build(agent): molt-by#23c260 iteration

src/energiamesh/core.py

@@ -80,6 +80,8 @@ class PlanDelta:
     - updates: optional updates payload
     - timestamp: time of the delta generation
     - metadata: per-message metadata (e.g., version, source)
+    - nonce: optional cryptographic nonce for replay protection
+    - source: optional source identifier for the delta (e.g., adapter name)
     """
 
     delta: Dict[str, Any] = field(default_factory=dict)
@@ -87,6 +89,10 @@ class PlanDelta:
     updates: Dict[str, Any] = field(default_factory=dict)
     timestamp: datetime = field(default_factory=datetime.utcnow)
     metadata: Dict[str, Any] = field(default_factory=dict)
+    # Lightweight anti-replay protections; optional
+    nonce: str | None = None
+    # Optional source attribution for auditing and routing
+    source: str | None = None
 
 
 @dataclass