Charlaquin
Goblin Queen (She/Her/Hers)
Did you read both versions? Yes, in the original version attacking, taking damage, and casting a spell were all sufficient to interrupt a rest, regardless of how long it took. In the second version though, all three of these things are noted as strenuous action, any of which interrupts a rest unless the interruption takes less than an hour. If it wasn’t already abundantly clear that fighting and casting spells are meant to be included in the list of strenuous activities, one hour of which interrupts a long rest, this clinches it. It also reveals that at one point in the testing process, any amount of strenuous activity interrupted the rest, and for whatever reason, they deemed it necessary to change it so that the interruption only forces you to start the rest over if it lasts an hour or longer.So in those early drafts any amount of attacking, taking damage or casting a spell were strenuous activity, and would interrupt the rest. While reading, talking, eating, or standing watch were light activity and could be done for 2 hours without interrupting.
This makes the intent crystal clear. 599 rounds of combat is not intended to interrupt a long rest, unless you’ve also done 6 seconds of some other strenuous activity. You can certainly rule otherwise if you want to, but there should be no question about the intent of the rule at this point.