fix(docs): rename V2 Changes subsection to Layout Notes in graph.rs

The subsection referenced the old DIND_STATE_HASH_V2 versioning
scheme which created ambiguity next to the echo:state_root:v1
header. Renamed to Layout Notes per CodeRabbit review feedback.

Author: flyingrobots

CHANGELOG.md

@@ -25,7 +25,9 @@
   knowledge as a structured implementation companion to ADR-0007.
 - **Stale Hash Domain:** Updated three stale `DIND_STATE_HASH_V2` references in
   `graph.rs` doc comment and `ADR-0007-impl.md` §2.1/§7 to match the actual
-  domain prefix `echo:state_root:v1` defined in `domain.rs`.
+  domain prefix `echo:state_root:v1` defined in `domain.rs`. Renamed the
+  adjacent `V2 Changes` subsection to `Layout Notes` to remove versioning
+  ambiguity.
 - **Module Count:** Fixed off-by-one module count in `ADR-0007-impl.md` metadata
   and §1 prose (36 → 37) and added qualifier noting tables cover key modules only.
 - **Stale Design Doc:** Deleted `docs/WARP-GRAPH.md` (1,219-line chat transcript

crates/warp-core/src/graph.rs

@@ -483,9 +483,9 @@ impl GraphStore {
     /// 4. Edge Count (u64 LE)
     /// 5. Edges (sorted by `EdgeId`): `b"E\0"` + `EdgeId` + From + To + Type + Attachment(if any)
     ///
-    /// # V2 Changes
+    /// # Layout Notes
     ///
-    /// V2 uses `u64` for all counts and lengths (node count, edge count, blob length)
+    /// Uses `u64` for all counts and lengths (node count, edge count, blob length)
     /// to align with the WSC format and avoid truncation issues with large graphs.
     #[must_use]
     pub fn canonical_state_hash(&self) -> Hash {