Why isn't making my Swift app scriptable working?

Question

I'm trying to make a Swift app, 'Earwig.app', MacOS, scriptable. I've started by shamelessly stealing an example from Making Cocoa Application Scriptable Swift, adding two files, a .sdef and a .swift as listed below. I've set Scriptable and scripting definition filename in info.plist

My AppleScript is:

tell application "EarwigServer" to save in "path/to/file"

Running the script gives me an error, 'EarwigServer got an error: Can’t continue save.'

At this point I'm stuck. Any suggestions appreciated

sdef file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dictionary SYSTEM "file://localhost/System/Library/DTDs/sdef.dtd">

<dictionary title="ScriptableSwift Terminology">

    <suite name="ScriptableSwift Scripting Suite" code="SSss" description="Standard suite for application communication.">

        <command name="save" code="SSssSave" description="Save something.">
            <cocoa class="ScriptableSwift.SaveScriptCommand"/>
            <parameter name="in" code="Fpat" type="text" description="The file path in which to save the document.">
                <cocoa key="FilePath"/>
            </parameter>
            <result type="text" description="Echoes back the filepath supplied."/>
        </command>

    </suite>
</dictionary>

swift file:

import Foundation
import Cocoa

class SaveScriptCommand: NSScriptCommand {
    override func performDefaultImplementation() -> Any? {
        print( "in" )
        let filePath = self.evaluatedArguments!["FilePath"] as! String

        print( "here" )
        return filePath
    }
}

info.plist:

Answer 1

It started working when I changed ScriptableSwift.SaveScriptCommand to EarwigServer.SaveScriptCommand. Which seems obvious, I know but I'd done this before with no effect. It seems that changes don't take effect until I cleaned the build folder.

This xml works, the swift file remains unchanged:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE dictionary SYSTEM "file://localhost/System/Library/DTDs/sdef.dtd">

<dictionary title="EarwigServer Terminology">

    <suite name="EarwigServer Scripting Suite" code="ESss" description="Standard suite for application communication.">

        <command name="run" code="ESssErun" description="Save something.">
            <cocoa class="EarwigServer.SaveScriptCommand"/>

            <parameter name="in" code="Fpat" type="text" description="The file path in which to save the document.">
                <cocoa key="FilePath"/>
            </parameter>
            <result type="text" description="Echoes back the filepath supplied."/>
        </command>

    </suite>
</dictionary>

Thanks for the input