An instance of moderators not honoring their own advice with respect to meta commentary

Some disclosures: I handled some of the flags on the post in question. I did not send the moderator message. Probably should have followed up with my own later. Apologies for not doing that earlier.

That having been said, my objection to this more or less tracks with others. I think your rationale fails here

Knowing that users tend to disregard comments, I've tried to counteract the assumed-by-me-to-be-wrong signals with comments

The gist of what the other moderator seems to think here (and I don't think you or they are wrong in this) is that there is a chance (albeit small) it might get a response as a comment. There are use cases for that, where you have, say, an old and venerable answer that is being hammered into oblivion for now being wrong. A comment on the downvote pattern there is understandable, and possibly even useful.

Where I had a problem with this is that it was done for a single downvote. It made your answer 0/-1 (for all the fears of Meta effect, it's still at that score). On top of that, your opening gambit was an edited-in message, which is never OK. You then wanted to argue that point (where I got involved was a moderator flag about it). I tend to think the other moderator who sent the message was headed in the direction of comments, since (as mentioned) there are use cases where a comment can be marginally acceptable. Do you know how many comments we remove for being about a single downvote? A lot. And if we let this one stand, we're going to get lots more folks who want their meta-voting-commentary comments to remain. Or, as put in the FAQ

If a vote is in error—which can always happen—the expectation is that the "swarm intelligence" of future viewers will eventually correct the problem. A single vote is nothing, really. What matters is the sum of all votes, which is why we only display the aggregate score.

TL;DR

• Adding meta commentary about voting into the post itself is not allowed
• Single votes aren't considered a problem. Yes, there are drive-by downvoters who care nothing about site quality, but that's baked into the system. It's frustrating, but it comes with the territory
• Comments about downvoting are generally only useful when there's a recent pattern of downvotes without explanation. In some situations we may allow requests for clarity on voting in comments to remain

I hope that helps to clear things up.

Honestly? People aren't obligated to explain their downvotes, and I get that it would leave you in a lurch if you didn't receive feedback on how to improve your question.

But the exact wrong way to get that feedback is to put meta commentary in a comment. On the surface, it could come across as you complaining about downvotes when I think your intent is to figure out if there's anything wrong with your answer.

So here's what you do.

You start a new question about that specific answer and ask if there's something that needs to be improved about it. You don't mention anything about moderators or flags or even your manifesto since none of that has anything to do with why people think your answer isn't sufficient.

Anything besides that isn't gonna go well here since your apparent goal isn't going to be met by fussing about mods.

You are misinterpreting the mod team's message.

You may request feedback on posts in comments (e.g., "I would happily accept comments on any issues with this answer so that I may improve the answer to address the issues")

Emphasis mine. The request for feedback can be done via comments, the same place you would expect such feedback to end up. However... I don't see much value in requesting feedback on downvotes that happened 4, 7, and 9 years ago. The users who casted them likely don't even know the answer still exists.

First, a reality check: a quick look at your profile shows that you have more than 7500 answers written, of which four are at below zero score (all -1). That's an incredible record that places you among the elite of Stack Overflow's question-answering elite. So, to be frank, it seems kinda unproductive to have a complaint in the first place. If you didn't see anything wrong with the answer, and you're this much of an expert (apparently on PowerShell and a variety of related topics), how much can it really bother you that someone else seemingly does? Especially for something you apparently (assuming I can trust my research) wrote years ago?

If I were petty, I would be tempted to downvote the answer again just to make a point. Of course, that would be a clearly abusive use of the site software, and I also like to think I'm better than that, so I won't.

I try to only post answers that (a) I believe to be helpful and (b) whose efficacy I've verified myself (if I can't do the latter, I'll say so).... In the absence of such, I assume the - assumed by me to be unwarranted - down-votes to be a disservice to the community: they send the wrong signal, potentially causing future readers miss out on helpful answer that they might disregard out of hand due to their negative score.

Well, of course you think your answer is useful and effective, or at least you did at the time of writing it. You wouldn't have written it otherwise.

However, you aren't the only one who gets to have and express an opinion on this matter, and others are not required to justify their opinion, by design. It's not you assuming the downvote to be unwarranted; it's you disagreeing with someone else's assessment that the answer should be downvoted.

We don't get to upvote our own answers here (it would be self-congratulatory noise anyway), so you don't really have recourse in this debate. Sorry.

