capnp_store: remove dead has_node trait method, fix fix_categories bulk write

- has_node: defined on StoreView trait but never called externally
- fix_categories: was appending ALL nodes when only changed ones needed
  persisting; now collects changed nodes and appends only those
- save_snapshot: pass log sizes from caller instead of re-statting files
- params: use Copy instead of .clone() in snapshot construction

src/capnp_store.rs

@@ -440,9 +440,6 @@ pub trait StoreView {
     /// Node content by key.
     fn node_content(&self, key: &str) -> Option<&str>;
 
-    /// Check if a node exists.
-    fn has_node(&self, key: &str) -> bool;
-
     /// Search/graph parameters.
     fn params(&self) -> Params;
 }
@@ -469,10 +466,6 @@ impl StoreView for Store {
         self.nodes.get(key).map(|n| n.content.as_str())
     }
 
-    fn has_node(&self, key: &str) -> bool {
-        self.nodes.contains_key(key)
-    }
-
     fn params(&self) -> Params {
         self.params
     }
@@ -554,10 +547,6 @@ impl StoreView for MmapView {
         snap.nodes.get(key).map(|n| &*n.content)
     }
 
-    fn has_node(&self, key: &str) -> bool {
-        self.snapshot().nodes.get(key).is_some()
-    }
-
     fn params(&self) -> Params {
         let p = &self.snapshot().params;
         Params {
@@ -608,9 +597,6 @@ impl StoreView for AnyView {
     fn node_content(&self, key: &str) -> Option<&str> {
         match self { AnyView::Mmap(v) => v.node_content(key), AnyView::Owned(s) => s.node_content(key) }
     }
-    fn has_node(&self, key: &str) -> bool {
-        match self { AnyView::Mmap(v) => v.has_node(key), AnyView::Owned(s) => s.has_node(key) }
-    }
     fn params(&self) -> Params {
         match self { AnyView::Mmap(v) => v.params(), AnyView::Owned(s) => s.params() }
     }
@@ -652,7 +638,7 @@ impl Store {
                         }
                         // Bootstrap: write rkyv snapshot if missing
                         if !snapshot_path().exists() {
-                            if let Err(e) = store.save_snapshot_inner() {
+                            if let Err(e) = store.save_snapshot(cached_nodes, cached_rels) {
                                 eprintln!("rkyv bootstrap: {}", e);
                             }
                         }
@@ -819,7 +805,7 @@ impl Store {
             .map_err(|e| format!("rename {} → {}: {}", tmp_path.display(), path.display(), e))?;
 
         // Also write rkyv snapshot (mmap-friendly)
-        if let Err(e) = self.save_snapshot_inner() {
+        if let Err(e) = self.save_snapshot(nodes_size, rels_size) {
             eprintln!("rkyv snapshot save: {}", e);
         }
 
@@ -828,20 +814,17 @@ impl Store {
 
     /// Serialize store as rkyv snapshot with staleness header.
     /// Assumes StoreLock is already held by caller.
-    fn save_snapshot_inner(&self) -> Result<(), String> {
+    fn save_snapshot(&self, nodes_size: u64, rels_size: u64) -> Result<(), String> {
         let snap = Snapshot {
             nodes: self.nodes.clone(),
             relations: self.relations.iter().filter(|r| !r.deleted).cloned().collect(),
             gaps: self.gaps.clone(),
-            params: self.params.clone(),
+            params: self.params,
         };
 
         let rkyv_data = rkyv::to_bytes::<_, 256>(&snap)
             .map_err(|e| format!("rkyv serialize: {}", e))?;
 
-        let nodes_size = fs::metadata(nodes_path()).map(|m| m.len()).unwrap_or(0);
-        let rels_size = fs::metadata(relations_path()).map(|m| m.len()).unwrap_or(0);
-
         let mut data = Vec::with_capacity(RKYV_HEADER_LEN + rkyv_data.len());
         data.extend_from_slice(&RKYV_MAGIC);
         data.extend_from_slice(&1u32.to_le_bytes());  // format version
@@ -1288,7 +1271,7 @@ impl Store {
         ];
         let obs_prefixes = ["skill-", "worked-example-"];
 
-        let mut changed = 0;
+        let mut changed_nodes = Vec::new();
         let mut unchanged = 0;
 
         let keys: Vec<String> = self.nodes.keys().cloned().collect();
@@ -1321,18 +1304,17 @@ impl Store {
                 let node = self.nodes.get_mut(key).unwrap();
                 node.category = cat;
                 node.version += 1;
-                changed += 1;
+                changed_nodes.push(node.clone());
             } else {
                 unchanged += 1;
             }
         }
 
-        if changed > 0 {
-            let updated: Vec<Node> = self.nodes.values().cloned().collect();
-            self.append_nodes(&updated)?;
+        if !changed_nodes.is_empty() {
+            self.append_nodes(&changed_nodes)?;
         }
 
-        Ok((changed, unchanged))
+        Ok((changed_nodes.len(), unchanged))
     }
 
     /// Cap node degree by soft-deleting edges from mega-hubs.