fix: Resolve D-Bus property serialization issues

- Fix Deployments property to always return JSON string
- Resolve TypeError and ValueError in D-Bus property serialization
- Add JSON serialization for complex data structures
- Implement fallback values for empty collections
- Update TODO and changelogs to reflect completion
- Ensure full compliance with D-BUS.md and daemon-notes.md

test_dbus_properties.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+"""
+Test script to verify D-Bus properties are working correctly
+"""
+
+import dbus
+import json
+import sys
+
+def test_dbus_properties():
+    """Test D-Bus properties interface"""
+    try:
+        # Connect to system bus
+        bus = dbus.SystemBus()
+        
+        # Get the daemon object
+        daemon = bus.get_object('org.debian.aptostree1', '/org/debian/aptostree1')
+        
+        # Get the properties interface
+        props = dbus.Interface(daemon, 'org.freedesktop.DBus.Properties')
+        
+        print("Testing D-Bus properties...")
+        
+        # Test individual properties
+        properties_to_test = [
+            'Booted',
+            'Path', 
+            'ActiveTransaction',
+            'ActiveTransactionPath',
+            'Deployments',
+            'AutomaticUpdatePolicy'
+        ]
+        
+        for prop in properties_to_test:
+            try:
+                value = props.Get('org.debian.aptostree1.Sysroot', prop)
+                print(f"✓ {prop}: {value} (type: {type(value).__name__})")
+                
+                # Special check for Deployments - should be a string
+                if prop == 'Deployments':
+                    if isinstance(value, str):
+                        print(f"  ✓ Deployments is correctly returned as JSON string")
+                        try:
+                            parsed = json.loads(value)
+                            print(f"  ✓ JSON is valid: {parsed}")
+                        except json.JSONDecodeError as e:
+                            print(f"  ✗ JSON parsing failed: {e}")
+                    else:
+                        print(f"  ✗ Deployments should be a string, got {type(value).__name__}")
+                        
+            except Exception as e:
+                print(f"✗ {prop}: Error - {e}")
+        
+        # Test GetAll
+        print("\nTesting GetAll...")
+        try:
+            all_props = props.GetAll('org.debian.aptostree1.Sysroot')
+            print(f"✓ GetAll returned {len(all_props)} properties")
+            
+            # Check Deployments in GetAll
+            if 'Deployments' in all_props:
+                deployments = all_props['Deployments']
+                if isinstance(deployments, str):
+                    print(f"✓ Deployments in GetAll is correctly a JSON string")
+                else:
+                    print(f"✗ Deployments in GetAll should be a string, got {type(deployments).__name__}")
+            else:
+                print("✗ Deployments not found in GetAll")
+                
+        except Exception as e:
+            print(f"✗ GetAll failed: {e}")
+            
+    except Exception as e:
+        print(f"Failed to connect to D-Bus: {e}")
+        return False
+    
+    return True
+
+if __name__ == "__main__":
+    print("Testing apt-ostree D-Bus properties...")
+    success = test_dbus_properties()
+    sys.exit(0 if success else 1)