I think that is one of the changes that more focus on mitigating risk vs. avoiding it might have produced. E.g. when faced with heightened risk of terrorist attacks, a rational response would be to not focus so much on identifying potential attackers and stopping a specific plot, but spending more resources at looking into low impact ways to mitigate the consequences of at various broad modes of attack actually getting underway.

The specifics of 9/11 was probably near impossible to predict, but another eventual hijacking was a near certainty, and an eventual building collapse for whatever reason should have been considered a near certainty, as many high-rises have failed over the years too. The failure to reduce the potential impact of those known risks are the real failures of 9/11, not the failure to prevent the specific plot, as these were broad, known risks and the actual causes leading up to them would be largely irrelevant for a lot of mitigating actions.

It certainly is. The concept of negligence was reinvented or reintroduced into the Common Law starting in 1932 with Donoghue v Stevenson and the lawyers have been wrestling with it ever since. I hated Torts as a student, it's a damn fiddly area of law. Give me Trusts any day of the week.

Still: if you want to study how intelligent people have mapped out the concept of "reasonably foreseeable", then lawyers -- particularly Scots lawyers who also look to Roman law -- are the people to talk to for inspiration.