Idle? or Off?

[The Taipan]

OK, at the lights its clear, leave it in "D" or knock it out of gear, and
leave it running, if an emergency vehicle needs you out of the way you can
move, and its safer for all.

But my question relates more to a fuel usage vs. engine wear/heat problem.
Apparently you use more energy idling for more than 30 seconds than you do
stopping the engine and restarting again... that's fine I can accept that as
possibly being true, and started using it in places where it was safe to
shut down - eg macca's drive thru where you always have at least 2-3 mins
wait... but while waiting for my mcJack's Fried Chicken once I got to
thinking about heat soak, while the engine is running so is the coolant,
therefore oil temps stay stable, shortly after an engine is shut down, often
the oil temps rise due to heat soak, that would probably be OK if the engine
stayed shut down, but if you plan on starting shortly afterward would
certainly take much longer to cool off again...

After pondering this for a while, I decided to switch to thinking about
world peace and ask my expert friends on the internet... which is going to
protect my engine for the longest and possibly save fuel?