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.
Of course - given my position in this debate - I will point out that the early drafts speak to designer intent during the designing. That may have changed. Or - as I would naturally suspect - it may have stayed the same, but an unfortunate ambiguity was introduced letting in "1 hour of fighting". Which adherents reconciled with by supposing it intended a much smaller amount of fighting mixed in with other activities.
What I discern is this polarity
- For some, 1 round of fighting or 1 spell cast seems far too little to break a rest
- For others, 600 rounds of fighting (or 300, 200, or even 100!) is an absurd requirement
- That polarity is also informed by whether a DM prefers to make it harder or easier to refresh abilities in their game (with many ingenious supporting arguments constructed on both sides).
The words written in the book are
literally ambiguous. For me, the minimum fair-minded position is for each side to concede the validity of the others reading. I can say that I will have any amount of fighting interrupt a long rest, but if you feel it should be up to an hour of fighting as part of a mixture of activities, then so far as the words written on the page go that is equally valid.
EDIT
I described the polarity as I did with an intent in mind - perhaps a DM could ask themselves "what number of rounds of fighting, and how much spell casting, interrupts a rest in my world?" That could be used to adjudicate rests in a consistent way.