fix(#338): Log queue corruption and backup corrupted file

- Log ERROR when queue corruption detected with error details
- Create timestamped backup before discarding corrupted data
- Add comprehensive tests for corruption handling

Refs #338

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/coordinator/tests/test_queue.py

@@ -474,3 +474,142 @@ class TestQueueManager:
         item = queue_manager.get_item(159)
         assert item is not None
         assert item.status == QueueItemStatus.COMPLETED
+
+
+class TestQueueCorruptionHandling:
+    """Tests for queue file corruption handling."""
+
+    @pytest.fixture
+    def temp_queue_file(self) -> Generator[Path, None, None]:
+        """Create a temporary file for queue persistence."""
+        with tempfile.NamedTemporaryFile(mode="w", delete=False, suffix=".json") as f:
+            temp_path = Path(f.name)
+        yield temp_path
+        # Cleanup - remove main file and any backup files
+        if temp_path.exists():
+            temp_path.unlink()
+        # Clean up backup files
+        for backup in temp_path.parent.glob(f"{temp_path.stem}.corrupted.*.json"):
+            backup.unlink()
+
+    def test_corrupted_json_logs_error_and_creates_backup(
+        self, temp_queue_file: Path, caplog: pytest.LogCaptureFixture
+    ) -> None:
+        """Test that corrupted JSON file triggers logging and backup creation."""
+        # Write invalid JSON to the file
+        with open(temp_queue_file, "w") as f:
+            f.write("{ invalid json content }")
+
+        import logging
+
+        with caplog.at_level(logging.ERROR):
+            queue_manager = QueueManager(queue_file=temp_queue_file)
+
+        # Verify queue is empty after corruption
+        assert queue_manager.size() == 0
+
+        # Verify error was logged
+        assert "Queue file corruption detected" in caplog.text
+        assert "JSONDecodeError" in caplog.text
+
+        # Verify backup file was created
+        backup_files = list(temp_queue_file.parent.glob(f"{temp_queue_file.stem}.corrupted.*.json"))
+        assert len(backup_files) == 1
+        assert "Corrupted queue file backed up" in caplog.text
+
+        # Verify backup contains original corrupted content
+        with open(backup_files[0]) as f:
+            backup_content = f.read()
+        assert "invalid json content" in backup_content
+
+    def test_corrupted_structure_logs_error_and_creates_backup(
+        self, temp_queue_file: Path, caplog: pytest.LogCaptureFixture
+    ) -> None:
+        """Test that valid JSON with invalid structure triggers logging and backup."""
+        # Write valid JSON but with missing required fields
+        with open(temp_queue_file, "w") as f:
+            json.dump(
+                {
+                    "items": [
+                        {
+                            "issue_number": 159,
+                            # Missing "status", "ready", "metadata" fields
+                        }
+                    ]
+                },
+                f,
+            )
+
+        import logging
+
+        with caplog.at_level(logging.ERROR):
+            queue_manager = QueueManager(queue_file=temp_queue_file)
+
+        # Verify queue is empty after corruption
+        assert queue_manager.size() == 0
+
+        # Verify error was logged (KeyError for missing fields)
+        assert "Queue file corruption detected" in caplog.text
+        assert "KeyError" in caplog.text
+
+        # Verify backup file was created
+        backup_files = list(temp_queue_file.parent.glob(f"{temp_queue_file.stem}.corrupted.*.json"))
+        assert len(backup_files) == 1
+
+    def test_invalid_status_value_logs_error_and_creates_backup(
+        self, temp_queue_file: Path, caplog: pytest.LogCaptureFixture
+    ) -> None:
+        """Test that invalid enum value triggers logging and backup."""
+        # Write valid JSON but with invalid status enum value
+        with open(temp_queue_file, "w") as f:
+            json.dump(
+                {
+                    "items": [
+                        {
+                            "issue_number": 159,
+                            "status": "invalid_status",
+                            "ready": True,
+                            "metadata": {
+                                "estimated_context": 50000,
+                                "difficulty": "medium",
+                                "assigned_agent": "sonnet",
+                                "blocks": [],
+                                "blocked_by": [],
+                            },
+                        }
+                    ]
+                },
+                f,
+            )
+
+        import logging
+
+        with caplog.at_level(logging.ERROR):
+            queue_manager = QueueManager(queue_file=temp_queue_file)
+
+        # Verify queue is empty after corruption
+        assert queue_manager.size() == 0
+
+        # Verify error was logged (ValueError for invalid enum)
+        assert "Queue file corruption detected" in caplog.text
+        assert "ValueError" in caplog.text
+
+        # Verify backup file was created
+        backup_files = list(temp_queue_file.parent.glob(f"{temp_queue_file.stem}.corrupted.*.json"))
+        assert len(backup_files) == 1
+
+    def test_queue_reset_logged_after_corruption(
+        self, temp_queue_file: Path, caplog: pytest.LogCaptureFixture
+    ) -> None:
+        """Test that queue reset is logged after handling corruption."""
+        # Write invalid JSON
+        with open(temp_queue_file, "w") as f:
+            f.write("not valid json")
+
+        import logging
+
+        with caplog.at_level(logging.ERROR):
+            QueueManager(queue_file=temp_queue_file)
+
+        # Verify the reset was logged
+        assert "Queue reset to empty state after corruption" in caplog.text