More to the point, "helpful and effective" are not the standard for voting on answers. As long as it isn't explicitly abusive of the system, people are, again, allowed to cast their votes as they please. Moreover, the standard described by the tooltip is whether the answer is useful. An answer that is helpful and effective for the person who asked the question, can still fail to be useful for Stack Overflow:

• It can fail to explain a problem in a generic way that is meaningful to others who find the question with a search engine (as opposed to people who happen to have the OP's exact mindset)

• It can answer a question that should be closed and deleted, and thus be harmful to the site by its mere existence (as this interferes with automatic cleanup of such questions).

I understand that posting such comments as part of an answer is controversial

It's not "controversial"; it's explicitly against policy. Questions and answers are not to contain any meta content, because this is not a discussion forum.

Only answerers who firmly believe in the value of their answer would post such - very specific - meta commentary as part of their answer. Answerers who don't [care], wouldn't, as that would invite further down-votes.

On the contrary. By including such commentary, you actively degrade the value of the answer itself as an answer - it's that much extra text that someone who just needs the question answered, has to ignore. There's also nothing at all "specific" about the meta commentary you describe - it would be equally true of every answer written in good faith, ever.

I instead posted that meta commentary as a comment instead, as explicitly instructed by the message from the moderators.

Sure, that's fine and within intended use of the site. However, it is also fine and within intended use of the site that such comments routinely get deleted.

Also, given that this was not the first such incident, I posted a "meta meta" comment to said user, pointing out that such comments should be acceptable

It's not useful to say this, because this was the first time that you used comments instead of editing the answer. In the previous incidents that you refer to, the other user was completely in the right, because your commentary was not in the form of a comment, but instead noise added to an answer, which should rightfully be edited out (or rolled back).

Making such a comment is at best misguided and at worst comes across as expressing a personal vendetta in the comments section. Again, this is not a discussion forum, so we don't want those things to happen.

Said instance of moderation directly violated the advice given by the moderator team.

No, not at all. Just because you are supposed to post something as a comment rather than as part of an answer, doesn't mean that moderators aren't supposed to remove it from the comments.

Comments are intended to be ephemeral, regardless. They can be removed by a moderator as "no longer needed" at any time, as long as the moderator agrees that the comment is indeed "no longer needed". This could happen, for example, because you're using the comment to complain about a downvote on an old answer, when there is no way for you to know who cast the downvote or how long ago, and thus no reasonable way to direct the request for clearer feedback. It could also happen because requests for such feedback are considered implied for all answers, all the time, by the nature of the system.

In short: you are not entitled to a lasting mechanism for posting this request for feedback, no matter how altruistic, non-reputation-seeking, and non-bothered-by-someone-else-thinking-you're-wrong-on-the-Internet you are.

Let’s discuss the difference between the example comment the moderator message gave you vs what I assume to be your comment (since I can't view deleted comments). Note that I am keeping aside points mentioned in other answers here that I also agree with.

The example given by the moderators was:

I would happily accept comments on any issues with this answer so that I may improve the answer to address the issues

To potential readers, this comment conveys that the author of the answer is potentially open to feedback and will try to improve the answer given such. In my opinion though such a message should be implicit to all posts on Stack Overflow and posting this comment would be adding unnecessary noise. Such comments getting deleted without notice shouldn't startle a user.

Your commentary on the answer (and presumably the deleted comment):

Despite the down-vote, I think this answer offers effective solutions that work as advertised, while (hopefully) also being informative. Do tell us if it is not, so it can be fixed / improved.

The first sentence starts with "Despite the down-vote ..." tells a reader that you disagree with the downvote and the reason you are writing the comment is to address the downvote. Your trailing sentence tries to solicit feedback, but the sentences preceding it have already given a message to readers that their feedback might be met with disagreement.

Note that this is not an imaginary concern and users have devolved into abusing, etc. from what started as asking for downvote reasons.

What the moderators expected from you when suggesting the alternative of commenting (along with an example) was that you'd express that comment in a constructive manner focusing less on the downvotes and more on the content and improving it.

Addressing voting in posts or comments is not controversial, it is definitely improper.

Post meta & social commentary that is not disallowed--like "request feedback"--is mostly noise and best not there and properly edited out. "Anything that is not relevant to the post is noise and should be removed."

Anyway, the mod(s) didn't say "request feedback" commentary was allowed in posts, they said it was allowed in comments.

As a comment it is similarly noise and removable any time.