add GetInterchain: trace a transaction/block to validator blocks + interchain anchors

New Transaction.GetInterchain and Block.GetInterchain call the prime-node
/api/v1/{transaction,block}/{id}/interchain endpoints, returning an
InterchainTrace {blockId, validatorBlocks, interchainTransactions}. Adds local
VerificationBlock / InterchainTransaction / InterchainTrace model types.

block/block.go

@@ -25,3 +25,16 @@ func (bc *BlockClient) Get(ctx context.Context, blockID string) (*models.Block,
 	}
 	return &resp, nil
 }
+
+// GetInterchain traces a block to the validator (verification) blocks that
+// validated it and the public-chain interchain anchors those validator blocks
+// were bundled into.
+func (bc *BlockClient) GetInterchain(ctx context.Context, blockID string) (*models.InterchainTrace, error) {
+	var resp models.InterchainTrace
+	path := fmt.Sprintf("/api/v1/block/%s/interchain", blockID)
+	err := bc.client.Get(ctx, path, &resp)
+	if err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}

models/models.go

@@ -170,3 +170,39 @@ type ListResponse struct {
 	Items      []interface{} `json:"items"`
 	TotalCount int           `json:"total_count"`
 }
+
+// VerificationBlock is a validator's verification of a prime block.
+type VerificationBlock struct {
+	Version           string `json:"version"`
+	PrimeChainId      string `json:"primeChainId"`
+	PrimeBlockId      string `json:"primeBlockId"`
+	Timestamp         string `json:"timestamp"`
+	VerifierPublicKey string `json:"verifierPublicKey"`
+	VerifierSignature string `json:"verifierSignature"`
+}
+
+// InterchainTransaction is an anchor broadcast to a public blockchain (e.g. ETH
+// or BTC) that bundles one or more validator blocks. ValidatorBlocks holds the
+// prime block ids covered; CoveredPrimeChainIds the prime chains they belong to.
+type InterchainTransaction struct {
+	Id                   int      `json:"id"`
+	Version              string   `json:"version"`
+	Timestamp            string   `json:"timestamp"`
+	ChainId              string   `json:"chainId"`
+	TransHash            string   `json:"transHash"`
+	BlockId              string   `json:"blockId"`
+	ValidatorBlocks      []string `json:"validatorBlocks"`
+	ValidatorBlockhash   string   `json:"validatorBlockhash"`
+	Signature            string   `json:"signature"`
+	CoveredPrimeChainIds []string `json:"coveredPrimeChainIds"`
+}
+
+// InterchainTrace links a prime block to the validator (verification) blocks
+// that validated it and the public-chain interchain anchors those validator
+// blocks were bundled into. Returned by Transaction.GetInterchain and
+// Block.GetInterchain.
+type InterchainTrace struct {
+	BlockId                string                  `json:"blockId"`
+	ValidatorBlocks        []VerificationBlock     `json:"validatorBlocks"`
+	InterchainTransactions []InterchainTransaction `json:"interchainTransactions"`
+}

transaction/transaction.go

@@ -52,6 +52,20 @@ func (tc *TransactionClient) Get(ctx context.Context, transactionID string) (*mo
 	return &resp, nil
 }
 
+// GetInterchain traces a transaction to the validator (verification) blocks that
+// validated its prime block and the public-chain interchain anchors those
+// validator blocks were bundled into. If the transaction is still pending (not
+// yet in a block) the trace's slices are empty.
+func (tc *TransactionClient) GetInterchain(ctx context.Context, transactionID string) (*models.InterchainTrace, error) {
+	var resp models.InterchainTrace
+	path := fmt.Sprintf("/api/v1/transaction/%s/interchain", transactionID)
+	err := tc.client.Get(ctx, path, &resp)
+	if err != nil {
+		return nil, err
+	}
+	return &resp, nil
+}
+
 func (tc *TransactionClient) List(ctx context.Context) (*models.ListTransactionsResponse, error) {
 	var resp models.ListTransactionsResponse
 	path := "/api/v1/transaction/"