🌸 Cherry-pick request for #25007 into #25319 (Approved)

[dvoytenko]

Cherry-pick request

Issue	PR	Production?	RC?	Release issue
#25007	#25321	NO	YES	#25319
#25007	#25357	NO	YES	#25319

Why does this issue meet the cherry-pick criteria?

The fixes unbreak a4a ads in shadow mode, which has significant impact.

Mini-postmortem

The reason for this bug is an incorrect use of the top level window.document API which has different meaning in shadow docs, FIE, scoped services, etc.

Summary

We received the report in #25007 that A4A ads would not render at all into PWA shell. This is a regression, but is unclear when exactly it started. The issue got attention from representatives from multiple companies, indicating it was a problem breaking all users of PWA model.

Users affected	Impact
All users of A4A ads served into PWA	Ads would not render at all.

Root Causes

1. Incorrect use of window.document API instead of ampdoc.

Action Items

Action Item	Type	Owner	PR #
Prohibit window.document API	Investigate	@dvoytenko	#25418
Investigate executing realWin unit tests in shadow mode	Investigate	@dvoytenko	#25419

Lessons Learned

Things that went well

• The issue was debugged and resolved

Things that went wrong

• A fairly deep-in-the-core bug. We need better tools to prevent such bugs from happening.

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/cc @ampproject/wg-approvers @ampproject/cherry-pick-approvers
/cc @calebcordry @jeffjose

[cramforce]

Approved

[jridgewell]

/to @dvoytenko for postmortem.

[dvoytenko]

postmortem posted. /ht @calebcordry