Self-hosting slice 1: Queen /hosting endpoints, trios-host agent, demo tests (TRIOS_HOSTING=on) #1757

Part of #1756 (self-hosting MVP, slice 1), on the integration branch hosting-mvp.

The runtime half of slice 1. Every rule lives in gHashTag/t27#8707: the specs specs/hosting/{host,placement,proof,credit,toolchain}.t27, vendored here as wasm cards plus t27c gen-ts constants. The work is behind TRIOS_HOSTING=on, which is off by default.

Scope

• Queen endpoints:
  • POST /hosting/hosts registers a host with an Ed25519 key, a tier claim and its slots. The tier comes from the owner's allowlist, TRIOS_HOSTING_ALLOWLIST.
  • POST /hosting/hosts/:id/beat
  • POST /hosting/lease
  • POST /hosting/receipts takes signed receipts.
  • POST /hosting/jobs accepts jobs from owner-tier hosts only.
  • GET /hosting/ledger is a public read.
  • GET /hosting/verdicts and GET /hosting/jobs/:id are also reads.
  • Storage is Postgres, with an in-memory twin for tests. The route-guard audit pins the new mount with its reason.
• Host agent trios-host, one self-contained binary built with bun build --compile. join does four things:
  • it keeps an Ed25519 key in ~/.trios-host/key with mode 0600;
  • it fetches and verifies the pinned toolchain, or uses one the operator names;
  • it registers and beats;
  • it leases a shard, runs t27c test-report on the pinned inputs with an environment built from nothing, and posts the normalized output hash in a signed receipt.
• Demo as tests, run locally on a VirtualClock:
  • two honest hosts and one that tampers;
  • a lapsed lease that is reassigned;
  • a public host refused a job that declares a secret.
• Benchmark: the cost per job of the verification path against one run, and the message count per job.