tercet

The book of record for machine payments. Every agent purchase is recorded as it happens (request → quote → signed authorization), matched against on-chain settlement, and every difference gets a name — delivered-but-uncollected, paid-without-delivery, replay, chain-orphan. tercet never touches keys, balances or the payment path: it observes and produces evidence.

A tercet is a stanza of three lines that belong together — here, every purchase is one: the request, the authorization, the settlement. Dante chained his tercets so none could be pulled out without breaking the poem; this ledger chains its entries the same way.

The Python package is still named mesa (working name); it renames to tercet with the first PyPI release. Project docs under docs/ are written in Portuguese — they are the build diary and per-phase design docs; code, schemas and this README are English.

The app — the ledger, live, in six screens

uv run mesa-app        # -> http://127.0.0.1:8400

01 blotter (what your agents bought, with derived state and the event chain of each purchase) · 02 tca (waste, dedup across agents, cost per delivered result) · 03 risk (budget per task tree, human approvals, the payer passport) · 04 lab (point-in-time spend-policy backtest with honest confidence intervals) · 05 books (three-way reconciliation, sealed periods with two third-party timestamps, per-counterparty statement, BR tax view) · 06 operations (run the audited engines from the screen — demo, collectors, exports — testnet only).

The app is read-only by construction: its Postgres session opens with default_transaction_read_only=on, so it cannot write to the ledger even if it wanted to — and tests/test_app.py proves it. Real data always; testnet and synthetic rows are labeled on the screen itself. Press any pill for its legend.

Related MCP server: ACA PoC MCP Tools Server

The MCP server — the ledger as tools for agents

claude mcp add tercet -- uv run mesa-mcp    # then ask: "how much did my agents spend?"

Seven READ tools (closed list, proven by test): status_do_livro, gasto, compras (filterable), compra (one purchase + its event chain), vereditos, passaportes, fiscal. Same guarantee as the app: the session is structurally read-only — the MCP server has no write path; tests/test_mcp_livro.py proves it. Transport: stdio, local.

The exports — universal accounting + OECD CARF view

uv run python scripts/fase13/contabil_build.py   # -> contabil/<yyyy-mm>/  (universal CSV, QuickBooks, Xero + per-tx audit detail)
uv run python scripts/fase13/carf_build.py       # -> fiscal/carf/<year>/  (OECD CARF view, born as OECD11 test data)

A double-entry journal per period (debits == credits proven; micro-payments aggregated honestly, with a 6-decimal audit bridge tying every cent to a tx hash), and the CARF view — what a reporting crypto-asset service provider would report about these transactions under the OECD framework (official July 2025 guide) — labeled as a demo, synthetic identities, real numbers. Details and caveats: docs/fase13-export.md.

From zero, with only this README

Prerequisites: uv, Docker, Python 3.11+.

# 1. dependencies + database (Postgres 17 on 127.0.0.1:5433 — your machine only)
uv sync
docker run -d --name mesa-pg -e POSTGRES_USER=mesa -e POSTGRES_PASSWORD=mesa `
  -e POSTGRES_DB=mesa -p 127.0.0.1:5433:5432 `
  -v mesa-pgdata:/var/lib/postgresql/data postgres:17
uv run python scripts/check_db.py            # migrations + hash-chain genesis, idempotent

# 2. TEST wallets (written to a local .env; never committed) + faucet USDC
uv run python scripts/setup_wallets.py
#    -> paste the buyer address into https://faucet.circle.com (USDC / Base Sepolia)
uv run python scripts/check_balance.py       # balance read on-chain

# 3. a toy seller + 10 REAL x402 payments on testnet
uv run uvicorn mesa.http.seller:app --port 8402     # terminal 1
uv run python scripts/fase1/buyer.py 10             # terminal 2 (writes the ledger)

# 4. the chain is the source of truth: collect and reconcile
uv run python -m mesa.collector              # matches (authorizer, nonce) with the ledger
uv run python -m mesa.cli                    # the verdict table, orphans in red

# 5. the product
uv run mesa-app                              # -> http://127.0.0.1:8400

Costs zero real money: faucet USDC, and under the exact scheme the facilitator pays gas.

• What happened, what it proved, what comes next: docs/DIARIO.md (Portuguese) — the per-task build diary; per-phase design docs live in docs/faseN.md.

• Secrets (the private keys setup_wallets.py generates) go to a local .env (gitignored, never committed). To keep them elsewhere, point MESA_ENV_FILE at the file — and keep it out of synced folders (OneDrive/Dropbox): a key in a synced folder is a key in the cloud.

Repo map

Environment

uv sync
docker run -d --name mesa-pg -e POSTGRES_USER=mesa -e POSTGRES_PASSWORD=mesa `
  -e POSTGRES_DB=mesa -p 127.0.0.1:5433:5432 `
  -v mesa-pgdata:/var/lib/postgresql/data postgres:17
# 127.0.0.1 is mandatory: without it the ledger is open to any machine on the same
# Wi-Fi (docs/seguranca.md, hole #1). scripts/saude.py checks this, always.
uv run python scripts/setup_wallets.py   # generates the EOAs -> .env (NEVER committed)
uv run python scripts/check_db.py        # Postgres up + migrations + genesis
uv run python scripts/check_balance.py   # USDC balance read on-chain
uv run python scripts/saude.py           # ONE command: ruff+mypy+pytest+verifier+ports+secret scan
uv run python scripts/backup_db.py       # ledger dump -> backups/ (routine, ~5s)

Faucet: https://faucet.circle.com → USDC → Base Sepolia (20 USDC / 2h per address). Anthropic key (only for the invoice-rail agent demo): ANTHROPIC_API_KEY=... in your secrets env file.

Run the proofs of each phase

# Phase 1 — the ledger closes on dirty data
uv run uvicorn mesa.http.seller:app --port 8402     # terminal 1: HTTP seller
uv run python scripts/fase1/chaos_run.py            # terminal 2: chaos + reconciliation + asserts

# Phase 2 — x402 over MCP
uv run python -m mesa.mcp.seller                    # terminal 1: MCP seller (port 8403)
uv run python scripts/fase2/mcp_once.py             # terminal 2: 1 paid tool call + ledger

# Phase 10 — the payer passport (emits, verifies, gates a seller)
uv run python scripts/fase10/gate10_demo.py

# Any time: sweep the chain and reconcile
uv run python -m mesa.collector                      # testnet (seller payTo)
uv run python -m mesa.collector --pagador            # mainnet (payer-side)
uv run python -m mesa.cli

Quality ("done" has a definition)

uv run python scripts/saude.py    # ONE command: ruff+mypy+pytest+verifier+ports+secret scan

Threat model, and what is out of scope — by name: docs/seguranca.md.