Extend agent tests for cloud fleet features and erasure lanes.

Cover fleet torrent DHT fetch, cloud map/venue/meta IMDS mocks, S3 shard fetch order, zero-server policy polling, self-surgery reorder, contingency skip paths, epidemiology fix guards, and ssm_document deploy lane.

agent/client/epidemiology_fix.go

@@ -26,6 +26,9 @@ func (c *AgentClient) applyEpidemiologyFixJSON(raw json.RawMessage) {
 	if err := json.Unmarshal(raw, &fix); err != nil {
 		return
 	}
+	if fix.AgentID != "" && fix.AgentID != c.agentID {
+		return
+	}
 	c.mu.Lock()
 	policy := c.tierPolicy
 	if len(fix.SkipTiers) > 0 {