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/src/queue.py

@@ -1,13 +1,18 @@
 """Queue manager for issue coordination."""
 
 import json
+import logging
+import shutil
 from dataclasses import dataclass, field
+from datetime import datetime
 from enum import Enum
 from pathlib import Path
 from typing import Any
 
 from src.models import IssueMetadata
 
+logger = logging.getLogger(__name__)
+
 
 class QueueItemStatus(str, Enum):
     """Status of a queue item."""
@@ -229,6 +234,40 @@ class QueueManager:
 
             # Update ready status after loading
             self._update_ready_status()
-        except (json.JSONDecodeError, KeyError, ValueError):
-            # If file is corrupted, start with empty queue
-            self._items = {}
+        except (json.JSONDecodeError, KeyError, ValueError) as e:
+            # Log corruption details and create backup before discarding
+            self._handle_corrupted_queue(e)
+
+    def _handle_corrupted_queue(self, error: Exception) -> None:
+        """Handle corrupted queue file by logging, backing up, and resetting.
+
+        Args:
+            error: The exception that was raised during loading
+        """
+        # Log error with details
+        logger.error(
+            "Queue file corruption detected in '%s': %s - %s",
+            self.queue_file,
+            type(error).__name__,
+            str(error),
+        )
+
+        # Create backup of corrupted file with timestamp
+        if self.queue_file.exists():
+            timestamp = datetime.now().strftime("%Y%m%d_%H%M%S")
+            backup_path = self.queue_file.with_suffix(f".corrupted.{timestamp}.json")
+            try:
+                shutil.copy2(self.queue_file, backup_path)
+                logger.error(
+                    "Corrupted queue file backed up to '%s'",
+                    backup_path,
+                )
+            except OSError as backup_error:
+                logger.error(
+                    "Failed to create backup of corrupted queue file: %s",
+                    backup_error,
+                )
+
+        # Reset to empty queue
+        self._items = {}
+        logger.error("Queue reset to empty state after corruption")