Let's be clear about the laws:
OP's question tilts on whether the "bright line" is the US border, or the CBP immigration desk.
You can't bring them into the United States
US law 7 USC 7712 gives the Secretary of Agriculture (a)broad authority to "prohibit or restrict the importation, entry," etc. "of any plant"... and (c) issue regulations to implement this, including (c)(1) permits. Congressional intent here is clear, but as is typical, they leave the details to the department. Let's see what the Secretary has done with it.
7 CFR § 319.56-3 General requirements for all imported fruits and vegetables.
(1) All fruits and vegetables imported under this subpart, whether commercial or noncommercial consignments, must be imported under permit issued by APHIS.
Whoops. You don't have one of those, so that's the end of that. Regulations (CFR) are law, for all practical purposes.
In their consumer-facing dumbing-down of the CFR, USDA says
Almost all fresh fruits and vegetables (whole or cut) are prohibited from entering the United States because of the potential pest and disease risks to American agriculture. This includes fresh fruits or vegetables given to you on your airplane or cruise ship. Please plan to leave them behind.
That's clear enough.
Catch the part about "given to you on your airplane"? One implementation practicality is that airlines serve food. They probably don't run the permit process for it. So another reg allows this, as long as it stays on the plane. When you bring your own food and abandon it on the plane, you are shaded by that rule.
The ruling words are "United States" which is a nation with clearly established borders and a 12 mile nautical limit. It plainly does not mean the CBP desk; thinking otherwise is wishful thinking. The plane, sitting on the tarmac, is in the United States.
That is the rule. OP asks what the rule is.
Why do some immigration points (Atlanta) have bins in advance of the Customs point, even though that should be illegal? Two reasons. First, this is normal in lawmaking: Congress writes laws (stated in USC) giving the agencies broad leeway in implmentation (both the regulations written in CFR and the actual field execution). Likely they ran into a practical overwhelm of people needing to throw things away, so this was just the easiest way to do it. Second, CBP (much like the IRS) loves traps. So don't put it past them to have a video camera aimed at the bin.
So if you want to comply with the law, the bright line is the airplane door. Any further and you're depending on implementation practices of CBP, which are not reliable.
You didn't ask about Preclearance in a foreign country, but that's a different deal because it's enabled by a different law (19 CFR 162.8). Entering preclearance areas, you shall "comply with all U.S. Customs laws and other civil and criminal laws of the United States relating to importation of merchandise" which brings to bear the above laws. Up until then you're in the foreign country's law, which is why there, yes, the line is the immigration desk because you are not in the U.S. And under Irish law right up to the desk.
With greater power comes greater responsibility
Global Entry isn't just some government hoop. It's a program whereby you identify yourself as a more sophisticated traveler who is volunteering to be more knowledgeable about the rules and follow them. Quid pro quo is that CBP gives you lighter oversight at the customs desk.
You eagerly collect your half of the bargain, which is less standing in line and less being treated like a common tourist.
But you need to pay your half, which wasn't the $100. It is to follow the immigrations and customs rules to a higher standard than they expect from a casual traveler. You agreed to be the person they don't have to worry about.
As seen elsewhere, agricultural items are top of the list of concern - so much so that they're mentioned separately (even though they'repart of "customs"):
Reasons for Ineligibility [for Global Entry]
- Have been found in violation of any customs, immigration or agriculture regulations or laws in any country;
- Cannot satisfy CBP of your low-risk status.
These are things you're expected to know. And respect.
A rotten idea in the first place
Wondering over where exactly in the immigration line to throw away your fruits entirely misses the point of the anti-fruit regulations: To prevent the spread of invasive species -- plant diseases, spores, bugs and bug eggs which travel on fruit, etc. -- which can do a whole lot of damage to crops. Some people disbelieve that invasive species are a real problem; ask Australia. Or a botanist.
What if you had bare fruit in a bag, and the insect eggs or fungal spores transferred onto the bag, which you then carry through customs? What if the fruit went into the bin before Customs, but the eggs hatched and the insects flew away before the trash got burned? Point is, if you think about the reason for the rule, these are unnecessary risks.
All trash on international-arriving aircraft, in the disembark area, the bathrooms, the aisles, and Customs is all treated as dangerous biohazard, and burned. But the burn process is not 100%! So the best thing is to not even bring prohibited materials on the plane.
That said, the CBP question is asking what you brought into the USA, not what you brought past the imaginary "admitted to USA" line at the immigration desk. At the risk of stating the obvious, when you are standing in the immigration queue at LAX, you are in the USA. The airplane on which you abandoned your fruit is also in the USA.
Of course, if you tick "yes", you'll stand in a longer line. I gather that's what you want to avoid. OK then, don't bring fruit.