Whisper

Whisper's gold says "If able, that hero performs a movement action on the card they defended with, moving full distance in a straight line." Does the defender control the straight line? Can they choose to run into an obstacle to move shorter than the full distance? Does the straight line have to be away from Whisper?

No. This is why the card text specifies "the full distance".

Does Whisper's gold card automatically make me move 3, or can I move 1 into a wall to stop my movement?

Lack of “up to”. Same reason brogan can’t choose to “move into the adjacent target” with charge red.

Whisper attacks with his gold card and Snorri defends with his level 1 green card, which has the active effect "This turn: You are immune to enemy actions." In what order are these cards resolved? The attack is blocked by the green card, which is then in the discard pile, tapped and active. Is the rest of Whisper's gold (Snorri having to move 2 spaces in a straight line) blocked because the immunity from the green card is already active?

“After the attack” part of gold won’t trigger.

Can Whisper's Handicap gold target minions?

Simply follow the card text exactly as it’s written. If it doesn’t say that you can “target a unit” or “target a minion”, it means it cannot target minions.

if whisper uses silver to become immune to enemy actions, can mrak use silver to stone grip whisper? stone grip does not say target, but whisper is being selected to be gripped

The answer is on Page 10 of the rulebook. "Selecting targets" section.

When Ursafar blocks Whisper's gold, does he get to perform the rest of the effects on his card, given that he is not Enraged because the active effect would be in the discard?

Correct. Each Razzle is targeted separately, so only the original Razzle is restricted

If a hero is immune to enemy actions (e.g. via Whisper's Silver), can an enemy Rowenna still use her Silver to teleport close to Whisper, since Rowenna's Silver targets a space? She then couldn't ask Whisper "Would you like to move away 1? If you do, I get two coins" — how does that interaction play out? Does the card fizzle at that part?

In current printed rules, Rowenna cannot do placement in that scenario as that placement also targets the unit in that same step (it requires both space in range and unit in range).

For whisper gold card, the hero defending performs movement action. If the card has movement as primary action, does defender read and apply text?

Yes. Whisper's gold doesn't specify secondary movement, so yes, primary movement can be performed, which includes text.