fix: implement concatenate_files operation in file_ops

Add support for concatenate_files operation which is used by the Rust
wit-bindgen wrapper to combine multiple generated binding files into a
single output file. This operation:

1. Accepts a list of source file paths to concatenate
2. Opens the destination file for writing
3. Reads and writes each source file sequentially
4. Handles errors gracefully with proper logging

This fixes the "Unknown operation type: concatenate_files" error that was
blocking CI on the Phase 4 feature branch.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: avrabe

tools/file_ops/main.go

@@ -152,6 +152,47 @@ func main() {
 			})
 			log.Printf("DEBUG: Copied directory contents from %s to %s", srcDir, destDir)
 
+		case "concatenate_files":
+			// Concatenate multiple files into one
+			srcPaths, ok := opMap["src_paths"].([]interface{})
+			if !ok {
+				log.Printf("ERROR: concatenate_files operation missing src_paths")
+				os.Exit(1)
+			}
+
+			destPath := filepath.Join(workspaceFullPath, opMap["dest_path"].(string))
+			os.MkdirAll(filepath.Dir(destPath), 0755)
+
+			// Open destination file for writing
+			destFile, err := os.Create(destPath)
+			if err != nil {
+				log.Printf("ERROR: Failed to create destination file %s: %v", destPath, err)
+				os.Exit(1)
+			}
+			defer destFile.Close()
+
+			// Concatenate each source file
+			for _, srcPath := range srcPaths {
+				srcPathStr, ok := srcPath.(string)
+				if !ok {
+					log.Printf("ERROR: Invalid source path in concatenate_files")
+					os.Exit(1)
+				}
+
+				data, err := ioutil.ReadFile(srcPathStr)
+				if err != nil {
+					log.Printf("ERROR: Failed to read source file %s: %v", srcPathStr, err)
+					os.Exit(1)
+				}
+
+				if _, err := destFile.Write(data); err != nil {
+					log.Printf("ERROR: Failed to write to destination file %s: %v", destPath, err)
+					os.Exit(1)
+				}
+			}
+
+			log.Printf("DEBUG: Concatenated %d files to %s", len(srcPaths), destPath)
+
 		default:
 			log.Printf("WARNING: Unknown operation type: %s", opType)
 		}