Fix missing content type encoding in Record struct

Author: ekkolon

minikv-core/src/record.rs

@@ -167,18 +167,36 @@ impl Record {
 
         let mut s = String::new();
 
+        // DELETED prefix
         if self.deleted == Deleted::Soft {
             s.push_str("DELETED");
         }
 
+        // HASH prefix
         if let Some(ref h) = self.hash {
-            // Defensive check: only write well-formed hashes.
             if h.len() == Self::HASH_HEX_LEN && h.chars().all(|c| c.is_ascii_hexdigit()) {
                 s.push_str("HASH");
                 s.push_str(h);
+            } else {
+                return Err(Error::RecordDecode("invalid hash format".into()));
             }
         }
 
+        // TYPE prefix
+        if let Some(ref ct) = self.content_type {
+            if ct.is_empty() || ct.contains('|') {
+                return Err(Error::RecordDecode("invalid content type".into()));
+            }
+            s.push_str("TYPE");
+            s.push_str(ct);
+            s.push('|');
+        }
+
+        // 4. Volumes (required)
+        if self.volumes.is_empty() {
+            return Err(Error::RecordDecode("record has no volume entries".into()));
+        }
+
         s.push_str(&self.volumes.join(","));
         Ok(s.into_bytes())
     }