refactor: canonicalize vector index path via KinLayout

- Add kindb_vector_index_path() to KinLayout (.kin/kindb/graph.kvec)
- Use canonical path in backend, daemon, and snapshot loading
- Simplify offline/fallback graph opening

Author: troyjr4103

crates/kin-cli/src/backend.rs

@@ -55,7 +55,7 @@ pub fn open_kindb_snapshot(
 
 /// Path where the HNSW vector index is stored alongside the graph snapshot.
 pub fn vector_index_path(layout: &kin_core::KinLayout) -> PathBuf {
-    layout.kindb_dir().join("vector.hnsw")
+    layout.kindb_vector_index_path()
 }
 
 /// Daemon-first graph open: tries the daemon's `/graph/bootstrap` endpoint
@@ -74,9 +74,7 @@ pub async fn open_snapshot_daemon_first(
 ) -> std::result::Result<kin_db::SnapshotManager, kin_db::KinDbError> {
     // Respect explicit offline mode
     if std::env::var("KIN_OFFLINE").is_ok() {
-        let snap = open_kindb_snapshot(layout)?;
-        load_vector_index_if_exists(&snap, layout);
-        return Ok(snap);
+        return open_kindb_snapshot(layout);
     }
 
     // Try daemon bootstrap
@@ -87,25 +85,21 @@ pub async fn open_snapshot_daemon_first(
             load_vector_index_if_exists(&snap, layout);
             Ok(snap)
         }
-        None => {
-            let snap = open_kindb_snapshot(layout)?;
-            load_vector_index_if_exists(&snap, layout);
-            Ok(snap)
-        }
+        None => open_kindb_snapshot(layout),
     }
 }
 
 /// Load the persisted HNSW vector index into the graph if available.
 /// Non-fatal: if the file doesn't exist or fails to load, semantic search
 /// gracefully returns empty results.
 fn load_vector_index_if_exists(snap: &kin_db::SnapshotManager, layout: &kin_core::KinLayout) {
-    let vi_path = vector_index_path(layout);
-    if vi_path.exists() {
+    let path = vector_index_path(layout);
+    if path.exists() {
         let graph = snap.graph();
-        match graph.load_vector_index(&vi_path) {
+        match graph.load_vector_index(&path) {
             Ok(count) => {
                 if count > 0 {
-                    tracing::debug!(count, "loaded vector index from disk");
+                    tracing::debug!(count, path = %path.display(), "loaded vector index from disk");
                 }
             }
             Err(e) => {

crates/kin-core/src/layout.rs

@@ -72,6 +72,11 @@ impl KinLayout {
         self.kindb_dir().join("graph.kndb")
     }
 
+    /// `.kin/kindb/graph.kvec` — persisted vector index aligned with the snapshot.
+    pub fn kindb_vector_index_path(&self) -> PathBuf {
+        self.kindb_snapshot_path().with_extension("kvec")
+    }
+
     /// `.kin/kindb/text-index/` — Persistent tantivy text index directory.
     pub fn text_index_dir(&self) -> PathBuf {
         self.kindb_dir().join("text-index")

crates/kin-daemon/src/daemon.rs

@@ -139,7 +139,7 @@ pub async fn run(state: DaemonState, config: DaemonConfig) -> Result<()> {
                 Ok(Ok(count)) if count > 0 => {
                     info!(count, remaining = pending.saturating_sub(count), "embedded entities");
                     // Persist vector index after each batch so progress survives restarts.
-                    let vi_path = embed_state.layout.kindb_dir().join("vector.hnsw");
+                    let vi_path = embed_state.layout.kindb_vector_index_path();
                     if let Err(e) = embed_state.graph.save_vector_index(&vi_path) {
                         error!(error = %e, "failed to persist vector index");
                     }