docs: clarify persistent storage rollback limits

Author: kvinwang

docs/security/security-model.md

@@ -24,6 +24,8 @@ dstack protects the execution environment, not your application code. Bugs in yo
 
 Infrastructure operators can still deny service. They can shut down your workload, throttle resources, or block network access. If availability matters, plan for redundancy across providers.
 
+**Persistent-storage freshness and availability.** Disk encryption protects the confidentiality of data at rest and detects unauthorized modification within the cryptographic/filesystem mechanisms in use. It does not prove that an attached disk represents the latest application state. An infrastructure operator can withhold, delete, replace, or restore an earlier valid encrypted disk image. Applications that require rollback-resistant state must anchor a monotonic version or state commitment in an external trusted service, ledger, or equivalent freshness mechanism.
+
 ## Security Guarantees
 
 ### Confidentiality