store: internal locking, remove Arc<Mutex<Store>> wrapper

Store now has internal Mutex for capnp appends and AtomicU64 for
size tracking. All methods take &self. The external Arc<Mutex<Store>>
is replaced with Arc<Store>.

- Store::append_lock protects file appends
- local.rs functions take &Store (not &mut Store)
- access_local() returns Arc<Store>
- All .lock().await calls removed from callers

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/hippocampus/store/capnp.rs

@@ -269,8 +269,15 @@ impl Store {
         }
 
         // Record log sizes
-        store.loaded_nodes_size = fs::metadata(&nodes_p).map(|m| m.len()).unwrap_or(0);
-        store.loaded_rels_size = fs::metadata(&rels_p).map(|m| m.len()).unwrap_or(0);
+        use std::sync::atomic::Ordering;
+        store.loaded_nodes_size.store(
+            fs::metadata(&nodes_p).map(|m| m.len()).unwrap_or(0),
+            Ordering::Relaxed
+        );
+        store.loaded_rels_size.store(
+            fs::metadata(&rels_p).map(|m| m.len()).unwrap_or(0),
+            Ordering::Relaxed
+        );
 
         // Orphan edges filtered naturally during for_each_relation (unresolvable UUIDs skipped)
 
@@ -408,7 +415,9 @@ impl Store {
     }
 
     /// Append nodes to the log file. Returns the offset where the message was written.
-    pub fn append_nodes(&mut self, nodes: &[Node]) -> Result<u64> {
+    pub fn append_nodes(&self, nodes: &[Node]) -> Result<u64> {
+        use std::sync::atomic::Ordering;
+
         let mut msg = message::Builder::new_default();
         {
             let log = msg.init_root::<memory_capnp::node_log::Builder>();
@@ -421,6 +430,9 @@ impl Store {
         serialize::write_message(&mut buf, &msg)
             .with_context(|| format!("serialize nodes"))?;
 
+        // Lock for file append
+        let _guard = self.append_lock.lock().unwrap();
+
         let path = nodes_path();
         let file = fs::OpenOptions::new()
             .create(true).append(true).open(&path)
@@ -433,12 +445,17 @@ impl Store {
         (&file).write_all(&buf)
             .with_context(|| format!("write nodes"))?;
 
-        self.loaded_nodes_size = file.metadata().map(|m| m.len()).unwrap_or(0);
+        self.loaded_nodes_size.store(
+            file.metadata().map(|m| m.len()).unwrap_or(0),
+            Ordering::Relaxed
+        );
         Ok(offset)
     }
 
     /// Append relations to the log file.
-    pub fn append_relations(&mut self, relations: &[Relation]) -> Result<()> {
+    pub fn append_relations(&self, relations: &[Relation]) -> Result<()> {
+        use std::sync::atomic::Ordering;
+
         let mut msg = message::Builder::new_default();
         {
             let log = msg.init_root::<memory_capnp::relation_log::Builder>();
@@ -451,6 +468,9 @@ impl Store {
         serialize::write_message(&mut buf, &msg)
             .with_context(|| format!("serialize relations"))?;
 
+        // Lock for file append
+        let _guard = self.append_lock.lock().unwrap();
+
         let path = relations_path();
         let file = fs::OpenOptions::new()
             .create(true).append(true).open(&path)
@@ -459,7 +479,10 @@ impl Store {
         (&file).write_all(&buf)
             .with_context(|| format!("write relations"))?;
 
-        self.loaded_rels_size = file.metadata().map(|m| m.len()).unwrap_or(0);
+        self.loaded_rels_size.store(
+            file.metadata().map(|m| m.len()).unwrap_or(0),
+            Ordering::Relaxed
+        );
         Ok(())
     }
 

src/hippocampus/store/mod.rs

@@ -34,6 +34,8 @@ use crate::graph::{self, Graph};
 
 use anyhow::{bail, Result};
 use redb::Database;
+use std::sync::atomic::AtomicU64;
+use std::sync::Mutex;
 
 /// Strip .md suffix from a key, handling both bare keys and section keys.
 /// "identity.md" → "identity", "foo.md#section" → "foo#section", "identity" → "identity"
@@ -46,11 +48,13 @@ pub fn strip_md_suffix(key: &str) -> String {
     }
 }
 
