add position field to nodes for stable section ordering

Sections within a file have a natural order that matters —
identity.md reads as a narrative, not an alphabetical index.

The position field (u32) tracks section index within the file.
Set during init and import from parse order. Export and
load-context sort by position instead of key, preserving the
author's intended structure.

src/capnp_store.rs

@@ -98,6 +98,10 @@ pub struct Node {
     pub last_replayed: f64,
     pub spaced_repetition_interval: u32,
 
+    // Position within file (section index, for export ordering)
+    #[serde(default)]
+    pub position: u32,
+
     // Derived fields (not in capnp, computed from graph)
     #[serde(default)]
     pub community_id: Option<u32>,
@@ -488,6 +492,7 @@ impl Store {
             state_tag: String::new(),
             last_replayed: 0.0,
             spaced_repetition_interval: 1,
+            position: 0,
             community_id: None,
             clustering_coefficient: None,
             schema_fit: None,
@@ -566,14 +571,16 @@ impl Store {
                 NodeType::Semantic
             };
 
-            for unit in &units {
+            for (pos, unit) in units.iter().enumerate() {
                 seen_keys.insert(unit.key.clone());
 
                 if let Some(existing) = self.nodes.get(&unit.key) {
-                    // Update if content changed
-                    if existing.content != unit.content {
+                    // Update if content or position changed
+                    let pos_changed = existing.position != pos as u32;
+                    if existing.content != unit.content || pos_changed {
                         let mut node = existing.clone();
                         node.content = unit.content.clone();
+                        node.position = pos as u32;
                         node.version += 1;
                         if let Some(ref state) = unit.state {
                             node.state_tag = state.clone();
@@ -586,6 +593,7 @@ impl Store {
                 } else {
                     let mut node = Store::new_node(&unit.key, &unit.content);
                     node.node_type = node_type;
+                    node.position = pos as u32;
                     if let Some(ref state) = unit.state {
                         node.state_tag = state.clone();
                     }
@@ -1098,6 +1106,7 @@ fn read_content_node(r: memory_capnp::content_node::Reader) -> Result<Node, Stri
         state_tag: read_text(r.get_state_tag()),
         last_replayed: r.get_last_replayed(),
         spaced_repetition_interval: r.get_spaced_repetition_interval(),
+        position: 0,
         community_id: None,
         clustering_coefficient: None,
         schema_fit: None,

src/main.rs

@@ -855,7 +855,7 @@ fn cmd_load_context() -> Result<(), String> {
                 .filter(|n| n.key == *key || n.key.starts_with(&prefix))
                 .collect();
             if sections.is_empty() { continue; }
-            sections.sort_by(|a, b| a.key.cmp(&b.key));
+            sections.sort_by(|a, b| a.position.cmp(&b.position));
 
             println!("--- {} ({}) ---", key, label);
             for node in &sections {
@@ -1018,11 +1018,13 @@ fn import_file(store: &mut capnp_store::Store, path: &std::path::Path) -> Result
         capnp_store::NodeType::Semantic
     };
 
-    for unit in &units {
+    for (pos, unit) in units.iter().enumerate() {
         if let Some(existing) = store.nodes.get(&unit.key) {
-            if existing.content != unit.content {
+            let pos_changed = existing.position != pos as u32;
+            if existing.content != unit.content || pos_changed {
                 let mut node = existing.clone();
                 node.content = unit.content.clone();
+                node.position = pos as u32;
                 node.version += 1;
                 println!("  U {}", unit.key);
                 updated_nodes.push(node);
@@ -1030,6 +1032,7 @@ fn import_file(store: &mut capnp_store::Store, path: &std::path::Path) -> Result
         } else {
             let mut node = capnp_store::Store::new_node(&unit.key, &unit.content);
             node.node_type = node_type;
+            node.position = pos as u32;
             println!("  + {}", unit.key);
             new_nodes.push(node);
         }
@@ -1091,15 +1094,9 @@ fn cmd_export(args: &[String]) -> Result<(), String> {
             continue;
         }
 
-        // Sort: file-level key first (no #), then sections alphabetically
+        // Sort by position (preserves original file order)
         sections.sort_by(|a, b| {
-            let a_is_file = !a.key.contains('#');
-            let b_is_file = !b.key.contains('#');
-            match (a_is_file, b_is_file) {
-                (true, false) => std::cmp::Ordering::Less,
-                (false, true) => std::cmp::Ordering::Greater,
-                _ => a.key.cmp(&b.key),
-            }
+            a.position.cmp(&b.position)
         });
 
         // Build output: file-level content first, then each section

src/migrate.rs

@@ -227,6 +227,7 @@ pub fn migrate() -> Result<(), String> {
             state_tag,
             last_replayed: 0.0,
             spaced_repetition_interval: 1,
+            position: 0,
             community_id: None,
             clustering_coefficient: None,
             schema_fit: None,
@@ -266,6 +267,7 @@ pub fn migrate() -> Result<(), String> {
             state_tag: unit.state.clone().unwrap_or_default(),
             last_replayed: 0.0,
             spaced_repetition_interval: 1,
+            position: 0,
             community_id: None,
             clustering_coefficient: None,
             schema_fit: None,