When Ravenbloom Student's trigger goes on the chain after an action spell resolves, does focus pass to the defender and then back to the attacker, allowing the attacker to 'lock' the defender from playing action spells?

Ruling: No, the attacker cannot lock the defender this way. When the action spell resolves, the Student's trigger becomes a pending item on the chain before cleanup completes, so the chain never closes and focus does not pass to the defender.

Sequence:

• Player A plays Hextech Ray as an action spell
• Both players pass priority and the spell resolves
• Student's trigger condition is fulfilled and immediately becomes a pending item on the chain
• During cleanup, the pending trigger gets finalized
• Since the chain is not empty (the pending trigger is already on it), focus does not pass
• The chain continues without closing

Nuances:

• Pending items are placed on the chain as soon as their conditions are fulfilled, which happens before the cleanup checks if the chain is empty
• The rule about triggers resulting from playing a spell includes them as part of that spell's resolution sequence