Infinitely hangs inserting complex document with recursive schema

[hunkydoryrepair]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Mongoose version

8.4.1+

Node.js version

20.x

MongoDB server version

5.x,6.x

Typescript version (if applicable)

5.4.5

Description

mongoose_test.zip

This test case demonstrates inserting a single document with a complex schema. it is actually simplified from out actual schema in use, and I've replace several subdocuments with Mixed. But I expect it is very likely due to the potential recursive nature of the schema.

Works as expected in version 8.2.2, 8.3.0 and 8.4.0.
Hangs in 8.4.1 - 8.6.3

Steps to Reproduce

build and run attached app.

Expected Behavior

inserts the document.

[hunkydoryrepair]

Note, when simplifying the schema and replacing other portions with .Mixed, it does not hang, leading me to believe this is not a mongo driver bug.

[hunkydoryrepair]

There appears to be an infinite loop in isDirectModified

Although, I don't understand if debugger is showing the correct values. I don't see how .join could return undefined with these values

[hunkydoryrepair]

I see...it isn't that it is INFINITE. It is just effectively infinite. We have a document 40 levels deep and the isDirectModified appears to be on order of N! (factorial). So it will run until we are all dead, but not infinitely.
I know a document 40 levels deep is extreme and we've improved our document generation techniques since this document was made. But it worked fine on earlier versions.

And I don't understand the why it would need to check each level. If it checks the top level, which recursively checks all of the sublevels, it would then need to check the sublevel separately.
I'm also confused why this even runs on a CREATE call, since nothing is modified, it is a completely new document. Hence, "create"