feat: US-002 - Modify Tool interface to return *ToolResult

- Update all Tool implementations to return *ToolResult instead of (string, error)
- ShellTool: returns UserResult for command output, ErrorResult for failures
- SpawnTool: returns NewToolResult on success, ErrorResult on failure
- WebTool: returns ToolResult with ForUser=content, ForLLM=summary
- EditTool: returns SilentResult for silent edits, ErrorResult on failure
- FilesystemTool: returns SilentResult/NewToolResult for operations, ErrorResult on failure
- Temporarily disable cronTool in main.go (will be re-enabled in US-016)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pkg/tools/edit.go

@@ -50,20 +50,20 @@ func (t *EditFileTool) Parameters() map[string]interface{} {
 	}
 }
 
-func (t *EditFileTool) Execute(ctx context.Context, args map[string]interface{}) (string, error) {
+func (t *EditFileTool) Execute(ctx context.Context, args map[string]interface{}) *ToolResult {
 	path, ok := args["path"].(string)
 	if !ok {
-		return "", fmt.Errorf("path is required")
+		return ErrorResult("path is required")
 	}
 
 	oldText, ok := args["old_text"].(string)
 	if !ok {
-		return "", fmt.Errorf("old_text is required")
+		return ErrorResult("old_text is required")
 	}
 
 	newText, ok := args["new_text"].(string)
 	if !ok {
-		return "", fmt.Errorf("new_text is required")
+		return ErrorResult("new_text is required")
 	}
 
 	// Resolve path and enforce directory restriction if configured
@@ -73,7 +73,7 @@ func (t *EditFileTool) Execute(ctx context.Context, args map[string]interface{})
 	} else {
 		abs, err := filepath.Abs(path)
 		if err != nil {
-			return "", fmt.Errorf("failed to resolve path: %w", err)
+			return ErrorResult(fmt.Sprintf("failed to resolve path: %v", err))
 		}
 		resolvedPath = abs
 	}
@@ -82,40 +82,40 @@ func (t *EditFileTool) Execute(ctx context.Context, args map[string]interface{})
 	if t.allowedDir != "" {
 		allowedAbs, err := filepath.Abs(t.allowedDir)
 		if err != nil {
-			return "", fmt.Errorf("failed to resolve allowed directory: %w", err)
+			return ErrorResult(fmt.Sprintf("failed to resolve allowed directory: %v", err))
 		}
 		if !strings.HasPrefix(resolvedPath, allowedAbs) {
-			return "", fmt.Errorf("path %s is outside allowed directory %s", path, t.allowedDir)
+			return ErrorResult(fmt.Sprintf("path %s is outside allowed directory %s", path, t.allowedDir))
 		}
 	}
 
 	if _, err := os.Stat(resolvedPath); os.IsNotExist(err) {
-		return "", fmt.Errorf("file not found: %s", path)
+		return ErrorResult(fmt.Sprintf("file not found: %s", path))
 	}
 
 	content, err := os.ReadFile(resolvedPath)
 	if err != nil {
-		return "", fmt.Errorf("failed to read file: %w", err)
+		return ErrorResult(fmt.Sprintf("failed to read file: %v", err))
 	}
 
 	contentStr := string(content)
 
 	if !strings.Contains(contentStr, oldText) {
-		return "", fmt.Errorf("old_text not found in file. Make sure it matches exactly")
+		return ErrorResult("old_text not found in file. Make sure it matches exactly")
 	}
 
 	count := strings.Count(contentStr, oldText)
 	if count > 1 {
-		return "", fmt.Errorf("old_text appears %d times. Please provide more context to make it unique", count)
+		return ErrorResult(fmt.Sprintf("old_text appears %d times. Please provide more context to make it unique", count))
 	}
 
 	newContent := strings.Replace(contentStr, oldText, newText, 1)
 
 	if err := os.WriteFile(resolvedPath, []byte(newContent), 0644); err != nil {
-		return "", fmt.Errorf("failed to write file: %w", err)
+		return ErrorResult(fmt.Sprintf("failed to write file: %v", err))
 	}
 
-	return fmt.Sprintf("Successfully edited %s", path), nil
+	return SilentResult(fmt.Sprintf("File edited: %s", path))
 }
 
 type AppendFileTool struct{}
@@ -149,28 +149,28 @@ func (t *AppendFileTool) Parameters() map[string]interface{} {
 	}
 }
 
-func (t *AppendFileTool) Execute(ctx context.Context, args map[string]interface{}) (string, error) {
+func (t *AppendFileTool) Execute(ctx context.Context, args map[string]interface{}) *ToolResult {
 	path, ok := args["path"].(string)
 	if !ok {
-		return "", fmt.Errorf("path is required")
+		return ErrorResult("path is required")
 	}
 
 	content, ok := args["content"].(string)
 	if !ok {
-		return "", fmt.Errorf("content is required")
+		return ErrorResult("content is required")
 	}
 
 	filePath := filepath.Clean(path)
 
 	f, err := os.OpenFile(filePath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
 	if err != nil {
-		return "", fmt.Errorf("failed to open file: %w", err)
+		return ErrorResult(fmt.Sprintf("failed to open file: %v", err))
 	}
 	defer f.Close()
 
 	if _, err := f.WriteString(content); err != nil {
-		return "", fmt.Errorf("failed to append to file: %w", err)
+		return ErrorResult(fmt.Sprintf("failed to append to file: %v", err))
 	}
 
-	return fmt.Sprintf("Successfully appended to %s", path), nil
+	return SilentResult(fmt.Sprintf("Appended to %s", path))
 }