Add exception logging to effect registry (Issue #14)

Effect handler exceptions now logged at ERROR level with full context:
- effect_id, source_player_id, source/target card IDs, params
- Full traceback via logger.exception()

Game still returns safe EffectResult.failure() to prevent crashes,
but debugging information is now preserved in logs.

backend/SYSTEM_REVIEW.md

@@ -227,17 +227,21 @@ Added 9 new tests covering:
 
 ---
 
-### 14. Exception Swallowing Hides Errors
-**File:** `app/core/effects/registry.py:97`
+### 14. ~~Exception Swallowing Hides Errors~~ FIXED
+**File:** `app/core/effects/registry.py:93-107`
 
-```python
-except Exception as e:
-    return EffectResult.failure(f"Effect '{effect_id}' failed: {e}")
-```
+~~This catches all exceptions including programming errors, making debugging difficult.~~
 
-This catches all exceptions including programming errors, making debugging difficult.
+**Resolution:** Added proper logging with `logger.exception()` which captures the full traceback at ERROR level. The log message now includes:
+- The effect_id that failed
+- Source player ID
+- Source and target card IDs
+- Effect parameters
+- Full exception traceback
 
-**Fix:** Log full traceback at ERROR level, or only catch expected exceptions.
+The game still returns a safe `EffectResult.failure()` to prevent crashes, but debugging information is now preserved in the logs.
+
+Added 1 test verifying that exceptions are logged with full context and traceback.
 
 ---
 

backend/app/core/effects/registry.py

@@ -22,10 +22,13 @@ the actual effect implementations, allowing cards to be defined in JSON/database
 while effect logic lives in Python.
 """
 
+import logging
 from collections.abc import Callable
 
 from app.core.effects.base import EffectContext, EffectResult
 
+logger = logging.getLogger(__name__)
+
 # Type alias for effect handler functions
 EffectHandler = Callable[[EffectContext], EffectResult]
 
@@ -93,7 +96,18 @@ def resolve_effect(effect_id: str, ctx: EffectContext) -> EffectResult:
     try:
         return handler(ctx)
     except Exception as e:
-        # Catch any exceptions from handlers to prevent game crashes
+        # Log full traceback for debugging, but return safe failure result
+        # to prevent game crashes. This preserves the exception details
+        # while allowing the game to continue gracefully.
+        logger.exception(
+            "Effect handler '%s' raised an exception. Context: source_player=%s, "
+            "source_card=%s, target_card=%s, params=%s",
+            effect_id,
+            ctx.source_player_id,
+            ctx.source_card_id,
+            ctx.target_card_id,
+            ctx.params,
+        )
         return EffectResult.failure(f"Effect '{effect_id}' failed: {e}")
 
 

backend/tests/core/test_effects/test_registry.py

@@ -233,6 +233,44 @@ class TestResolveEffect:
         assert "failed" in result.message
         assert "Intentional error" in result.message
 
+    def test_resolve_effect_logs_exceptions(self, caplog: pytest.LogCaptureFixture) -> None:
+        """
+        Verify resolve_effect logs full exception details when handler fails.
+
+        This ensures debugging information is preserved even though the game
+        continues gracefully. The log should include the effect_id, context
+        details, and the full traceback.
+        """
+        import logging
+
+        @effect_handler("logging_buggy_effect")
+        def buggy_handler(ctx: EffectContext) -> EffectResult:
+            raise ValueError("Detailed error message for logging test")
+
+        ctx = make_test_context()
+        ctx.source_card_id = "test-source-card"
+        ctx.target_card_id = "test-target-card"
+        ctx.params = {"test_param": 123}
+
+        with caplog.at_level(logging.ERROR):
+            result = resolve_effect("logging_buggy_effect", ctx)
+
+        # Verify the result is still a failure
+        assert result.success is False
+
+        # Verify the exception was logged with context
+        assert len(caplog.records) == 1
+        log_record = caplog.records[0]
+        assert log_record.levelname == "ERROR"
+        assert "logging_buggy_effect" in log_record.message
+        assert "player1" in log_record.message  # source_player_id
+        assert "test-source-card" in log_record.message
+        assert "test-target-card" in log_record.message
+
+        # Verify traceback is included (logger.exception includes exc_info)
+        assert log_record.exc_info is not None
+        assert "Detailed error message for logging test" in str(log_record.exc_info[1])
+
     def test_resolve_effect_returns_handler_result(self) -> None:
         """
         Verify resolve_effect returns the handler's result.