How do the various bitcoin roles interact?

Question

I think I've reached a reasonable (-ish) understanding of blockchain and bitcoin as it works just below the surface, but I still don't get that surface view. So, from the umpteen videos I've watched, I can see that there are at least three roles -- i.e. kinds of people/companies -- involved:

A. End Users -- people who just want to use bitcoin. For example, I might have BTC in a bitcoin wallet on my smartphone and I use it to buy a pizza via Lightning. And then transaction ends up correctly residing in the blockchain

B. Miners -- people who bundle up a bunch (two to three thousand I believe?) of End User transactions like mine, do the POW "stuff", and package the whole lot into a new block to be offered for acceptance into the blockchain

C. Chain Maintainers - I made that name up 'cos I'm not sure what to call them. But they are the people/agents responsible for accepting the newly mined blocks from the various Miners and deciding if/when to fork, which forked chain is longest, when to discard a branch deemed to be dead, and so on. In other words, they are the ones who make decisions on which blocks are accepted, based on the Proofs of Work done by the various Miners.

So my questions are:

1. How, and in what form, do my End User transactions between me and my pizza purchase say get out into the world and eventually reach the Miners? Do they go directly -- but that would mean gazillions of pizza purchases etc flying about? Or do they all go to some kind of aggregator -- one of the "Chain Maintainers" perhaps -- who bundles them up into batches and sends those bundles out to the Miners?
2. Once my transaction gets to the Miners, and they have then packaged it and others together into a POW'ed block ready to be offered to the "Chain Maintainers" for acceptance, exactly what does it broadcast? Is it just the new block itself? Or is it the entire chain with the new block appended? BUT SPECIFICALLY:
3. How does the Proof of Work information itself get from the Miners to the Chain Maintainers? I don't mean the hash itself -- I mean the fact that Miner A expended 4 GigaOodles of Work to produce its version, whereas Miner B expended 800 TeraOddles of Work to produce its version? I presume it's in the newly mined block itself, but where and in what form? AND FINALLY:
4. Where, exactly, does the famed Blockchain actually reside? Or rather, who maintain copies? Since it's currently several hundred GB in size and growing, I know I don't have a copy in the wallet in my phone, so who does? Is it just the various people/organizations in the "Chain Maintainers" group; every single Miner as well; someone else; who?

Thx.

Answer 1

The role that you call "chain maintainers" are actually referred to as nodes. A node receives blocks and transactions, verifies them, and forwards them onto other nodes. An important thing is that all miners are also nodes - this allows miners to also receive blocks and transactions.

How, and in what form, do my End User transactions between me and my pizza purchase say get out into the world and eventually reach the Miners?

Your end user software will connect to one or more nodes and send your transaction to those nodes. Those nodes will verify your transaction, and if it is valid, they will send your transaction on to other nodes that they are connected to. In this way, your transaction is spread throughout the network of nodes. Because all miners are also nodes, they will eventually learn of your transaction as some nodes will eventually relay the transaction to them.

Once my transaction gets to the Miners, and they have then packaged it and others together into a POW'ed block ready to be offered to the "Chain Maintainers" for acceptance, exactly what does it broadcast? Is it just the new block itself?

It is just the block itself, and the relay is done in the same way that your end user transaction was relayed, but with a block instead of a transaction. So once a miner finds a valid block, it will send it to the nodes that it is connected to. Those nodes will verify the block, and if it is valid, they will forward it on to the other nodes they are connected to. In this way, a block is spread throughout the network. Eventually, all nodes, including the other miners, will learn of the new block.

How does the Proof of Work information itself get from the Miners to the Chain Maintainers? I don't mean the hash itself -- I mean the fact that Miner A expended 4 GigaOodles of Work to produce its version, whereas Miner B expended 800 TeraOddles of Work to produce its version? I presume it's in the newly mined block itself, but where and in what form?

The block header itself is the proof of work. There is no need to know how much hashrate a specific miner has. That is completely irrelevant. The mere existence of a block header which has a low enough hash is proof that work has been done. When a miner sends their blocks to other nodes, the block header is their proof that they have done work.

Where, exactly, does the famed Blockchain actually reside? Or rather, who maintain copies?

Many nodes will maintain a copy of the blockchain. When a new node is started, it obtains a copy of the blockchain by asking nodes it has connected to for all the blocks in the blockchain.

Some nodes will have enabled pruning which allows them to delete old blocks for storage. Obviously those nodes will not have the full blockchain, but they will have verified every block prior to deleting it.