weld build

Inputs: a policy crate. Steps: nargo check → generate the three bin packages under target/weld/{initiate,accept,reject} → nargo compile → bb write_vk (recursive flavor) → hash VKs → sample or reuse vk_salt → compute vk_root → emit weld.json:

{
  "name": "corridor", "version": "1.2.0", "protocol": "weld-v1", "schema_min": 1,
  "toolchain": { "nargo": "…", "bb": "…", "weld": "…" },
  "phases": {
    "initiate": { "vk_hash": "0x…", "gates": 41213 },
    "accept":   { "vk_hash": "0x…", "gates": 22890 },
    "reject":   { "vk_hash": "0x<noop>", "gates": 0 }
  },
  "vk_root": "0x…", "vk_salt_ref": "keychain:corridor/vk_salt",
  "params": { "schema_hash": "0x…", "fields": [{ "name": "cap", "type": "u128" }, …] },
  "state":  null,
  "asserts": ["corridor/over-cap", "corridor/blocked", "weld/params-weld", …]
}

weld build --check-reproducible rebuilds in a clean sandbox and compares VK hashes (the salt is excluded from the comparison).