Angular UpgradeModule: can't get element to bind during app bootstrap - angularjs

Question

I have an old AngularJS app I'm trying to implement an upgrade-in-place using the Angular 6 UpgradeModule. I can get all the code to execute -- I'm logging out states as expected through both the Angular 6 and AngularJS apps.
The problem is that I'm failing utterly to bind anything to the DOM.
All the documentation and examples use NgDoBootstrap thus, inside the core AppModule of the new Angular 6 app:
this.upgrade.bootstrap(document.body, ['angularJS-app-name'], {strictDi: true});
I can execute that. I can see my AngularJS app bootstrapping (via console.logs) via the UpgradeModule. I can see my Angular 6 app bootstrapped (via console.logs). But nothing is bound to the DOM.
Logging out document gives me the HTML document I'd expect. I can manually examine that in the Chrome console, and see all the elements I would expect to. But all document methods and properties seem to be returning null.
document.body: null.
document.getElementById('an-elementId-I-can-see-when-logging-out-document'): null.
Tell me I'm just doing something dumb like not injecting something properly so that Angular/TS is interpreting document differently than vanilla JS does.
master.app.ts
import {APP_BASE_HREF} from "#angular/common";
import {Component, NgModule, Inject} from '#angular/core';
import {BrowserModule} from '#angular/platform-browser';
import {UpgradeModule} from '#angular/upgrade/static';
import {platformBrowserDynamic} from '#angular/platform-browser-dynamic';
import {RouterModule, Routes, UrlHandlingStrategy} from '#angular/router';
#Component({
selector: 'ng6-router-root',
template: '<router-outlet></router-outlet><div class="ng-view"></div>'
})
export class Ng6RouterRoot{}
export class HybridUrlHandlingStrategy implements UrlHandlingStrategy {
shouldProcessUrl(url: any) {return false;}
extract(url:any) {return url;}
merge(url:any, whole:any) {return url;}
}
#NgModule({
declarations: [
Ng6RouterRoot
],
imports: [
BrowserModule,
UpgradeModule,
RouterModule.forRoot([])
],
providers: [
{ provide: UrlHandlingStrategy, useClass: HybridUrlHandlingStrategy },
{ provide: APP_BASE_HREF, useValue: '/' }
]
})
export class AppModule {
constructor (private upgrade: UpgradeModule) {
}
ngDoBootstrap() {
console.log('master.app.ts ngDoBootstrap start', document);
console.log('document.body', document.body);
this.upgrade.bootstrap(document.getElementById('master'), ['angularJsApp'], {strictDi: true});
console.log('master.app.ts bootstrap end');
}
}
platformBrowserDynamic().bootstrapModule(AppModule);
console.log('master.app.ts end readyState', document.readyState);
relevant html
<div id="master">
<ng6-router-root>
</ng6-router-root>
</div>