 
+### Fixed
+
+- log: Clear handlers in `setup_logger()` by default to avoid duplicate log
+  lines, with optional clear=False to keep existing handlers (#88).
+
 ## [1.8.0] - 2026-05-22
 
 ### Added

src/log/rfl/log/__init__.py

@@ -26,8 +26,13 @@ def setup_logger(
     debug_flags: Optional[List[str]] = None,
     formatter: logging.Formatter = auto_formatter(),
     component: Optional[str] = None,
+    clear: bool = True,
 ) -> None:
-    """Setup root logger debug level, debug flags and formatter."""
+    """Setup root logger debug level, debug flags and formatter.
+
+    When clear is True (default), existing root logger handlers are removed
+    before adding a new one, similarly to logging.basicConfig(force=True).
+    """
     if debug:
         logging_level = logging.DEBUG
     else:
@@ -39,6 +44,10 @@ def setup_logger(
         debug_flags = []
 
     root_logger = logging.getLogger()
+    if clear:
+        for existing_handler in root_logger.handlers[:]:
+            root_logger.removeHandler(existing_handler)
+            existing_handler.close()
     root_logger.setLevel(logging_level)
     handler = logging.StreamHandler()
     handler.setLevel(logging_level)

src/log/rfl/tests/test_setup.py

@@ -102,6 +102,21 @@ def test_setup_filter_debug_all(self):
             handler, {"name": "fail.pkg", "levelno": logging.DEBUG, "msg": "test"}
         )
 
+    def test_setup_clears_handlers(self):
+        setup_logger()
+        setup_logger()
+        logger = logging.getLogger()
+        self.assertEqual(len(logger.handlers), 1)
+
+    def test_setup_clear_false_stacks_handlers(self):
+        root_logger = logging.getLogger()
+        for handler in root_logger.handlers[:]:
+            root_logger.removeHandler(handler)
+            handler.close()
+        setup_logger(clear=False)
+        setup_logger(clear=False)
+        self.assertEqual(len(root_logger.handlers), 2)
+
 
 class TestEnforceLogger(TestLogFilterer):
     def setUp(self):