> The long tail of linux distributions work precisely because they need very little trust
Regardless of which distribution you use, the distribution itself controls code that runs as root on your machine, and the users are by and large not reading all of the code themselves. It works entirely by reputation. If you ship trash, most people aren't looking, but if even one person is, they point it out to everyone else and then no one trusts you anymore. This works perfectly fine with 30+ distributors.
> Hardware attestation, financial clearing networks, or even physical supply chains. Ie, you have multiple independent parties who need mutual, verifiable trust to operate.
There are large numbers of financial clearing networks. The reason Visa and Mastercard are an effective duopoly for credit cards isn't the trust issue, it's the network effect. A lot of people have a Visa, so merchants want to accept Visa, and then customers want the card which is accepted at many merchants. It's essentially regulatory capture that they're allowed to get away with this, i.e. that the networks are allowed to force you to use their card in order to use their protocol. The way this should work is closer to how checks work, i.e. Alice tells her bank that she wants to transfer money to Bob, Bob's bank routing number is on the check and the banks just talk to each other using a standard protocol to work out how much money to transfer from one bank to the other on net, with no for-profit middle man taking a cut.
Supply chains are a pretty weird example to pick because they're actually a huge counter-example. When Walmart wants to stock some USB cables or camping stoves they're going to vet the supplier so they don't get sued for selling a fire hazard but there are still dozens or hundreds of suppliers, because they have to vet the ones they use, but they don't have to be the same ones Amazon or Target or Costco uses and frequently aren't.
Hardware attestation is a dumpster fire. It keeps getting pushed because it's excellent at monopolizing a market but anyone actually trying to rely on it has had nothing but a series of swift kicks between the legs. People should stop even attempting it. It should simply be banned.
> Establishing that requires transaction costs like audits, SLAs, legal liability, and cryptographic integration.
Most of that stuff scales really well to large numbers of entities. The entire point of things like SLAs and legal liability is that they operate by preventing you from needing to enforce them. No company wants to get sued so they meet the SLA and satisfy the contract in order to minimize their legal costs, which is what allows you to contract with smaller companies as long as they're not so small you're concerned they'll go out of business, and the threshold for that is far smaller than any of these oligopolists.
> The economics don't work for 30 different players to cross-verify each other.
Which is why it's not supposed to be fully meshed. You don't need everyone to verify everyone, you only need the pairings that actually exist. If there are 1000 companies that make shoes and Walmart contracts with 10 of them then they need to verify 10 rather than 1000. Meanwhile the 1000 shoe companies each only have to contract with a dozen retailers, they're just not the same dozen retailers for every manufacturer.