Why does a diode placed in series before an inductor not protect from surge?

I answered this SE EE question just a few minutes ago.

My answer

Let's finally summarize all these specific explanations in a "current source philosophy".

The problem is how to interrupt (stop) the current produced by an (almost) ideal current source, which here is a charged coil.

The answer is the current cannot be stopped by breaking (opening a series-connected switch); current can be stopped only by diverting (closing a parallel-connected switch). In short, the rule is:

Current is stopped not by interrupting but by diverting.

The "current steering" observed in transistor differential amplifier stages is a typical application of this rule.