Miners do not execute other tasks until they receive the micropayment from the last code portion.
Any other task at all or any other task from this work distribution node?
So let's say we have 2 miners, and a Elastic Dist job with a public work distribution node. Imagine we want to render a video. The job is split into 100 different sub-tasks (which fit in the maximum allowed WCET per program). The work author announces this job and says it pays 100 XEL per execution. The 2 miners then poll 1 subpackage each, calculate it and submit it to the Elastic Dict node and wait for the micropayment of 100 XEL. Once received, they poll the next subpackages. If not, they wasted at most WCET computation time.
How I, as a work author, can be sure that the work is really performed and I've got not just a noise? Running the same job on 2+ miners? Miners reputation?
The second scheme was just a first idea, open for discussion ;-) And you have perfectly argued that probably such tasks (as rendering) should be performed on centralized services.
But we can brainstorm a little, to identify if its really so bad and we should leave it out, or if it's worth pursuing this idea.
To your first question: Only for the work distribution node (or any other that the miner is connected to). The blockchain would not track any work, it would be used only to negotiate work between "distribution node" and "worker node" and keep them working by periodically sending micropayments.
To your second question: of course you canot be sure, this is of course a problem and this is why i personally think Zennet is inferior to us. You have to "trust" or somehow ensure that the result is plausible or not yourself. If you think the result is bad, you can deny the micropayment and not distribute any work to the connected worker node anymore.
This scheme is of course fragile! I am just interested if it could somehow work as an "additional work type" or if we better leave it out and stick to our "verifiable computation scheme" which is robust.