Add action preview builder for write tool confirmation

Introduces `ActionPreviewBuilder` to generate before/after previews for
destructive operations. Write tools are now deferred with apply/cancel
UI instead of executing immediately. Includes `ProposedAction` type,
CSS for diff views, and state management in `ChatView`.

tests/chat-view.test.ts

@@ -6,7 +6,12 @@ import { ErrorHandler } from '../src/error-handler';
 interface MockVault {
   getMarkdownFiles: () => any[];
   read: () => Promise<string>;
+  cachedRead: () => Promise<string>;
+  getAbstractFileByPath: () => any;
   create: () => Promise<any>;
+  modify: () => Promise<void>;
+  rename: () => Promise<void>;
+  delete: () => Promise<void>;
 }
 interface MockWorkspace {
   getLeaf: () => any;
@@ -67,11 +72,17 @@ describe('ChatView', () => {
   let mockApp: MockApp;
 
   beforeEach(() => {
+    jest.clearAllMocks();
     mockApp = {
       vault: {
         getMarkdownFiles: jest.fn().mockReturnValue([]),
         read: jest.fn().mockResolvedValue(''),
+        cachedRead: jest.fn().mockResolvedValue(''),
+        getAbstractFileByPath: jest.fn().mockReturnValue(null),
         create: jest.fn().mockResolvedValue(null),
+        modify: jest.fn().mockResolvedValue(undefined),
+        rename: jest.fn().mockResolvedValue(undefined),
+        delete: jest.fn().mockResolvedValue(undefined),
       },
       workspace: {
         getLeaf: jest.fn(),
@@ -388,7 +399,7 @@ describe('ChatView', () => {
       expect(lastMessage.isStreaming).toBe(false);
     });
 
-    it('should process tool calls with follow-up context', async () => {
+    it('should show preview for write tool calls and defer follow-up', async () => {
       view['sendButton'] = document.createElement('button');
       view['inputEl'] = document.createElement('textarea');
       (view['inputEl'] as HTMLTextAreaElement).value = 'test';
@@ -413,12 +424,136 @@ describe('ChatView', () => {
       const followUpSpy = jest
         .spyOn(view['ollamaClient'], 'chat')
         .mockResolvedValue({ role: 'assistant', content: ' follow-up' });
+
+      // Mock preview builder
+      jest.spyOn(view['actionPreviewBuilder'], 'buildPreview').mockResolvedValue({
+        id: 'tool_1',
+        toolCall: {
+          id: 'tool_1',
+          type: 'function',
+          function: {
+            name: 'create_file',
+            arguments: '{"path":"test/file.md","content":"Test content"}',
+          },
+        } as unknown as any,
+        operation: 'create',
+        path: 'test/file.md',
+        description: 'Create note: test/file.md',
+        preview: { after: 'Test content' },
+        status: 'pending',
+      });
+
       await (view as any).handleUserInput('test');
-      expect(followUpSpy).toHaveBeenCalled();
-      // Verify that tool calls resulted in follow-up messages
+      expect(chatSpy).toHaveBeenCalled();
+      // With write tools, follow-up should be deferred until apply
+      expect(followUpSpy).not.toHaveBeenCalled();
+      expect((view as any).pendingActions.length).toBe(1);
       expect((view as any).messages.length).toBeGreaterThan(1);
     });
 
