Handle minimum signed varint safely

fix.txt

@@ -211,14 +211,14 @@ Priority 3: configuration, UI, and binding hardening
     atomic value to 1.0 in New, apply configured volume during connect, allow
     zero, and save volume changes.
 
-27. Config address and file error handling can panic
+[x] 27. Config address and file error handling can panic
     File: config/user_config.go
     makeHostPort splits on ':' and panics for malformed addresses or IPv6.
     fileExists dereferences info after non-ENOENT Stat failures. Replace with
     net.SplitHostPort (with explicit default-port policy) and return/report
     errors from Stat rather than dereferencing nil.
 
-28. Config SaveConfig panics and is not robust
+[x] 28. Config SaveConfig panics and is not robust
     File: config/user_config.go
     Configuration write/rename errors panic the client. Return errors to the
     caller, preserve the prior config on failure, and consider fsyncing the