auto-coder: validate file presence before executing coding command

- Add a check to ensure files are added before executing the coding command
- Return an error message if no files are added, guiding users to use the /add command first

Signed-off-by: codiing-hui <wecoding@yeah.net>

Author: coding-hui

internal/ui/coders/commands.go

@@ -225,6 +225,10 @@ func (c *CommandExecutor) dropFiles(_ context.Context, _ ...string) error {
 }
 
 func (c *CommandExecutor) coding(ctx context.Context, args ...string) error {
+	if len(c.coder.absFileNames) == 0 {
+		return errbook.New("No files added. Please use /add to add files first")
+	}
+
 	addedFiles, err := c.getAddedFileContent()
 	if err != nil {
 		return err