-// The full in-memory store
+// The full in-memory store with internal locking
 pub struct Store {
     /// Log sizes at load time — used for staleness detection.
-    pub(crate) loaded_nodes_size: u64,
-    pub(crate) loaded_rels_size: u64,
+    loaded_nodes_size: AtomicU64,
+    loaded_rels_size: AtomicU64,
+    /// Protects capnp log appends (redb handles its own locking)
+    append_lock: Mutex<()>,
     /// redb index database
     pub(crate) db: Option<redb::Database>,
 }
@@ -58,8 +62,9 @@ pub struct Store {
 impl Default for Store {
     fn default() -> Self {
         Store {
-            loaded_nodes_size: 0,
-            loaded_rels_size: 0,
+            loaded_nodes_size: AtomicU64::new(0),
+            loaded_rels_size: AtomicU64::new(0),
+            append_lock: Mutex::new(()),
             db: None,
         }
     }

src/hippocampus/store/ops.rs

@@ -16,7 +16,7 @@ pub fn current_provenance() -> String {
 
 impl Store {
     /// Add or update a node (appends to log + updates index).
-    pub fn upsert_node(&mut self, mut node: Node) -> Result<()> {
+    pub fn upsert_node(&self, mut node: Node) -> Result<()> {
         if let Some(existing) = self.get_node(&node.key)? {
             node.uuid = existing.uuid;
             node.version = existing.version + 1;
@@ -30,7 +30,7 @@ impl Store {
     }
 
     /// Add a relation (appends to log + indexes)
-    pub fn add_relation(&mut self, rel: Relation) -> Result<()> {
+    pub fn add_relation(&self, rel: Relation) -> Result<()> {
         let db = self.db.as_ref().ok_or_else(|| anyhow!("store not loaded"))?;
         let txn = db.begin_write()?;
         self.append_relations(std::slice::from_ref(&rel))?;
@@ -70,13 +70,13 @@ impl Store {
     ///
     /// Provenance is determined by the POC_PROVENANCE env var if set,
     /// otherwise defaults to Manual.
-    pub fn upsert(&mut self, key: &str, content: &str) -> Result<&'static str> {
+    pub fn upsert(&self, key: &str, content: &str) -> Result<&'static str> {
         let prov = current_provenance();
         self.upsert_provenance(key, content, &prov)
     }
 
     /// Upsert with explicit provenance (for agent-created nodes).
-    pub fn upsert_provenance(&mut self, key: &str, content: &str, provenance: &str) -> Result<&'static str> {
+    pub fn upsert_provenance(&self, key: &str, content: &str, provenance: &str) -> Result<&'static str> {
         let db = self.db.as_ref().ok_or_else(|| anyhow!("store not loaded"))?;
 
         if let Some(existing) = self.get_node(key)? {
@@ -105,7 +105,7 @@ impl Store {
     }
 
     /// Soft-delete a node (appends deleted version, removes from index).
-    pub fn delete_node(&mut self, key: &str) -> Result<()> {
+    pub fn delete_node(&self, key: &str) -> Result<()> {
         let prov = current_provenance();
         let db = self.db.as_ref().ok_or_else(|| anyhow!("store not loaded"))?;
 
@@ -129,7 +129,7 @@ impl Store {
     /// Graph edges (source/target UUIDs) are unaffected — they're already
     /// UUID-based. We update the human-readable source_key/target_key strings
     /// on relations, and created_at is preserved untouched.
-    pub fn rename_node(&mut self, old_key: &str, new_key: &str) -> Result<()> {
+    pub fn rename_node(&self, old_key: &str, new_key: &str) -> Result<()> {
         if old_key == new_key {
             return Ok(());
         }
@@ -199,7 +199,7 @@ impl Store {
     }
 
     /// Cap node degree by soft-deleting edges from mega-hubs.
-    pub fn cap_degree(&mut self, max_degree: usize) -> Result<(usize, usize)> {
+    pub fn cap_degree(&self, max_degree: usize) -> Result<(usize, usize)> {
         let db = self.db.as_ref().ok_or_else(|| anyhow!("store not loaded"))?;
         let keys = index::all_keys(db)?;
 
@@ -306,7 +306,7 @@ impl Store {
     }
 
     /// Set a node's weight directly. Returns (old, new).
-    pub fn set_weight(&mut self, key: &str, weight: f32) -> Result<(f32, f32)> {
+    pub fn set_weight(&self, key: &str, weight: f32) -> Result<(f32, f32)> {
         let weight = weight.clamp(0.01, 1.0);
         let db = self.db.as_ref().ok_or_else(|| anyhow!("store not loaded"))?;
         let mut node = self.get_node(key)?
@@ -327,7 +327,7 @@ impl Store {
 
     /// Set the strength of a link between two nodes.
     /// Returns the old strength. Creates link if it doesn't exist.
-    pub fn set_link_strength(&mut self, source: &str, target: &str, strength: f32) -> Result<f32> {
+    pub fn set_link_strength(&self, source: &str, target: &str, strength: f32) -> Result<f32> {
         let strength = strength.clamp(0.01, 1.0);
 
         let source_uuid = self.get_node(source)?
@@ -372,7 +372,7 @@ impl Store {
 
     /// Add a link between two nodes with Jaccard-based initial strength.
     /// Returns the strength, or a message if the link already exists.
-    pub fn add_link(&mut self, source: &str, target: &str, provenance: &str) -> Result<f32> {
+    pub fn add_link(&self, source: &str, target: &str, provenance: &str) -> Result<f32> {
         let source_uuid = self.get_node(source)?
             .map(|n| n.uuid)
             .ok_or_else(|| anyhow!("source not found: {}", source))?;