invoices/sql: replace catch-all GetInvoice with indexed lookups

diff --git a/invoices/sql_store.go b/invoices/sql_store.go
index a31d354..0628a5d 100644
--- a/invoices/sql_store.go
+++ b/invoices/sql_store.go
@@ -1,6 +1,7 @@
 package invoices
 
 import (
+	"bytes"
 	"context"
 	"crypto/sha256"
 	"database/sql"
@@ -13,7 +14,6 @@ import (
 	"github.com/lightningnetwork/lnd/clock"
 	"github.com/lightningnetwork/lnd/graph/db/models"
 	"github.com/lightningnetwork/lnd/lntypes"
-	"github.com/lightningnetwork/lnd/lnutils"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
 	"github.com/lightningnetwork/lnd/sqldb"
@@ -100,12 +100,12 @@ type SQLInvoiceQueries interface { //nolint:interfacebloat
 	FilterInvoicesReverse(ctx context.Context,
 		arg sqlc.FilterInvoicesReverseParams) ([]sqlc.Invoice, error)
 
-	GetInvoice(ctx context.Context,
-		arg sqlc.GetInvoiceParams) ([]sqlc.Invoice, error)
-
 	GetInvoiceByHash(ctx context.Context, hash []byte) (sqlc.Invoice,
 		error)
 
+	GetInvoiceByAddr(ctx context.Context,
+		paymentAddr []byte) (sqlc.Invoice, error)
+
 	GetInvoiceBySetID(ctx context.Context, setID []byte) ([]sqlc.Invoice,
 		error)
 
@@ -398,73 +398,76 @@ func getInvoiceByRef(ctx context.Context,
 		return sqlc.Invoice{}, ErrInvoiceNotFound
 	}
 
-	// If the reference is a hash only, we can look up the invoice directly
-	// by the payment hash which is faster.
-	if ref.IsHashOnly() {
+	// If the reference contains a payment hash we can look up the invoice
+	// directly by hash using the unique index, avoiding a full table scan.
+	// The hash alone uniquely identifies any invoice so additional fields
+	// in the ref (payment address, set ID) are not needed for the lookup.
+	if ref.PayHash() != nil {
 		invoice, err := db.GetInvoiceByHash(ctx, ref.PayHash()[:])
 		if errors.Is(err, sql.ErrNoRows) {
 			return sqlc.Invoice{}, ErrInvoiceNotFound
 		}
+		if err != nil {
+			return sqlc.Invoice{}, fmt.Errorf("unable to fetch "+
+				"invoice by hash: %w", err)
+		}
 
-		return invoice, err
-	}
-
-	// Otherwise the reference may include more fields, so we'll need to
-	// assemble the query parameters based on the fields that are set.
-	var params sqlc.GetInvoiceParams
+		// If the ref also specifies a payment address, verify it
+		// matches the invoice found by hash. A mismatch means the ref
+		// is equivocating — the hash points to one invoice and the
+		// address points to another.
+		payAddr := ref.PayAddr()
+		if payAddr != nil && *payAddr != BlankPayAddr {
+			if !bytes.Equal(invoice.PaymentAddr, payAddr[:]) {
+				return sqlc.Invoice{}, ErrInvRefEquivocation
+			}
+		}
 
-	if ref.PayHash() != nil {
-		params.Hash = ref.PayHash()[:]
+		return invoice, nil
 	}
 
-	// Newer invoices (0.11 and up) are indexed by payment address in
-	// addition to payment hash, but pre 0.8 invoices do not have one at
-	// all. Only allow lookups for payment address if it is not a blank
-	// payment address, which is a special-cased value for legacy keysend
-	// invoices.
-	if ref.PayAddr() != nil && *ref.PayAddr() != BlankPayAddr {
-		params.PaymentAddr = ref.PayAddr()[:]
-	}
+	// If the reference contains a payment address (AMP payments), look up
+	// directly by payment address using the unique index.
+	//
+	// NOTE: Pre-0.8 invoices do not have a payment address, and blank
+	// payment addresses are a special case for legacy keysend invoices.
+	// Those are handled by the hash fast path above.
+	payAddr := ref.PayAddr()
+	if payAddr != nil && *payAddr != BlankPayAddr {
+		invoice, err := db.GetInvoiceByAddr(ctx, payAddr[:])
+		if errors.Is(err, sql.ErrNoRows) {
+			return sqlc.Invoice{}, ErrInvoiceNotFound
+		}
+		if err != nil {
+			return sqlc.Invoice{}, fmt.Errorf("unable to fetch "+
+				"invoice by payment address: %w", err)
+		}
 
-	// If the reference has a set ID we'll fetch the invoice which has the
-	// corresponding AMP sub invoice.
-	if ref.SetID() != nil {
-		params.SetID = ref.SetID()[:]
+		return invoice, nil
 	}
 
-	var (
-		rows []sqlc.Invoice
-		err  error
-	)
-
-	// We need to split the query based on how we intend to look up the
-	// invoice. If only the set ID is given then we want to have an exact
-	// match on the set ID. If other fields are given, we want to match on
-	// those fields and the set ID but with a less strict join condition.
-	if params.Hash == nil && params.PaymentAddr == nil &&
-		params.SetID != nil {
-
-		rows, err = db.GetInvoiceBySetID(ctx, params.SetID)
-	} else {
-		rows, err = db.GetInvoice(ctx, params)
-	}
+	// If only the set ID is given, look up via the AMP sub-invoice index.
+	if ref.SetID() != nil {
+		rows, err := db.GetInvoiceBySetID(ctx, ref.SetID()[:])
+		if err != nil {
+			return sqlc.Invoice{}, fmt.Errorf("unable to fetch "+
+				"invoice: %w", err)
+		}
 
