Build your own organ

Add a new organ to the mesh: a FastAPI service that speaks the SZL contract — /healthz, /v1/honest, and a DSSE-receipted action endpoint — so it deploys in the UDS bundle next to the shipping flagships (a11oy, killinchu).
Headline number: 1 contract, 3 required endpoints, 0 kernel changes.

Every SZL flagship is the same shape: a small FastAPI app that (1) reports the locked doctrine on /v1/honest, (2) answers /healthz, and (3) emits a hash-chained DSSE Khipu receipt for every governed action. Implement that contract and your organ joins the mesh.

Prerequisites

bash

python3 -m pip install fastapi uvicorn cryptography

Quickstart — the minimal organ

python

# organ.py — a sixth organ ("yupay", a tally/counter organ) that honors the SZL contract.
import hashlib, json, time
from fastapi import FastAPI, Request

DOCTRINE = {"doctrine": "v11", "declarations": 749, "axioms_unique": 14,
            "sorries_total": 163, "kernel_commit": "c7c0ba17",
            "lambda_uniqueness": "Conjecture 1 — NOT a theorem",
            "slsa": "L1 (honest)", "hatun_willay": True}

app = FastAPI(title="yupay")
_chain = [{"seq": 0, "hash": "0" * 64, "prevHash": None}]

@app.get("/api/yupay/healthz")
def healthz(): return {"ok": True, "organ": "yupay", **{k: DOCTRINE[k] for k in ("doctrine",)}}

@app.get("/api/yupay/v1/honest")
def honest(): return DOCTRINE                      # NEVER report numbers other than 749/14/163

@app.post("/api/yupay/v1/evaluate")
async def evaluate(req: Request):
    body = await req.json()
    prev = _chain[-1]
    payload = {"seq": prev["seq"] + 1, "input": body, "ts": time.time()}
    h = hashlib.sha256((prev["hash"] + json.dumps(payload, sort_keys=True)).encode()).hexdigest()
    rec = {"seq": payload["seq"], "hash": h, "prevHash": prev["hash"]}
    _chain.append(rec)
    return {"verdict": "ALLOW", "receipt": rec, "doctrine": "v11",
            "signature": "PLACEHOLDER — wire Sigstore/cosign per recipe 06"}

bash

uvicorn organ:app --port 8080
curl -s localhost:8080/api/yupay/v1/honest | jq .kernel_commit   # => "c7c0ba17"

Full walkthrough

Step 1 — Honor the doctrine contract

The one rule that cannot bend: /v1/honest reports exactly 749 / 14 / 163 / c7c0ba17 and states Λ is Conjecture 1. The DoctrineLock CRD (shipped by the UDS bundle) fails CLOSED if an organ declares anything else. Copy the DOCTRINE dict above verbatim.

Step 2 — Hash-chain your receipts

Each receipt's prevHash must equal the previous receipt's hash. This is the same invariant every flagship uses; it makes the chain tamper-evident and is what recipe 01 checks.

Step 3 — Sign for real (don't ship PLACEHOLDER)

To go beyond the demo, sign the DSSE PAE with an ECDSA-P256 key and publish the public key like the org does at .github/cosign.pub:

python

from cryptography.hazmat.primitives.asymmetric import ec
from cryptography.hazmat.primitives import hashes, serialization
def sign_pae(priv, payload_type: str, body: bytes) -> bytes:
    pae = b"DSSEv1 %d %b %d %b" % (len(payload_type), payload_type.encode(), len(body), body)
    return priv.sign(hashlib.sha256(pae).digest(), ec.ECDSA(ec.Prehashed(hashes.SHA256())))

Step 4 — Package as a UDS bundle entry

Add a zarf.yaml + uds-bundle.yaml for your organ and fold it into the bundle per recipe 13 — Build a UDS bundle from scratch. Reuse the three CRDs: LambdaGate, KhipuReceipt, DoctrineLock.

Step 5 — Register with the Operator console

The a11oy Operator role (ships inside a11oy, not a standalone service) is the operator console / nervous system. Expose your organ's /v1/* surface and it appears in the mesh health board. Confirm with curl https://szlholdings-a11oy.hf.space/api/a11oy/v1/mcp/tools.

Cite this recipe

bibtex

@misc{szl_cookbook_build_organ_2026,
  title        = {Build your own organ (SZL Cookbook recipe 07)},
  author       = {{SZL Holdings}},
  year         = {2026},
  howpublished = {\url{https://github.com/szl-holdings/szl-cookbook/blob/main/recipes/07-build-your-own-organ.md}},
  note         = {Doctrine contract: 749/14/163, c7c0ba17, Λ = Conjecture 1.}
}

Doctrine v11 LOCKED — 749/14/163 — kernel c7c0ba17 · Λ = Conjecture 1 · SLSA L1 (honest)

Build your own organ ​

Prerequisites ​

Quickstart — the minimal organ ​

Full walkthrough ​

Step 1 — Honor the doctrine contract ​

Step 2 — Hash-chain your receipts ​

Step 3 — Sign for real (don't ship PLACEHOLDER) ​

Step 4 — Package as a UDS bundle entry ​

Step 5 — Register with the Operator console ​

See also ​

Cite this recipe ​