docs: clarify checksum ranges in encoding spec

Fix xxHash32 document checksum example to hash bytes[20..] (encode mode + body).\n\nClarify SSTable block meta checksum excludes the initial block count.\n\nCo-authored-by: lody <agent@lody.ai>

Author: codex

docs/encoding-xxhash32.md

@@ -164,9 +164,9 @@ function verifyLoroDocument(bytes) {
   // Read stored checksum (bytes 16-20, little-endian)
   const storedChecksum = readU32LE(bytes, 16);
 
-  // Calculate checksum of body (bytes 22+)
-  const body = bytes.slice(22);
-  const calculatedChecksum = xxHash32(body, 0x4F524F4C);
+  // Calculate checksum of encode_mode + body (bytes 20+)
+  const payload = bytes.slice(20);
+  const calculatedChecksum = xxHash32(payload, 0x4F524F4C);
 
   if (storedChecksum !== calculatedChecksum) {
     throw new Error("Checksum mismatch");

docs/encoding.md

@@ -222,7 +222,7 @@ Both `oplog_bytes` and `state_bytes` use a KV Store format based on SSTable (Sor
 │ variable      │   last_key (bytes) - only if !is_large          │
 ├───────────────┼─────────────────────────────────────────────────┤
 │ 4             │ Checksum (xxHash32, little-endian)              │
-│               │ Covers all block meta entries                   │
+│               │ Covers all block meta entries (excluding count) │
 └───────────────┴─────────────────────────────────────────────────┘
 ```