> ## Documentation Index
> Fetch the complete documentation index at: https://docs.nacrelabs.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Signature aggregator

> The stateless coordination service that collects and forwards validator signatures, runs pre-flight checks, and broadcasts the resulting Pearl / Solana transactions.

The aggregator is a stateless coordination service. It does **not** have any
signing authority; it cannot mint, burn, or move PRL on its own.

## What it does

* **Collect signatures.** P-256 signatures keyed by `proposal_id` come in
  from the validator quorum. Invalid signatures, and signatures from
  unknown validators, are rejected.
* **Pre-flight checks.** Before forwarding to the signing quorum, the
  aggregator runs multi-RPC consistency checks, per-validator rate
  limits, an output-address whitelist, and a circuit breaker that
  pauses forwarding on consistency failures.
* **Forward at threshold.** At 3-of-4 it forwards to the TEE-enforced
  signing quorum (Privy) with the three validator signatures as
  authorization.
* **Assemble + broadcast.** It assembles the resulting Pearl /
  Solana transaction, verifies it locally against the
  validator-attested intent, and broadcasts to the right chain.
* **Emit lifecycle events.** Each transition fires through
  `sig_event_publisher` and the `sqs_publisher` → SQS → NacreScan
  ingester so the explorer's intent timeline stays current with the
  on-chain state.

Two to three aggregator instances run in parallel. Validators POST to all of
them; whichever reaches threshold first broadcasts.

## Crate layout

The aggregator is split into a library plus a binary entry plus two
broadcaster impls; the binary composes them at startup via a
`CompositeBroadcaster` that routes on the proposal's `ProposalKind`.

| Crate                      | Role                                                                                                              |
| -------------------------- | ----------------------------------------------------------------------------------------------------------------- |
| `nacre-sig-aggregator`     | Library: signature collection, pre-flight checks, lifecycle event publisher, broadcaster trait.                   |
| `nacre-sig-aggregator-bin` | Binary entry; wires the library against the concrete broadcasters at boot.                                        |
| `nacre-pearl-broadcaster`  | `Broadcaster` impl for Pearl `ProposalKind`s — Cold Reserve sweep, redemption broadcast.                          |
| `nacre-solana-broadcaster` | `Broadcaster` impl for Solana `ProposalKind`s — `mint_deposit`, `complete_redemption`, `claim_cold_reserve_utxo`. |