Once you are back and able. This PR is ready to be merged. @choumx @estherkim

Does this PR contain any changes other than a roll-forward of #26479?

Since .getResources() call caused type check not be able to find out the type mismatch

Do we know why this was and did we fix the root cause?

@choumx It does not contain anything else.

Do we know why this was and did we fix the root cause?

The reason is that element does not have type declaration. We have changed them to use Services.mutatorForDoc which guarantees correct type inference, so this should not happen.

The reason is that element does not have type declaration.

So this.element in base-element.js has a type of *?

Oh I see, the element used in amp-auto-lightbox.js didn't have the right type.

To catch these kinds of bugs in the future, we'd need a warning system for underspecified types. Please file an issue for this and reference it in your cherry-pick post-mortem (#26483).

@choumx make sense! created an issue.