Is it required to report climbs and descents within a block altitude assignment? The following is assuming US FAA and IFR.
This question stems from a question on CRUISE clearance. Section 4-4-3.d.3 of the 2021 AIM says that in a CRUISE clearance

Climbs/Descents within the block is to be made at the discretion of
the pilot.

I've never been given a CRUISE clearance, but I have been given a Block altitude assignment before (e.g. 8000-12000). I could climb and descend to my heart's content without telling ATC every time I changed altitude within my assigned block. In fact, I've been voluntarily given a block altitude assignment by ATC just to shut me up after asking for too many altitude deviations for weather.
The AIM says about CRUISE clearance,

However, once the pilot starts descent and verbally reports leaving an
altitude in the block, the pilot may not return to that altitude
without additional ATC clearance.

Some of my fellow pilots interpret this to mean that you must report to ATC when you descend, but the way I read this is that you don't have to report leaving any altitude in a Block until you are finished with that altitude or the block, and once you descend AND report leaving an altitude, then that signifies to ATC that they can assign that vacated altitude or block to other aircraft. However, none of this appears to says to me, that you have to report descending within the block if you intend to climb back up in the block later.
In other words, don't report to ATC that you're descending until you are done with the block. For example, if I'm given 8000-12000. And I start my final descent and I know I'm not going to be climbing back up then I'll tell them Cessna 123 10000 descending 8000. Then ATC can assign the 10000-12000 block.
Questions:

When given a CRUISE clearance (which includes a block altitude assignment from MEA to CRUISE altitude) where does it say that a pilot must report altitude changes (climbs or descents) within the block altitude. If not, then where does it say you don't have to report altitude changes.

Is there an FAA publication that provides more information on Block altitude assignments and Cruise clearances besides the AIM?
When given a CRUISE clearance [...] where does it say you don't have to report altitude changes.

In my opinion, it say that by implication in the text you quoted, emphasis mine:

The pilot may level off at any intermediate altitude within this block of airspace. Climb/descent within the block is to be made at the discretion of the pilot. However, once the pilot starts descent and verbally reports leaving an altitude in the block, the pilot may not return to that altitude without additional ATC clearance.

I read that to mean, and as a controller I was taught that that means, you can climb and descend to your heart's content while operating on a cruise clearance. Only once you report leaving an altitude are you required to remain below that altitude; therefore by implication you are allowed to return to that altitude so long as you don't report leaving it, and therefore by further implication you are not required to so report in the first place.
The AIM references the Pilot/Controller Glossary term &quot;cruise&quot; which contains the same exact verbiage.
The 7110.65 contains instructions to controllers that further this interpretation, particularly 6–6–2c under the Non-Radar section and 5–6–6a under the Radar section, which say that controllers cannot use Mode C altitudes to guarantee vertical separation if one of the aircraft involved is on a cruise clearance—because the aircraft is allowed to climb or descend without notice.