> Yes, someone in customs at an airport can be treated as functionally “at the border” with reduced protections. But you are conflating seeking entry with being present inside the country. That’s the legal line, and the Supreme Court has stated it clearly.

At least in terms of being "at the border", United States v. Martinez-Fuerte would appear to disagree.

That legal line you mention is both figuratively and literally not at the border; protections are weakened up to 100 miles away.