graph: add implicit temporal edges between episodic nodes

Compute parent/child (session→daily→weekly→monthly) and prev/next
(chronological ordering within each level) edges at graph build time
from node metadata. Parse dates from keys for digest nodes (whose
timestamps reflect creation, not covered date) and prefer key-parsed
dates over timestamp-derived dates for sessions (timezone fix).

Result: ~9185 implicit edges, communities halved, gini improved.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

poc-memory/src/store/view.rs

@@ -19,6 +19,9 @@ pub trait StoreView {
     /// Iterate all nodes. Callback receives (key, content, weight).
     fn for_each_node<F: FnMut(&str, &str, f32)>(&self, f: F);
 
+    /// Iterate all nodes with metadata. Callback receives (key, node_type, timestamp).
+    fn for_each_node_meta<F: FnMut(&str, NodeType, i64)>(&self, f: F);
+
     /// Iterate all relations. Callback receives (source_key, target_key, strength, rel_type).
     fn for_each_relation<F: FnMut(&str, &str, f32, RelationType)>(&self, f: F);
 
@@ -39,6 +42,12 @@ impl StoreView for Store {
         }
     }
 
+    fn for_each_node_meta<F: FnMut(&str, NodeType, i64)>(&self, mut f: F) {
+        for (key, node) in &self.nodes {
+            f(key, node.node_type, node.timestamp);
+        }
+    }
+
     fn for_each_relation<F: FnMut(&str, &str, f32, RelationType)>(&self, mut f: F) {
         for rel in &self.relations {
             if rel.deleted { continue; }
@@ -110,6 +119,20 @@ impl StoreView for MmapView {
         }
     }
 
+    fn for_each_node_meta<F: FnMut(&str, NodeType, i64)>(&self, mut f: F) {
+        let snap = self.snapshot();
+        for (key, node) in snap.nodes.iter() {
+            let nt = match node.node_type {
+                ArchivedNodeType::EpisodicSession => NodeType::EpisodicSession,
+                ArchivedNodeType::EpisodicDaily => NodeType::EpisodicDaily,
+                ArchivedNodeType::EpisodicWeekly => NodeType::EpisodicWeekly,
+                ArchivedNodeType::EpisodicMonthly => NodeType::EpisodicMonthly,
+                ArchivedNodeType::Semantic => NodeType::Semantic,
+            };
+            f(key, nt, node.timestamp);
+        }
+    }
+
     fn for_each_relation<F: FnMut(&str, &str, f32, RelationType)>(&self, mut f: F) {
         let snap = self.snapshot();
         for rel in snap.relations.iter() {
@@ -176,6 +199,9 @@ impl StoreView for AnyView {
     fn for_each_node<F: FnMut(&str, &str, f32)>(&self, f: F) {
         match self { AnyView::Mmap(v) => v.for_each_node(f), AnyView::Owned(s) => s.for_each_node(f) }
     }
+    fn for_each_node_meta<F: FnMut(&str, NodeType, i64)>(&self, f: F) {
+        match self { AnyView::Mmap(v) => v.for_each_node_meta(f), AnyView::Owned(s) => s.for_each_node_meta(f) }
+    }
     fn for_each_relation<F: FnMut(&str, &str, f32, RelationType)>(&self, f: F) {
         match self { AnyView::Mmap(v) => v.for_each_relation(f), AnyView::Owned(s) => s.for_each_relation(f) }
     }