How to diagnose spurious SwiftDataMacros error

I have a Package.swift file that builds and runs from Xcode 15.2 without issue but fails to compile when built from the command line ("swift build"). The swift version is 6.0.3. I'm at wits end trying to diagnose this and would welcome any thoughts.

The error in question is

error: external macro implementation type 'SwiftDataMacros.PersistentModelMacro' could not be found for macro 'Model()'; plugin for module 'SwiftDataMacros' not found

The code associated with the module is very vanilla.

import Foundation
import SwiftData

@Model
public final class MyObject {
    @Attribute(.unique) public var id:Int64
    public var vertexID:Int64
    public var updatedAt:Date
    public var codeUSRA:Int32

    init(id:Int64, vertexID:Int64, updatedAt:Date, codeUSRA:Int32) {
        self.id = id
        self.vertexID = vertexID
        self.updatedAt = updatedAt
        self.codeUSRA = codeUSRA
    }
    
    public static func create(id:Int64, vertexID:Int64, updatedAt:Date, codeUSRA:Int32) -> MyObject {
        MyObject(id: id, vertexID: vertexID, updatedAt: updatedAt, codeUSRA: codeUSRA)
    }
}

Thank you.