feat: establish secure update foundation

internal/buildinfo/version.go

@@ -1,5 +1,21 @@
 package buildinfo
 
+const (
+	// UpdateProtocolVersion is returned by the privileged update agent. Version
+	// 2 requires the running version so the agent can verify it independently.
+	UpdateProtocolVersion = 2
+
+	// The contracts below are deliberately stable across normal releases. A
+	// breaking container or database change must use a new contract and cannot
+	// be installed through the unattended update path.
+	RuntimeContractVersion  = 2
+	DatabaseContractVersion = 1
+	CurrentSchemaVersion    = 11
+	MinimumUpdateVersion    = "v1.4.0"
+	MinimumAgentVersion     = "v1.4.0"
+	MinimumAgentProtocol    = 2
+)
+
 // Version is replaced through -ldflags for release images. The source fallback
 // keeps local builds and tests honest about the currently checked-out release.
-var Version = "v1.3.0"
+var Version = "v1.4.0"