Unity 2021 Editor crash on startup with 8.5.0 Firebase SDK

A skeleton project set up with Firebase App and Firebase Auth crashes Unity 2021.2 immediately on startup. The relevant error from the Editor.log is thus:

* Assertion at loader.c:345, condition `is_ok (error)' not met, function:mono_field_from_token, Could not resolve field token 0x0400001c, due to: Could not load type of field 'Firebase.Editor.GenerateXmlFromGoogleServicesJson:<>f__mg$cache0' (17) due to: Could not load file or assembly 'Google.JarResolver, Version=1.2.0.0, Culture=neutral, PublicKeyToken=null' or one of its dependencies. assembly:/Users/mdb/projects/bugs/unity-2021-firebase-files/Library/PackageCache/com.google.firebase.app@25e0485ee6cf-1636337084685/Firebase/Editor/Firebase.Editor.dll type:GenerateXmlFromGoogleServicesJson member:(null)

You can clone this repo: https://github.com/samskivert/unity-2021-firebase-crash and then put the requisite .tgz files from https://developers.google.com/unity/archive into GooglePackages in the top-level directory to repro the crash:

GooglePackages/com.google.external-dependency-manager-1.2.167.tgz
GooglePackages/com.google.firebase.app-8.5.0.tgz
GooglePackages/com.google.firebase.auth-8.5.0.tgz

Notably it does not happen if the Unity SDK is added via the .unitypackage files, so something about installing the SDK via the package manager is tickling the bug.

I have not been able to devise a workaround, so it prevents us from upgrading from Unity 2020 (where it works) to Unity 2021 (where it crashes on startup).

[ewnu]

still suffers from this issue in 8.6.2

[samskivert]

FWIW if you’re just making a cursory examination of the error message Google.JarResolver.dll does exist, at the right location and it is the right version. So I think the or one of its dependencies is the pertinent information here, but Mono helpfully does not tell us what downstream dependency is sticking a fork in things.