Add automatic folder creation for file operations and improve chat session handling

Implement `ensureFolderExists` in `ToolExecutor` to create parent directories when creating, moving, or renaming notes.
Update `ChatView` to properly persist agent mode and derive session titles from the first user message. Fix error
handling in tool execution to return structured failures instead of null, and include failure details in follow-up
messages.

tests/chat-view.test.ts

@@ -234,6 +234,18 @@ describe('ChatView', () => {
       const messages = view.contentEl.querySelectorAll('.ollama-message');
       expect(messages.length).toBe(1);
     });
+
+    it('should update the system prompt when mode selector changes', async () => {
+      await view.render();
+      const selector = view.contentEl.querySelector('.ollama-mode-selector') as HTMLSelectElement;
+      selector.appendChild(new Option('Edit', 'edit'));
+      selector.value = 'edit';
+      selector.dispatchEvent(new Event('change'));
+
+      const systemPrompt = view['conversationStateManager'].getLongTermContext()[0].content;
+      expect(view.getAgentMode()).toBe('edit');
+      expect(systemPrompt).toContain('helps edit and manage notes');
+    });
   });
 
   describe('handleUserInput', () => {
@@ -600,6 +612,8 @@ describe('ChatView', () => {
         messages: [],
         tools: [],
         assistantMessageId,
+        allToolCalls: [],
+        assistantText: 'test',
       };
 
       const followUpSpy = jest
@@ -653,6 +667,8 @@ describe('ChatView', () => {
         messages: [],
         tools: [],
         assistantMessageId,
+        allToolCalls: [],
+        assistantText: 'Proposed actions...',
       };
 
       view.cancelPendingActions();