Does Sanctuary end on a familiar that delivers a touch spell?

Question

Updates to Sanctuary and Find Familiar since the 2014 rules¹ have led to new considerations regarding the interaction between these spells.

Sanctuary ends if:

... the warded creature makes an attack roll, casts a spell, or deals damage.

On the other hand, Find Familiar allows a familiar to deliver a touch spell on behalf of its summoner, seemingly without casting the spell or dealing damage itself:

... when you cast a spell with a range of touch, your familiar can deliver the touch ... it must take a Reaction to deliver the touch when you cast the spell.

This raises an interesting question: does Sanctuary end if a familiar delivers a touch spell?

Similar topics have been addressed in questions like:

• How does the Warlock's invocation Gaze of Two Minds interact with the Unseen rule?

• How does the Warlock's invocation Gaze of Two Minds interact with a creature with the Invisible Condition?

• Can a familiar maintain invisibility while delivering a touch spell?

• Does a touch spell have advantage when delivered by an invisible Familiar?

where it seems generally clear that pertinent spellcasting mechanics are basically determined by the Warlock, rather than the proxy creature.

^{1: Using a familiar to deliver a spell attack while both of us are under Sanctuary}

Answer 1

No

The Find Familiar spell states (emphasis mine):

[...] when you cast a spell with a range of touch, your familiar can deliver the touch. Your familiar must be within 100 feet of you, and it must take a Reaction to deliver the touch when you cast the spell.

From this we can conclude that it's the spellcaster, not the familiar, who casts the touch spell, makes the attack roll (if required by the touch spell), or deals damage with it (if applicable). The familiar simply delivers that touch.

Thus, Sanctuary wouldn't end for a familiar delivering a touch spell but it would end for the spellcaster.