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the key here is
'has the wrench handle come nearly to a stop and is not changing in speed'

an extension
between the ratchet and socket
does not affect 'steady speed' torque
as long as the handle is not
accelerating or decelerating

think of the extension as a type of
'torsion bar spring'

when you apply torque to a spring
the torsion bar will at first speed up its twist
until the bar is applying an equal and opposite torque
back to whatever is applying the torque

This is Issac Newton's famous 2nd Law:
Force=Mass times acceleration (straight line)
Torque =Mass times acceleration (circular equivalent)
where acceleration = 0 = steady state
in this case

to carry the idea to a silly extreme.....
if you used a 10 foot long extension
of a small diameter (think coat hanger wire)
but made of very strong steel
as you applied the torque
the handle would make several rotations
as the tiny extension bar twisted round and round
but as long as you don't exceed the 'yield point' of the steel of the extension
as the handle slowed down and came to a stop
where everything was 'balanced'
then the torque wrench would show the correct torque

you might think the above example silly
but it actually describes a very common
'real world' situation
... an oil well where 25,000 feet of strong steel drill pipe is twisting a rotary bit at a steady speed deep underground

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