-	switch {
-	case len(rows) == 0:
-		return sqlc.Invoice{}, ErrInvoiceNotFound
+		if len(rows) == 0 {
+			return sqlc.Invoice{}, ErrInvoiceNotFound
+		}
 
-	case len(rows) > 1:
-		// In case the reference is ambiguous, meaning it matches more
-		// than	one invoice, we'll return an error.
-		return sqlc.Invoice{}, fmt.Errorf("ambiguous invoice ref: "+
-			"%s: %s", ref.String(), lnutils.SpewLogClosure(rows))
+		if len(rows) > 1 {
+			return sqlc.Invoice{}, fmt.Errorf("ambiguous "+
+				"invoice ref: set_id=%x matches %d invoices",
+				ref.SetID(), len(rows))
+		}
 
-	case err != nil:
-		return sqlc.Invoice{}, fmt.Errorf("unable to fetch invoice: %w",
-			err)
+		return rows[0], nil
 	}
 
-	return rows[0], nil
+	return sqlc.Invoice{}, ErrInvoiceNotFound
 }
 
 // fetchInvoice fetches the common invoice data and the AMP state for the
diff --git a/sqldb/sqlc/invoices.sql.go b/sqldb/sqlc/invoices.sql.go
index 911c4e1..99e9739 100644
--- a/sqldb/sqlc/invoices.sql.go
+++ b/sqldb/sqlc/invoices.sql.go
@@ -476,6 +476,38 @@ func (q *Queries) GetInvoice(ctx context.Context, arg GetInvoiceParams) ([]Invoi
 	return items, nil
 }
 
+const getInvoiceByAddr = `-- name: GetInvoiceByAddr :one
+SELECT i.id, i.hash, i.preimage, i.settle_index, i.settled_at, i.memo, i.amount_msat, i.cltv_delta, i.expiry, i.payment_addr, i.payment_request, i.payment_request_hash, i.state, i.amount_paid_msat, i.is_amp, i.is_hodl, i.is_keysend, i.created_at
+FROM invoices i
+WHERE i.payment_addr = $1
+`
+
+func (q *Queries) GetInvoiceByAddr(ctx context.Context, paymentAddr []byte) (Invoice, error) {
+	row := q.db.QueryRowContext(ctx, getInvoiceByAddr, paymentAddr)
+	var i Invoice
+	err := row.Scan(
+		&i.ID,
+		&i.Hash,
+		&i.Preimage,
+		&i.SettleIndex,
+		&i.SettledAt,
+		&i.Memo,
+		&i.AmountMsat,
+		&i.CltvDelta,
+		&i.Expiry,
+		&i.PaymentAddr,
+		&i.PaymentRequest,
+		&i.PaymentRequestHash,
+		&i.State,
+		&i.AmountPaidMsat,
+		&i.IsAmp,
+		&i.IsHodl,
+		&i.IsKeysend,
+		&i.CreatedAt,
+	)
+	return i, err
+}
+
 const getInvoiceByHash = `-- name: GetInvoiceByHash :one
 SELECT i.id, i.hash, i.preimage, i.settle_index, i.settled_at, i.memo, i.amount_msat, i.cltv_delta, i.expiry, i.payment_addr, i.payment_request, i.payment_request_hash, i.state, i.amount_paid_msat, i.is_amp, i.is_hodl, i.is_keysend, i.created_at
 FROM invoices i
diff --git a/sqldb/sqlc/querier.go b/sqldb/sqlc/querier.go
index 9472373..5b9c7d5 100644
--- a/sqldb/sqlc/querier.go
+++ b/sqldb/sqlc/querier.go
@@ -111,6 +111,7 @@ type Querier interface {
 	// from different invoices. It is the caller's responsibility to ensure that
 	// we bubble up an error in those cases.
 	GetInvoice(ctx context.Context, arg GetInvoiceParams) ([]Invoice, error)
+	GetInvoiceByAddr(ctx context.Context, paymentAddr []byte) (Invoice, error)
 	GetInvoiceByHash(ctx context.Context, hash []byte) (Invoice, error)
 	GetInvoiceBySetID(ctx context.Context, setID []byte) ([]Invoice, error)
 	GetInvoiceFeatures(ctx context.Context, invoiceID int64) ([]InvoiceFeature, error)
diff --git a/sqldb/sqlc/queries/invoices.sql b/sqldb/sqlc/queries/invoices.sql
index f9b9238..22e5cd0 100644
--- a/sqldb/sqlc/queries/invoices.sql
+++ b/sqldb/sqlc/queries/invoices.sql
@@ -59,6 +59,11 @@ SELECT i.*
 FROM invoices i
 WHERE i.hash = $1;
 
+-- name: GetInvoiceByAddr :one
+SELECT i.*
+FROM invoices i
+WHERE i.payment_addr = $1;
+
 -- name: GetInvoiceBySetID :many
 SELECT i.*
 FROM invoices i