feat(rules): add data synchronization guidelines to backend-logic

.cursor/rules/backend-logic.mdc

@@ -11,6 +11,8 @@ When implementing features that involve business logic:
    - Timestamp management
    - Access control and authorization
    - Complex calculations or data transformations
+   - Relationship management and graph traversal
+   - Link extraction and validation
 
 2. Frontend should only handle:
    - UI state management
@@ -18,6 +20,7 @@ When implementing features that involve business logic:
    - Data display and formatting
    - Basic input validation for UX
    - UI-specific transformations
+   - Relationship visualization
 
 3. Security-sensitive operations must always be in backend:
    - Cryptographic operations
@@ -31,9 +34,17 @@ When implementing features that involve business logic:
    - If it needs to work without JavaScript → backend
    - If it's purely for display/interaction → frontend
 
+5. Data synchronization guidelines:
+   - Backend owns the source of truth for relationships
+   - Frontend should never compute relationships locally
+   - Use backend-provided relationship data for display
+   - Cache relationship data in frontend stores
+   - Update relationship cache on mutations
+   - Preload relationships when beneficial for UX
+
 metadata:
   priority: high
-  version: 1.0
+  version: 1.1
 </rule>
 
 examples:
@@ -54,3 +65,10 @@ examples:
       if (response.status === 403) {
         showError('Not authorized');
       }
+
+  - input: |
+      # Bad: Computing relationships in frontend
+      const links = content.match(/\[\[(.*?)\]\]/g);
+    output: |
+      // Use backend-provided relationships
+      const { linksTo, linkedBy } = await api.getNote(id);