fix(logger): prevent duplicate logs when callback raises exception

Clear _logs_since_flush before iterating callbacks by capturing logs
into a local variable first. This prevents duplicate logs if a
callback raises an exception, since the instance variable is already
cleared before any callback runs.

Add test to verify logs are cleared even when callbacks raise.

app/logger.py

@@ -39,9 +39,10 @@ class LogInterceptor(io.TextIOWrapper):
             # This is safe to ignore as write() already succeeded
             if e.errno != 22:
                 raise
-        for cb in self._flush_callbacks:
-            cb(self._logs_since_flush)
+        logs_to_send = self._logs_since_flush
         self._logs_since_flush = []
+        for cb in self._flush_callbacks:
+            cb(logs_to_send)
 
     def on_flush(self, callback):
         self._flush_callbacks.append(callback)

tests-unit/app_test/test_logger.py

@@ -132,6 +132,42 @@ class TestLogInterceptorFlush:
         assert callback2_results == [3]
         assert callback3_results == [3]
 
+    def test_flush_clears_logs_even_if_callback_raises(self):
+        """Test that logs are cleared even if a callback raises an exception."""
+        from app.logger import LogInterceptor
+
+        class MockStream:
+            def __init__(self):
+                self._buffer = io.BytesIO()
+                self.encoding = 'utf-8'
+                self.line_buffering = False
+
+            @property
+            def buffer(self):
+                return self._buffer
+
+        mock_stream = MockStream()
+        interceptor = LogInterceptor(mock_stream)
+
+        # Register a callback that raises
+        def raising_callback(logs):
+            raise ValueError("Callback error")
+
+        interceptor.on_flush(raising_callback)
+
+        # Add some logs
+        interceptor._logs_since_flush = [
+            {"t": "test", "m": "message1"},
+            {"t": "test", "m": "message2"}
+        ]
+
+        # Flush should raise but logs should still be cleared
+        with pytest.raises(ValueError, match="Callback error"):
+            interceptor.flush()
+
+        # Logs should be cleared to prevent duplicates on next flush
+        assert interceptor._logs_since_flush == []
+
 
 class TestLogInterceptorWrite:
     """Test that LogInterceptor.write() works correctly."""