+    it('should apply pending actions and trigger follow-up', async () => {
+      view['sendButton'] = document.createElement('button');
+      view['inputEl'] = document.createElement('textarea');
+      (view['inputEl'] as HTMLTextAreaElement).value = 'test';
+      const assistantMessageId = 'test-assistant-id';
+      view['messages'] = [
+        {
+          id: 'user-id',
+          role: 'user',
+          content: 'test',
+          timestamp: Date.now(),
+        },
+        {
+          id: assistantMessageId,
+          role: 'assistant',
+          content: 'test',
+          timestamp: Date.now(),
+          isStreaming: false,
+        },
+      ];
+
+      view['pendingActions'] = [
+        {
+          id: 'tool_1',
+          toolCall: {
+            id: 'tool_1',
+            type: 'function',
+            function: {
+              name: 'create_file',
+              arguments: '{"path":"test/file.md","content":"Test content"}',
+            },
+          } as unknown as any,
+          operation: 'create',
+          path: 'test/file.md',
+          description: 'Create note: test/file.md',
+          status: 'pending',
+        },
+      ];
+      view['pendingReadResults'] = [];
+      view['pendingFollowUpContext'] = {
+        messages: [],
+        tools: [],
+        assistantMessageId,
+      };
+
+      const followUpSpy = jest
+        .spyOn(view['ollamaClient'], 'chat')
+        .mockResolvedValue({ role: 'assistant', content: ' follow-up' });
+
+      const toolExecutor = view['toolExecutor'];
+      jest.spyOn(toolExecutor, 'handleToolCall').mockResolvedValue({
+        success: true,
+        message: 'Note created successfully',
+      });
+
+      await view.applyPendingActions();
+      expect(followUpSpy).toHaveBeenCalled();
+      expect((view as any).pendingActions.length).toBe(0);
+    });
+
+    it('should cancel pending actions', async () => {
+      view['sendButton'] = document.createElement('button');
+      view['inputEl'] = document.createElement('textarea');
+      (view['inputEl'] as HTMLTextAreaElement).value = 'test';
+      const assistantMessageId = 'test-assistant-id';
+      view['messages'] = [
+        {
+          id: assistantMessageId,
+          role: 'assistant',
+          content: 'Proposed actions...',
+          timestamp: Date.now(),
+          isStreaming: false,
+        },
+      ];
+      view['pendingActions'] = [
+        {
+          id: 'tool_1',
+          toolCall: {
+            id: 'tool_1',
+            type: 'function',
+            function: {
+              name: 'create_file',
+              arguments: '{"path":"test.md","content":"test"}',
+            },
+          } as unknown as any,
+          operation: 'create',
+          path: 'test.md',
+          description: 'Create note: test.md',
+          status: 'pending',
+        },
+      ];
+      view['pendingFollowUpContext'] = {
+        messages: [],
+        tools: [],
+        assistantMessageId,
+      };
+
+      view.cancelPendingActions();
+      const msg = (view as any).messages.find((m: any) => m.id === assistantMessageId);
+      expect(msg.content).toContain('cancelled');
+      expect((view as any).pendingActions.length).toBe(0);
+    });
+
     it('should handle tool call errors gracefully and continue with partial results', async () => {
       view['sendButton'] = document.createElement('button');
       view['inputEl'] = document.createElement('textarea');
@@ -449,14 +584,31 @@ describe('ChatView', () => {
         tool_calls: [],
       });
 
-      // Mock tool executor to return mixed results
+      // Mock preview builder for write tool
+      jest.spyOn(view['actionPreviewBuilder'], 'buildPreview').mockResolvedValue({
+        id: 'call_1',
+        toolCall: {
+          id: 'call_1',
+          type: 'function',
+          function: {
+            name: 'create_file',
+            arguments: '{"path":"test.md","content":"test"}',
+          },
+        } as unknown as any,
+        operation: 'create',
+        path: 'test.md',
+        description: 'Create note: test.md',
+        preview: { after: 'test' },
+        status: 'pending',
+      });
+
+      // Mock tool executor — read tool fails
       const toolExecutor = view['toolExecutor'];
       jest.spyOn(toolExecutor, 'handleToolCall').mockImplementation(async (call) => {
-        if (call.function.name === 'create_file') {
-          return { success: true, message: 'Note created successfully' };
-        } else {
+        if (call.function.name === 'nonexistent_tool') {
           throw new Error('Tool not found');
         }
+        return { success: true, message: 'Done' };
       });
 
       const consoleSpy = jest.spyOn(console, 'error').mockImplementation(() => {});
@@ -465,7 +617,8 @@ describe('ChatView', () => {
       await (view as any).handleUserInput('test');
 
       expect(chatSpy).toHaveBeenCalled();
-      expect(followUpSpy).toHaveBeenCalled(); // Should still call follow-up with partial results
+      // Write tools trigger preview, not immediate follow-up
+      expect(followUpSpy).not.toHaveBeenCalled();
       expect(errorHandlerSpy).toHaveBeenCalledWith(expect.any(Error), 'ChatView.handleUserInput');
       expect((view as any).messages.length).toBeGreaterThan(1);
       consoleSpy.mockRestore();