feat: add safe miner control foundation

backend/app/agent_commands/exceptions.py

@@ -0,0 +1,17 @@
+"""Domain-neutral Agent command protocol errors."""
+
+
+class AgentCommandError(Exception):
+    """Base Agent command protocol error."""
+
+
+class AgentCommandNotFound(AgentCommandError):
+    """The submitted command identifier is unknown."""
+
+
+class AgentCommandConflict(AgentCommandError):
+    """The queue row cannot accept the requested transition."""
+
+
+class AgentResultValidationError(AgentCommandError):
+    """The Agent result does not match its command contract."""