feat: Implement committee resolution

poi-rs/src/lib.rs

@@ -4,13 +4,19 @@
 #![doc = include_str!("../README.md")]
 #![warn(missing_docs, rustdoc::all)]
 
+/// Shared boxed source error used by the crate's typed errors.
+pub(crate) type BoxError = Box<dyn std::error::Error + Send + Sync + 'static>;
+
+/// Committee resolution for checkpoint verification.
+pub mod committee;
 /// Proof data types and offline verification.
 pub mod proof;
 /// Sources for constructing proofs.
 pub mod source;
 /// Target claims authenticated by a proof.
 pub mod target;
 
+pub use committee::{CommitteeResolutionError, CommitteeResolutionErrorKind, CommitteeResolver};
 pub use proof::{
     Proof, ProofVerifier, ProofVersion, SerializationError, SerializationErrorKind, TransactionProof, VerifyError,
     VerifyErrorKind, VersionError,

poi-rs/src/proof.rs

@@ -1,8 +1,6 @@
 // Copyright 2020-2026 IOTA Stiftung
 // SPDX-License-Identifier: Apache-2.0
 
-use std::error::Error as StdError;
-
 use iota_types::{
     committee::Committee,
     digests::ChainIdentifier,
@@ -12,9 +10,7 @@ use iota_types::{
 };
 use serde::{Deserialize, Serialize};
 
-use crate::target::ProofTargets;
-
-type BoxError = Box<dyn StdError + Send + Sync + 'static>;
+use crate::{BoxError, target::ProofTargets};
 
 /// Error returned when a proof-format version is not supported.
 #[derive(Debug, thiserror::Error)]

poi-rs/src/source.rs

@@ -1,7 +1,7 @@
 // Copyright 2020-2026 IOTA Stiftung
 // SPDX-License-Identifier: Apache-2.0
 
-use std::{error::Error as StdError, fmt};
+use std::fmt;
 
 use async_trait::async_trait;
 use iota_grpc_client::{
@@ -20,9 +20,7 @@
     transaction::Transaction,
 };
 
-use crate::{Proof, ProofTargets, TransactionProof};
-
-type BoxError = Box<dyn StdError + Send + Sync + 'static>;
+use crate::{BoxError, Proof, ProofTargets, TransactionProof};
 
 /// Source target requested by the caller.
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -301,7 +299,7 @@
                     },
                 )
             })?
             .try_into()
             .map_err(|source| {
                 SourceError::object(
                     object_ref,

poi-rs/tests/committee.rs

@@ -0,0 +1,43 @@
+// Copyright 2020-2026 IOTA Stiftung
+// SPDX-License-Identifier: Apache-2.0
+
+use iota_grpc_client::Client as GrpcClient;
+use iota_types::committee::Committee;
+use poi_rs::{CommitteeResolutionErrorKind, CommitteeResolver};
+
+fn committee_at(epoch: u64) -> Committee {
+    let (committee, _) = Committee::new_simple_test_committee();
+    Committee::new(epoch, committee.voting_rights.iter().cloned().collect())
+}
+
+fn disconnected_client() -> GrpcClient {
+    GrpcClient::new("http://127.0.0.1:1").expect("create lazy gRPC client")
+}
+
+#[tokio::test]
+async fn anchor_mode_returns_the_trusted_committee_for_its_epoch() {
+    let trusted_committee = committee_at(7);
+    let resolver = CommitteeResolver::anchor(disconnected_client(), trusted_committee.clone());
+
+    let resolved = resolver.resolve(7).await.unwrap();
+
+    assert_eq!(resolved, trusted_committee);
+}
+
+#[tokio::test]
+async fn anchor_mode_rejects_an_epoch_before_the_trust_anchor() {
+    let resolver = CommitteeResolver::anchor(disconnected_client(), committee_at(7));
+
+    let error = resolver.resolve(6).await.unwrap_err();
+
+    assert_eq!(error.target_epoch, 6);
+    assert!(matches!(
+        error.kind,
+        CommitteeResolutionErrorKind::TargetBeforeAnchor { anchor_epoch: 7 }
+    ));
+}
+
+#[tokio::test]
+async fn node_mode_has_an_explicit_constructor() {
+    let _resolver = CommitteeResolver::node(disconnected_client());
+}